In situ flow cell for combined X-ray absorption spectroscopy, X-ray diffraction, and mass spectrometry at high photon energies under solar thermochemical looping conditions.

Recently, Prussian blue analogues (PBAs) have been reported to exhibit a low voltage charge/discharge behavior with high capacity (300–545 mAh/g) in lithium-ion secondary batteries (LIBs) [...]

Structural changes in an equimolar ceria–zirconia solid solution were determined from room temperature to 1773 K under typical reducing and oxidizing conditions in a reactor for the solar thermochemical dissociation of water or carbon dioxide in a two-step redox cycle. We report the first in situ X-ray absorption spectroscopy (XAS) measurements at both the Ce K and Zr K edges under the conditions of thermochemical carbon dioxide splitting and a temperature swing of 1773 to 1073 K and isothermal conditions at 1773 K. The shift in the Ce K absorption edge reveals quantitative information about changes in the electronic structure of cerium. The maximum extent of reduction at 1773 K was 53% ± 5%; about 9% ± 5% of the cerium atoms changed valence from 4+ to 3+ and vice versa during isothermal looping in a flow of argon and carbon dioxide, respectively. Zr K edge XANES indicated a transformation of the oxygen coordination of zirconia to a more centrosymmetric cubic geometry upon reduction. During isothermal cyc...

Introduction Research focusing on iron-based cathode materials for lithium ion batteries tends to favor materials that operate on the (de) intercalation of one Li per Fe atom (based on Fe2+/Fe3+redox couple); thereby imposing an intrinsic limitation on the energy density of the cathode material. To drastically enhance the energy density, intercalation materials with more than one electron per Fe atom are needed. In commonly used cathode materials, however, more than one electron reaction has not been utilized for charge-discharge reaction. For the development of cathode materials which achieve more than one electron reaction, it is essential to investigate the reaction mechanism.This study investigates reaction mechanism of more than one electron reaction in cathode materials. Li2-x FeTiO4 is selected as an appropriate model compound, as both the Fe2+/Fe3+ as well as Fe3+/Fe4+ redox couples are expected to be utilized to achieve high capacity. The possibility of de (intercalation) of two lithiums from the spinel-type Li2-x FeTiO4 is examined and the mechanism underlying the Li+ (de) insertion mechanism in Li2-x FeTiO4is discussed. Experimental Spinel-type LiFeTiO4 was synthesized via the conventional solid state ceramics route. Electrodes prepared from this material were examined in two-electrode coin-type cells, using lithium metal as a counter electrode. Electrodes were prepared from LiFeTiO4 to which carbon black was added and ball-milled at 400 rpm for 6 hours. Polytetrafluoroethylene (PTFE) binder was thereafter added. The weight ratio of LiFeTiO4, carbon black and PTFE was 6:3:1. The electrolyte used was a 1 M solution of LiClO4 in ethylene carbonate / diethyl carbonate. Initial lithium extraction from LiFeTiO4 was carried out based on the capacity of one lithium per Fe atom. Cells were then cycled between 1.6V and 4.2V at various current densities. The electrochemical measurements were conducted at 55.0oC. X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS) measurements were conducted at SPring-8 and at SR Center, Ritsumeikan University. Results and Discussion The pristine LiFeTiO4 was characterized by Rietveld analysis. As shown in Fig. 1, all the reflections of the XRD patterns of the pristine LiFeTiO4 are fully indexed to a cubic structure (space group Fd3m). The rietveld analysis shows that all cations are randomly distributed on the tetrahedral (8a) and octahedral (16d) sites. The refined lattice parameters are consistent with the previously reported values [1-3].The spinel-type LiFeTiO4 can be electrochemically delithiated below the voltage of 4.2 V, to obtain FeTiO4. The subsequent discharge and charge measurements show that a reversible capacity of about 250 mAhg-1can be obtained under C/20 rate at an average voltage of 2.5 V with good capacity retention.For the discharged and charged Li2-x FeTiO4, XRD and XAS measurements were conducted to elucidate the crystal and electronic structural changes underlying the high capacity in spinel-type LiFeTiO4. Fig. 2 shows XRD pattern of charged and discharged Li2-x FeTiO4. The spinel structure of LiFeTiO4 is maintained during both charge and discharge reaction. Additionally, changes in the lattice constants obey Vegard’s law, indicating a solid-solution behavior during the charge and discharge reaction in Li2-x FeTiO4. References M. A. Arillo, M. L. Lopez, E. Perez-Cappe, C. Pico, M. L. Veiga, Solid State Ion., 107, 307-312 (1998).M. A. Arillo, M. L. Lopez, C. Pico, M. L. Veiga, A. Jimenez-Lopez, E. Rodriguez-Castellon, J. Alloys Comp., 160-163, 317-318 (2001).M. A. Arillo, M. L. Lopez, C. Pico, M. L. Veiga, A. Jimenez-Lopez, M. L. Vega, Chem. Mater., 17, 4162-4167 (2005).

Magnesium battery is one of the candidates for the next generation battery system due to the high energy density and the environmentally friendly nature 1,2. Developing suitable cathode materials is a clue to the practical application. Divalent Mg2+ insertion/extraction reactions in host compounds is difficult, due to the stronger ionic interaction and harder charge redistribution of magnesium compared to lithium ions 3. Therefore suitable cathode materials are limited at this moment. In order to design the host materials for magnesium battery cathodes, it is important to understand the difference between the reaction dynamics of magnesium and that of lithium. Olivine-type lithium iron phosphate (LiFePO4) is a well-known cathode material in lithium ion batteries 4. By using delithiated FePO4, the electrochemical insertion/extraction of magnesium ions in FePO4 was reported by Le Paul et al. 5 Hence, FePO4 is suitable as a model compound to clarify the reaction dynamics of magnesium battery. In this study, we investigated the crystal structure change and the reaction dynamics during electrochemical magnesium insertion/extraction reactions of olivine-type FePO4.LiFePO4 was prepared by using a solid state reaction using Li2CO3, FeC2O4-2H2O and (NH4)2HPO4 as raw materials. After carbon-coated with acetylene black 10 wt% to LiFePO4, the mixture was pelletized and calcined. FePO4 was prepared by chemical oxidation of the obtained carbon coated LiFePO4 using nitronium tetrafluoroborate (NO2BF4) as an oxidizing agent. The particle size of the completed carbon coated FePO4 was about 65 nm determined by SEM observation. Electrochemical measurements were carried out using a three-electrode cell with an Ag+/Ag double junction reference electrode. The cathode material consists of 80 wt% FePO4, 15 wt% acetylene black and 5 wt% polytetrafluoroethylene. The counter electrode was a magnesium rod and the electrolyte was 0.5 M magnesium trifuluoromethanesulfonyl-imide (Mg(TFSI)2) in acetonitrile (AN). Galvanostatic discharge/charge measurements were conducted with C/30 rate at 55°C. X-ray absorption spectroscopy (XAS) measurements were carried out in a transmission mode at BL02B2 at SPring-8, Japan. Synchrotron X-ray diffraction (XRD) measurements were also carried out at BL01B1 and BL14B2 at SPring-8, Japan. Figure 1 shows discharge/charge profile of FePO4 in 0.5 M Mg(TFSI)2/AN. The obtained discharge capacity indicates 0.4 magnesium ions insertion into FePO4, comparable to 0.8 lithium ions insertion. In the charge process, the obtained capacity corresponds to the extraction of 0.3 magnesium ions. This result shows that magnesium insertion /extraction reaction of FePO4is irreversible and that the extraction is more difficult than the insertion process. In addition, discharge/charge curves are considerably dissimilar, suggesting that the reaction mechanism could be quite different between insertion and extraction processes. In order to characterize discharged and charged MgxFePO4, XAS and XRD measurements were performed. Fe K-edge XANES spectra shows lower and higher energy shifts with the discharge/charge reactions, respectively. This indicates the reduction and oxidation of Fe in FePO4 by magnesium insertion/extraction. XRD patterns show lower and higher peak shifts with the discharge/charge reactions, respectively. The peaks attributed to the two-phase reaction did not appear as shown in the charge/discharge reactions of LiFePO4. This result reveals that magnesium ions insertion/extraction reactions of FePO4proceeds via not a two-phase but a single-phase mechanism. Furthermore, we will present the reaction dynamics of magnesium ions insertion/extraction by using FePO4thin film as a model electrode. Acknowledgments This work was supported in part by Core Research for Evolutional Science and Technology (CREST) program of Japan Science and Technology Agency (JST) in Japan.

Polyanionic electrode materials such as lithium iron phosphate (LiFePO4) have demonstrated significant success, but are hampered by low conductivity. Conductive additives such as carbon are often used and are most frequently employed by coating or simply being mixed with the active material. These additives have shown success, however they decrease the volumetric capacity of the electrode. Bimetallic materials like silver vanadium oxide (Ag2V4O11) offer the ability to discharge multiple electrons per formula unit cell, generate a conductive network in-situ and thus provide high volumetric energy density. The design of bimetallic materials that form conductive networks in-situ can be used to eliminate the need for conductive additives. In these materials, a polyanionic metal center can be combined with a metal that reduces to form a conductive metal. By utilizing active cathode materials that form conductive networks in-situ we can reduce or potentially eliminate the need for conductive additives that do not add to the capacity of the cell and require additional processing, thereby reducing processing complexity while providing a greater overall energy density. In one such polyanionic material, silver vanadium diphosphate (Ag2VP2O8), both the vanadium and silver ions are reduced during discharge [1]. The silver metal formation provides a conductive matrix which allows for higher power output. By determining the spatial location of silver as well as the discharge conditions under which the silver network is formed we can optimize the formation of this network, thereby improving performance of these electrodes [2]. In this study we use the combination of in-situ energy dispersive x-ray diffraction (EDXRD) and ex-situ x-ray absorption spectroscopy (XAS) measurements to spatially resolve the formation of the conductive silver network in Ag2VP2O8electrodes and to determine the effect of increased current on the discharge processes. Li/ Ag2VP2O8 coin cells were discharged to various depths of discharge and left intact for in-situ EDXRD measurements performed at the National Synchrotron Light Source at Brookhaven National Laboratory. The height of the incident beam was set to 20 μm, and the width of the slits on the detector was set so that the gauge volume (volume of cathode measured) was 0.02 x 2 x 2 mm3 (see Fig. 1A). The coin cells were placed on a 3-axis stage so that diffraction patterns as a function of position could be obtained. Fig. 1B shows an example of EDXRD spectra obtained within the cathode as a function of beam position. By measuring the intensity of the Ag and Ag2VP2O8peaks we can determine the spatial distribution of silver metal within the cathode. In addition to determining the location of silver, we can separate the Ag+ to Ag0 and V4+ to V3+reduction processes using XAS, the results of which are shown in Fig. 1C. By measuring the fractions of reduced silver and vanadium in cells discharged at different rates, we find that silver is reduced preferentially at lower discharge rates, and conversely at higher rates more vanadium is reduced. By combining the results from spatially-resolved EDXRD and XAS measurements, it is possible to determine the conditions under which a more isotropic silver network is formed. In addition to materials where conductive networks are formed in-situ, these techniques have applications for a broader range of electrode materials. Using these techniques it may be possible to determine the effect of discharge rate on the reduction processes in any material with multiple metal centers or structural changes as a function of discharge, and we will present our results in this broader context. 1. E. S. Takeuchi, C. Y. Lee, P. J. Cheng, M. C. Menard, A. C. Marschilok, K. J. Takeuchi, Silver vanadium diphosphate Ag2VP2O8: Electrochemistry and characterization of reduced material providing mechanistic insights. J Solid State Chem 200, 232-240 (2013); published online EpubApr (DOI 10.1016/j.jssc.2013.01.020). 2. K. C. Kirshenbaum, D. C. Bock, Z. Zhong, A. C. Marschilok, K. J. Takeuchi, E. S. Takeuchi, In situ profiling of lithium/Ag2VP2O8 primary batteries using energy dispersive X-ray diffraction. Physical chemistry chemical physics : PCCP 16, 9138-9147 (2014); published online EpubApr 16 (10.1039/c4cp01220h). Figure 1

X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS) are two main x-ray techniques in synchrotron radiation facilities. In this Note, we present an experimental setup capable of performing simultaneous XRD and XAS measurements by the application of a pixel-array area detector. For XRD, the momentum transfer in specular diffraction was measured by scanning the X-ray energy with fixed incoming and outgoing x-ray angles. By selecting a small fixed region of the detector to collect the XRD signal, the rest of the area was available for collecting the x-ray fluorescence for XAS measurements. The simultaneous measurement of XRD and X-ray absorption near edge structure for Pr0.67Sr0.33MnO3 film was demonstrated as a proof of principle for future time-resolved pump-probe measurements. A static sample makes it easy to maintain an accurate overlap of the X-ray spot and laser pump beam.

Understanding of the structural and the chemical properties of Pt catalysts in polymer electrolyte fuel cells (PEFCs) is necessary to improve the activity for the durability of the catalysts. The small-angle X-ray scattering (SAXS) and the X-ray absorption spectroscopy (XAS) measurements are widely used to investigate these properties. We developed a system that combines in situ A-SAXS/XAS measurements in the same field of observation using a channel flow electrode (CFE) cell and characterized the chemical states, average diameter and size distributions of Pt catalysts under controlled electrochemical conditions. In this study, we investigated an effect of dissolved gases on Pt nanoparticle catalysts using the system.All experiments were carried out at SPring-8 BL19B2. A commercial Pt/carbon black catalyst (TEC10E50E, Tanaka Kikinzoku Kogyo) was used as test electrode in this experiment. Prior to SAXS and XAS measurements, the electrochemical potential was cycled between 0.6 and 1.0 V vs. the RHE in O2 or N2-saturated 0.1 M HClO4. For the XAS measurements, the Pt LⅢ edge was used. The ionization chamber and a seven-elements silicon drift detector were used to obtain the XAS spectra. For the SAXS measurements, the X-ray energy was set to 11.5 keV and 11.55 keV, which are below and near to the Pt LIII absorption edge, respectively. The scattered X-ray was detected using an area detector (PILATUS 2M). Figure 1 show the X-ray absorption near edge structure (XANES) spectra of the Pt catalyst after the potential cycles in O2-saturated 0.1 M HClO4. The white-line peak intensity increased and became higher at a higher potential cycle. This indicates the partial electron-transfer from Pt atoms or initial stage of Pt oxidation. We also will discuss the effect of dissolved gases for morphological and chemical states from SAXS and XAS data. Figure 1

Identifying Key Descriptors for the Single-Atom Catalyzed CO Oxidation

The preparation and characterization of Sb-doped Bi(2)UO(6) solid solutions, in a limited composition range, is reported for the first time. The solid solutions were prepared by solid-state reactions of Bi(2)O(3), Sb(2)O(3) and U(3)O(8) in the required stoichiometry. The reaction products were characterized by X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS) measurements at the Bi and U L(3) edges. The XRD patterns indicate the precipitation of additional phases in the samples when Sb doping exceeds 4 at%. The chemical shifts of the Bi absorption edges in the samples, determined from the XANES spectra, show a systematic variation only up to 4 at% of Sb doping and support the results of XRD measurements. These observations are further supported by the local structure parameters obtained by analysis of the EXAFS spectra. The local structure of U is found to remain unchanged upon Sb doping indicating that Sb(+3) ions replace Bi(+3) during the doping of Bi(2)UO(6) by Sb.

All-solid-state fluoride-ion batteries (FIBs), which are based on the shuttling of fluoride ions, have been considered as one of the promising alternates for next-generation energy storage devices because of high theoretical energy density and safety. Benefiting from the multi-covalent fluorination process, metal/metal fluorides (M/MFx) have been firstly utilized as electrode materials for FIBs with high theoretical energy densities.[1] However, M/MFx systems suffer from exceptionable volume expansion upon fluorination process due to the close-packed metal atoms, which would cause blockage of the F- diffusion pathway, resulting in devastating damage to the electrode-electrolyte interfaces. To solve these problems, cathode materials that utilize topotactic fluoride ion intercalation reactions, similar to the electrode materials applied in lithium-ion secondary batteries, are being developed.[2] Cathode materials that utilize topotactic intercalation of fluoride ions are often composed of heavier elements than the cathodes of lithium-ion batteries that use the same type of reaction mechanism, and effective anion redox is required if capacity is to be increased beyond that of lithium-ion secondary batteries.In this research, we investigated Sr2F2Fe2OS2 (SFFOS) compound with a layered structure as a novel cathode material for all-solid-state FIBs, and evaluated its electrochemical properties and elucidated the charge compensation mechanism using anion redox of sulfur.SFFOS was synthesized by a solid-state reaction under vacuum environment using SrF2, SrO, Fe, and S.[3] SFFOS/La0.9Ba0.1F2.9/vapor grown carbon fiber (VGCF) was used as the composite cathode, La0.9Ba0.1F2.9 as the electrolyte and Pb/PbF2/ La0.9Ba0.1F2.9/VGCF as the composite anode to construct the electrochemical cell. Charge-discharge measurements were carried out in the cut-off voltage range of -1.5 to 1.5 V at 140°C. Ex-situ X-ray Diffraction (XRD), X-ray absorption spectroscopy (XAS) measurements of Fe K-edge, S K-edge, O K-edge and F K-edge were carried out under different state of charge during the 1st and the 2nd cycle.SFFOS showed reversible intercalation/de-intercalation of fluoride ions and a capacity of ~6.1 fluoride ions per unit cell (403 mAh g-1). The charge compensation mechanism was revealed for SFFOS by XAS measurements, where S redox contributed to the whole voltage range from -1.5 V to 1.5 V vs. Pb/PbF2, and Fe+2/+3 redox contributed from the middle SOC. The S-S dimers were formed upon charging, which was similar to the trapped O2 molecules observed in lithium-excess metal oxide during charge process[4]. Not only can the F- anions insert around Fe to form Fe-F bonds, but the excess F- anions can also occupy the Sr-S interstitial layers in the original lattice. Compared to the Fe-based layered oxide Sr3Fe2O5, the Fe-based oxysulfide SFFOS showed a lower average voltage but a higher specific capacity. We believe that this study could provide a new understanding of sulfur-based charge compensation and electrochemical fluorination reactions. Reference s : [1] D. Zhang, K. Yamamoto, Y. Uchimoto et al., J. Mater. Chem. A, 2021, 9, 406–412.[2] Y. Wang, K. Yamamoto, Y. Uchimoto, et al., Chem. Mater., 2022, 34, 609–616.[3] Kabbour H, Janod E, Corraze B, et al ., J. Am. Chem. Soc., 2008, 130(26): 8261-8270.[4] R. A. House, P. G. Bruce, et al., Nat. Energy 2020, 5, 777–785. Figure 1

We demonstrate that x-ray absorption spectroscopy (XAS) can be used as an unconventional characterization technique to determine the proportions of different crystal phases in polymorphic samples. As an example, we show that ratios of anatase and rutile phases contained in the TiO2 samples obtained by XAS are in agreement with conventional x-ray diffraction (XRD) measurements to within a few percent. We suggest that XAS measurement is a useful and reliable technique that can be applied to study the phase composition of highly disordered or nanoparticle polymorphic materials, where traditional XRD technique might be difficult.

Lately, sodium ion batteries (SIB) have been studied very intensively as a potential alternative to Li ion batteries (LIB). As sodium is 6th most abundant element in Earth which makes it very cheap compared to lithium. Also, the cell chemistry is similar to LIB system. In addition, cheap and lighter aluminum can be used as a current collector at the anode side instead of copper foil. Among the studied cathodes, P2-type Na0.7MnO2 cathode is more attractive as it can deliver high capacity and high energy density, moreover Mn is one of the cheap elements. However, the long cyclability of the composite has been an issue due to the Jahn-Teller distortion which is associated with the existence of Mn3+. In this study, our approach was to suppress the Jahn-Teller distortion by Ni doping by varying the dopant amount from 0%, 10% and 20%. The composites were synthesized by combustion method. The aqueous solution of stoichiometric values of sodium nitrate (98%), manganese (II) nitrate hexahydrate (97%), and nickel (II) nitrate hexahydrate (98%) were added to aqueous citric acid solution (nitrates : citric acid, 1 : 0.5 in weight). The solution was heated on a hot plate at 100 °C for overnight under constant stirring to evaporate the solvent. Then dried powder was further heated to 200 °C for auto combustion of citric acid. Burnt powder further heated at 500 °C for 3 h to decompose the nitrates and yield a homogeneously mixed amorphous powder containing carbon residues. The obtained decomposition product was pelletized and heated in a tube furnace at 900 °C (heating rate – 5 °C / min) for 10 h in air atmosphere and then slowly cooled to room temperature. The obtained powder was transferred to Ar-filled glove box to avoid the contact with moisture in the air. X-ray diffraction (XRD, Xpert, PANalitical) using Cu-Kα radiation was employed to characterize the crystal structure of the synthesized powders. XRD measurement was carried out in the 2θ range of 10−80° with a step size of 0.03°. The FULLPROF Rietveld program was used to analyze the observed powder diffraction patterns. Structural studies during cycle were examined by means of in-situ synchrotron X-ray diffraction (XRD) and ex-situ X-ray Absorption Spectroscopy (XAS). In-situ XRD and ex-situ XAS measurement was respectively carried out at 9B beamline and 8C beamline of Pohang Accelerator Laboratory (PAL), Pohang, South Korea. Electrochemical properties were studied in an half-cell configuration assembling a R2032 coin-type cell using sodium metal as the negative electrode in an Ar-filled glove box. The electrolyte solution comprised 0.5 M NaPF6 in propylene carbonate and fluorinated ethylene carbonate (PC:FEC, 98:2 in volume). The cells were charged and discharged between 2.0 V and 4.3 V at a rate of 0.1C at 25 °C. Among the successfully synthesized samples Na0.7Mn0.8Ni0.2O2 composite displayed better electrochemical performance. As shown in Figure 1 the composite delivered initial discharge capacity of 160 mAh g-1 at 0.1C between voltage of 2.0 V and 4.3 V and the capacity retention is remarkably improved compared to bare composite. Data on structural change during cycling and other detailed studies will be presented at the meeting. Figure 1. Initial charge-discharge profiles of P2-Na0.7Mn1-xNixO2 composites at 0.1C. Figure 1

The structure of the eutectic liquid alloy is investigated both under ambient conditions and at high pressure/high temperature using X‐ray absorption spectroscopy (XAS) and X‐ray diffraction (XRD) techniques. The local structure of the liquid alloy at ambient conditions is analyzed using double‐edge refinements of the XAS data. Solid–liquid phase transitions under high‐pressure and high‐temperature conditions are monitored by combined XAS and XRD measurements along several quasi‐isobaric heating runs, allowing to draw a melting line up to 10 GPa. The established melting line is found to be slightly below the one of pure gallium (Ga) and to follow its trend as expected from the eutectic nature of the compound. A series of Ga K‐edge X‐ray absorption fine structure (XAFS) spectra measured at different pressures indicates the absence of large structural modifications at local Ga sites in the liquid within the investigated pressure and temperature range.

To drive the further development of electrochemical CO2 reduction technologies, there is an urgent need for highly active catalysts that minimize unwanted side reactions and that also possess a large specific surface area. While nanostructured catalysts typically fulfill the latter requirement, they often use porous carbon supports that improve the nanoparticles’ dispersion but can shift the product selectivity towards undesirable H2 formation.[1] This challenge could be solved by using unsupported aerogels consisting of interconnected nanodomain networks of highly porous materials such as nano-wires or -particles, which provide a large surface area while minimizing unwanted side reactions.[2] So far, precious metals such as gold (Au) and silver (Ag) have shown remarkable activity and selectivity as CO2-reduction catalysts for CO production.[3] However, due to the high cost of such noble metals, improving their mass-specific activity is essential. One strategy to attain this, especially for Au, is to reduce the adsorption energy of the catalyst’s surface towards CO by changing the electronic structure of the d-band through alloying with other metals. In this context, ordered AuCu structures have proven to be promising candidates for improving the CO2-to-CO activity and selectivity.[4] With the motivation to combine both of the above approaches (i.e., Au-alloying with Cu and the absence of a C-support), in this study we present an AuCu aerogel with an average domain size of ≈ 7 nm that exhibits an exceptionally high faradaic efficiency of 87 % for CO at -0.6 V versus the reversible hydrogen electrode (RHE). This corresponds to a ≈ 2-fold higher Au-mass-specific partial current density for CO when compared to an equivalent, monometallic Au aerogel. Notably, this enhanced activity and selectivity are achieved by performing a potential cycling procedure prior to the CO2 reduction potential hold that involves cyclic voltammetry (CV) between 0.1 and 1.7 V vs. RHE at a scan rate of 50 mV/s until a stable voltammogram is achieved. To investigate the changes in the electronic and structural properties which have happened to the catalyst during this potential cycling, we performed an in situ grazing incidence X-ray absorption spectroscopy (XAS) measurements in the course of these CVs. Chiefly, these spectroelectrochemcial tests were carried out in the same cell used for the assessment of the CO2 reduction performance, ensuring for the first time that the mass-transport conditions encountered by the catalyst during these XAS measurements are identical to those in the CO2-reduction activity and selectivity tests. Figure 1 illustrates the changes observed throughout the potential cycling procedure in the Cu K- and Au L3-absorption edges, whereby the acquired spectra were submitted to a multivariate curve resolution (MCR) analysis. For the Cu K spectra, a total of three components were identified to describe the whole dataset, and it becomes evident that as the number of cycles increases, the copper oxide phase (component 1 in Figs. 1b and 1c) diminishes while a metallic phase (component 2, identified as an AuCu alloy through EXAFS fitting) becomes more prominent. In the case of the Au L3 data, only two components were discerned to describe the dataset, and both of them were identified as distinct AuCu alloy phases through EXAFS fitting. With an increasing number of cycles, component 2 (featuring a higher oxide content than component 1) becomes dominant at positive potentials, suggesting an increasing Au content on the aerogel’s surface as the potential cycling procedure progresses.In summary, in this contribution we present an AuCu aerogel catalyst exhibiting a high activity and selectivity for CO production that is achieved by cyclic voltammetry treatment prior to holding CO2 reduction potential. The results derived from the in situ XAS measurements on this material indicate that this process effectively removes the copper oxide domains initially present in the catalyst, forming a novel AuCu alloy phase while simultaneously enriching the aerogel’s surface with Au. References Baturina, O.A., et al., CO2 Electroreduction to Hydrocarbons on Carbon-Supported Cu Nanoparticles. ACS Catalysis, 2014. 4(10): p. 3682-3695. Cai, B. and A. Eychmuller, Promoting Electrocatalysis upon Aerogels. Adv Mater, 2019. 31(31): p. e1804881. Hori, Y.M., A.; Kikuchi, K.; Suzuki, S, Electrochemical Reduction of Carbon Dioxides to Carbon Monoxide at a Gold Electrode in Aqueous Potassium Hydrogen Carbonate. J. Chem. Soc., Chem. Commun., 1987. 10: p. 728-729. Liu, K., et al., Electronic Effects Determine the Selectivity of Planar Au-Cu Bimetallic Thin Films for Electrochemical CO(2) Reduction. ACS Appl Mater Interfaces, 2019. 11(18): p. 16546-16555. Figure 1

The understanding of the structural and the chemical properties of Pt catalysts in polymer electrolyte fuel cells (PEFCs) is necessary to improve the activity for the durability of the catalysts. The small-angle X-ray scattering (SAXS) and the X-ray absorption spectroscopy (XAS) measurements are widely used to investigate the properties of Pt catalysts. Recently, Povia et al developed a powerful tool by combining the SAXS and XAS measurements for the characterization of the Pt nanoparticle catalysts [1]. However, this technique is difficult to investigate the chemical states of the low-concentrated catalysts. In this study, we developed the combined SAXS and the fluorescence-yield (FY) XAS measurement systems to investigate the structural and the chemical properties of low-concentrated catalysts. The combined SAXS-FYXAS measurement system was developed at BL19B2 in SPring-8. For the XAS measurements, the Pt LⅢ edge was used. The ionization chamber and a single-element Ge solid state detector were used to obtain the FYXAS spectra. For the SAXS measurements, the X-ray energy was set to 11.5 keV and 11.55 keV, which are below and near to the Pt LⅢ absorption edge, respectively. The scattered X-ray was detected using an area detector (PILATUS 2M). The PtCo alloy nanoparticle for the oxygen reduction reaction was used as the sample in this experiment. As the result, we could demonstrate the combined SAXS-FYXAS measurement systems. We will discuss the degradation mechanism of the PtCo alloy nanoparticle catalyst from both SAXS and FYXAS data. [1] M. Povia et al. ACS. Catal., 8, 7000 (2018).