Strikingly, owing to both the HER and OER performance, an electrolyzer with RuNi‐NCNFs as both the anode and cathode catalysts requires only a cell voltage of 1.564 V to drive a current density of 10 mA cm−2 in an alkaline medium, which is lower than the benchmark of Pt/C||RuO2 electrodes. This study opens a novel avenue toward the exploration of high efficient but low‐cost electrocatalysts for overall water splitting.Developing high‐performance, low‐cost, and robust bifunctional electrocatalysts for overall water splitting is extremely indispensable and challenging. It is a promising strategy to couple highly active precious metals with transition metals as efficient electrocatalysts, which can not only effectively reduce the cost of the preparation procedure, but also greatly improve the performance of catalysts through a synergistic effect. Herein, Ru and Ni nanoparticles embedded within nitrogen‐doped carbon nanofibers (RuNi‐NCNFs) are synthesized via a simple electrospinning technology with a subsequent carbonization process. The as‐formed RuNi‐NCNFs represent excellent Pt‐like electrocatalytic activity for the hydrogen evolution reaction (HER) in both alkaline and acidic conditions. Furthermore, the RuNi‐NCNFs also exhibit an outstanding oxygen evolution reaction (OER) activity with an overpotential of 290 mV to achieve a current density of 10 mA cm 2 electrocatalyst.A facile strategy based on electrospinning and a postcarbonization process is demonstrated to prepare carbon nanofibers incorporating Ru and Ni nanoparticles, which exhibits admirable Pt‐like hydrogen evolution reaction activity and superior oxygen evolution reaction performance. The electrolyzer with this hybrid as both anode and cathode displays a remarkable electrocatalytic activity and outstanding long‐term durability, which outperforms the commercial Pt/C||RuO Compared with other synthetic approaches, the N‐doping and the incorporation of Ru/Ni catalysts can be simultaneously realized, which avoid the complicated procedure. Benefiting from the synergistic effect between Ru and Ni, conductive N‐doped carbon supports, and large active surface area, our prepared RuNi‐NCNFs catalyst exhibits excellent HER catalytic activity in both alkaline and acidic media, with low overpotentials of 35 and 23 mV (at j = 10 mA cm−2), which are comparable with the state‐of‐the‐art Pt‐based catalyst. In addition, this catalyst also exhibits an outstanding OER activity in an alkaline solution, with a low overpotential of 290 mV (at j = 10 mA cm−2). More importantly, our home‐made alkaline electrolyzer using Ru1Ni1‐NCNFs as both anodic and cathodic catalysts only requires a cell voltage of 1.564 V to drive current density of 10 mA cm−2 and performs robustly during continuous operation for 20 h, superior to the integrated Pt/C and RuO2 counterparts. This facile, rapid, and cost‐effective method provides a novel opinion to fabricate high efficiency bifunctional electrocatalyst for overall water splitting.In this study, a facile and cost‐effective electrospinning technique combined with carbonization process has been adopted to fabricate Ru and Ni nanoparticles‐embedded in nitrogen‐doped CNFs (RuNi‐NCNFs) as both superior HER and OER electrocatalysts. Although there have been some studies on RuNi electrocatalysts, the preparation of RuNi nanoparticles embedded in CNFs via electrospinning for water splitting has not been reported. 1D nanostructure with tunable compositions can be obtained by regulating the content of RuClFigure3/Ni(NO3)2 (nRu/Ni = 1) nanofibrous membranes have been first fabricated via electrospinning an N,N‐dimethylformamide (DMF) solution containing RuCl3, Ni(NO3)2, and PAN. It can be discovered that the nanofibers have a smooth surface with an average diameter of around 1 µm . As shown in Figure S2a,d (Supporting Information), the control samples of the electrospun PAN/RuCl3/Ni(NO3)2 (nRu/Ni = 2) and PAN/RuCl3/Ni(NO3)2 (nRu/Ni = 0.5) nanofibrous membranes have also been prepared, showing similar fiber‐like morphologies and diameters. Second, these nanofibrous membranes are carbonized at 800 °C under Ar flow to produce Ru1Ni1‐NCNFs, Ru2Ni1‐NCNFs, and Ni2Ru1‐NCNFs. The fibrous structure is well maintained while the carbon matrix suffers obvious shrinkage with an average diameter of around 515 nm for Ru1Ni1‐NCNFs  and Ni2Ru1‐NCNFs . As shown in Figure S3 (Supporting Information), the average diameters of Ni and Ru nanoparticles in Ru1Ni1‐NCNFs are about 16.09 nm. We have also prepared Ru‐NCNFs and Ni‐NCNFs for comparison. Figure S4 (Supporting Information) shows the morphologies of PAN/RuCl3 and PAN/Ni(NO3)2 fiber membranes before carbonization, showing uniform fibrous structures. After a carbonization treatment at 800 °C, the density of nanoparticles in Ru1Ni1‐NCNFs is significantly higher than that of pure Ru‐NCNFs 2, a large amount of gas was generated in the carbonization process, leading to the rupture of the nanofibers and the formation of the pores on the surface of nanofibers.1Ni1‐NCNFs exhibits more active sites and facilitates the decreasing contact between the gas bubbles and electrode, thus leading to the fast kinetics and enhanced electrocatalytic activity. Furthermore, since the carbonization temperature is significant for the catalytic activity of carbon‐based electrocatalysts, Ru1Ni1‐NCNFs that are prepared under different carbonization temperatures have also been investigated. As shown in Figure S5a (Supporting Information), the nanofibers carbonized at 700 °C still maintain 1D morphology, but there is almost no pores on the surface of the fibers. The crystallinity of the nanoparticles is relatively inferior due to the insufficient degree of carbonization, and the morphology of the particles is not easily observed from the TEM image . When the temperature is raised to 900 °C, gaps and cracks appear on the surface of the fiber, and the nanoparticles tend to be agglomerated .As displayed in 1Ni1‐NCNFs catalyst displays a slight shift to higher diffraction angle in comparison with Ru‐NCNFs and the peaks of Ni in Ru1Ni1‐NCNFs migrate to a lower angle compared to Ni‐NCNFs, revealing the strong interactions between Ru and Ni components in the Ru1Ni1‐NCNFs sample , 1575 cm−1 for the G band (hybridized graphitic carbon atoms), and 2684 cm−1 for the 2D band (graphitic sp2‐bonded carbon atoms).IG/ID) is corresponding to the degree of graphitization of carbon. It is proved that the addition of a Ni source is propitious to the formation of the highly graphitized carbon material. Thus, the maximum IG/ID value and obvious 2D band of Ru1Ni1‐NCNFs indicate that the carbon structure produced by the synergistic effect of Ru and Ni has a higher graphitization degree, which may promote the charge transfer of the electrocatalytic process.The X‐ray diffraction (XRD) measurement obviously identifies the harvest of Ru–Ni heterostructures in the final products , in which the phases of Ru (JCPDS NO.: 06–0663) and Ni (JCPDS NO.: 04–0850) are clearly observed. With the enlargement of the content of Ru, the crystallization property and peak strength enhance obviously. The same phenomenon happens when the proportion of Ni increases. However, the pattern of Ru in RuFigure1Ni1‐NCNFs  images Figure2a,b diFigure1Ni1‐NCNFs exhibits a doublet situated at 462.2 and 484.5 eV, assigning to metallic Ru 3p3/2 and Ru 3p1/2 states.3+ is almost completely reduced to Ru0 species during carbonization process, which are highly expected for displaying satisfactory electrocatalytic activity for HER. Compared with Ru‐NCNFs, the Ru 3p peaks of Ru1Ni1‐NCNFs shift 0.2–0.3 eV in negative direction. As shown in Figure 3/2 and Ni 2p1/2 peaks appear at 853.8 and 870.8 eV with a splitting of 17 eV, demonstrating the formation of metallic Ni atoms in Ru1Ni1‐NCNFs. Furthermore, Ni 2p3/2 and Ni 2p1/2 signals at 856.3 and 874.4 eV with their corresponding satellite peaks at 860.8 and 880.8 eV suggest the oxidation of some surface of Ni atoms to NiO.2+ species can effectively boost water dissociation to H* and that Ru can promote the combination of H* to H2 through a synergistic effect.1Ni1‐NCNFs shift to a higher binding energy. The binding energy shifts of the Ni 2p and Ru 3p are in the opposite direction, which can be ascribed to the charge transfer from less electronegative Ni to more electronegative Ru across their interfaces.1Ni1‐NCNFs caused by effective electronic transfer can result in a relatively moderate hydrogen‐metal binding energy and improve the catalytic performance of HER. In order to investigate the effect of different ratios of RuCl3 and Ni(NO3)2 on the valence states of Ru and Ni in RuNi‐NCNFs, the electrocatalysts of Ru2Ni1‐NCNFs and Ni2Ru1‐NCNFs are also characterized by XPS measurement. As displayed in Figure S8 (Supporting Information), the samples with different Ru/Ni ratios have little effect on the valence state of metallic Ru. However, when the molar ratio of Ru to Ni is 1:2 and 2:1, the content of Ni2+ is higher than that of Ni0 species. The C1s peak of Ru1Ni1‐NCNFs can be deconvoluted into three independent peaks at 284.6, 285.2, and 280.3 eV , which corresponds to C=C, C—N, and the overlapped Ru 3d5/2 (Ru0), respectively.The surface compositions of the as‐prepared samples are further investigated by X‐ray photoelectron spectroscopy (XPS) to shed light on the chemical and structural information. As shown in m KOH. First, the HER activity of three electrocatalysts with different molar ratios of Ru and Ni is evaluated. Figure S10a (Supporting Information) provides one cycle of the cyclic voltammetries (CVs) together with the curve after iR‐correction of the as‐synthesized Ru1Ni1‐NCNFs, which exhibits the lowest overpotentials of 35 and 80 mV at 10 and 50 mA cm−2, respectively. These values are better than those of the Ru2Ni1‐NCNFs (49 mV at 10 mA cm−2) and the Ni2Ru1‐NCNFs (186 mV at 10 mA cm−2) , indicating that metallic Ru is the main active source of HER. Subsequently, we have investigated the HER performances of a series of Ru1Ni1‐NCNFs obtained at different carbonization temperatures. To obtain the current density of 10 mA cm−2, the overpotentials required for Ru1Ni1‐NCNFs‐700 and Ru1Ni1‐NCNFs‐900 catalysts are 48 and 83 mV, respectively, which are higher than that of Ru1Ni1‐NCNFs‐800, suggesting that 800 °C is the optimal carbonization temperature . Ru‐NCNFs, Ni‐NCNFs, and commercial Pt/C (20 wt%) are also tested under the same conditions , Ni‐NCNFs (233 mV), and the state‐of‐the‐art Pt/C (37 mV). Due to the excellent intrinsic activity of metallic Ru, Ru‐NCNFs perform much better HER activity than Ni‐NCNFs. Notably, Ru1Ni1‐NCNFs display much lower overpotential values than Pt/C at jHER > 8.4 mA cm−2, indicating that Ru1Ni1‐NCNFs exhibit better HER performance than commercial Pt/C at high current densities. For the physical mixture of Ru‐NCNFs and Ni‐NCNFs, the HER activity is located between those of its counterpart catalysts and is considerably inferior to that of the Ru1Ni1‐NCNFs catalyst. It is proved that the synergistic effect of chemical coupling of Ru and Ni metals by electrospinning technique is the main reason to enhance the performance of HER. As displayed in Figure 1Ni1‐NCNFs reveal a Tafel slope of 30 mV dec−1, which is much lower than those of Ru‐NCNFs (35 mV dec−1), Ni‐NCNFs (79 mV dec−1), and the physical mixture of Ru‐NCNFs and Ni‐NCNFs (41 mV dec−1) and identical with that of Pt/C (30 mV dec−1), demonstrating a faster HER kinetics of Ru1Ni1‐NCNFs. In light of the Tafel slope range, the HER catalyzed by Ru1Ni1‐NCNFs in this system is presumably conducted by a Volmer–Tafel mechanism. The inherent HER activity of these catalysts has been evaluated by the exchange current density (j0) according to the Tafel plots. Remarkably, the Ru1Ni1‐NCNFs catalyst exhibits the largest j0 of 0.745 mA cm−2 among the as‐prepared catalysts and is nearly close to that of Pt/C (0.920 mA cm−2). It is commonly known that a large j0 is generally associated with the large electrochemically active surface area (ECSA),Cdl) through CV measurements at various scan rates .Cdl of 44.27 mF cm−2 for Ru1Ni1‐NCNFs is larger than the 34.1 mF cm−2 for Ru‐NCNFs and 26.99 mF cm−2 for Ni‐NCNFs, revealing that more active sites are available for the Ru1Ni1‐NCNFs catalyst . Then the ECSA values are proportional to the Cdl values according to typical reported values.1Ni1‐NCNFs possess the largest ECSA compared with the Ru‐NCNFs and Ni‐NCNFs. The large j0 and high ECSA indicate that the Ru1Ni1‐NCNFs catalyst with high surface roughness reveals more active sites and promotes the rapid formation and separation of hydrogen bubbles on the electrode surface, giving rise to the fast kinetics and increased HER activity.1N1‐NCNFs catalyst possesses a high TOF of 0.076 s−1 at overpotential of 80 mV, which is larger than most of recently reported catalysts . The high TOF of Ru1Ni1‐NCNFs is agreement with its outstanding activity toward the HER. The mass activity (MA) has also been calculated to further evaluate the intrinsic activity. It is found that the MA value of Ru1Ni1‐NCNFs (16.44 A g−1) is the highest among the all samples . Furthermore, the advantageous electrical conductivity of Ru1Ni1‐NCNFs enables rapid electron transport, which was confirmed by the electrochemical impedance spectroscopy (EIS). As the Nyquist diagram shown in Figure 1Ni1‐NCNFs manifest a charge‐transfer resistance (Rct) of 9.11 Ω, which is much lower than that of pure Ru‐NCNFs or Ni‐NCNFs. The smallest Rct of the Ru1Ni1‐NCNFs catalyst can be ascribed to its porous composite structure, which enables ultrafast faradaic processes and superior HER kinetics. To evaluate the durability of Ru1Ni1‐NCNFs, continuous CV cycles were carried out on the rotating disk electrode (RDE) at a scan rate of 100 mV s−1. As shown in Figure 1Ni1‐NCNFs catalyst displays excellent stability for HER. The chronoamperometric test was conducted under a constant overpotential of 62 mV for Ru1Ni1‐NCNFs on carbon paper with a loading of 2.5 mg cm−2 without iR‐compensation and the corresponding polarization plot is shown in Figure S15a (Supporting Information). After a continuous 12 h electrolysis, it displays superior durability with merely very little decline .We have employed a typical three‐electrode configuration to assess the HER performance of the as‐prepared electrocatalysts in Ar‐saturated 1 ns Figure4a. Str1Ni1‐NCNFs without or with iR‐compensation in 0.5 m H2SO4 at a scan rate of 1 mV s−1 are exhibited in Figure S10c (Supporting Information). As shown in Figures S11c and S12c (Supporting Information), when the molar ratio of Ru to Ni is 1:1 and the carbonization temperature is 800 °C, the best HER performance of RuNi‐NCNFs in an acidic electrolyte is achieved. The polarization plots of different samples in 0.5 m H2SO4 are displayed in Figure S16a (Supporting Information). It is clearly remarkable that the onset overpotential of Ru1Ni1‐NCNFs is about 0 mV, and the overpotential at the current density of 10 mA cm−2 is 23 mV, which is comparable to the commercial Pt/C (17 mV). The η10 of the physical mixture (63 mV) is between the value of Ru‐NCNFs (50 mV) and Ni‐NCNFs (389 mV) and is extremely higher than the Ru1Ni1‐NCNFs, further confirming that the chemical coupling between Ru and Ni produces catalytically synergistic effect. The Tafel slope for Ru1Ni1‐NCNFs is 29 mV dec−1, indicating that a Volmer–Tafel reaction mechanism controlled the HER process and that electrochemical desorption is the rate‐determining step (H* + H+ + e −→ H2) in acidic media .1Ni1‐NCNFs (16.83 A g−1) was ≈4.4‐times and 12‐folds than Ru‐NCNFs and Ni‐NCNFs, respectively . The Ru1Ni1‐NCNFs catalyst reveals a high TOF of 0.074 s−1 at an overpotential of 55 mV, which is superior to other recently reported HER catalysts , indicating that Ru1Ni1‐NCNFs possess a much higher intrinsic activity for the HER in an acidic condition. Furthermore, we also estimated the electrocatalytic HER stability in 0.5 m H2SO4. Figure S16c,d (Supporting Information) displays the linear sweep voltammetry (LSV) curves of Ru1Ni1‐NCNFs before and after 6000 CV cycles and the i–t curve at an overpotential of 40 mV without iR‐compensation, respectively. After the long‐term durability measurements, no evident variations are observed in both polarization and i–t curves, proving Ru1Ni1‐NCNFs with outstanding HER stability in acidic electrolyte. Therefore, our‐prepared Ru1Ni1‐NCNFs catalyst outperforms most of the recently developed HER electrocatalysts in acidic media .The HER catalytic activity in acidic media has been further investigated. The CV curves of the Ru1Ni1‐NCNFs catalyst was also observed to be active for OER in 1 m KOH. Figure S10b (Supporting Information) provides the CV curves before and after iR‐compensation of the as‐synthesized sample. The OER activities of RuNi‐NCNFs with three different molar ratios of Ru and Ni have been first evaluated, and the results are shown in Figure S11b (Supporting Information). It is very clear that the Ru1Ni1‐NCNFs display a low overpotential of 290 mV with respect to Ni2Ru1‐NCNFs (320 mV) and Ru2Ni1‐NCNFs (380 mV) to reach a current density of 10 mA cm−2. These results indicate that the optimum ratio between Ru and Ni is 1:1, and metallic Ni is the main active component for OER. Afterward, we have optimized the carbonization temperature of Ru1Ni1‐NCNFs. As shown in Figure S12b (Supporting Information), the overpotentials required by Ru1Ni1‐NCNFs‐700 and Ru1Ni1‐NCNFs‐900 to drive the current density of 10 mA cm−2 are 406 and 327 mV, respectively, which are higher than that required by Ru1Ni1‐NCNFs‐800, revealing that the optimum carbonization temperature of Ru1Ni1‐NCNFs is 800 °C. FigureiR‐drop corrections, along with that of the benchmark RuO2 catalyst for reference. The Ru1Ni1‐NCNFs afford a η10 of 290 mV, which was 50 and 143 mV less than those of the Ni‐NCNFs and the state‐of‐the‐art RuO2, respectively. For the physical mixture of Ni‐NCNFs and Ru‐NCNFs, its OER activity is located between those of its counterpart catalysts and is substantially inferior to that of the Ru1Ni1‐NCNFs catalyst, indicating that the strong chemical coupling effect plays a vital role in the Ru1Ni1‐NCNFs composite catalyst. The individual Ru‐NCNFs catalyst exhibits poor OER activity, and even at 1.75 V  voltage, its current density does not reach 10 mA cm−2, indicating that Ni nanoparticles in Ru1Ni1‐NCNFs are the main active species for electrocatalytic OER. In addition, from the XPS spectra . Similarly, compared with other samples, the Ru1N1‐NCNFs possess the maximum MA value of 16.64 A g−1 at definite overpotential of 290 mV , confirming the excellent intrinsic electrocatalytic activity of Ru1Ni1‐NCNFs for OER. Moreover, this composite material is considerably stable, in 4500 cycles of CV test, the curve before and after the cycle almost coincides , only a small decrease of the current density was observed after continuous electrolysis for 12 h .Furthermore, the Ruu1‐NCNFs 20 mV and1Ni1‐NCNFs for both HER and OER, we further evaluated the overall water splitting activity in 1 m KOH electrolyte by adopting two‐electrode configurations. The Ru1Ni1‐NCNFs catalyst was supported on the carbon paper and was employed as both the cathode and the anode for a home‐made electrolyzer. As depicted in Figure 1Ni1‐NCNFs electrodes achieve a current density of 10 mA cm−2 at a cell voltage of 1.564 V (vs RHE) (without iR‐compensation) and a great deal of H2 and O2 bubbles were observed on the surface of both electrodes during electrolysis  corresponds to the oxidation of M(II) to M(III or IV) (M = Ni and Co), which is common during the electrochemical process of Ni‐based electrocatalysts.1Ni1‐NCNFs stays ahead of commercial catalysts (Pt/C||RuO2 is 1.571 V (vs RHE)@10 mA cm−2) and many of the previously reported bifunctional electrocatalysts . The long‐term stability of the water‐splitting reaction was estimated by continuous operation at 1.57 V (vs RHE) (without iR‐compensation). There was only a little degradation at the initial time, and after that the activity remains stable or even increases, displaying the favorable chemical stability and its excellent potential for practical electrolytic water system. By contrast, the benchmark electrodes of Pt/C||RuO2 deliver an obvious decline of current density after 20 h, revealing their instability.In view of the outstanding activity and stability of Ru1Ni1‐NCNFs catalyst was characterized in detail after HER and OER stability tests to further prove its favorable morphology and structural stability. From the SEM and TEM images , it can be observed that our‐prepared Ru1Ni1‐NCNFs catalyst maintained a well fibrous morphology either after HER tests in alkaline or acidic media or after OER test in alkaline electrolyte. The nanoparticles are still firmly embedded in the carbon skeleton because carbon fibers protect the inner nanoparticles from corrosion and oxidation under strong acid and alkaline conditions.m H2SO4 , the signal intensity of Ni element is obviously weakened, which is due to the metallic Ni easily dissolved in acidic electrolyte, consistent with the results of following XRD analysis . The Ru and Ni structure of the nanoparticles is well‐preserved after the stability tests, while in the XRD pattern after HER test in 0.5 m H2SO4, the peak intensities of metallic Ni at 51.6° and 76.0° are significantly weakened, indicating that the main active substance for catalyzing HER is metallic Ru, while the active substance for OER is metallic Ni, and the chemical coupling of Ru and Ni in carbon matrix imparts excellent bifunctional electrocatalytic activity to Ru1Ni1‐NCNFs. XPS has been further performed on Ru1Ni1‐NCNFs after stability measurements. The high‐resolution XPS spectra of Ru 3p  indicate that the post‐HER samples share similar features with the fresh sample, whether in 1 m KOH or 0.5 m H2SO4, whereas the post‐OER sample displays visible Ru4+ signals, revealing that part of Ru is converted to RuO2 in the electrocatalytic process, thus further improving the OER activity.0 decreases significantly and that of Ni2+ increases obviously after HER test in 1 m KOH. It is noteworthy that Ni2+ species as water dissociation promoters can crack HO—H bonds and generate H*, which is considered to be effective active sites for water dissociation (Volmer step), thereby accelerating the overall reaction rate of HER.3+ species appear clearly in the XPS spectrum of the post‐OER sample, which is known to be highly active for OER.1Ni1‐NCNFs after OER test, which are conducive to the enhanced OER activity. By observing the sample after HER test in acidic media, it is found that the signal of Ni0 almost disappears, whereas the majority of surface Ni in Ru1Ni1‐NCNFs is oxidized with a +2 oxidation state, which is consistent with the previous results of EDX and XRD. According to the aforementioned analysis, our prepared Ru1Ni1‐NCNFs electrocatalyst exhibits satisfactory stability and is capable to withstand continuous operation in practical applications.The Ru1Ni1‐NCNFs is presumably ascribed to the following reasons. First, the introduction of Ni largely downshifts the d‐band center of the Ru–Ni hybrids and effectively modulates the surface environment for HER. Simultaneously, the Ru in Ru1Ni1‐NCNFs will lightly transfer electrons between the catalysis substrate and intermediate molecules and promote O—O bond generation.2+ species on the surface of Ru1Ni1‐NCNFs can boost water dissociation to H* and that Ru promotes the combination of H* to H2 via a greatly efficient synergistic catalysis, resulting in fast kinetics of HER. In addition, the abundant Ni3+ can facilitate the formation of surface‐hydrated oxides and (oxy)hydroxides phases 2 and NiOOH), which provides the main reactive sites for OER. On the other hand, nitrogen‐doped carbon nanofibers with porous surfaces improve the conductivity of the catalyst, accelerate rapid electron and mass transport, and avoid the agglomeration of nanoparticles. Heteroatom N (such as graphitic N and pyrrolic N) can affect the charge delocalization of C, thereby increasing the conductivity of materials.2 in the reaction process is also the key factor to enhance the performance of OER. Finally, the Ru1Ni1‐NCNFs with large electrochemical active surface area and surface roughness can expose more active sites, thus improving the performance of electrocatalytic reaction.The outstanding HER and OER bifunctional electrocatalytic performance of Ru1Ni1‐NCNFs via electrospinning, followed by a carbonization process. The synthesized Ru1Ni1‐NCNFs catalyst possesses high conductivity, large electrochemical active surface area, and abundant active sites, thus resulting in superior activity, fast charge transport, rapid release of generated gas bubbles, and favorable durability for electrocatalytic processes. Accordingly, the robust Ru1Ni1‐NCNFs as novel bifunctional electrocatalysts revealed excellent HER and OER catalytic performance in alkaline solution. In regard to overall water splitting, a low cell potential of merely 1.564 V was required to achieve a current density of 10 mA cm−2, which is superior to the state‐of‐the‐art catalysts Pt/C||RuO2 (1.571 V@10 mA cm−2). Moreover, the Ru1Ni1‐NCNFs catalyst also exhibited remarkable HER performance in acidic media and the overpotential required by the Ru1Ni1‐NCNFs to drive a current density of 10 mA cm−2 was comparable with that of commercial Pt/C. This work hints at the opportunity to combine cheap transition metals with relatively low‐price noble metals (such as Ru), both maintaining the excellent intrinsic activity of the precious metal and reducing the cost of electrocatalyst, which is highly desirable for sustainable energy development.In summary, we have developed a facile and convenient strategy to fabricate RuChemicals and Reagents: Polyacrylonitrile , ruthenium (III) chloride hydrate (RuCl3·xH2O), and ruthenium(IV) oxide (RuO2) were commercially available from Sigma‐Aldrich. Nickel (II) nitrate hexahydrate (Ni(NO3)2·6H2O) and DMF were purchased from Beijing Chemical Works. Commercial 20 wt% Pt/C was provided by Johnson Matthey.Preparation of RuNi‐NCNFs: Typically, 0.5 g of PAN was added into 4.5 g of DMF and stirred at 90 °C for 1 h. 0.244 g of Ni(NO3)2·6H2O and 0.174 g of RuCl3·xH2O were then added into the PAN solution (the molar ratio of Ru to Ni was 1:1) and stirred vigorously until to yield a homogeneous solution. Subsequently, the precursor solution was inhaled into a syringe with a single stainless steel nozzle for electrospinning. The power supply was maintained at 16 kV between the spinneret and the aluminum foil collector with a distance of 24 cm. In the following, the as‐collected PAN/RuCl3/Ni(NO3)2 fiber membrane was heated at 280 °C for 2 h in air atmosphere, followed by carbonization at 800 °C for 5 h in argon to prepare Ru and Ni nanoparticles encapsulated in N‐doped CNFs (denoted as Ru1Ni1‐NCNFs). In addition, the RuNi‐NCNF electrocatalysts with molar ratios of Ru to Ni = 2:1 and 1:2 were labeled as Ru2Ni1‐NCNFs and Ni2Ru1‐NCNFs . The pure Ru‐NCNFs and Ni‐NCNFs were fabricated similarly with that of Ru1Ni1‐NCNFs, only without the addition of Ni(NO3)2·6H2O and RuCl3·xH2O, respectively. For comparison, the electrospun PAN/RuCl3/Ni(NO3)2 (nRu/Ni = 1) fiber membrane carbonized at 700 and 900 °C (expressed as Ru1Ni1‐NCNFs‐700 and Ru1Ni1‐NCNFs‐900) were fabricated with the other conditions unchanged.Characterization: The morphology and structure of the resulting products were studied using a scanning electron microscope (FEI Nova NanoSEM) and a TEM (JEOL JEM‐2000 EX). HRTEM images and EDX spectrum were obtained using an FEI Tecnai G2 F20. The crystallographic structures of the samples were characterized by XRD  with Cu Kα radiation. Raman tests were carried out on a Horiba LabRAM HR Evolution apparatus. XPS (Thermo Scientific ESCALAB250) was used to analyze the surface elemental composition of the synthesized materials. ICP‐AES (Agilent 725) was employed to estimate the weight percentages of Ni and Ru in the Ru1Ni1‐NCNFs.Electrochemical Measurements: All electrochemical measurements were conducted on a CHI760E electrochemical workstation in a three electrode setup, in which a RDE made of glassy carbon electrode (geometric area: 0.196 cm2) with catalysts was used as the working electrode, a standard Hg/HgO electrodes as the reference (in 1 m KOH), a graphite rod and a Pt wire as the counter electrodes for HER and OER, respectively. In 0.5 m H2SO4, RHE is directly used as reference electrode. The calibration of the Hg/HgO was performed in a conventional three‐electrode system with platinum plates as the working electrode and counter electrode and the Hg/HgO as a reference electrode. The current–voltage scans were measured in high purity hydrogen (H2) saturated 1 m KOH solution at a scan rate of 1 mV s−1, and the average of the two potentials at which the current crossed zero was recorded to be the thermodynamic potential for the hydrogen electrode reaction . The zero current potential was −0.93 V, so E (RHE) = E (Hg/HgO) + 0.93 V. The catalyst ink was prepared by putting samples (2 mg) to disperse in ethanol (500 µL), and then the mixture was sonicated for at least 30 min to form a homogeneous solution. After that, 30 µL of the dispersion was casted onto the RDE, followed by the coverage of 5 µL 0.5 wt% Nafion solution with a catalyst loading of about 0.612 mg cm−2. The commercial Pt/C and RuO2 modified electrodes were also made in the same way for comparison. LSV was conducted at a scan rate of 1 mV s−1 with a rotation rate of 1600 rpm. The computation of TOF value is according to the equation listed below: TOFHER = j ×  S/(2Fn) and TOFOER = j ×  S/(4Fn). j represents the current density (A cm−2) at a given overpotential, S is the value of the surface area for RDE electrode (0.196 cm2). The constants 4 and 2 are the number of electrons required to product each mole of O2 and H2, respectively. F is the value of the Faraday constant (96 485.3 C mol−1), and n (mol) represents the moles of the metal atoms on the electrode calculated from ICP results of the Ru1Ni1‐NCNFs. It is assumed that all Ru and Ni atoms are active and contribute to the catalytic reaction . The mass activity  values were compulated at a definite overpotential by following equation: MA =jM,where j (mA cmgeo−2) is measured current density; M (mg cmgeo−2) is mass loading of the catalysts.6 to 0.1 Hz.−2 for HER and OER chronoamperometric tests in a three‐electrode system. The Ru1Ni1‐NCNFs catalyst anchored on carbon paper was also used as both cathode and anode in a two‐electrode configuration for overall water splitting, and the polarization curve was measured at a scan rate of 1 mV s−1.The catalyst was supported on carbon paper with a mass loading of 2.5 mg cmThe authors declare no conflict of interest.Supporting InformationClick here for additional data file.


The release of uranyl(VI) is a hazardous environmental issue, with limited ways to monitor accumulation in situ. Here, we present a method for the detection of uranyl(VI) ions through the utilization of a unique fluorescence energy transfer process to europium(III). Our system displays the first example of a “turn‐on” europium(III) emission process with a small, water‐soluble lanthanide complex triggered by uranyl(VI) ions. This species, a potent nephrotoxin,The development of nuclear technologies has led to many cases of accidental and intentional release of radionuclides, with accumulation of significant levels of uranium in the environment.22+ detection, with scintillation counting and X‐ray based methods generally preferred.22+ to more immobile UIV‐containing minerals, a strategy currently under development as a bioremediation tool.22+, which allow distinct identification over other oxidation states and, with the correct design, afford an opportune and selective handle with which to monitor local concentration fluctuations of this environmentally hazardous species.To date, there has been limited development of probes for UO22+ cation arise from formally forbidden charge transfer transitions from oxo‐based molecular orbitals to nonbonding, unoccupied f‐orbitals.22+ detection via energy transfer to other longer wavelength (and longer‐lived) emissive species. Of particular interest here is the spectral overlap of the UO22+ emission (ca. 520 nm) and the europium(III) excitation bands ,The intrinsic photophysical properties of the UO22+ to lanthanide energy transfer in a water‐soluble, molecular europium(III) complex, [EuL].22+ detection, due to the unique photophysical properties of UO22+ that allow this process to occur.Here, we report the first example of UO22+  is typical of Eu3+ emission with the narrow emission bands corresponding to the 5D0→7FJ transitions .3+ emission intensity observed upon ligand‐centered excitation at 280 nm . The decrease in ligand‐excitation efficiency can be explained by the strong competing absorption associated with the increasing presence of UO22+ species .Initial spectrophotometric titrations were performed by following the absorption, steady‐state emission and excitation spectra of [EuL] as a function of added UOitation 20 nm is tλem=613 nm) at 430 and 320 nm was observed upon addition of UO22+  transition and from the LMCT from the equatorial ligands, respectively.22+, or by its corresponding hydrolysis species, is transferred to Eu3+. Moreover, a red shift (ca. 14 nm) in the band at 330 nm is observed upon further addition of uranyl(VI) nitrate, providing evidence for the alteration of the equatorial coordination environment of the UO22+ ion from 0.5 to 1 equivalents. Such energy transfer from UO22+, and other actinides, to the 5D0 excited state of Eu3+ is known to be efficient in solid matrixes, polymers and glasses;The appearance of two new excitation bands λem=63 nm at 422+ LMCT bands led to Eu3+ emission from the 5D0 excited state. Significant variations are observed in the emission intensity of Eu3+, pointing to the formation of several UO2–Eu coordination species in solution  species. After 0.5 equivalents, the Eu3+ emission intensity decreases, pointing to the formation of additional species in solution. Broad bands at around 530 nm, corresponding to UO22+ emission, only became significant in the presence of an excess of 1 equivalent of UO22+ . Linear regression analysis of the initial addition of UO22+ to [EuL] provided limit of detection (LOD) values down to 12 μm . It however should be noted that here, neither the complex nor the titrations were desgined to maximise the LOD.Further titrations were carried out upon excitation into the uranyl‐based LMCT transitions at 320 nm Figure  and 420 n Figure . The add11β and 21β, respectively, corresponding to the formation of [(EuL)UO2] and [(EuL)2UO2] species. Excitation into the LMCT UO22+ transition, at 420 nm , revealed a similar evolution.The spectral variations were analysed using the nonlinear regression analysis provided by SPECFIT (see the Supporting Information).3+ (λem=613 nm) were monitored with excitation at 280 nm and 340 nm (Table S1). In the absence of UO22+, the excited state lifetime of [EuL] in TRIS buffer upon ligand excitation was 589 μs, in excellent agreement with previously reported data.τ1=340 μs and τ2=688 μs, in almost equal proportions. This behavior is likely due to the formation of an asymmetric 2:1 Eu3+/UO22+species and points to the presence of two distinct coordination environments around Eu3+. From 0.6 equivalents and beyond, a short component corresponding to the 1:1 Eu3+/UO22+species is observed with a lifetime of 180 μs.During the titration, the intensity decays of Euλexc=280 nm) shows that the 589 μs component reflects the disappearance of [EuL] according to the species distribution diagram in Figure S4 and the gradual increase of the 340 μs component (from 4 % to 54 %) corresponds well with the formation of the 2:1 species.Detailed examination of the contribution of each lifetime between 0 and 0.7 equivalents . The time‐resolved emission decay of UO2(NO3)2 was initially recorded in the same conditions and a mono‐exponential decay was observed with a luminescent lifetime of 1.9 μs, as expected for aqueous UO22+ ions.1=379 ns (92 %) and a minor component τ2=54 ns (8 %). The obvious shortening of the lifetime of the UO22+ fluorescence corroborates the depopulation of the UO22+ excited states due to an intramolecular energy transfer. The relative populations of the two species are in strong agreement with the species distribution postulated. For the EuL/U ratio of 1:0.75, bi‐exponential decay was also observed, with a major component , accounting for the (EuL)2UO2 species, and a minor component , which can be attributed to the formation of the 1:1 complex. At a twofold excess of UO22+ a bioexponential decay is observed, with the predominant species  being related to the presence of uncomplexed UO22+. On the basis of these observations, the 379 ns lifetime was attributed to the [(EuL)2UO2] heterotrinuclear complex, while the heterodinuclear species, [(EuL)UO2], presented an average lifetime of 47 ns. Considering that the UO22+‐based luminescence lifetime shortening is due to resonant energy transfer to Eu3+, it was possible to calculate U→Eu energy transfer efficiencies of 80 % in the [(EuL)2UO2] species and almost quantitative (97 %) in the [(EuL)UO2] dinuclear complex. The differences observed may be attributed to a stronger, essentially electrostatic interaction in the dinuclear species, as a result of the attraction of the positively charged UO22+ cation with the negatively charged [EuL]3/4− complex.Significant changes were also observed by monitoring the UO22+, we turned our attention to DFT calculations , while the second oxygen atom remains uncoordinated. Four oxygen atoms of phosphonate groups are coordinated to the UO22+ ion with U–O distances of 2.21–2.22 Å. The two U=O distances are nearly identical , being close to those observed by EXAFS for UO2(CO3)34− in solution3+ complex coordinated through the O atom of the UO22+ and 5.62 Å for the unbound uranyl oxygen atom.To gain insights into the polynuclear species formed in solution in the presence of UO2)(H2O)3]2− species . The UO22+ group is coordinated to the Eu3+ center with a Eu–O distance of 2.57 Å and a Eu–U distance of 4.02 Å. Two oxygen atoms of phosphonate groups coordinate to the UO22+ ion , while three water molecules complete the equatorial coordination positions with relativley long U–O distances in the range 2.49–2.54 Å.DFT calculations were also performed on the dinuclear  complex itself,22+ to the second Eu3+ centre likely prevents water coordination, resulting in an increased lifetime (τ=690 μs) compared to the [EuL] complex (τ=590 μs). Although Raman spectroscopy was attempted to characterise these interactions further, overlapping bands and weak signals precluded any definitive conclusion by this technique.Our DFT calculations should be taken with some care in view of the complexity of the systems under study, and the fact that our simplified model did not include explicit water molecules (bulk solvent effects were included using a polarizable continuum model). Nevertheless, they suggest that the polynuclear species formed upon UO1H NMR spectroscopy in D2O . To avoid the complexity associated with paramagnetic contributions, the association behaviour of UO2(NO3)2 with the diamagnetic surrogate complex, [YL], was studied.Cv2 symmetry and a coordination around YIII in which the nitrogen atoms and two phosphonate functions form a quasi‐planar pentadentate chelating arrangement; the two remaining phosphonate moieties are coordinated on the upper and lower hemisphere of the complex, with the in‐plane and out‐of‐plane phosphonate functions in rapid exchange on the NMR timescale.The solution assembly process was studied by 22+ results in a progressive decrease in intensity of the [YL] signals as a new set of peaks emerges. The new signals present significant downfield shifts with respect to the parent complex (Δδ≈+0.5 to +0.7 ppm), except for the aromatic methylene bridges, which show a significant shift to higher fields (Δδ≈−0.6 ppm). In contrast to the UV/Vis and emission spectroscopy titration, 1H NMR spectroscopy did not provide evidence for the formation of different heteronuclear species, suggesting they are in fast exchange under the conditions applied, even at lower temperatures . The relatively broad peaks of the new resonances compared with those of the [YL] complex are in line with this hypothesis. Additionally, the observation of up to five broad signals in the aliphatic region  suggests that the overall symmetry around the YIII ion is decreased to 2C, pointing to a rigidification of the structure upon UO22+ interaction and slower in/out‐of‐plane exchange of the phosphonate functions.Addition of UO22+. This example adds to the scope of recent examples of energy transfer in molecular lanthanide(III) complexes,22+ to [EuL], our data indicate the formation of heteronuclear adducts in solution, accompanied by an appearance of characteristic UO22+ transitions at 320 and 430 nm in the Eu3+ excitation spectra. Such transitions can only be due to resonant energy transfer from the UO22+ ion to Eu3+, with energy transfer efficiencies up to 97 %. Multiplex sensing may also be feasible through resonance fluorescence measurements.m) is higher than some previously reported (destructive) fluorescence sensors,m or ppm);Despite their widespread use as cation sensors, through both luminescence22+ and so, while other cations cannot cause the energy transfer presented, competing metal ions (e.g. Mg2+)22+ and lower the detection limit in actual environmental samples. However, up to 200 equivalents of environmentally ubiquitous Ca2+ ions have been shown not to significantly interact with [GdL].3+ complex specifically designed with a high UO22+ binding constant would result in a powerful and relatively inexpensive tool that could be developed to selectively detect environmental UO22+ in situ in contaminated groundwater sites.The complex used in this study was not designed to selectively bind UOThe authors declare no conflict of interest.As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re‐organized for online delivery, but are not copy‐edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors.SupplementaryClick here for additional data file.


Results of the investigated systems revealed the presence of the magnetic transition specific for UO2 in all three intermediate compositions of the uranium-thorium dioxide  and in the 238Pu-doped UO2 around 25 K. The magnetic behaviour of UO2 exposed to the high alpha dose from the 238Pu isotope was studied over time and it was found that 1.6% 238Pu affects the magnetic transition substantially, even after short period of time after annealing. In both systems the antiferromagnetic transition changes intensity, shape and Néel temperature with increasing Th-content and radiation dose, respectively, related to the increasing disorder on the crystal lattice resulting from substitution and defect creation.The low-temperature heat capacity of (U R per mole as established by Einstein and Debye, and can be studied with low-temperature calorimetric techniques.The regular substitution of one or more atoms in the crystal lattice of solid solution phases can affect their thermodynamic properties significantly. Since a substitutional atom has different characteristics compared to the original one, substitution can lead to lattice adjustment and strain, lattice disorder, breaking of magnetic order, etc., which all can affect the phonon states and their dispersion in the material and thus the thermal capacity and the thermal transport. Effects on the thermal capacity are generally observed at low temperature, well below the limit of 32 dioxide close-packed fluorite structure and complete solid solution series exists between all end members. Low-temperature calorimetric measurements of (Thy1−Puy)O21 showed that there is a substantial composition effect and the excess heat capacity was explained by the strain resulting from the substitution of isovalent ions of significantly different size on the cation sublattice, 96 pm for Pu4+ and 105 pm for Th4+. Similar measurements on (Uy1−Amy)Ox2− with y = 0.08 and 0.20 yielded less obvious results2. Again a substantial excess heat capacity was observed at very low temperature but also the complete absence of the magnetic transition due to the antiferromagnetic ordering of the U4+ ions even at a minor extent of dilution. However, the (Uy1−Amy)Ox2− solid solution is complicated by the fact that a charge transfer takes place and that americium becomes trivalent, compensated by a equimolar amount of pentavalent uranium. This results in a more complex O2 composition, and thus a higher “dilution” effect than formally. Moreover, americium is a highly radioactive material  and radiation effects due to alpha decay of 241Am create disorder that also may affect the phonon states and dynamics.All tetravalent actinide ions can be hosted in the AnOy1−Thy)O2 with y = 0.05, 0.09 and 0.12. In this material the non-magnetic Th4+ acts as diluent for the magnetic U4+ ions (no charge transfer), whereas the additional effect of distortion in the lattice due to the mismatch of the ionic radii (103 pm for U4+ and 108 pm for Th4+) is expected to be relatively small. Both elements are only mildly radioactive, and their handling allows to obtain heat capacity data of the highest quality and accuracy with the instrument employed, and radiation-induced disorder is negligible. Secondly, we measured the low-temperature heat capacity of uranium dioxide doped with the highly radioactive 238Pu isotope  as a function of aging time to assess the effect of alpha decay and the concomitant lattice disorder in the fluorite structure.In order to obtain information on the separate effects of dilution-induced disorder and radiation-induced disorder on the heat capacity of actinide oxides and particularly on the magnetic transition in uranium-based fluorite dioxide systems we have performed studies on two highly different materials. Firstly, we measured the low-temperature heat capacity of O2 solid solution with y = 0.05, 0.09 and 0.12 is shown in Fig. 23 and ThO25. λ-type anomalies are observed around 27.2 K, 25.1 K and 21.8 K, respectively for the intermediate compositions Th5, Th9 and Th12 with a maximum CP (J · K−1 · mol−1) of 33.3, 23.3 and 20.5, respectively. This heat capacity anomaly is related to the long range antiferromagnetic ordering of the spins of the U4+ ions in UO2 at low temperature, which was first observed by Jones et al.6 and analysed in detail later by Huntzicker and Westrum3. The nature of the transition has been further analyzed by neutron diffraction8 and NMR studies9. These studies showed that at low temperature the oxygen cage of the UO2 unit cell shows a Jahn-Teller distortion. The physics of the transition is very complex and is still subject of investigations. It is beyond the scope of this work and for details the readers are referred to the review by Lander and Caciuffo10.The heat capacity of U−y,ThyO2 N, as in the case of UO2. This should be taken into account when discussing the entropy values.This peak amplitude could be due to the fact that Huntziker and Westrum made a very detailed scan through the transition region (temperature step < 0.01 K) whereas we made a standard scan (>0.1 K). On the other hand it is a known weak point of our technique that it cannot accurately fit the time dependent relaxation data in case of a large heat capacity dependence near T2 solid solution. Both Comly11 and Hinatsu and Fujino12 studied the magnetic transition by magnetic susceptibility measurements and found a linear dependence of TN OCP/T over the squared temperature, as shown in Fig. y1−Thy)O2 solid solutions are well above those of the end members, UO2 and ThO2, revealing the significant excess heat capacity.When plotting 23 and ThO24 end-members, and by neglecting the magnetic transition for UO2 using the lattice heat capacity suggested by Huntzicker and Westrum3. The experimental results of (Uy1−Thy)O2 solid solution are in a good agreement with the computed values from the Neumann-Kopp rule and no significant difference for the measured temperature interval is observed, except the low-temperature range below the characteristic antiferromagnetic transition. Further, we have calculated the difference between the two heat capacity curves (measured and computed) and will refer to it as the excess heat capacity O2 solid solution. Overall, the N-K approximation is providing a straightforward approach to assess this and thus the For a further analysis of the magnetic anomalies, the “ideal” heat capacity (Neumann-Kopp) of the mixed oxides was estimated by interpolation based on the low-temperature literature data of UO2. The expected entropy of the triplet 3H4 multiplet of U4+ in pure UO2 is R ln(3) = 9.1 J · K−1 · mol−1. Huntzicker and Westrum3 reported 8.4 J · K−1 · mol−1 for the total anomaly and ~6.3 J · K−1 · mol−1 at the Néel temperature. The latter becomes 7.24 J · K−1 · mol−1 using the same analysis as for our measurements.Each individual peak has been been integrated using Origin Software (version 8.1) and the results are shown in Table 0.95Th0.05)O2, (U0.91Th0.09)O2 and (U0.88Th0.12)O2 at the Néel temperature were found to be 4.64, 4.26 and 3.74 J · K−1 · mol−1, respectively −1). These values should not be compared to the values for pure UO2 by Huntziker and Westrum because of the different calorimetric techniques. As stated earlier, Huntziker and Westrum made a very detailed scan through the transition region (temperature step < 0.01 K) resulting in a very sharp peakw, which our measurement technique does not capture fully. It is also a known weak point of the PPMS technique that it cannot accurately fit the time dependent relaxation data in case of a large heat capacity dependence near TN15, as in the case of UO2.The entropy values associated to the magnetic transition of O2 sample in the temperature interval from 5 to 50 K for different storage times after annealing of the sample are presented in Fig. λ transition rapidly changes shape and position with the aging time, c.q. accumulated dose.The results of the series low-temperature heat capacity measurements of the , the peak evaluation has been performed and the related thermodynamic data are given in Table 2 based on the same corrections made by Huntzicker and Westrum3 the excess entropies at the Néel temperature of the magnetic transition are found to decrease with time O2 solid solution. Moreover, the maximum of the peak O2 with about 2% Putotal, used in this work, has not been measured. Pure UO2 cannot serve as reference, as our results for O2 show that the heat capacity is already affected at low concentrations.As shown in Fig. 4+ ions in uranium dioxide is dramatically affected by the continuous self-irradiation from the high α activity of 238Pu, which leads to atomic displacements in the lattice and the subsequent formation of point defects and extended defects. Each α-decay produces about 1500–2000 displacements, which accumulate over time in substantial lattice disorder. In about 24 hours after annealing the intensity of the heat capacity peak specific to UO2 has diminished to about 5% from its original intensity, and further flattening of the peak occurs with increasing alpha-decays per mole of material. Since the change in the entropy is minimal, it must be concluded that the antiferromagnetic transition gradually changes into a Schottky-type anomaly with a significant part of the residual entropy redistributed over the entire temperature interval. This can be understood from the changes in the phonon dynamics and anharmonicity due to radiation induced disorder created by the strong 238Pu alpha emitter and magnetoelastic interaction between the magnetic moments in the uranium atoms and lattice distortions.Our results show that the antiferromagnetic ordering of the spins of the Uα self-irradiation in (Uy1−Thy)O2 is limited in this system, and the principal disorder mechanism is substitution on the metal sublattice. Our analysis of the antiferromagnetic transition in (Uy1−Thy)O2 shows that the substitution of five of the twelve uranium atoms in the unit cell by thorium suppresses the long-range magnetic ordering in the solid solution. The cation size difference between U4+ (100 pm) and Th4+ (105 pm) is smaller than between Pu4+ (96 pm) and Th4+, but the excess heat capacity at low temperature (<20 K) is substantially larger than for a similar extent of substitution in (Thy1−Puy)O2 samples measured previously1, as shown in Fig. P/T vs T2. We attribute this to the broadening of the λ-transition and its shift and extension to lower temperatures with increasing extent of substitution; the excess heat capacity due to lattice strain being masked in the tail of the transition, which changes from a sharp λ-type peak to a more broad and diffuse transition. This phenomenon is known from other antiferromagnetic materials such as Zn2VO(PO4)2 doped with Ti4+16, doped LaSr2Mn2O717, or Mg2O418.The heat capacity of a fluorite-structured mixed dioxide is strongly driven by the interaction of the phonons with the metal atoms of the end-members of the solid solution. Taking into account that both uranium and thorium have long half lives, lattice disorder (displacements and vacancies) resulting from y1−Thy)O2 and (Thy1−Puy)O2 extrapolate to zero at 0 K, indicating perfect crystal properties and no effect of substitution on the metal sublattice. In contrast the heat capacity of O2 sample shows a significant residual heat capacity at 0 K which can be attributed to disorder caused by self-radiation, since the residual value clearly increases with time/dose. We conclude that the principal causes for this are the creation of uranium Frenkel pairs and oxygen Frenkel pairs in the crystal lattice, and extended defects at high doses. With increasing dose (c.q. concentration of defects) the antiferromagnetic transition in this sample transforms from a sharp peak to a broad anomaly. According to X-ray diffraction measurements, the lattice expansion due to accumulated dose (time) reaches saturation  in this sample after about 300 days and results in a disordered quasi-equilibrium state in which defect creation and recombination balance each other. Staicu et al.19 concluded from thermal annealing experiments of 238Pu-doped UO2 that both oxygen and uranium interstitials are present in the material. Moreover, defects that escape from the recombination can concentrate into loops and voids20. Molecular dynamics simulations of alpha decay in UO2 by Van Brutzel and Rarivomanantsoa21 showed that the number of oxygen Frenkel pairs is twice as high as the uranium Frenkel pairs, and that the number of displaced atoms in stable point defects at the end of the cascade is 13% for uranium and about 2% for oxygen. Thus it can be concluded that the disordered quasi-equilibrium state has not yet been achieved in our experiments after 277 days and further change in the transition thermodynamics can be expected.The heat capacity of both . Considering that both Uranium Frenkel Pairs (UFP) and Oxygen Frenkel Pairs (OFP) are formed in the damaged crystal lattice, the Néel transition in the O2 sample will no longer correspond to a disorder-order transformation, but to a transition between two disordered states with reduced long-range magnetic ordering. The strong lattice disorder in the material with formation of UFPs and OFPs will lead to changes in the dynamics between the U4+ and the surrounding O neighbours and likely results in a splitting of the It is interesting to hypothesise how the radiation affects the electronic states of UT - TN as temperature axis . Although, the overall change in peak shape of the two investigated systems is comparable, the strong asymmetry of the 238Pu-doped system evidences that disorder on the metal and oxygen sublattice may lead to similar magnetoelastic effects.In Fig. 2 is highly sensitive to disorder in the crystal lattice, as discussed by Huntzicker and Westrum3 in their seminal paper. They explained the difference between their results and those by Jones et al.6, that revealed a much less pronounced anomaly at a lower temperature, by the presence of oxygen interstitials as a result of a hyperstoichiometric composition of the UO2.01 sample. We, here, have shown that lattice disorder caused by metal ion dilution and radiation damage has a similar effect on the transition characteristics, with a measurable impact at already low concentrations and moderate doses.In conclusion we can state that the antiferromagnetic heat capacity anomaly in UO2 samples with three Th concentrations  were prepared using a hydrothermal method24. The synthesis was conducted under argon and in the presence of minute amounts of hydrazine in order to limit the oxidation of the U4+. As starting materials we have used solutions of Th4+ (1.9 M in 8 M HNO3) and U4+ 2 solution in 4 M HNO3 containing 0.5 M of hydrazine). The other reagents  were of analytical grade and used as supplied by Merck.O4+ solutions in nitric acid with ammonium hydroxide (10–20% excess). The obtained coprecipitates were washed several times with distilled water in order to remove any trace of nitrate, which may induces the oxidation of U4+ to soluble U6+ under the working temperature conditions. The decomposition was conducted under hot compressed water for 5 h at 250 °C in teflon autoclaves. The resulting nanocrystals (circa 3.5 nm) were washed with water, ethanol and acetone, in order to gradually decrease the polarity of the solution. Pellets of 3.5 mm diameter and several mm in height were produced by pressing and heated for 5 h at 1000 °C (1st step) and 24 h at 1650 °C (2nd step) under Ar-H2 (4%).The hydroxides were firstly produced by direct coprecipitation of the AnThe real U and Th concentration in the samples was measured by Inductively Coupled Plasma Mass Spectrometry (ICP-MS) using a A ThermoFinnigan Element instrument with auto-sampler, according to an appropriate standardisation method. The results are summarized in Table 2-238PuO2 sample was obtained by pressing and sintering of a powder produced via liquid route, guaranteeing a homogeneous and intimate mixing. The metal content of the 238PuO2 was 87%wt Pu, 73%wt being 238Pu, the remaining 13% being the decay product uranium 234. The composition was chosen considering the activity of the dopant powder and tuning the dopant concentration to fit the aging of the sample to a reasonable period of time. The Pu dopant powder was dissolved as received using HNO3 and dropwise addition of HF, and then added to the corresponding amount of uranyl solution. Precipitation was achieved by adding ammonia to the solution, and the resulting precipitate was washed with distilled water several times and then filtered on paper filters. The paper filters were burnt away during a pre-calcination step (6 h at 400 °C) under air and then the powder was calcined at 700 °C for first 2 h in air (N2 + 20%O2) to remove any remaining paper and finally for 2 h under Ar-H2 (4%). This powder was then pressed in 5 mm disks of roughly 80 mg each with a force of 14.5 kN (738 MPa) and sintered for 6 h under Ar-H2 at 1650 °C. Based on elemental and isotopic composition analysis done in March 2016 by ICPMS the actual composition of the investigated sample is (234U0.0037235U0.0070238U0.9680238Pu0.0156239Pu0.0047240Pu0.0008)O2 and represents 99.98%. The diference of 0.02% is given by the sum of the isotopes 241Am, 233U and 236U. From chemical point of view the sample contains just uranium and plutonium being virtually free of americium and other impurities. We will refer to this composition as O2. Table The UO2 samples agree excellently with the cell parameters derived from Vegard’s law. Also the value for the O2 sample corresponds well to the lattice parameter derived Vegard’s law considering the actual composition. This confirms that all our samples are homogeneous solid solutions of stoichiometric composition. Homogeneity of the mixtures is evident also in the SEM images  diffractometer mounted in a Bragg–Brentano configuration with a curved Ge  monochromator and a ceramic copper tube  and supplied with a LinxEye position sensitive detector. The cell parameters of the investigated compositions derived from a Rietveld analysis, are listed in Table ges Fig.  that havy1−Thy)O2 with y = 0.05, 0.09 and 0.12 was measured using a low-temperature vacuum calorimeter based on a hybrid adiabatic relaxation method  as described in our previous paper2. The measurements of the Th5, Th9 and Th12 samples were carried out using small solid pieces with the masses of 47.4 mg, 37.1 mg and 57.1 mg, respectively, in the temperature intervals of 2.05 to 304.10 K, 1.86 to 292.93 K and from 1.94 to 297.50 K. Different from our measurements of other actinide oxide solid solutions2, these samples have been measured without protective encapsulation into Stycast (for radioprotection purposes) which results in a high accuracy of the PPMS apparatus with estimated uncertainties for the heat capacities of about 1 to 2% as reported by Lashley et al.15.The heat capacity of (U238Pu)O2 sample, the same instrument has been used for measuring the heat capacity as a function of aging time. Since the main objective of this study was to study the behavior of the magnetic peak, we have focused our investigation in the interested temperature region and measurements have been performed in the temperature interval from about 5 K to 50 K. The sample consisted of one small solid piece with mass of 1.4 mg and for radiation protection reason it was wrapped in Stycast25 which increased the uncertainty to about 4 to 5% after the corresponding heat capacity was subtracted. Before the first measurement, the sample was annealed for 4 hours into Ar/H2 atmosphere (1 L/min.) at 1650 °C to eliminate the self-radiation damage in the lattice accumulated during the storage at room temperature in the period between fabrication and measurement. After annealing and Stycast encapsulation the first measurements have been carried out after about 24 hours and we consider this moment as being the reference time point (t1) with minimum radiation damage. The subsequent measurements have been performed after different time intervals, 15 days (t2), 53 days (t3), 78 days (t4), 102 days (t5), 130 days (t6), 165 days (t7), 176 days (t8), 192 days (t9), 221 days (t10), 254 days (t11) and 277 days (t12) for better understanding the influence of the cumulative radiation dose on the thermal properties of the mixed oxide. In between the measurements the sample was stored at room temperature.In the case of (U,


Methanol is a benchmark for understanding tropospheric oxidation, but is underpredicted by up to 100% in atmospheric models. Recent work has suggested this discrepancy can be reconciled by the rapid reaction of hydroxyl and methylperoxy radicals with a methanol branching fraction of 30%. However, for fractions below 15%, methanol underprediction is exacerbated. Theoretical investigations of this reaction are challenging because of intersystem crossing between singlet and triplet surfaces – ∼45% of reaction products are obtained via intersystem crossing of a pre-product complex – which demands experimental determinations of product branching. Here we report direct measurements of methanol from this reaction. A branching fraction below 15% is established, consequently highlighting a large gap in the understanding of global methanol sources. These results support the recent high-level theoretical work and substantially reduce its uncertainties. The reaction of hydroxyl and methylperoxy radicals has recently been suggested as the source of missing methanol in the remote troposphere. Here, the authors present direct experimental measurements demonstrating the reaction leads to further underprediction of modelled methanol. In the absence of substantial anthropogenic contributions, dominant atmospheric sinks of OH are reactions with CO and CH4. The reaction of OH with CH4 (1) yields the simplest and most abundant atmospheric alkylperoxy radical, methylperoxy (CH3OO)3The hydroxyl radical, OH, sometimes called the tropospheric detergent, is an essential oxidant3 atmospheric sinks include reaction with NO, HO2, and self- and cross-reactions with other peroxy radical species4. The latter reactions lead to methanol production of 48 teragrams (Tg) per year5 and are consequently an important source of atmospheric methanol, in particular over remote regions where primary emission sources, such as plant growth, plant decay, and anthropogenic sources are negligible7.Steady-state concentrations of methylperoxy range between 1–20 ppt;9. Oxidation of methanol forms species including CO, formaldehyde, and tropospheric ozone10, and reactions of alcohols may have subtle, indirect effects in the formation of secondary organic aerosols11, therefore impacting the tropospheric oxidising capacity, air quality and human health. Atmospheric methanol abundances are dominated by direct emissions but sources also include oxidation pathways of methane and other volatile organic species. Methanol is thus a benchmark for the performance of atmospheric models. Despite inclusion of multiple methanol production pathways, global atmospheric chemical models are presently unable to reconcile the modelled and measured methanol abundances over remote regions5, and so other production pathways have been sought.Methanol concentrations range from 1–15 ppbv in the continental boundary layer and 0.1–1 ppbv in the remote troposphere3OO had not been investigated, despite the large rate coefficient recommended by Tsang and Hampson12 (k = 1 × 10-10 cm3 s-1) and the suggestion that a major product would be methanol (CH3OH)13. Four likely product channels exist:Until recently, the coupling between OH and CH15 established a high rate coefficient for reactions of OH with methylperoxy (CH3OO), between 1–2 × 10−10 cm3 s−1, with similar rate coefficients for larger alkylperoxy radicals17. The branching fractions for the product channels of the OH + CH3OO reaction have been estimated through theoretical approaches by Müller et al.18 and channels (2) and (3) probed experimentally by Yan et al.14 and Assaf et al.19. To date, no experimental studies have directly measured ϕCH3OH.Recent experiments18, which characterise key stationary points on the reaction potential energy surface including the three bimolecular product channels (2–4), the trioxide association product (CH3OOOH) (5) and a pre-product complex. Müller et al. ascertained product branching ratios through RRKM calculations, which, notably, identify triplet entrance routes as “entirely negligible,” and show the dominance of the singlet trioxide intermediate, which can rapidly convert to the pre-product complex (CH3O…HOO), which has only a 40 ps lifetime at its initial energies. The coupling via intersystem crossing (ISC) of the singlet and triplet states of the product complex affects the product branching. The singlet state primarily undergoes rapid H-bond scission to yield bimolecular products CH3O + HO2 (2) with a small (~5%) component dissociating to CH3OH and O2 (1Δ). The triplet state has competing pathways: direct and indirect CH3O + HO2 production (the latter via ISC back to the singlet state) or rearrangement and subsequent decomposition to CH3OH + O2 (3Σg−). The multiple favourable routes to (2) serve to facilitate high yields of HO2 and CH3O; branching from the triplet state of the pre-product complex to methanol (4) is calculated to be about twice as favourable (~10%) as its formation from the singlet surface. However, Müller et al18. estimated that the uncertainty in the stationary point energies and in the ISC probability gave uncertainties of a factor of 3.5 in the branching fractions. Dramatically different tropospheric effects are encompassed by the upper and lower limits of the methanol yield, ϕCH3OH, given by Assaf et al.19 (0–40%), Müller et al.18 (2–30%) and Ferracci et al.20 (0–40%).Substantial mechanistic insight into this reaction is given by the high-level ab initio calculations in Müller et al.21 based on box model analysis and was built on by Fittschen et al.22 using data from the remote Cape Verde Observatory. Khan et al.5 included this reaction in a global model and noted the importance of this reaction with respect to background methanol if the channel (4) forming methanol were significant. Recent studies  suggest that a large ϕCH3OH would dramatically change methanol levels. Applying a yield of 0% for (4) within a global chemical transport model, Müller et al.18 find that the discrepancy between modelled and measured atmospheric methanol is significantly exacerbated, owing to the loss of CH3OO through reaction with OH, rather than the self-reaction, which yields CH3OH. Only with a yield of 30% for (4) were Müller et al.18 able to reconcile measured and modelled methanol.The potential importance of this reaction, especially in the remote troposphere, was noted by Archibald et al.20 argue that the total rate coefficient indicated by the most recent determinations15, lower than that used by Müller et al.18 would place even more stringent requirements on the methanol yield needed to improve model-measurement agreement; the yield of (4) would need to be in excess of 0.8 to reconcile modelled and measured methanol abundances. We report direct determinations of the methanol yield using two different experimental approaches: isotopologues of OH + CH3OO via multiplexed photoionization mass spectrometry (MPIMS) and a chamber study coupled to proton-transfer reaction time-of-flight mass spectrometry (PTR-TOFMS).The existing error bounds on the methanol yield, therefore, leave uncertainties not merely on the magnitude but even on the direction of the impact of this reaction, which highlights the need for direct experimental quantification of the yield. Ferracci et al.3OO reaction were quantified at 30 Torr in pulsed photolytic experiments using the Sandia multiplexed photoionization mass spectrometer, and at 740 Torr using a new high-pressure reactor, both interfaced with the tuneable-VUV-output of the Chemical Dynamics Beamline (9.0.2) at the Advanced Light Source of Lawrence Berkeley National Laboratory (see the Methods section for further details). At 30 Torr methylperoxy radicals were produced by photolysis of 13CH3I (to move the methanol mass away from 32O2 background) in the presence of a large excess of O2, and OH was produced by photolysis of H2O2. In the 740 Torr experiment, reactions of F-atom (generated by photolysis of XeF2)15 with CH4 and D2O produced CH3 and OD in the presence of O2. Photoionization mass spectrometry detects precursors, intermediates, and products. Primary and secondary reaction products were observed, including HCHO, HO2 and methanol, confirmed by their photoionization spectra  and product concentrations in the photoionization measurements . No evidence is found for the formation of the Criegee intermediate (reaction 3), consistent with the upper limit of 5% reported elsewhere19.The products of the OH + CH3OO reaction, with the branching fraction of CH3OH from the OH + CH3OO reaction as a fitted parameter % (assuming negligible branching to (3) and (5)) from a series of six measurements of the 13CH3OO + OH reaction. Figure φCH3OH from Müller et al.18The observed product concentrations were compared to a kinetic model including the OH + CH18 also showed that at increased pressures, a greater fraction of the trioxide association product (5) is stabilised, predicting a trioxide fraction of approximately 11% at ~1 atm total pressure (c.f. ~0.02% at 30 Torr), at the expense of bimolecular product channels. We find significant evidence for the stabilisation of the trioxide at 740 Torr, but not at total pressures ≤ 30 Torr, consistent with the calculations of Müller et al. , and insensitive to photolysis fraction or overall rate coefficients. Analysis returns ϕCH3OH = (6 ± 2)%  and generation of the reactants. Oxygen  atoms were formed by 254 nm photolysis of O3 in the presence of CH4 and H2O at 760 Torr of synthetic air, producing OH radicals (further details in Supplementary Note 3OO through reaction (1), which after a few seconds reached a steady-state concentration , as demonstrated in Fig. 3/CH4 ratios, surface/volume ratios and photolysis rates %.Reactions were also carried out at atmospheric pressure in a 300 L Teflon bag18 yield of ~11% at atmospheric pressure, and observed in the 740 Torr MPIMS experiments (Supplementary Note 18) in the chamber or sampling line, or fragment upon protonation in the PTR-TOFMS detection system, as has been observed for many organic species31. The laser photolysis measurements probe reaction times before substantial heterogeneous reaction and directly photoionize molecules sampled by rapid molecular beam expansion. PTR-TOFMS does not detect sizeable concentration of CH3OOOH . We have undertaken preliminary ab initio calculations that demonstrate that even if trioxide survives the sampling, it may be detected as protonated methanol  has a barrier, but there is a barrierless water-catalysed dissociation pathway . It is, therefore, likely that the appreciable yield of trioxide stabilised at the higher pressures of the chamber experiments will lead to additional signal at the protonated methanol mass, resulting in artificially enhanced methanol yields in the chamber experiments. Because there is no method for calibrating the PTR-TOFMS for trioxide, the degree of interference cannot be directly determined.The methanol fractions obtained in the chamber experiments are higher than in the pulsed photolysis experiments, even considering the respective error bars. The relevant differences between the experiments lie in the sampling, detection, and residence time. Based on these three factors we conclude that the stabilised trioxide (5), with a predicted3OO reaction and its branching on tropospheric composition, we compared a STOCHEM-CRI model that included the title reaction  and φCH3OH = 7% to a base case integration that omitted it. This base case scenario is in accordance with other studies18 that isolate the effect of the OH + CH3OO reaction; any assignment of φCH3OH would serve to change predicted CH3OH, HOx, or products of CH3OO reactions. Compared to the base case, addition of the OH + CH3OO reaction with the φCH3OH = 7% made only small changes to the global burdens of OH (−0.9%), CO ( + 1.0%), O3 (−1.3%), CH3OH (−1.7%) and HCHO (−0.6%)  but had a substantial impact on the global burdens of HO2 ( + 7%), CH3OO (−19.6%), CH3OOH (−11.7%) and other alkyl hydroperoxides (ROOH) ( + 4.8). The OH + CH3OO reaction decreases CH3OO (−19.6%) because of removal via reaction with OH and increases the production flux of HO2 through reaction 2 and thereby increases the production of other ROOH. Simultaneously, reaction 4 increases the net production flux of methanol by only 3 Tg/yr from the base case scenario, with 28.7 Tg/yr obtained from peroxy radical reactions (within the range of previous estimates of 15–38 Tg/yr)23.To determine the effect of the OH + CHφCH3OH of 17%  estimated for φCH3OH = 30% by Müller et al.18.However, a 18 utilised a yield of 30% for reaction (2c), the upper limit of their calculated range and also the higher rate coefficient32, k = 2.8 × 10−10 cm3 molecule−1 s−1. However, Ferracci et al.20 used k = 1.6 × 10−10 cm3 molecule−1 s−1 in their modelling study and found comparatively lower CH3OH production (60 Tg/yr) using the yield of 40%, suggesting that a far higher yield would be needed to reconcile models with measurements. The experimental data presented herein demonstrates that the branching fraction at 298 K is instead closer to the calculated value of ~7% producing only 22.4 Tg/yr methanol, which is smaller than required to rationalise atmospheric observations.To reconcile modelled and measured methanol abundances, Müller et al.3 (−4%), CO ( + 2.5%) and HCHO (−2.5%), and significant changes are observed for HO2 ( + 25%), CH3OOH (−18%) and ROOH ( + 40%) . Increases in CH3OH are found over terrestrial locations, but substantial reductions of up to 30% are estimated in remote tropical regions. Here, the reduction in CH3OO due to its reaction with OH has retarded the in-situ production of CH3OH through the self-reaction of CH3OO and its cross-reactions with other peroxy radicals at remote sites33. Therefore, rather than provide a new source of remote CH3OH, with a ~7% yield of 2(c), inclusion of the OH + CH3OO reaction exacerbates the underestimation of remote CH3OH.The spatially resolved changes in annual surface levels, compared with the base case integration, are shown in Fig. 3OO  can begin to contribute to tropospheric CH3OH over remote tropical oceans. Using the experimentally determined methanol branching fraction of 6%–9% would lead to a significant decrease in atmospheric methanol, specifically in remote regions.Further integrations with different methanol yields ranging from 0.1 to 1 from OH + CH3OO Fig.  show tha18, which shows that the reaction 4 has little impact on modelled CH3OH level over mid-latitudinal remote oceanic areas . Müller et al.18 use a fraction of 0.65 for tropospheric conversion of trioxide to CH3OH, assuming gas-phase release of methanol from the condensed phase. However a peak fraction of only about 0.2  is predicted to directly produce gas-phase methanol, with most trioxide removed by wet deposition (and condensed phase formation of CH3OH)18. Assuming 65% conversion of trioxide to methanol, in addition to our experimentally determined methanol yield of 6–9%, leads to an effective yield around the compensation point of 15%.Figure 3OO, agrees with the small methanol production predicted by Müller et al.18. In their calculations, the constrained nature of the transition state to hydrogen transfer leads to a preference for direct scission of the pre-product complex to the HO2 and CH3O products over methanol formation on both the singlet and triplet surfaces. The present results confirm this preference for CH3O, but because both spin manifolds can produce both products, and the uncertainty in the yield encompasses the predicted methanol branching fractions on both surfaces, it is difficult to draw strong conclusions about the role of intersystem crossing in the reaction. However, the experiments considerably improve the uncertainty bounds on the yield, with the MPIMS-determined yields in remarkable agreement with the high-level calculations. Characterisation of the methanol signal in the MPIMS experiment via photoionization energy spectroscopy through comparison with the known literature photoionization energy spectra ; further investigations as a function of RH may help to determine whether a water effect on reaction 2, or perhaps unexplored functionalized peroxy radical cross-reactions, may be part of the missing source of atmospheric methanol.Inclusion of this reaction in a global atmospheric chemistry and transport model could not improve the methanol discrepancy between model and observations; the direct methanol branching fraction results in a factor of 1.5 underprediction of methanol in remote environments. This work highlights the necessity for further characterisation of potential atmospheric methanol sources, including understanding the tropospheric fate of the trioxide (5). Moreover, Khan et al.3I or 13CH3I, H2O2, O2) and bath gases (He) were flowed into a halocarbon wax-coated quartz reactor via a set of calibrated mass flow controllers. H2O2 was produced by heating urea hydrogen peroxide and was entrained into the He flow via a pressure- and temperature-controlled bubbler. At the high concentration of O2 utilised in the experiments (2.6 × 1017 cm−3) a significant O2 peak was observed ~m/z = 32, ionised by the small amount of transmitted higher undulator harmonics. Because the masses of 16O2 (31.98984 amu) and 12CH3OH (32.02622 amu) could not be completely resolved, experiments were performed using 13CH3OO, such that the resultant methanol signal was well separated in mass from O2. OH and 13CH3, the chemical precursor to 13CH3OO, were produced photolytically via a 248 nm excimer laser aligned along the axis of the reactor. 13CH3OO was produced from the subsequent reaction of 13CH3 with excess O2, yielding a [13CH3OO] excess over [OH] of a factor of 3–6. Reactant and product species were continuously sampled via a 600 μm orifice in the reactor sidewall. The resultant molecular beam was intercepted by the ionising tuneable-VUV radiation, and ions were detected via time-of-flight mass spectrometry. Single photon-energy measurements at 11 eV yielded simultaneous obtained kinetic plots over the whole m/z range (~2–159 amu). Photoionization spectra, whereby the ionisation energy was scanned stepwise in 25 meV steps, are used to definitively identify the detected species.Measurements were performed at 298 K and 30 Torr using the Sandia Multiplexed Photoionization Mass Spectrometer (MPIMS) instrument coupled to the tuneable-VUV-output of the Chemical Dynamics Beamline (9.0.2) at the Advanced Light Source, Lawrence Berkeley National Laboratory. Reagent (CH3 and OD by reaction of F atoms (formed by 248 nm photolysis of XeF2) with CH4 and D2O in the presence of ~1018 cm−3 [O2] and excess He. Details of the conditions at which the experiments were performed, and the chemical model are given in Additional measurements performed at 740 Torr were carried out in a quartz-lined metal reactor sampled through the end wall. The higher-pressure experiments produced CH3 in the presence of water vapour (2.5–3.8 × 1016 cm−3) was carried out using 1–8 Hg lamps. Methane  was introduced in the reactor using ml syringes to get initial concentrations between 1.8 × 1014 and 3.7 × 1014 cm−3. The CH4 relative concentrations were determined both by infrared spectroscopy at around 1800 cm−1 and by high-resolution proton-transfer reaction time-of-flight mass spectrometry (HR-PTR-TOFMS Ionicon 8000). Although the CH4 proton affinity is lower than the water proton affinity, a small signal scaling with the CH4 concentration was detected by the PTR-TOFMS instrument due to the high concentrations used in these experiments. Ozone was produced by a commercial O3 generator  and initial concentrations of (2.0–8.4) × 1013 cm−3 were obtained. The O3 time-dependent concentrations were measured using a UV-absorption analyser (Environnement SA 42 M) while methanol and formaldehyde were measured by PTR-TOFMS. Absolute methanol concentrations were determined after daily calibrations of the PTR-TOFMS transmission curve using a Gas Calibration Unit  and a gas standard composed of methanol, acetaldehyde, acetone, benzene, toluene, o-xylene and 1,2-dichlorobenzene . Formaldehyde measurements were also calibrated by adsorption on 2,4-DiNitro Phenyl Hydrazine cartridges and analysis through High-Pressure Liquid Chromatography (HPLC-UV) for some of the experiments36. The agreement between PTR-TOFMS and HPLC was within 20%. Methanol and formaldehyde wall losses were also negligible (<1% h−1).Chamber experiments were performed in a 300 L Teflon simulation chamber suspended in a closed box where photolysis of O38 and pertinent details are given herein.The STOCHEM-CRI model has been described in previous papers39. The UM works on a grid resolution of 1.25° longitude, 0.833° latitude and 12 unevenly spaced  vertical levels between the surface and a upper boundary of ~100 mb40. The description about the meteorological parameterisations  can be found in Percival et al.41. The model used in this experiment is an ‘offline’ model and hence the meteorological data are archived within the code itself. Each air parcel contains the complete 229 species in the code, which can take part in any of the reactions detailed. The chemical mechanism used in STOCHEM is the common representative intermediates version 2 and reduction 5 (CRI v2-R5), which was built using a series of five-day box model simulations on each compound, on a compound-by-compound basis. The performance of the chemistry of these simulations was optimised using the Master Chemical Models (MCM version 3.1)42. More details of the CRI v2-R5 mechanism can be found in Watson et al.43 and Utembe et al.42. The photolysis reactions were calculated by integrating  the product of flux, absorption cross-section and quantum yield40, which were included in the model as described in Khan et al.3. In addition to the gas-phase chemical reaction and photolysis, the air parcels also consider emissions and physical removal processes (dry and wet deposition). Air parcels within the planetary boundary layer can see removal of certain species by dry or wet deposition. The rate of dry deposition is dependent on whether the air parcel is over land or ocean with appropriate species dependent deposition velocities. The dry deposition velocities used in STOCHEM were adapted from the annual mean values calculated using the MATCH global model45. The scavenging coefficients for convective and dynamic precipitation taken from Penner et al.46 were combined with precipitation rates and scavenging profiles to calculate the loss rates of species (wet deposition) from an air parcel. Emissions are treated as an additional term to the source fluxes of each species during each integration time step, rather than a step change in species concentration47. Emissions are from the surface and split into five main classes: anthropogenic, biomass burning, oceans, soils and vegetation. Emission data is mapped onto a monthly 5o longitude × 5o latitude resolution, two-dimensional source map. The emissions data employed in the base case STOCHEM model were adapted from the Precursor of Ozone and their Effects in the Troposphere (POET) inventory for the year 199848. More details about the emissions data can be found in Khan et al.5. The concentrations produced from an integration is mapped onto an Eulerian grid resolution 5o × 5o with 9 vertically spaced pressure levels, each 100 hPa thick. Summing the 50,000 air parcels produces a global burden for each species, which can be broken down into the respective source and sink fluxes.STOCHEM is a global 3-dimensional chemistry transport model that adopts a Lagrangian approach splitting the troposphere into 50,000 constant mass air parcels. As it is a Lagrangian model, the transport and chemistry can be decoupled and hence these air parcels are advected with a 3-hour time step by meteorological data from the UKMO Hadley Centre global general circulation model called the Unified Model (UM)−3 s−1. In this study, base case experiment involves the STOCHEM being integrated with the CRI v2-R5 mechanism subsequently referred to as ‘STOCHEM-base’37. A further simulation was performed in the study, which involved the STOCHEM-base being integrated after including the reaction OH + CH3OO with two product channels (2 and 4). The simulations were conducted with meteorology from 1998 for a period of 24 months with the first 12 allowing the model to spin up. Analysis were performed on the subsequent 12 months of data.The flux outputs are calculated within each grid square by dividing the average flux per air parcel by its volume, which gives volume-averaged fluxes with units of cmSupplementary InformationPeer Review File


This study aims to assess both feasibility and accuracy of renal dosimetry imaging protocols in patients receiving Lutate therapy for neuroendocrine tumours (NETs), when data acquisition over multiple days is not possible on all cycles.t1/2 average) derived from the first half of contributing patient data was used to estimate absorbed dose for subsequent patients based on 4 h imaging alone; method 2: t1/2 average was applied to subsequent patients on 24 h imaging alone; method 3: a patient-specific clearance rate (t1/2 patient) was determined from complete image data of cycle 1 and applied subsequently to remaining cycles using 4 h image data alone; method 4: t1/2 patient was applied to 24 h imaging alone in subsequent cycles; method 5: the 120 h data was estimated on subsequent cycles based on the cycle 1 fraction of injected activity (%IA) at 24 and 120 h.Patients who had received a full 4 cycles of Lutate therapy with complete imaging at each cycle were included. Imaging consisted of quantitative SPECT/CT of the kidneys at 4, 24 and 96–120 h post injection. Renal absorbed dose was calculated for each data set, and in addition, five alternative methods were explored for comparison. Method 1: a patient average clearance time . The use of complete image data on cycle 1 and the derivation of t1/2 patient led to improved dose estimates, with an average deviation from true values of 13% and 2% when using 4 h data only and 24 h data only, respectively. The use of a 120 h %IA derived from cycle 1 led to an average deviation from true dose estimates of 14%.Twenty treatments from 18 patients, resulting in 80 cycles of therapy, were analysed. The measured average renal absorbed dose per cycle of treatment was 0.38 ± 0.19 Gy/GBq when derived from full imaging data. The use of In instances where demands on both patients and facilities make multiple time point data acquisition impractical, renal dosimetry is best derived through complete imaging at cycle 1 only followed by a single 24 h imaging time point on subsequent cycles, assuming no significant changes in renal function during the time course of therapy. This The aim of this retrospective study was to compare various methods of deriving renal dose estimates in Lutate patients when full imaging data sets are not available and so propose an alternative imaging protocol for clinics that are unable to perform multiple time point image acquisitions for all treatment cycles.177LuCl3 that was used. For carrier-added 177LuCl3 , synthesis was performed using the manual bench-top method. For non-carrier-added 177LuCl3 , synthesis was performed using the Eckert & Ziegler Modular Lab PharmTracer automated synthesis system.Our centre performs 4 cycles for each course of Lutate treatment, each of a standard ~ 8 GBq. The Lutate used for treatment in this cohort of patients was synthesised by two different methods depending on the type of Patients that had completed all cycles of treatment with full imaging performed at each of the 4 cycles were considered for review. Full imaging consisted of quantitative SPECT/CT with the kidneys in the centre of the axial field of view (FoV) at time points 4, 24 and 96–120 h after injection. Image quantification included CT-derived corrections for scatter and attenuation  as well Dose estimates were derived by defining kidney volumes of interest (VOIs) on the co-registered CT data and using the calculated percent injected activity at each time point to fit time-activity curves (TACs) in OLINDA-EXM . The appt1/2 average). This was then applied to the other half of the cohort assuming they had only 4 h imaging acquired. As such, the 24 h and 120 h imaging data were estimated by applying t1/2 average to the 4 h percent injected activity value, and all time points used in OLINDA-EXM to estimate dose to kidneys at each cycle.Half of the available patient cohort was used to derive an average renal clearance half-time  for each patient. This was then applied to subsequent cycles for that patient assuming they only had 4 h imaging acquired. As such, the 24 h and 120 h imaging data were estimated by applying t1/2 patient to the 4 h percent injected activity value, and all time points used in OLINDA-EXM to estimate dose to kidneys at cycles 2, 3 and 4.The complete imaging data for cycle 1 were used to derive a patient-specific renal clearance half-time  present at 120 h as a fraction of that at 24 h. Subsequent cycles were assumed to have only 4 and 24 h imaging available, which were scaled by the derived fraction to create a pseudo-120 h time point. All time points were then used in OLINDA-EXM to estimate dose to kidneys at cycles 2, 3 and 4.Comparison of each method with the gold standard approach using all available image data was assessed with Bland-Altman analysis based on relative differences. The relative difference in derived absorbed dose estimates between each method and the gold standard approach were calculated, and the standard deviation was estimated treating variability at both the intra- and inter-patient level equally. Whilst the absorbed doses across the total 80 cycles of therapy are not strictly independent, given the relatively high number of degrees of freedom, this was thought to be a valid assumption for statistical interpretation. The limits of agreement were defined as the average difference ± twice the standard deviation (2SD).A total of 20 complete courses of treatment from 18 different patients , resulting in a total of 80 cycles of therapy, were included in the analysis. The average and standard deviation of the injected radioactivity per cycle of treatment was 7756 ± 418 MBq. The average renal absorbed dose per cycle of treatment was measured as 2.9 ± 1.4 Gy, or 0.38 ± 0.19 Gy/GBq of injected Lutate. The average renal clearance half-time derived from the first 40 cycles of therapy included in the study was 54.2 ± 12.6 h, or 53.0 ± 15.6 h from the complete cohort. This was derived through a mono-exponential fit to the data.t1/2 average to estimate both 4 h and 120 h time point data (method 2) leads to more accurate dose estimates when compared to using t1/2 average to scale 4 h imaging only (method 1). Similarly, the use of 4 h imaging only in conjunction with a cycle 1 derived patient-specific half-time (method 3) demonstrated relatively large random differences with limits of agreement 14 ± 68%. The method that achieved results most consistent with the gold standard approach was method 4 (the use of full imaging at cycle 1 and 24 h imaging at cycles thereafter) resulting in limits of agreement of 2 ± 30%. The use of full data on cycle 1 to estimate 120 h time point data on subsequent cycles (method 5), i.e. two imaging time points still required, also produced acceptable estimates of kidney dose with limits of agreement of 14 ± 30%.Table In Australia, most patients receiving Lutate therapy do so on an out-patient basis. Given the large distance for referrals to specialist NET centers, this can make temporal imaging for dosimetry purposes challenging. Even in the case of centers who keep patients in following therapy for radiation protection purposes, prolonged camera time may not be easily accessible or optimal for patients comfort. If clinical and/or patient logistics do not allow more than one imaging time point to be performed on any cycle, then the use of an average patient clearance time is best applied for scaling of a 24 h acquisition as opposed to a 4 h acquisition. Application to a sole late time point 120 h) acquisition was not investigated as, in our experience, this is the most difficult time point for patients to return for imaging. The measured average renal dose in this study is in keeping with other SPECT/CT-based estimates presented in the literature, being slightly higher than that of Claringbold  (0.3 Gy/ h acquisIf complete data (3 imaging time points) can be acquired at cycle 1, it appears that a single imaging time point at 24 h at subsequent cycles is adequate to estimate renal dose. This method (method 4) can be expected to lead to, on average, a deviation of 2% from dose values that would have been acquired under full data set conditions and offers a good compromise between patient-specific dosimetry and management of clinical camera time as well as demands on the patient. This result is in keeping with the findings of Garske et al , who conGiven the assumptions involved in dosimetry analysis, ranging from limitations of scanner spatial resolution to the model assumptions of patient size and geometry, the deviations demonstrated when utilising full imaging at cycle 1 to inform kinetics at subsequent cycles would seem acceptable . In addition to easing the burden on department facilities and patients, the approach of lesser imaging time points also has benefits in the reduction of patient radiation exposure associated with multiple CT scans. It should certainly be noted that patient renal function, generally measured at stages before, after and during cycles of treatment, will also have a bearing on clearance rate and kidney dose . As suchThis study suggests that dose estimates made from single time point imaging are feasible and more accurate when derived from 24 h as opposed to 4 h single time point imaging. Ideally, a full data set should be acquired at cycle 1 to derive a patient-specific renal clearance half-time, as opposed to the use of an average patient renal clearance half-time.