The electrochemical synthesis of CO2RR catalysts that are highly selective for C2+ products via electrolyte‐driven nanostructuring is presented. Nanostructured Cu catalysts synthesized in the presence of specific anions selectively convert CO2 into ethylene and multicarbon alcohols in aqueous 0.1 m KHCO3 solution, with the iodine‐modified catalyst displaying the highest Faradaic efficiency of 80 % and a partial geometric current density of ca. 31.2 mA cm−2 for C2+ products at −0.9 V vs. RHE. Operando X‐ray absorption spectroscopy and quasi in situ X‐ray photoelectron spectroscopy measurements revealed that the high C2+ selectivity of these nanostructured Cu catalysts can be attributed to the highly roughened surface morphology induced by the synthesis, presence of subsurface oxygen and Cu+ species, and the adsorbed halides.Production of multicarbon products . Operando spectroscopy measurements showed that apart from enhanced roughness from the pre‐treatment, the subsurface oxygen and Cu+ species and the adsorbed halides favor C−C coupling, leading to high selectivity for ethylene, ethanol, and n‐propanol. CO2 electroreduction reaction (CO2RR) to multicarbon hydrocarbons and oxygenates (C2+) with high energy density is highly desirable, but is severely limited by the slow kinetics of multiple proton and electron transfer steps during C−C coupling.2+ selectivity.2+ products during CO2RR has been found to be extremely sensitive to the catalyst structure.2RR might be developed through rational design.The electrochemical production of fuels and chemical feedstocks from CO2RR catalysts strongly depend on the precise control of their structure, such as the content of defects,+ species,2RR,2RR. These important findings might be used in the design and development of new electrodes via electrochemical modifications.It is well‐known that the activity and selectivity of CO2RR catalysts. The nanostructured Cu catalysts synthesized in the presence of specific anions can selectively convert CO2 to ethylene and multicarbon alcohols in aqueous 0.1 m KHCO3 solution, with the KI‐pretreated catalyst displaying the highest FE of about 80 % and partial current density of about 31.2 mA cm−2 for C2+ products at −0.9 V vs. RHE. The high C2+ selectivity of these nanostructured Cu catalysts is attributed to their rough morphology, the presence of subsurface oxygen, Cu+ species, and adsorbed halides on the surface.The morphology and composition of electrochemically synthesized catalysts is strongly affected by the applied potential and electrolyte employed.m potassium salt solutions (between 0.3 and 2.2 V vs. RHE) and were denoted by Cu_X  and Cu_CO3, respectively. Additional details on the synthesis parameters are shown in the Supporting Information, Table S1. Figure m KHCO3 solution, as well as after 1 h of CO2RR at −1.0 V vs. RHE. Cu nanocubes with an edge size of 250–300 nm are formed on the surface of the Cu_Cl , and an increased oxygen content and decreased halide content are observed due to the slow decomposition of the Cu halide (CuX) in the aqueous solution . The highest halide content of the three Cu_X samples is consistent with the highest stability of CuI among the possible CuX compounds that could be formed.2O peaks owing to the instability of CuCl.Nanostructured Cu catalysts were synthesized by cycling electropolished Cu foils in different 0.1 2RR, although most of the halides and carbon atoms have been removed during the reaction . Numerous particles with average size of 220±60 nm are formed on the surface of the Cu_Br sample  measurements. While extended X‐ray absorption fine‐structure spectroscopy (EXAFS) data measured in total fluorescence yield mode did not show any significant difference from the metallic structure apart from a highly defective structure , high‐energy resolution fluorescence detected X‐ray near edge structure (HERFD‐XANES) spectra are more sensitive to the chemical state and coordination environment of Cu under reaction conditions.2RR at −1.0 V vs. RHE along with the reference spectra of bulk Cu, Cu2O, CuI, and CuBr. The spectra suffer from significant self‐absorption effects, but a normalization was used here to have equal self‐absorption in the reference spectra and halide‐ and carbonate‐modified samples. The spectra of the as‐prepared Cu_I and Cu_Br samples show distinctive features of CuI . A slightly more intense feature at 8986 eV and lower intensity of the above mentioned metallic feature in the as‐prepared Cu_Cl indicate the presence of CuCl species. Finally, there is no clear evidence of cationic Cu in the as‐prepared Cu_CO3 sample.To monitor the evolution of the chemical state and local environment of Cu during CO2RR conditions after 1 h of activation indicate nearly complete reduction of Cu, showing a close resemblance to the reference spectrum of the Cu foil. An exception however is the Cu_I sample measured at −1.0 V vs. RHE, which has the position of the pre‐edge feature shifted to the energy typical for Cu2O. To support the described qualitative observations, linear combination analysis (LCA) of the XANES spectra was carried out using various combinations of reference spectra as basis sets , the relative content of which follows the sequence Cu_I> Cu_Br > Cu_Cl . Notably, no CuOx could be detected in the as‐prepared Cu_I and Cu_Br samples, while the Cu_Cl and Cu_CO3 samples contained correspondingly Cu2O (14 at %) and CuO (3 at %). As mentioned above, the Cu_CO3 sample is fully reduced after 1 h under CO2RR, while Cu_I, Cu_Br, and Cu_Cl show the presence of Cu2O in the amounts of 8, 3 and 1 at %, respectively, albeit the latter two numbers are within the experimental error. The reduced Cu_I sample still contained ca. 7 at % of residual CuI. These results also reveal the higher sensitivity of HERFD‐XANES measurements acquired in grazing configuration to Cu2O and CuI species as compared to GI‐XRD which only shows metallic Cu peaks after CO2RR .HERFD‐XANES spectra of all four samples measured under CO2RR. The electrochemical cell was directly attached to the XPS analysis system and the sample transfer was conducted in UHV. The Cu_X and Cu_CO3 samples were measured with XPS in the as‐prepared state and after 1 h of CO2RR at −1.0 V vs. RHE as shown in Figure 2O (65 at %) and CuBr (35 at %), and that of Cu_Cl is composed of Cu2O (31 at %), CuCl (56 at %) and CuCl2 (12 at %). The composition difference is also consistent with the relative stability of the three Cu halides.3 sample has a starting Cu oxidation state of Cu2+ in the form of CuO and CuCO3. After CO2RR, most of the Cu+ and Cu2+ species in the as prepared samples were reduced to metallic Cu. However, a small amount of CuBr still survived  measurements were performed to probe the chemical state and composition of the surface of the Cu catalysts during CO2‐saturated 0.1 m KHCO3 solution. All the nanostructured Cu catalysts show significantly higher geometric current density than an electropolished Cu foil (EP_Cu), and Cu_I shows the highest current density in the measured potential range  at −0.9 V vs. RHE. At more negative potentials (<‐1.0 V vs. RHE), all the catalysts show decreased C2+ FE and increased H2 FE, which is due to CO2 mass‐transport limitations. The potential‐dependent partial current densities of the various CO2RR products are shown in Figure 3,2RR measurements were done in KHCO3. Furthermore, higher activity, lower onset potential and higher C2+ selectivity were obtained for the present electrolyte pre‐nanostructured catalysts as compared to the case where iodine was added to the electrolyte during the reaction . Although the Cu_CO3 sample showed high partial current density for C2+, its methane partial current density was also higher, comparable to that of EP_Cu. The simultaneously favorable production of ethylene and methane over the porous Cu_CO3 is slightly different from that reported for Cu foam catalysts, which simultaneously favored the production of ethylene and ethane, which is probably due to the smaller pore size (430 nm) in our Cu_CO3. Overall, the iodine modified Cu catalyst (Cu_I) synthesized via electrolyte‐driven nanostructuring showed a high C2+ geometric current density of about 31.2 mA cm−2 at −0.9 V vs. RHE , superior to previously reported Cu catalysts .The total FEs of C3 samples at potentials for which the highest C2+ FEs were detected  and of CO and H2 FE for Cu_CO3. However, the morphology  at the expense of C2H4 was not caused by morphological changes, but most likely by the gradual depletion of subsurface oxygen species+ species as well as the loss of adsorbed iodine ions in the Cu_I sample. In clear contrast, a large number of NPs were formed during CO2RR on the surface of the Cu_CO3 sample  and quasi in situ XPS measurements (surface sensitive). We found a positive correlation between the production of C2+ and the amount of Cu+ species in the halide‐modified Cu catalysts in the following order: Cu_I> Cu_Br > Cu_Cl. Previous theoretical studies predicted that subsurface oxygen as well as the presence of a Cu+/Cu0 interface plays a crucial role in CO2 activation and CO dimerization, ultimately resulting in higher C2+ selectivity.2RR required to obtain C2+ products. On the other hand, the Cu_CO3 sample with only metallic Cu species under reaction conditions, showed higher CH4 selectivity than all Cu_X samples. The latter is probably attributed to its nanoporous structure.2RR,+) via an electrolyte‐driven nanostructuring pre‐treatment strategy, which was found to lead to enhanced C2+ selectivity.Although the activity, selectivity, and stability of CO2RR electrocatalysts highly selective to C2+ products. The proposed synthesis not only leads to strong morphological modifications of the sample surface, but also to the presence of residual halides and cationic Cu species. These Cu electrocatalysts can selectively convert CO2 into ethylene and multicarbon alcohols in a KHCO3 solution, with the iodine‐modified catalysts showing the highest FE for C2+ of about 80 % and partial geometrical current density of about 31.2 mA cm−2 at −0.9 V vs. RHE. The superior C2+ selectivity of the halide‐modified Cu catalysts was attributed to their rough surface morphology combined with electronic and chemical effects arising from the stabilization of subsurface oxygen as well as Cu+ species and adsorbed halides on the surface. Cu_CO3 shows both high C2+ and methane selectivity, which is attributed to its particular nanoporous structure. Stability tests suggested that the gradual depletion of subsurface oxygen/Cu+ species and the increased number of low‐coordinated sites formed under reaction conditions are behind the distinct catalytic performance of the halide‐ and carbonate‐modified Cu catalysts, respectively. This work provides new insights required for the design of highly active C2+‐selective CO2RR catalysts.We have presented an electrolyte‐driven nanostructuring strategy for the facile synthesis of CO3 catalysts were prepared by electrochemically cycling an electropolished Cu foil in 0.1 m KCl, KBr, KI, and K2CO3 solutions with triangular potential scans at a rate of 500 mV s−1, respectively. During each cycle, the potential was held at the negative (E1) and positive (E2) limits for 5 and 10 s, respectively. The cycled Cu catalysts were prepared with the indicated potential ranges and number of cycles as shown in the Supporting Information, Table S1. For other experimental details, including operando and ex situ characterizations and electrochemical measurements, see the Supporting Information.Cu_Cl, Cu_Br, Cu_I, and Cu_COThe 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.


Twenty‐four 3‐month‐old male Wistar aging model rats were randomly divided into four groups, that is, three treatment groups with daily 300 mg kgBW−1d‐Galactose injection administrated intraperitoneally for 4 weeks and 1 control group with normal saline injection. Two of the d‐Galactose treated groups were given low and moderate treadmill exercise for 4 weeks. It was concluded that low intensity treadmill exercise significantly lowered the degree of d‐Galactose‐exposed hepatic fibrosis, and moderate treadmill exercise was able to restore the injured liver tissue back to the non‐aging state. Administration of d‐Galactose causes inflammation marked by the elevated number of M1 and M2 macrophages. Moderate treadmill exercise drove M1/M2 ratio back to the control condition.Aging increases liver susceptibility to diseases and it causes inflammation in liver tissue which can lead to fibrosis. Studies suggest that aging is caused by the accumulation of free radicals. Lack of physical activity can lower hormone levels and increase free radicals that can accelerate the aging process. Hence, physical activity is very important to maintain functions of organs. This research was aimed to study the effects of low and moderate treadmill exercise on  d‐Galactose‐exposed ageing rat model. Administration of d‐Galactose caused liver fibrosis and inflammation marked by the elevated number of M1 and M2 macrophages. Low and moderate treadmill exercise could significantly lower the degree of hepatic fibrosis and restored the M1/M2 ratio back to the non‐aging state.We investigated the potential hepatoprotective effects of treadmill exercise in  Aging is a decline in fitness components due to a progressive deterioration in body functions and the loss of the ability to maintain homeostasis  which also occur in normal aging, particularly in the liver and brain  Universitas Gadjah Mada with reference number 00055/04/LPPT/VI/2017 on 05 June 2017.The experimental protocol was performed in accordance with guidelines established by the Ministry of Research, Technology, and Higher Education and was approved by the Animal Ethics Committee of d‐Galactose exposure but given intraperitoneal saline injection and no exercise), K2 , K3 , and K4 . d‐Galactose in 0.9% NaCl  was given as a dose of 300 mg kgBW−1 and was injected daily to all rats in K2, K3, and K4 groups for 4 weeks.This study used 24 male Wistar rats weighing 200–300 g which were obtained from the animal houses of Universitas Islam Indonesia, the Faculty of Pharmacy, and the Department of Pharmacology and Therapy, Faculty of Medicine, Public Health and Nursing, Universitas Gadjah Mada. The rats were acclimatized at controlled room temperature with 12‐h light‐dark cycle for 7 days prior to the experiment and ad libitum access to water and food. The rats were randomly divided into four groups: K1  with 0° slope. Rats which were reluctant to run on the adaptation period were put in K2 group. Later on, the maximum speeds of each rat in K3 and K4 groups were measured to estimate the VO2max index. VO2max index was calculated using the following formula:Treadmill adaptation was given to all rats with n et al.  protocol2max Index, respectively.Slope of 0° equals to 1 in the equation. Afterward, the rats in K3 and K4 groups were given treadmill exercise at the speed of 45% (low intensity) and 55% (moderate intensity) of the previously determined individual VOam, and the slope was maintained at 0° during exercise. The exercise started with 5 min of warming‐up period at 20% of maximum speed, 20 min of main exercise at low (K3) or moderate (K4) intensity, followed by 5 min of cooling‐down period at 20% of maximum speed.The treadmill exercise was given four times a week for 4 weeks. Each exercise was conducted after 9 Tissue collection was performed at the end of the fourth week of treadmill exercise. All rats were anesthetized using ketamine HCl 40 mg/kgBW  and euthanized. Right lobe of the liver was harvested and put in fixative  for 24 h.μm and placed on deck glasses for picro‐sirius red staining. The histological slides were stained with Weigert’s hematoxylin to dye the nucleus and stained with picro‐sirius red for 1 h to dye the collagen fibres. The histological slides were then mounted and ready for microscopic observation. Fifteen random fields of view were observed from each sample and photos were taken. Fibrosis score ranging from 0 to 6 was assigned to each photo and data were documented. The fibrosis score was determined using Ishak system  and arginase‐1  antibodies. Antigen retrieval was performed by incubation in citrate buffer solution and heated in a microwave. Blocking peroxidase was conducted with 3% H2O2 solution in PBS. The slides were then incubated with background sniper solution. The slides were examined using light microscope and photos of 15 random fields of view for each slide were taken with Optilab software using 400× magnification. Cell count was performed using ImageJ software.Sectioned liver tissues with thickness of 4 Degree of fibrosis data were not normally distributed, Kruskal–Wallis test was used consequently. Mann‐Whitney post hoc test was performed to see the differences between groups.Number of M1 data were normally distributed after data transformation, therefore number of M2, M1/M2 ratio, and transformed number of M1 were analyzed using one‐way ANOVA followed by post hoc test to see significant differences between groups.d‐Galactose treated group (K2) demonstrated hepatic fibrosis as shown by the significant higher degree of fibrosis compared to control (K1) group (P = 0.002). Kruskal–Wallis analysis of these data revealed significant differences among groups. Exercise‐treated groups (K3 and K4) showed significant lower degree of fibrosis compared to K2 group with p values of 0.004 and 0.002, respectively. However, there was no significant difference between K3 and K4 groups. Meanwhile, the statistical analysis showed significant difference between K1 and K3 groups (P = 0.041) while the degree of fibrosis between K1 and K4 groups was insignificant.Figure d‐Galactose‐exposed groups  had higher number of M1 and M2 than the control (K1) group. Higher number of M1 than M2 was observed in K1 group while the K2 group demonstrated the opposite pattern. The given exercise treatments showed higher number of M1 than M2. The number of M1 in K1 group was significantly lower than in K3 group while the number of M2 in K2 group was significantly higher than in K1 and K3 groups  as much as 3‐5 times of the normal value, elongation of QT interval on ECG results and also proteinuria. The results of this preliminary study show that this dose induced aging. This was in accordance with studies by Mutlu‐Turkoglu et al. , indicating that fibrous expansion of portal areas with marked bridging portal to portal and portal to central was observed. This showed that intraperitoneal administration of d‐Galactose causes fibrosis in liver tissue. This result is in accordance with the study conducted by Ji et al. . These results showed that marked portal to portal and portal to central bridging of collagen fibers was reduced after performing treadmill exercise. There was no significant difference between K1 and K4 groups, indicating that the given moderate intensity treadmill exercise was able to repair the injured liver tissue back to its non‐aging condition. It has been known that exercise can improve the antioxidant system of the body  (Wynn and Vannella, d‐Galactose‐exposed M2. Exercise ameliorates inflammation and fibrosis by decreasing macrophage infiltration in liver tissue (Kawanishi et al. Hepatic macrophages play an important role in liver disease by activating HSCs and releasing cytokines and pro‐inflammatory chemokines. These cells are crucial in the pathogenesis of hepatic injury and are able to differentiate into various subtypes of alternatively‐activated M1 and classically‐activated M2 macrophages which function in both fibrosis progression and regression. According to Weng et al. , macrophd‐Galactose induction, the liver might have undergone inflammation resolution and fibrosis regression which are dominated by M2. A study by Troeger et al. (d‐Galactose exposure and exercise are known to increase the expression of PPARγ which mediates the activation of M2 (Goh et al. The abundance presence of M2 in fibrotic liver protects against hepatocyte apoptosis, hence lethal consequences can be avoided (Bai et al. r et al.  showed td‐Galactose‐exposed hepatic fibrosis, and moderate treadmill exercise was able to restore the fibrotic liver tissue back to the non‐aging state. Administration of d‐Galactose causes inflammation marked by the elevated number of M1 and M2 macrophages. Moderate treadmill exercise drove M1/M2 ratio back to the control condition.In conclusion, this experiment shows that low and moderate treadmill exercise significantly lower the degree of All authors have no conflict of interests with respect to the data collected and procedures used within this study.


II hydride pincer complex as catalyst in the supported ionic liquid phase (SILP) reaction mode. Two different ionic liquids of the type [X4441][NTf2] with X=N or P were applied with mesoporous silica gel as support, which was coated first with a chemisorbed monolayer of the corresponding modified IL to remove acidic surface OH‐groups and to prevent IL leaching. Quantitative conversion with turn‐over frequencies in the order of 1000 h–1 were obtained for various aromatic and heteroaromatic aldehydes and highly selective aldehyde reduction was observed also for substrates containing reducible C=C bonds. Aldehydes with longer aliphatic chains or cycloalkyl substituents, however, showed no conversion here, in contrast to a previous study with an imidazolium‐based ionic liquid. These differences were ascribed primarily to differences in substrate/ionic liquid interactions. Whereas [N4441][NTf2] and [P4441][NTf2] gave essentially identical results for different substrates in single‐batch reactions, prolonged use of the catalyst in repeated reaction cycles lead to a quick drop‐off in catalyst activity in [P4441][NTf2], but a continuous, quantitative conversion in [N4441][NTf2].The catalytic hydrogenation of different aldehydes to the corresponding alcohols was investigated using an Fe Over the past 15 years, supported ionic liquid phase (SILP) catalysis has emerged as a powerful hybrid technology of classical homogeneous and heterogeneous reaction techniquesMe‐iPr)(CO)(H)(Br)] as catalyst was used. In the biphasic mode,+ [NTf2]– with the weakly coordinating [NTf2]– anion together with different types of cations A+  and was brought in contact with a second, immiscible organic solvent phase which contained the substrate. In the SILP mode,2im][NTf2]) and was applied as a thin layer coated onto two different support materials: silica[NTf2] which yielded complete conversion at a turn over frequency of 1330 h–1 compared to 2000 h–1 for the homogeneous reaction mode under otherwise equal conditions. One drawback of the biphasic mode, however, is the relatively large amount of ionic liquid that is needed, which dissolves a substantial part of the produced alcohol. The higher solubility of the formed alcohol compared to the starting materials complicated work‐up, and quantitative recovery of the reaction product, therefore, requires subsequent extraction of the IL phase and prevents a continuous operation in this biphasic configuration.Silica supports had to be coated first with a chemisorbed layer of ionic liquid in order to remove acidic surface hydroxyl groups which destroyed the catalyst. Carbon supports could be used without pretreatment but showed 4–10 times lower reaction rates due to their smaller pore sizes and the thereby reduced active area of the ionic liquid film. The influence of the ionic liquid on the catalytic activity was initially investigated in the biphasic reaction mode. Isolated yields were in the range from < 1 % to > 99 % and showed that the ionic liquid has a tremendous influence on the catalytic function. The best results were obtained with [P4441][NTf2] and [N4441][NTf2] – which gave the best results in the biphasic mode and tested them for SILP catalysis. By comparison with the biphasic data and with previous SILP data using an imidazolium‐based ionic liquid, we were hoping to gain deeper insights into the role of the ionic liquid in this model reaction.In the SILP mode, in comparison, the total amount of ionic liquid is much smaller and product losses due to dissolution in the ionic liquid phase are usually negligible. For this work, we, therefore, chose two ionic liquids –  (2), are strongly basic and thus sensitive to acidic functionalities such as the OH groups of the silica gel. To avoid catalyst decomposition by this group and to make the surface of silica gel “IL‐philic” to prevent IL leaching, the silica gel was covalently coated, in a three‐step procedure, with the corresponding IL  and 0.25 mmol/g (P‐SILP[NTf2]). With the corresponding BET surface areas , Si(OSi)3OH (Q3) and Si(OSi)2(OH)2 (Q2) species of the silica framework, respectively.3 and Q2 bands (T2) or one RSi(OSi)(OMe)2 (T1) siloxane bonds, respectively.The surface modification sequence depicted in Figure 29Si NMR spectrum of N‐SILP[I] 3] signal at –68 ppm appeared in the spectrum. It means that the functionalized ionic liquid is grafted via two or three siloxane bonds to the surface of the support. The 29Si NMR spectrum of P‐SILP[I] 3 moieties, indicating that tributylphosphine did not promote the above mentioned further condensation as efficiently as tributylamine. This observation can be explained by the higher basicity of N(Bu)3 (pKa = 10.9)3 (pKa = 8.4).No resonances appeared above –50 ppm, indicating the absence of physically adsorbed silane molecules. The solid‐state 3 pKa = .910 comp13C CP‐MAS NMR spectra also confirm the successful modification of the surface of silica gel 3 and P(Bu)3 reactants. The peaks of the propyl and butyl carbon atoms between 4–24 ppm in the spectra of N‐SILP[I] and P‐SILP[I] are broadened and not well‐resolved. The ion exchange of I– to [NTf2]– did not change the NMR spectra (not shown). 31P CP‐MAS NMR spectroscopy also confirmed the successful formation of the phosphonium‐based IL layer on the surface since the corresponding peak at 30 ppm can be found in the spectrum (not shown).–1 in Figure –1 and 2875 cm–1 appear in the spectrum of Figure –1 due to the ν(CH3) vibration of the OCH3 groups.3)3 anchor groups, in agreement with the previously discussed 29Si and 13C NMR spectra. The subsequent coupling of N(Bu)3 and P(Bu)3, respectively, to the surface (spectra 4C and 4E) yields changes in the ν(CH) stretching absorptions around 3000 cm–1 and the δ(CH) deformation modes (1400 cm–1–1500 cm–1) and, most noticeably, the disappearance of the methoxy ν(CH3) absorption at 2850 cm–1, indicating a base‐catalyzed progression of methoxy group hydrolysis and condensation. This has also been attested before in the 29Si and 13C NMR spectra. Finally, the ion exchange step [I]– → [NTf2]– is evidenced by the intense absorption of νas(SO2) at 1348 cm–1 and νas(CF3) at 1196 cm–1.Additional evidence for the successful modification of the silica support is provided by the infrared spectra shown in Figure 2] and P‐SILP[NTf2] were impregnated with 10, 20, 30, and 40 wt.‐% of 1 dissolved in ([N4441][NTf2]) and ([P4441][NTf2]) producing N‐SILP10, N‐SILP20, N‐SILP30, N‐SILP40 and P‐SILP10, P‐SILP20, P‐SILP30, P‐SILP40, respectively. These materials were characterized by N2 adsorption‐desorption  increases with the IL loading up to 100 % for SILP40s.Structural parameters derived from Nes Table . The por4441][NTf2] and [P4441][NTf2]. 50 bar H2 pressure, 5 mol‐% of DBU  as a base in n‐heptane at 25 °C were applied. The results are shown in Table n‐heptane solution, as evidenced from ICP‐OES and 19F{1H} NMR measurements. In that case, partial homogeneous hydrogenation in the n‐heptane solution is likely the reason for the high reaction rates.The hydrogenation of 4‐fluorobenzaldehyde to 4‐fluorobenzyl alcohol was used as a test reaction to investigate the performance of SILP catalysis with two different ionic liquids [N4441]NTf and [NTf2]) as IL. In that case, a three‐fold faster conversion was observed (entry 11).Increasing the S/C ratio from 200 to 1000 resulted in an increase of TON and TOF values to 1000 and 1333 hus study, this rea–1, while P‐SILP20 lost almost completely its activity after the first cycle. This apparent poisoning of the catalyst dissolved in [P4441][NTf2] might be related to the presence of residual surface OH groups, which was indicated by a comparison of the 29Si NMR spectra of P‐SILP20 and N‐SILP20 . Aldehydes with aromatic or heteroaromatic substituents showed quantitative conversions with all three ionic liquids, although an about three times lower reaction rate for N‐SILP and P‐SILP compared to Im‐SILP. Aldehydes with larger alkyl or cycloalkyl groups, on the other hand, gave no conversion with N‐SILP and P‐SILP in contrast to quantitative conversion with Im‐SILP. Solubility effects and/or specific substrate/ionic liquid interactions are believed to be the main reason for these differences, although further studies are needed here. The N‐SILP and the P‐SILP systems gave very similar results for single reactions. Catalyst recycling, however, by repeated aldehyde addition worked well only with the N‐SILP catalyst, whereas the P‐SILP catalyst became inactive after the first reaction cycle, probably which caused by catalyst poisoning by residual surface hydroxyl groups of the silica support. The trends which were observed in the biphasic catalytic reactions, where [P4441][NTf2] as the solvent gave the highest reaction rates followed by [bm2im][NTf2] and [N4441][NTf2], were not replicated in the SILP mode, where 3‐times higher reaction rates were observed in [bm2im][NTf2] compared to [P4441][NTf2] and [N4441][NTf2]. As mentioned in the introduction, a complex interplay of different factors, which are still poorly understood until today, determines the performance of a SILP catalyst. Further studies and molecular information of the interactions between catalyst, substrates, and products at the reaction interface ionic liquid/organic solution are needed to understand and optimize this powerful catalytic technique.In the present study, the catalytic reduction of aldehydes to alcohols in the SILP mode – using an FeMaterials: All operations were performed under argon atmosphere by using Schlenk techniques or in an MBraun inert‐gas glovebox. The solvents were purified according to standard procedures.4441][NTf2]) and tributylmethylphosphonium bis(trifluoromethanesulfonyl)imide ([P4441][NTf2]) were dried for at least 24 h at room temperature and 0.01 mbar before use and were stored under an argon atmosphere; resulting water contents were typically <500 ppm. The complex [Fe(PNPMe‐iPr)(CO)(H)(Br)] (1) was prepared according to the literature.[terature. All aldeSynthesis of SILPs2] and P‐SILP[NTf2]:N‐SILP was added to an extraction hull in the glovebox. It was brought to an evacuated 100 mL Soxhlet extractor and flushed with argon gas under a slight flow of argon. The SILP[I] was extracted with anhydrous ethanol for 16 h. The powder was dried under reduced pressure afterwards. Then, 2 g of tributylamine or tributylphosphine in 15 mL of toluene was added to 5 g of SILP[I] and refluxed for 48 h to prepare N‐SILP[I] and P‐SILP[I], respectively. The materials were extracted with anhydrous ethanol for 16 h. For ion exchange, the N‐SILP[I] and P‐SILP[I] were treated with 2 g of Li[NTf2] in 10 mL of CH2Cl2 at room temperature for 24 h. They were again extracted with a Soxhlet extractor as described before. N‐SILP[NTf2] and P‐SILP[NTf2] were dried under reduced pressure and stored in the glovebox.N‐SILP10–40 and P‐SILP10–40: 5 mg of 1, specific amount of N‐SILP[NTf2] or P‐SILP[NTf2] and 2 mL of anhydrous ethanol were added to a round‐bottomed flask equipped with a small stirring bar and a vacuum valve in the glovebox. The reaction mixture was stirred for 1 h. The solvent was carefully removed under reduced pressure. The powder was dried for an additional 5 min.Material Characterization29Si, 13C, and 31P CP‐MAS NMR measurements were recorded on a Bruker AVANCE 300 DPX spectrometer, equipped with a 5 mm broadband inverse probe head. Magic Angle Spinning was performed at 4 kHz spinning rate at 59.57 MHz for 29Si, at 75.40 MHz for 13C, and at 121.38 MHz for 31P NMR measurements. Textural properties were analyzed by N2 physisorption (ASAP 2020 Micrometics GmbH) using the Brunauer–Emmett–Teller (BET) theory for determining the surface area and the Barret–Joyner–Halenda (BJH) method for obtaining the pore size distribution. Infrared spectra were recorded with a Bruker Vertex 80 FTIR spectrophotometer using a narrow band MCT detector measuring diffuse reflectance. 256 Scans were collected for each spectrum with 4 cm–1 resolution. 1H, 19F{1H}, and 31P{1H} NMR spectra were recorded on Bruker AVANCE‐250 spectrometer. 1H spectra were referenced internally to residual protic‐solvent resonances and are reported relative to tetramethylsilane (δ = 0 ppm). 31P{1H} NMR spectra were referenced externally to H3PO4 (85 %) (δ = 0). 19F{1H} spectra were referenced externally to trifluorotoluene (0.05 %) (δ = 0 ppm). GC–MS analyses were recorded on an ISQ LT Single quadrupole MS (Thermo Fisher) directly connected to a TRACE 1300 Gas Chromatograph (Thermo Fisher), using a Rxi‐5Sil MS  cross‐bonded dimethyl polysiloxane capillary column. Fe leaching was monitored using an inductively coupled plasma (ICP) optical emission spectrometer PerkinElmer OPTIMA 8300 equipped with an SC‐2 DX FAST sample preparation system. A customized single‐element  standard was used for the calibration. All samples were extracted using ethanol and methanol (two times each), followed by solvent‐evaporation and acid‐digestion (HNO3 and H2O2 at a 2:1 ratio).The C, H, N, S content was double‐determined utilizing a Vario Macro elemental analyzer . Solid‐state General Procedure for the Hydrogenation of Aldehydesn‐heptane were mixed and taken up in a syringe. The vial was added to the autoclave, the septum was removed and the autoclave was evacuated and flushed 3 times with argon gas. The solution was injected into the autoclave under a slight flow of argon. The autoclave was then purged three times with hydrogen gas before the final pressure was adjusted to the specified value and the reaction was carried out for the stated time. Afterward, the hydrogen gas was released and the vial was taken out of the autoclave. The reaction mixture was three times extracted with 1.5 mL of diethyl ether, decanted and filtered through aluminum oxide. The solvent was then slowly removed under reduced pressure. The residue was analyzed by 1H and/or 19F{1H} NMR spectroscopy and yields were determined by integration of the aldehyde and alcohol signals and referenced to mesitylene. If the yields were detected by GC–MS, one drop of the extracted reaction solution was taken out and filled up with 1 mL of CH2Cl2 and injected via a 4 mm syringe filter  into a GC–MS vial which was then sealed with a septum.All hydrogenation reactions were carried out in a Carl Roth 100 mL stainless steel autoclave containing a 20 mL glass vial equipped with a stirring bar. In the glovebox, freshly prepared SILP20 was added to the glass vial which was sealed with a septum afterwards. 2 mmol of the substrate, 5 mol‐% DBU and 2 mL


The CH4 emitted from reservoirs is microbially produced in their sediments, but at present, the rate of CH4 formation in reservoir sediments cannot be predicted from sediment characteristics, limiting our understanding of reservoir CH4 emission. Here we show through a long-term incubation experiment that the CH4 formation rate in sediments of widely different tropical reservoirs can be predicted from sediment age and total nitrogen concentration. CH4 formation occurs predominantly in sediment layers younger than 6–12 years and beyond these layers sediment organic carbon may be considered effectively buried. Hence mitigating reservoir CH4 emission via improving nutrient management and thus reducing organic matter supply to sediments is within reach. Our model of sediment CH4 formation represents a first step towards constraining reservoir CH4 emission from sediment characteristics.Freshwater reservoirs, in particular tropical ones, are an important source of methane (CH Methane fluxes from hydroelectric reservoirs, especially from tropical reservoirs, have been debated over the past years4. Even though hydropower is often thought of as a ‘green’ source of energy, studies suggest that reservoirs are not carbon neutral and in extreme cases might have even higher carbon footprint than fossil fuel energy, particularly those situated in the tropics6. Tropical reservoirs have been estimated to emit about 3.0 Tg CH4-C year−1 2 and to contribute 64% of the total reservoir CH4 emission3. Conversely, latitude was not a strong predictor of reservoir CH4 emission in a more recent global analysis4. Apparently, the CH4 emission from reservoirs is currently not well understood.Methane  in sediment are temperature as well as the organic matter (OM) characteristics (i.e. its reactivity or bioavailability) and OM supply rate. Strong exponential relationships between temperature and CH4 formation rates were found in sediments of lakes11 and rivers12, and ecosystem-scale CH4 emission strongly depends on temperature13. In addition, methanogenesis relies on OM characteristics and supply rate. There is evidence that more CH4 is produced from autochthonous OM (derived from aquatic plants and phytoplankton) than from allochthonous OM (derived from land plants and soils)14. Also, a high OM supply rate can stimulate high sediment CH4 formation and emission, particularly if the OM is biologically reactive15. However, allochthonous OM might degrade slower but produce the same amount of CH4 over longer period of time16, since allochthonous OM contains more support tissues that are processed more slowly17. When the OM is being decomposed at steady conditions, its CH4 formation decreases over time due to rapid initial decay of labile substances16. However, at timescales relevant in sediments (years), the effect of decreasing reactivity during OM decomposition on sediment CH4 formation is currently not clear. While it has been shown that CH4 formation decreases over time18, the ageing effect on sediment OM reactivity and CH4 formation was not quantified. Therefore, sediment CH4 formation can at present not be predicted at environmentally relevant timescales (years), severely limiting our understanding of the globally important function of reservoir sediments as both sinks of OC and sources of atmospheric CH4.At an estimated global organic carbon (OC) burial rate of 0.06 Pg C year4 formation rates in sediment of three widely different tropical reservoirs. We performed a long-term incubation experiment (ca 739 days) of sediment varying in age between 1 and 48 years, in order to understand CH4 formation in reservoir sediments over the typical lifetime of reservoirs. We selected 3 reservoirs of different productivity and located in different biomes and, therefore, of a range of sediment OM characteristics. We expected a decrease of CH4 formation potential with increasing sediment age, and lower CH4 formation in the sediment of a reservoir with little autochthonous OM production than in a reservoir with high autochthonous OM production.Here, we investigate the impact of OM source, characteristics and age on CH−1) that was constructed in 1994 for water supply19. CUN is a mesotrophic hydroelectric reservoir  that was constructed in 197719. FUN is a eutrophic hydroelectric reservoir (mean TP 34 µg L−1) that was built in 196920. CDU and FUN are located in the Atlantic Forest biome, and CUN is located in the Amazon.Sediment samples were obtained from three Brazilian reservoirs of different trophic status: Chapéu D’ Uvas (CDU), Curuá-Una (CUN) and Funil (FUN). CDU is an oligotrophic reservoir  concentration, 12 µg Lth of March 2016, from FUN on the 14th of March 2016, and from CUN on the 20th–28th of February 2016.In each reservoir, coring sites  were distributed across the entire reservoir  layer of all sediment cores was used for the experiment to represent rather fresh but already anoxic sediment. We considered 2 cm sediment depth to be anoxic because oxygen penetration depths of 0.3–1.2 cm were reported from a Brazilian reservoir21. If possible the 4 cm layer of sediment just above the soil-sediment interface was used and up to 3 additional samples, distributed over the sediment core depth down to the soil-sediment interface, were obtained; for example, the longest core was FUN_48 (204 cm), and the soil-sediment interface was at 192 cm. This core was sampled at 2–6 cm, 32–36 cm, 60–64 cm, 116–120 cm, 172–176 cm. The total number of sediment samples per core varied between one and four, depending on the total length of each sediment core. In total, 17 samples were obtained from 2–6 cm deep sediment, and 25 samples were from deeper sediment layers. After slicing, the headspace in the sample containers (PP jars with LDPE snap lock) was filled with N2, and samples were placed in a N2-filled glove bag within 1–2 hours after slicing. The glove bag was filled with N2 and evacuated using a vacuum pump 2 times to minimize the oxygen exposure of the samples.Sediment cores were stored in dark at room temperature, i.e. similar to 2-bubbled water from the respective reservoir was added to the samples. 3 replicates of each sample were prepared. The samples were sealed and flushed with N2 after preparation. Vials were weighted before and after filling to know the exact mass of sediment in each vial. As a control treatment, 3 replicates of 10 mL of sterile water (filtered with 0.2 µm GF filter) from each reservoir were prepared in the same vials as sediment sample and sampled in the same way as sediment samples. Dissolved oxygen concentration was checked in those controls at the beginning of incubation with optical sensors (PreSens) and was below detection level (0.1 mg/L detection level).Each sample was homogenized in the glove bag, and a sub-sample of 10 mL of homogenized sediment was transferred into pre-weighted 60 mL serum vials. 2.5 or 5 mL (depending on the sediment density) of sterile-filtered (0.2 µm GF filter), NThe rest of the sediment was dried in a custom made oven at about 55 °C, and water content was gravimetrically determined.16) in comparison to the experiment duration, and thus considered negligible. The CH4 formation rate was measured in the samples at 7 sampling occasions. Each sampling occasion contained 2 measurements: start and end of incubation, which lasted for about 2 weeks. Exact days of sampling occasions varied for each sample, and were on average day 1–9 for the 1st sampling, day 9–28 the 2nd sampling, day 72–91 for the 3rd sampling, day 185–200 for the 4th sampling, day 275–290 for the 5th sampling, day 423–442 for the 6th sampling and day 719–736 for the 7th sampling . The lag phase until the onset of growth of methanogens in similarly handled sediment samples is very short  the procedure was repeated. 8 mL of N2 was added to the samples and the gas was extracted after shaking the vial for 1 min. Sample dilution after addition of N2 was calculated from pressure difference that was measured before and after the N2 addition. Samples were injected the day they were obtained into a GC equipped with a flame ionization detector (FID) . Concentrations of CH4 and CO2 in the sediment pore water were calculated according to the ideal gas law and Henry’s law, where coefficients for CH4 solubility in water at varying temperatures were obtained from Wiesenburg and Guinasso Jr27, and coefficients for CO2 were obtained from Weiss28.To measure initial gas concentration in the vials (at start of sampling occasions), 8 mL of N4 measurement was performed, the sediment was extracted from the serum vials. The sediment of replicates was pooled, mixed and dried in an oven at 60 °C; we decided to pool the replicates because no significant differences were detected in their CH4 formation.At the end of the experiment, after the last CHThe total C (TC) and total N (TN) content in the sediment were measured in each sample at the beginning and end of the incubation with a Costech Elemental Analyzer. We found no significant contribution of inorganic C in our samples.4 and CO2 formation were obtained by the difference in CH4 concentration between two measurements and divided the time interval. The obtained rates represent net CH4 formation rates, including both production and any potential consumption of CH4 (e.g. by anaerobic CH4 oxidation30) in the sediment.The rates of CH4 formation rate was obtained. Sediment age here represents, then, a measure of time since sediment deposition (and not since OM fixation by photosynthesis or since sediment formation in the aquatic system) assuming constant sedimentation rate. We acknowledge that there probably is year-to-year variability in the sedimentation rate, e.g. due to hydrological extremes, which adds uncertainty to the age estimate of individual sediment layers. However, since there is no reason to assume any systematic change in sedimentation rate with reservoir age, the uncertainty in the estimated age of individual sediment layers is unlikely to suffer from any systematic bias, and is therefore considered to add random error to the age estimates.The age of individual sediment layers was estimated from the multi-year average sedimentation rate, which can be precisely calculated from sediment thickness, and the time elapsed since dam closure, according to the formula:4 measurement occasion. Although it has been shown that the decrease of sediment TC and TN is exponential over timescales of several years-decades31, a linear approximation of TC and TN decrease over time is reasonable for relatively short timescales as used in this experiment. Accordingly, when we compared linear TN decrease with exponential TN decrease, modelled using the TN decay rate of 0.16 year−1 given by Gälman et al.31, the difference between TN estimates at any point of time was <0.002% TN, i.e. the potential error of assuming linearity is below analytical precision (data not shown). Since N is preferentially lost over C during sediment organic matter degradation31, the effect of interpolation approach on estimated TC will be even smaller than for TN.Because TC and TN contents were only measured at the start and end of the experiment, we assumed a linear change in TC and TN through the experiment to estimate TC and TN at every CH4 formation rates, the first 1–2 measurements were excluded because of possible oxygen contamination during sample preparation that delayed the establishment of methanogenic conditions .In some samples of the deepest sediment layers that had the lowest CH4 formation rates over reservoir lifetime we fitted an exponential decay model with 3 OM pools of different reactivity with core as a factor (gnls(CH4~a * exp(−b * Age) + c)33. The significance of the model parameters was assessed with the ANOVA function and the quality of the model was checked by visual examination of the residuals and predicted against measured data. We have also tested other non-linear models  but they did not converge.To estimate sediment CH4 formation over the typical lifetime of reservoirs (100 years), and in order to estimate the “transition age” to low background CH4 formation, we used exponential decay models (described above). We define the transition age as the age at which the slope of the modelled curve is 179°, i.e. almost flat and not distinguishable from 180°, and thus indicative of a constantly low background rate of CH4 formation that no longer changes over time  including the interaction between age and TN (lm (ln (CH4) ~ ln(Age) * TN). In the model CH4 formation rate per sediment dry weight (µmol g(dw)−1 d−1) was used because TC and TN are dependent on each other. The CH4 formation rates and sample age were ln transformed. The model assumptions were checked through model residual plots.The effect of sample age and TN on the CH4 formation was checked with repeated measures ANOVA. Both model assumptions were checked through model residual plots. We used R (R 3.4.334) for data analysis, modelling and plotting.Correlation between transition age and C:N ratio was checked with a Pearson correlation. The difference between fresh and old sediment CHThe sediment samples used in our study differed in sediment characteristics Table . The Ama4 formation per sediment dry weight (µmol g(dw)−1 d−1) significantly correlated with the amount of TC in the sediment  therefore CH4 formation rates were normalized for TC (µmol gC−1 d−1). There was a significant difference between CH4 production in sub-surface (2–6 cm) and deeper sediment layers , but remained rather stable in deeper sediment layers ). At the last measurement at day 736, the same sample had CH4 formation rate of 2.4 ± 0.1 µmol gC−1 d−1. On average FUN experienced highest CH4 formation rates in sub-surface sediment over the whole incubation period ), while in CUN and CDU mean CH4 formation rates in sub-surface layers were lower over the whole incubation period (2.7 ± 2.3 µmol gC−1 d−1 and 3.9 ± 1.8 µmol gC−1 d−1 respectively). CH4 formation rates decreased most rapidly in FUN sub-surface sediment over the time of the incubation. The final CH4 formation rates (day 739) in sub-surface sediment in FUN were 24 ± 12% of the initial rates, while in CUN and CDU the CH4 formation rates decreased less and were 50 ± 16% of the initial rates in CUN and 50 ± 15% in CDU.CHers Fig. . CO2 for4 formation rates of deepest sediment were significantly different between reservoirs . CDU had higher mean CH4 formation rates over the whole incubation period in bottom layers (1.07 ± 0.49 µmol gC−1 d−1) than FUN (0.44 ± 0.14 µmol gC−1 d−1) and CUN (0.44 ± 0.16 µmol gC−1 d−1).CH4 formation rates decreased exponentially with sediment age  and the lowest in 42.9 years old sediment (0.2 ± 0.005 µmol gC−1 d−1). We could also observe clear exponential decrease in sediment CH4 formation in CUN, where the estimated age of the samples varied from 2 to 38 years. In CUN, the highest CH4 formation of 11.4 ± 0.6 µmol gC−1 d−1 was measured at 7 years old sediment and the lowest CH4 formation rate was measured in 36 years old sediment (0.2 ± 0.01 µmol gC−1 d−1). CDU is the youngest of the studied reservoirs. Estimated sediment age in CDU varied from 1 to 22 years. The highest CH4 formation in CDU was measured at 6 years old sediment (8.0 ± 0.2 µmol gC−1 d−1) and the lowest was 0.1 ± 0.03 2 µmol gC−1 d−1 at 18 years old sediment.The decrease of CHFUN Fig. . The hig4 formation over time achieved best fit on deeper sediment cores where a wide age gradient was covered by many samples. In cases where the age gradient was very short, model fits were sometimes poor. Model statistics and coefficients can be found in Supplementary Table Models for CH4 formation rates in these three widely different reservoir sediments (Table 4 formation rates could be predicted from the sediment TN (%) and the age of the sediment −1 d−1, TN is expressed in mass %, and age is expressed in years.Merging all 764 measured CHts Table  into one4 formation rate35. Therefore we corrected the predicted CH4 formation rate following36:4 formation is the ln transformed predicted CH4 formation rate and s2 = 0.28 is a residual variance of the model. CH4 formation corr is the corrected CH4 formation rate and s2corr is the corrected variance.The back-transformation of ln-transformed predictions renders residuals that are heavily skewed, leading to underestimation of predicted mean CH4 formation in freshwater sediment that is applicable at relevant timescales . Contrarily, our analysis revealed that not only the TN concentration was important for CH4 formation, but also the change of TN over sediment age . Second, the TN concentration in the sediment is representative of the OM source37: autochthonous OM is comparatively rich in protein and poor in cellulose (i.e. high in TN), while allochthonous OM is protein-poor and rich in lignocellulose (i.e. low in TN). It was previously shown that N-rich autochthonous OM is more biodegradable38 and produces more CH4 than the degradation of allochthonous OM14 , explaining the relationship between sediment TN for CH4 production (Eq. 18). Third, N is preferentially consumed during microbial degradation of sediment OM (e.g.31), meaning that over time, the sediment OM becomes poorer in TN and less reactive, in accordance with our finding that the interactive term (age * TN) was significant in the model. In fact, also sediment age is a proxy of OM reactivity, given the steep exponential decrease of the sediment OC decay with increasing sediment age39. The model presented here for the first time quantifies the influence of OM input (amount and source) and its diagenetic change, approximated by age, TN concentration and their interaction, on CH4 formation rates from sediment OM over decal timescales. In addition, the model is derived from tropical reservoirs of different trophic status and biomes, and in spite of the considerable variability of CH4 formation between reservoirs, all predicted CH4 formation rates for all cores from all reservoirs converge on one line . This age may therefore serve as an operationally defined age beyond which sediment OC may be considered “buried”, i.e. not degraded to an extent that is quantitatively significant for the standing stock of OC. The age of transition to low background CH4 formation calculated by this approach was about 11 years in CDU and 12 years in CUN and 6 years in FUN , the amount of C that is degraded through the CH4 formation is quantitatively negligible compared to typical carbon burial rates. According to our measured CH4 formation rates in sediment older than the transition age, on average 0.3 ± 0.2% of the C contained in a sediment layer is transformed into CH4 in a year.Despite a significant contribution of older sediment layers to CH416, but once the labile substances are decomposed the degradation rate declines steeply (Fig. 4 in reservoir sediment over the reservoir lifetime.We used the C:N ratio of the surface sediment to evaluate if the source of the sediment deposited onto the sediment surface has an effect on the transition age Fig. . We founply Fig. . Allocht4 formation rate of reservoir sediments is predictable although the fluxes may further vary with sediment temperature and dissolved oxygen concentration40. As CH4 emission from reservoirs is very difficult to measure representatively due to the strong spatial and temporal variability of CH4 emission via diffusion19, and particularly via ebullition42, the sediment CH4 formation model (Eq. 4 emission from sediment characteristics.Our study shows that the CHodel Eq.  represen4 emission from eutrophic reservoirs4 may stem primarily from CH4 formation in young sediment layers (e.g. FUN, <6 years old; Table 4 emission to the atmosphere.Further, our study indicates that the high CH43 carries a risk of creating new reservoirs that are large CH4 emitters: the high potential for soil erosion in the tropics45 implies that new tropical reservoirs may have high sedimentation rates and thus high supply of young and reactive OM that stimulates CH4 formation in the reservoir sediment (Fig. 4 in reservoir sediment results in an anthropogenic enhancement of atmospheric radiative forcing46.Lastly, the current hydropower boom in tropical areasent Fig. . This efSupplementary info


Preliminary X-ray studies revealed that the compound has a cubic structure at room temperature. The formation of the compound has been confirmed by X-ray powder diffraction studies and Raman spectroscopy. Electrical and dielectric properties of the compound have been studied using complex impedance spectroscopy in the frequency range 209 Hz–1 MHz and temperature range 586–679 K. The impedance data were modellized by an equivalent circuit consisting of series of a combination of grains and grains boundary. We use complex electrical modulus M* at various temperatures to analyse dielectric data. The modulus plots are characterized by the presence of two relaxation peaks thermally activated. The morphologies and the average particle size of the resultant sodium tungstate sample were demonstrated by atomic force microscopy, scanning electron microscopy and transmission electron microscopy. The thicknesses and optical constants of the sample have been calculated using ellipsometric measurements in the range of 200–22 000 nm by means of new amorphous dispersion formula which is the objective of the present work. The results were obtained for Na2WO4 particles from experimental (EXP) and measured (FIT) data showed an excellent agreement. In addition, the energy gap of the Na2WO4 sample has been determined using ellipsometry and confirmed by spectrophotometry measurements.A solid-state reaction technique was used to synthesize polycrystalline Na When the radius of the cation ion is greater than 1 Å, the structure crystallizes in a scheelite CaWO4 type. The tungsten occupies a tetrahedral site, while Ca2+ ions are placed at the centre of a distorted cube. By contrast, when the latter is less than 1 Å, the structure leads to a wolframite FeWO4 kind, that consists of oxygen octahedrons which join together by common edges made with chains [WO4]n and [FeO4]n parallel to the axis Oz. These chains are interconnected by common vertices [The tungsten compounds of general formula AWO2WO4) and sodium molybdate (Na2MoO4) crystals are isostructural, and they belong to the class of spinel crystals with general formula Na2XnOn+13  [2WO4 has been used for many applications such as the preparation of coated electrodes for electrocatalysis and as a fire retardant for fabrics [Sodium tungstate NaWO4 and s fabrics . In orga fabrics .2XnOn+13 have been studied for a long time in order to understand the physical and chemical behaviour, such as structure, phase transition and vibrational investigation [2WO4 and Na2MoO4 systems which were made by Pistorius [2WO4 exhibits at least one first-order phase transition at around 901 K. It was suggested that the new phase has an orthorhombic symmetry, possibly Pnam. It was also suggested that another phase exists, which is stable only between 860.6 and 861.8 K [2WO4 elaborated by a solid-state method at 630 K using impedance spectroscopy. In addition, the results show for the first time, to our knowledge, the optical properties of the Na2WO4 sample using spectroscopic ellipsometry (SE) in the range of 200–2200 nm with a step of 1 nm by means of the Delta Psi2 software based on a new amorphous dispersion formula at room temperature.These kinds of samples Natigation ,8. In Na2.2WO4 was prepared with a high-temperature solid-state reaction technique using high-purity Na2CO3 and WO3 compounds in a suitable stoichiometry. The powder was thoroughly mixed in an agate mortar for 3 h and then calcined at 450°C for 6 h in a pure alumina crucible. After cooling, it was again powdered thoroughly during 2 h and then recalcined at 600°C during 6 h. Finally, the recalcined powder was used to make pellets with a diameter of 8 mm and a thickness of 1.6 mm. The pressed pellets were sintered at 650°C during 7 h. The density of the obtained sintered pellets compounds to 95% of the theoretical value. The quality  and formation of the compound were checked by the X-ray diffraction (XRD) technique.The polycrystalline sample of Naα (λ = 1.5418°A) radiation in a wide range of Bragg angles (10 ≤ 2θ ≤ 80) at a scanning rate of 2° min−1.XRD of the calcined powder of the compound was recorded at room temperature (27°C) with a Philips X-ray powder diffractometer (PM 9920) with CuK−1.An infrared spectroscopic study is very important to confirm the presence of O–W–O groups and to determine their modes of vibration. The apparatus used was a Perkin–Elmer FTIR spectrometer Spectrum 100. The spectral range is between 1400 and 400 cmThe impedance spectroscopy permits us to resolve the contributions of various processes such as bulk, grain boundary and electrode effect in the specified frequency domain. In addition, it was used to estimate the resistance and the capacitance associated with the solids.Electrical impedances were measured as a function of both temperature and frequency. This measurement is done in the frequency ranging from 209 Hz to 1 MHz with the TEGAM 3550 and in the ranges of temperature 586–679 K.Both the flat faces of pellet samples were electroded with high-purity fine silver particle paste for all the electrical and dielectric measurements. Two platinum electrode configurations were used to perform the electrical measurements.2WO4 sample. We found a thickness of 0.15 mm close to the ellipsometry results of 0.154 mm. It can be seen that the standard deviation (σ) between the exact and measured values of the Na2WO4 particles is 0.0028. The lower the standard deviation, the closer the data points tend to be to the mean .The digital vernier calliper (0–150) mm range is used to measure the thickness of the Na3.3.1.ullprof with the Rietveld method. The X-ray powder diffractogram reveals that the synthesized compound crystallizes in the cubic space group Fd-3 m with a = b = c = 9.122 (2)Å. The formation of a pure phase Na2WO4 has been confirmed. These refinement results are in good agreement with those reported in the literature for Na2WO4 ceramic [θ, where 2θ is the angle between the incident and reflected X-ray beams and this spectrum corresponds to an Na2WO4 pellet sample. The figure displays the accustomed peaks seen in this pellet sample. Sharp and wide peaks refer to large grains and small grains, respectively. The Williamson–Hall (W–H) plot [2WO4 ceramic. 2WO4 sample. Based on this method, the reciprocal of the broadening is specified by d* and t* are the reciprocal of d and t, respectively. As d* = 0, the reciprocal of the intercept with the y-axis estimates the crystalline size and the slope is the strain ε. The extrapolation of the best straight line passing through the average data gives an intercept at , with a particle size t = 33.3 nm. The slope of that line corresponds to a strain The room temperature XRD pattern is shown in  ceramic . Figure –H) plot  has been3.2.2WO4 for easy viewing. The structure of this compound has the normal spinel type with Na+ ions on the 16c sites in octahedral coordination and W+6 ions on 8b sites in tetrahedral coordination. The Td symmetry with W–O bond lengths of 1.7830 (2)  Å. The unit-cell parameters for this compound are in excellent agreement with the literature [2WO4 structure stands apart as being conspicuously inaccurate, giving significantly longer W–O distances, 1.819 (8) Å, and shorter Na–O distances, 2.378 (8) Å, than the ones reported here or in many other simple tungstates [+6 obtained from our analysis of a large range of crystal structures are nearly identical, being 0.42 Å. The values reported here agree very well with the majority of W–O bond lengths in isolated terature . Howeverngstates . Indeed,terature .Figure 3.3.2WO4 is shown in 4) groups are assigned on the basis of the characteristic vibrations of the O–W–O bridge and υas and υs refer to asymmetric and symmetric stretching vibrations of the terminal (WO4) or bridging (OWO) bonds, respectively, while δ refers to the corresponding bond binding vibrations, which are in general of lower frequency. In these conditions, the peak at 551 cm−1 can be attributed to the bending vibration of the −1 [−1 originates from the O–W–O stretches of the WO4 tetrahedron. The absorption bands at 1688 and 3302 cm−1can be ascribed to the O–H bending and stretching vibrations of the residual water in the samples [The infrared spectrum of Narahedron . The str800 cm−1 . The str samples .Figure 2WO4crystal including all vibrational modes is presented in −1 range [−1 range (banding vibrations), and a group of medium bands in the 70–260 cm−1 range . The assignment to the respective normal modes is presented in The Raman spectrum of the Na−1 range ,17, two The presence of the oxide tungstate groups in the title compound were confirmed by band assignments for the fundamental modes of this compound and are given in 3.4.2WO4 compound at different temperatures are shown in The impedance spectroscopy is one of the most important experimental techniques to determine the electrical properties of the sample and to resolve the contributions of various processes such as bulk, grain boundary and electrode effects in the specified frequency domain. This technique is useful to estimate the resistivity and capacitance and it analyses the charge transport processes in the grain–grain boundary of solids. The complex impedance spectra of the NaR, of the sample. However, experimental data show a depressed semicircle with the centre below the real axis, which is the reason for using constant-phase elements (CPE) rather than ordinary capacitors in equivalent circuits. The CPE is an empirical impedance function of the type:Q indicates the value of the capacitance of the CPE element and α the degree of deviation with respect to the pure capacitor.This spectrum can be interpreted by means of an equivalent circuit. Ideally, such a semicircle arc passes through the origin of a complex plot and gives a low-frequency intercept on the real axis corresponding to the resistance Rg) and capacitances (Cg), whereas the grain boundary 1 consists of parallel combination of resistance (Rgb) and constant-phase element CPEgb. An appearance of a little semicircle in the low-frequency region can be explained by another combination . This semicircle is owing to the electrode polarization effect [Z′ and Z′′ versus the frequencies at different temperatures, which are fitted by equations (3.1) and (3.2). It is observed that the magnitude of Z′′ decreases with the increase in temperature and the peak frequency shifts to the higher values. This shift indicates the temperature dependence of the relaxation time. The good conformity of calculated lines with experimental data indicates that the suggested equivalent circuit describes the crystal–electrolyte interface reasonably well:The appropriate equivalent circuit to the semicircles consisting of series of a combination of grains and boundary grain elements. Bulk 1 consists of a parallel combination of resistances  for grain boundaries, three parameters  for bulk and  for electrode effect. The extracted parameters for the circuit elements are summarized in The equivalent circuit modelling gives eight parameters at each temperature (3.4.1.M*) is calculated from the following equation:M = ωC0Z, M′ = ωC0Z′′ and M′′ = ωC0Z′, C0 is the vacuum capacitance of the cell. The variation of the imaginary part of the modulus (M′′) as a function of frequencies at several temperatures is shown in M′′ shows a slightly asymmetric peak at each temperature. There are two relaxation peaks located at lower frequencies which are associated with the grain boundary, and at higher frequency with the grain effect. Moreover, when the temperature increases, modulus peak maxima shift to higher frequencies.Electric modulus formalism is an important theory. It has been used in the analysis of the electrical properties because it gives the main response of the bulk of the crystal sample and is particularly suitable to extract phenomena, and it permits us to study charge transport processes  in ion conductors and eliminates the electrode polarization effect . The eleM′′ in the frequency domain:ωmax are the peak maximum and the peak angular frequency of the imaginary part of the modulus, respectively, and β was extracted from the analysis. To account for the grain boundary effects, our experimental data have been modelled with two Bergman functions. The measured data are well fitted to equation (3.4). In the present ceramic sample, β may be considered as independent of the temperature in the temperature range studied. For the peaks at low and high frequencies, the β parameter values were found to be between 0.18–0.57 and 0.89–0.92, respectively.Bergman has proposed a function that describes the variation of the imaginary part of the modulus 4.2WO4 sample were investigated by using an atomic force microscope , scanning electronic microscope , energy-dispersive X-ray spectroscopy  and transmission electron microscopy , respectively, after sintering at 650°C as shown in figures The morphology and microstructure, composition and average particle size of Na2WO4 sample showing a root mean square (RMS) value and an average surface roughness (Rave) of about 92.7 and 59.7 nm, respectively.2WO4 particles consist of a nanoparticle that creates a homogeneous surface. 2WO4 sample was prepared by a solid-state technique using EDX. The figures confirm O, Na and W as the elemental compositions in the inset of The SEM image illustrates that Na2WO4 sample prepared in deionized water. One can see clearly that the prepared sample exhibited a uniform structure, which indicated that Na doping changes the morphologies of Na2WO4. In addition, the influence of NaCO3 on the surface of the tungsten changes the average diameter of the particles of about 600 nm owing to the chemical bounding theory of a single crystal growth.5.Optical experiments provide a good way of examining the properties of semiconductors; especially, the absorption coefficient for various wavelengths gives information about the band gap of the material. Knowledge of these optical gaps is very important for understanding the electrical properties of a semiconductor.2WO4 samples have been analysed by ellipsometry, which is based on the measurements of the complex ratio ρ of the Fresnel reflection coefficients rp and rs ), respectively. The standard ellipsometric parameters ψ and Δ are given bypδ − δs is the phase shift difference, and f an optical function dependent on the layer thickness. The fitting process adopted a new amorphous model, this model is described in the following equations [k(ω) is the extinction coefficient, n(ω) the refractive index, jc = 2.jf.jΓ.(ω − gω), n∞ the value of the refractive index when (ω → ∞), jf (eV) the peak of the extinction coefficient, Γj(eV) the peak of absorption, jω (eV) the energy at which the extinction coefficient is maximum and ωg (eV) the optical band gap Eg of the new amorphous model.Naquations ,26:k(ω)ψ, Δ and Is, Ic is shown in figure 12a,b.The comparison between the measured and calculated spectra of ψEXP and ψFIT in the visible range is about 42.6°–42.5°, respectively, while the average values for ΔEXP and ΔFIT are in the same range of about 0.03° to 0.02°; thus, the standard deviation (σ) of the experimental values of ψ and Δ gives a fitting value of about 0.07 for ψ and 0.007 for Δ values.As one can see, the average value of Is and Ic for the experimental values and fitting are about 0.002 and 0.014, respectively. A low σ denotes that the data points are inclined to be very close to the mean value (as shown in our case), on the contrary, a high σ indicates that the data points are spread out over a large range of values.In the same method, the average values for χ2 (MSE) is about 0.81; which mention the differences between the experimental and fitting points for the sample. So, all these experimental and fitted data for the optical parameters of the Na2WO4 sample are very close according to the value of χ2 that we acquired. The value of χ2 should be as small as possible and χ2 can be defined byi is the standard deviation of the points. The smallest value of χ2 refers to a better fitting results.The physical parameters for a new amorphous model are presented in T), reflectance (R) and absorption (A) of the Na2WO4 sample in dependence of the wavelength measured and calculated spectra's.2WO4 sample measured and calculated by SE measurements are in the spectral range of about 200 nm to 2200 nm. These results are obtained with the DeltaPsi2 software.The average values of the transmittance, reflectance and absorption spectras of the Na2WO4 sample are about 0.9% and 1.3% respectively, whereas the average reflectance value is about 68% and 70%, respectively. The average absorptance value is about 31% and 29%, respectively. Thus, a good agreement of the different values for T, R and A of the samples are obtained using ellipsometry .As one can see, the average measured and fitted transmission value in the visible region for the Nan, k, gE, εr, εi of the Na2WO4 sample were investigated experimentally and theoretically.Based on the transmission and reflection curves, measurements have been obtained from the new amorphous model, the other optical parameters such as α (λ) of the Na2WO4 sample presented according to the optical transmittance curves and the thickness of the sample by the equationT and d are the sample's transmittance and thickness, respectively.The absorption coefficient 2WO4 sample can be determined by Tauc's equation given by the following equation [α is the absorption coefficient, A a constant, Eg the optical energy gap and E the photon energy. We use the absorption coefficient curve as a function of wavelength and the relationship with the incident photon energy. The values m = 2, 2/3, 0.5 and 1/3 refer to allowed direct transition (DT), forbidden direct transition (DFT) and allowed indirect transition (IDT) and forbidden indirect transition (IDFT), respectively. By extrapolating the linear part of the plot of versus the values E (eV), the optical band gap of the Na2WO4 sample is determined for αE = 0 with this graph. The values of Eg due to four transition modes of the sample measured and calculated are shown in figure 14a,b and Therefore, the optical band gap of the Naequation :5.3(αE)2WO4 sample for the measured and calculated optical energy gap of different transition modes.One can see that an excellent agreement is obtained with the Nan(λ) and k(λ) of the Na2WO4 sample measured and calculated are obtained using the following equations: R is the reflectance, k the extinction coefficient, α the absorption coefficient and λ the wavelength of the light.The refractive and extinction coefficients 2WO4 sample.n and k in the visible range as a function of the wavelengths of the sample are 3.24, 3.35 and 0.0017, 0.0015, respectively. The refractive index values n increase initially with the rises of the wavelength then decrease to the maximum value of 3.5 at 680 nm, and then decrease to the minimum value of 3.3 at 1180 nm and finally increases rapidly with the increase in wavelengths. The extinction coefficient data for the Na2WO4 sample increase initially to the maximum value of about 0.002 at 640 nm then decrease rapidly towards the shorter wavelength of about 0.01 at 1140 nm, and finally increase with the increase in wavelengths. In addition, nexp and kexp values for the Na2WO4 sample obtained by SE are in excellent agreement with those given by FIT points. These results confirmed that a very good model has been used to determine the optical properties of the Na2WO4 sample.One can see the average measured and calculated data of the εr = n2 − k2 and εi = 2nk.The complex dielectric constants  are investigated using the following equations: 2WO4 sample are shown in εr and εi of the sample decrease with the increase in wavelength.The real and imaginary parts of the dielectric constants of the Naεr and εi in the visible range as a function of the wavelengths are 10.62, 11.34 and 0.01107, 0.01042, respectively. The curves of the measured and calculated real εr(λ) and imaginary εi(λ) part of the dielectric constants versus wavelengths of the Na2WO4 sample are shown in this figure. The average values of εr(λ) of the sample are in the visible region of about 10.6 and 11.3, whereas the average values of the εi(λ) are 0.011 and 0.010. The maximum values of εr(λ) and εi(λ) for the Na2WO4 sample.One can see that the measured and calculated average values of 2WO4 sample measured by PerkinElmer Lambda 950 (UV/Vis/NIR) spectrophotometry (integrated sphere) compared with those obtained by ellipsometry  as shown in figure 17a. Based on these curves and equation (5.2), the optical band gap of the sample for indirect transition has been calculated to about 3.7 eV as shown in figure 17b, this value is in excellent agreement with that value measured by ellipsometry.In addition, the average values of transmittance, reflectance and absorption spectra of the Na6.2WO4 compound has been synthesized and identified by XRD. The sample was found to crystallize in cubic symmetry with the Fd-3 m space group. The infrared and Raman spectra were recorded and interpreted on the basis of the structural peculiarities of the In the present research work, the Na2WO4 was proposed. The average particle size of about 33.3 nm of the sample has been measured using XRD analysis based on the W–H method. A roughness of about 59.7 nm was found, while SEM images indicate the nanoparticle size of the sample. An EDX study is used to analyse the compositions of that sample and TEM analyses are used to determine the diameter of the particles of about 600 nm.Characteristically, two semicircles are observed in the impedance plot, indicating the presence of two relaxation processes in the studied compound associated with the grain and grain boundary. Consequently, an equivalent electrical circuit for the electrochemical cell with Na2WO4 particles have been demonstrated using SE measurements and spectrophotometry (integrated sphere) in the spectral range of 200–2200 nm at room temperature. The results that we have obtained from SE (EXP and FIT) showed an excellent agreement. In addition, the optical band gap of Na2WO4 sample has been calculated by SE and confirmed by spectrophotometry measurements with an excellent agreement too.Finally, the optical properties of the Na