XAS Measurements Research Articles

Intermetallic Single-Atom Alloy Bimetallene for Electrosynthesis of Ammonia from Nitrate

Ammonia (NH3), as a high-value industrial chemical and hydrogen carrier, can be synthesized via more sustainable electrocatalytic nitrate reduction reaction (NO3RR). The performance of an electrocatalyst is related to a number of factors, one of which is the intrinsic activity of metals (metal d-band center) that affects the adsorption energy of reaction intermediates. Intermetallic single atom alloys (ISAAs) is an emerging class of alloys where contiguous metal atoms are isolated into single sites by another metal. Such arrangement not only optimizes the density of single atoms which already maximizes atom utilization efficiency, but also modulates the hybrid orbitals of the intermetallics. Herein, we report ISAA In-Pd bimetallene that consists of Pd single atoms being surrounded by In atoms. The ISAA bimetallene can achieve an NH3 Faradaic efficiency of 87.2%, a yield rate of 28.06 mg h-1 mgPd -1, and an outstanding stability with increased activity and selectivity over 100 h and 20 cycles. DFT calculations reveal that, owing to the close proximity of Pd single atoms and their surrounding In atoms, the p-d hybridization of In-p and Pd-d states around the Fermi level were greatly narrowed, resulting in a more favorable adsorption and lower energy barrier for NO3RR. The ISAA bimetallene can further be used as a cathode in a Zn-NO3 - flow battery setup, achieving a power density of 12.64 mW cm-2 and a FE of 93.4% for NH3 synthesis. Acknowledgements: This work was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under award DESC0019019, the Welch Foundation Award F-1861, and the Camille Dreyfus Teacher−Scholar Award. XAS measurements were done at 20-BM at the Advanced Photon Source of the Argonne National Laboratory. The use of APS of ANL is supported by the DOE under Contract No. DE-AC02-06CH11357.

Understanding of Regeneration Processes of Ruthenium-Poisoned ORR Catalysts

PEM fuel cells, that are operated with a reformate gas (H2, CO2, CO), are of great interest in maritime applications. Despite its outstanding activity in the hydrogen oxidation reaction (HOR), platinum can be quickly poisoned by only very small amounts of CO. Therefore, high CO tolerant anode catalyst materials such as platinum (Pt)-ruthenium (Ru) alloy nanoparticles (NPs) supported on carbon (Pt-Ru/C) are used for PEMFCs supplied with reformate gas. (1) However, these Pt-Ru/C catalysts strongly suffer from the Ru dissolution followed by the crossover through the membrane to the cathode. At the cathode, the soluble Ruz+ species quickly re-deposit at the Pt/C catalyst, resulting in a dramatic loss of performance for the oxygen reduction reaction (ORR). For instance, the kinetics of the ORR decreases by a factor of 8, when the Ru coverage on the surface of Pt nanoparticles is in the range of 20 at.%. (2, 3) Very recently, we have reported different electrochemical regeneration strategies of Ru-poisoned cathode catalyst using rotating disc electrode (RDE) technique. (4) Although the poisoned catalyst could be mostly re-activated, the atomic processes during the regeneration are poorly understood to date. Therefore, operando and in-situ spectroscopic and microscopic techniques are needed.In this work, we combined the electrochemical regeneration protocols with in-situ XAS technique to better understand the re-dissolution processes of the RuOx species from the Pt-based catalyst particle surface.Our regeneration strategies can be categorized into dynamic and steady-state conditions. Each protocol involved an initial pre-activation process by holding the potential at 1.40 VRHE for 5 minutes in 0.1 M HClO4. The dynamic regeneration protocol was performed by potential pulsing between 1.40 VRHE and 1.60 VRHE in 10-second intervals using chronoamperometric method. Additionally, single pulse measurements at 1.60 VRHE with a duration time of 100 s and 300 s were applied for the steady-state regeneration protocol. The regeneration procedure plays an important role in the recovery of the Ru-poisoned ORR activity. The best results of a recovery procedure for PtRu2 and PtRu catalysts are obtained under steady-state condition at 1.60 VRHE for 100 s.The next step was to correlate the electrochemical regeneration experiments with in-situ XAS investigations on commercially available PtRu2 and PtRu catalysts. The Ru K edge and Pt L2/3 edges XAS measurements were carried out in a home-made electrochemical flow cell. Based on the in-situ XAS data, we were able to monitor the changes in the electronic structure and atomic environment of both elements in the alloy nanoparticles as a function of the recovery parameters (potential, holding time). In addition, ex-situ scanning transmission electron microscopy with energy-dispersive X-ray spectroscopy (STEM-EDX) investigations were carried out on Ru-poisoned catalysts after the regeneration protocol to collaborate with the results from XAS.In summary, XAS is a powerful technique to elucidate the electronic structure and atomic arrangement of Ru and Pt atoms and link them with the electrochemical parameters of the regeneration protocol.

Examining the Structure-Activity Relationship for Acid Treated Ordered PtCo with Different Ordering Degree Using PDF and XAS Analysis for Oxygen Reduction Reaction

Proton exchange membrane fuel cells (PEMFCs) have garnered significant attention to fulfill the "carbon neutrality" goal. The ever-growing demand for PEMFCs necessitates the development of effective catalysts to maximize the utilization of platinum (Pt), given its rocketing price and inadequate availability.1 The formation of Pt alloys with earth-abundant transition metals such as Co, Fe, Cu, and Zn is recognized as one of the most promising approach to reduce the Pt content and increase the overall activity.2 Particularly, ordered PtCo intermetallic alloys that balance high catalytic activity and stability through ligand and strain effects due to the smaller Pt-Pt bond distance, which weaken the binding of oxygen-containing intermediate and boost the overall oxygen reduction reaction (ORR) performance.3 Despite numerous research efforts, there is still a lack of experimental evidence regarding the impact of an internally ordered phase on surface structure, especially after establishing a stable Pt-rich shell. This study comprehensively examines two essential aspects of ordered PtCo catalysts by integrating electrochemical investigations with advanced in-situ and ex-situ techniques. The first aspect involves quantifying the transition from disordered to ordered phases and its consequence on catalytic structure, while the second aspect aims to comprehend the role of the ordered structure in catalytic efficiency. Herein, we fabricated a series of PtCo catalysts with different ordering degrees by regulating the thermal treatment time and temperatures followed by acid treatment, aiming to investigate the surface structure and the activity relationship. Traditional powder X-ray diffraction (XRD) coupled with high-resolution scanning transmission electron microscopy (HR-STEM) to ascertain the degree of atomic ordering. The comprehensive electrochemical performance showed higher ORR activity for the PtCo alloy, which had a higher ordering degree. To establish a quantitative relationship between ordering degree and structure, PDF and XRD analyses were combined together. The comprehensive PDF analysis discloses the existence of different phases pFCC-Pt, FCC-Pt, FCC-PtCo, pBCT, and BCT phases post-acid treatment and higher ordering degree would contribute to a higher Co retention and minimize structure changes, which ultimately results in higher ORR activity (Figure 1). Additionally, operando XAS measurements indicated that catalysts with a higher order degree could suppress the formation of Pt-OH species compared to disordered alloys during ORR. These findings offer valuable insights into how ordering degree enhances ORR activity through strain effects and can be instrumental in designing next-generation catalysts. Acknowledgment This work is supported by the PEFC and the NEDO FC-Platform commissioned by the New Energy and Industrial Technology Development Organization (NEDO). Reference: C. Li, K. Yu, A. Bird, F. Guo, J. Ilavsky, Y. Liu, D. A. Cullen, A. Kusoglu, A. Z. Weber and P. J. Ferreira, Energy Environ. Sci., 2023,16, 2977-2990.X. Zhao, H. Cheng, L. Song, L. Han, R. Zhang, G. Kwon, L. Ma, S. N. Ehrlich, A. I. Frenkel and J. Yang, ACS Catal., 2020, 11, 184-192.S. Yu and H. Yang, Chem. Commun., 2023, 59, 4852-4871. Figure 1

Improving Catalytic Activity of Solid Oxide Electrolysers for the Electrosplitting of Water Vapor and CO2 by the Addition of Affordable and Eco-Friendly Promoter Metals

Recently, Solid Oxide Electrolysis Cells (SOECs) can be considered a solution for the elimination of atmospheric CO2 and limiting its negative environmental impact. Thanks to high operation temperatures, full-solid construction and high Faradaic efficiency it is a promising method for a production of great amounts of relatively cheap and pure hydrogen. Furthermore, these ceramic cells can be set to perform CO2 electroreduction along with water vapor. Thanks to that, it is possible to simultaneously supply various chemical processes with H2-CO feedstock using one, relatively simple setup. In that sense, the SOECs can provide ‘green’ hydrogen and reduce the CO2 amount by delivering the valuables such as syngas or other chemicals. Recently, high temperature H2O/CO2 coelectrolysis in SOECs became reasonable alternative to other technologies of syngas production such as steam reforming of biogas or coal gasification, which both release huge amount of the greenhouse gases.The main constituent of water-hydrogen electrode is bifunctional composite of NiO and Zr0.84Y0.16O2-δ, which upon the reduction forms metallic network of Ni within the scaffold of ionic conductor. This type of electrode is quite well established for working with water vapor in electrolysis mode but struggles under the atmosphere containing CO and/or CO2. Ni grains are considered active, but not the most efficient towards RWGS as well as electrochemical splitting of H2O/CO2. Over the years other transition metals - Cu, Fe, or Co - as well as their oxides - MnO, ZnO - were found to be more prominent and used in catalytic reactors. Further increase of the activity and the efficiency can be achieved thanks to promoter metals and their oxides e.g., K2O, Na2O, Rb2O, MgO, CaO. The addition of the transition metals can be promising alternative to the usage of the noble metals considering mostly their much lower price. On the other hand, the addition of alkaline metal oxides can increase the adsorption rate of CO2 and prolong the retention time in the proximity of the electrode. As the SOECs are generally non-pressurized systems, the efficiency of the electrode surface catalysts should be pushed to maximum in order to provide valuable yield of the outlet gases.A series of modified SOECs was prepared by the addition of 5 mol.% of the transition metal (Co, Cu, Mn, Fe) or alkaline metal oxide (Na, K, Ca, Mg, Rb, Li, Sr) nanoparticles. The samples have been fabricated by simple wet impregnation method. The SOECs were tested for the coelectrolysis of CO2/H2O mixture with an addition of H2 for electrode protection against the reoxidation. The electrical tests were considering the utilization factor of water vapor and electrochemical behavior of the cells under various CO2:H2:H2O ratios to better understand the mechanisms of syngas formation.It was found out that depending on the reducibility of the metals they got dissolved into Ni grains (e.g., Co, Fe) or formed the secondary phases on the top of the grains (e.g. MnO). It was observed as an accumulation of the metal ions inside Ni-rich grains or dissipation of the ions all over the imaging area as seen in STXM images. Alkaline metal oxides formed a mixture of the phases all over Ni and YSZ grains. A series of in-situ XAS measurements at the ESRF (France) was performed to observe the formation of various mixed compounds and the response of electrode's components to CO2-rich atmosphere at high temperature. The surficial changes of the oxidation states were determined using in-situ XPS imaging of modified electrode structure using SPEM at the Elettra (Italy). The addition of secondary metal alters the energy levels on Ni surface and increases the tendency to form carbonate-like compounds, what prolongs the retention time of CO2. The addition of guest metal highly increased CO2 conversion and selectivity towards CO production as well as the electrical efficiency due to the alterations of basic-acid sites and introduction of active redox couples. Acknowledgements This work was supported by a project funded by National Science Centre Poland, based on decision UMO-2021/43/B/ST8/01831 (OPUS 22). The XAS and XPS experiments were supported by CERIC-ERIC consortium and performed at the European Synchrotron Radiation Facility (ESRF) and the Elettra Sincrotrone Trieste, respectively. The access to ESRF was financed by the Polish Ministry of Education and Science – decision no. 2021/WK/11.

Physicochemical Characterization and Antimicrobial Properties of Lanthanide Nitrates in Dilute Aqueous Solutions.

This work presents the results of studying dilute aqueous solutions of commercial Ln(NO3)3 · xH2O salts with Ln = Ce-Lu using X-ray diffraction (XRD), IR spectroscopy, X-ray absorption spectroscopy (XAS: EXAFS/XANES), and pH measurements. As a reference point, XRD and XAS measurements for characterized Ln(NO3)3 · xH2O microcrystalline powder samples were performed. The local structure of Ln-nitrate complexes in 20 mM Ln(NO3)3 · xH2O aqueous solution was studied under total external reflection conditions and EXAFS geometry was applied to obtain high-quality EXAFS data for solutions with low concentrations of Ln3+ ions. Results obtained by EXAFS spectroscopy showed significant contraction of the first coordination sphere during the dissolution process for metal ions located in the middle of the lanthanide series. It was established that in Ln(NO3)3 · xH2O solutions with Ln = Ce, Sm, Gd, Yb (c = 134, 100, 50 and 20 mM) there are coordinated and, to a greater extent, non-coordinated nitrate groups with bidentate and predominantly monodentate bonds with Ln ions, the number of which increases upon transition from cerium to ytterbium. For the first time, the antibacterial and antifungal activity of Ln(NO3)3 · xH2O Ln = Ce, Sm, Gd, Tb, Yb solutions with different concentrations and pH was presented. Cross-relationships between the concentration of solutions and antimicrobial activity with the type of Ln = Ce, Sm, Gd, Tb, Yb were established, as well as the absence of biocidal properties of solutions with a concentration of 20 mM, except for Ln = Yb. The important role of experimental conditions in obtaining and interpreting the results was noted.

(Invited) Large Electromechanical Coupling in Zr-Doped Ceria

The catalytic, ion-transport and chemo-mechanical properties of Zr-doped ceria have been the subjects of broad ranging investigation by the materials research community. Yet, until recently, electromechanical coupling in ZrxCe1-xO2-δ has not been studied: ZrxCe1-xO2-δ ceramics were not expected to be electromechanically active. We have investigated the electrostriction (ES) effect, a second order electromechanical response, i.e., strain, u , is proportional to M·E 2, where E is the applied electric field and M is the longitudinal electrostriction strain coefficient. Large electrostriction in ceria has generally been associated with oxygen vacancies (Vo) which provide charge compensation for aliovalent dopants or for cerium reduction (Ce3+). The electrostriction effect induced by oxygen vacancies is restricted to frequency <1 Hz and is characterized by low saturation strain (|usat| <15 ppm).By contrast, isovalent doping with Zr (unexpectedly) results in a large electrostriction strain coefficient, reaching |M|=10-16 m2/V2 for x=0.1. This effect persists to frequency ≥3 kHz with |u| ≥220 ppm, making Zr0.1Ce0.9O2 competitive with the best commercial electrostrictor (PMN-PT15), but with ~100 times lower dielectric constant and three-fold higher elastic modulus. XAS data, DFT modelling and ab initio molecular dynamics (AIMD) calculations demonstrate that, unlike the permanent, but orientationally labile, elastic dipoles (i.e. local distortions with symmetry lower than that of the host lattice) formed by oxygen vacancies, elastic dipoles formed by Zr-doping are dynamic. In the absence of an E-field, [ZrO8]-local bonding units remain, on average, centered with respect to the second (cation) coordination shell. Due to bond anharmonicity, however, displacement of Zr by an anisotropic E-field requires less energy than displacement of the host cations, resulting in a large dynamic elastic dipole. This polarizable elastic dipole gives rise to large electrostrictive strain and constitutes the first example of non-classical electrostrictors (NCES) relying solely on substitutional point defects. In fact, a relatively small, isovalent dopant cation, such as Zr, along with nearest neighbor anions, vibrating anharmonically in a relatively large cage (compared to that of the host cation) may in fact facilitate electromechanical coupling.|M| of Zr-doped ceria increases exponentially with Zr content for x=0-0.1, suggesting that the contribution of Zr-ions to electrostrictive strain may not be simply additive. Zr-doping also increases the relative dielectric permittivity at 100Hz, from ~26 (x=0), to ~220 (x=0.1) and lowers the elastic modulus from 227GPa (x=0) to 214GPa (x=0.1), even though the number of chemical bonds remains unchanged. AIMD calculations report that stiffness for moving [CeO8]-local bonding units is essentially isotropic and is 2-2.4 times higher than for [ZrO8]. Stiffness for moving [CeO8] first nearest neighbor to Zr, is only slightly decreased from that in the bulk. These results can provide the theoretical basis for the reduction of the Young’s modulus and increase in the dielectric permittivity with Zr doping.When the concentration of Ce3+ is ≥ 100 ppm in ZrxCe1-xO2-δ, ( i.e., the material has not been completely re-oxidized), accompanied by the formation of oxygen vacancies (VO) for charge compensation, electrical conductivity is increased and electrostriction is suppressed. In addition, by co-doping Zr0.1Ce0.9O2 with 0.5mol% of aliovalent cations - Ca, Sc, Yb or La - we observed that the aliovalent dopant reduces the electrostriction strain coefficient by more than an order of magnitude and restores the values of Young’s modulus and dielectric permittivity to values close to those of undoped ceria. Since all these co-dopants, irrespective of valence and ionic radius, lead to a similar result, we concluded that the species responsible for the suppression of electrostriction in Zr doped ceria must be the oxygen vacancies. This finding is supported by XAS measurements and AIMD calculations. Fourier transform of Zr K-edge EXAFS spectra reveal that, even though the molar ratio ZrCe:VO is 40:1 in the co-doped compounds, oxygen vacancies nevertheless succeed in introducing enhanced disorder into the second coordination shell (cation) of Zr. DFT modelling predicts that a [ZrO7-VO] local bonding unit is stiff and asymmetrically distorts adjacent unit cells, leading to an elastic interaction length in the lattice between Zr-ions ≥ two-and-a-half-unit cells, which, in the absence of oxygen vacancies, can allow limited collective motion. However, such collective motion does not lead to a phase transition even at 123 K, implying that interaction between Zr-ions is neither sufficiently strong nor sufficiently long-range to produce freezing of the displacement, an effect that has been observed for perovskite relaxors.

In-situ electronic modulation of ultra-high-capacity S-modified Cu/Cu2O electrodes for energy storage applications

Due to the modification of anions, an electron redistribution occurs at the metal ions can affect the electronic structure, and induce excellent specific capacity. Herein, we report an effective and low time-consuming method by in-situ wet chemical reduction at room temperature to construct S-modified Cu/Cu2O negative electrode material. Moreover, the sulfur can occupy partial O sites in Cu2O to play a crucial role in the electronic structure of the material, demonstrated by DFT calculation, XRD, XPS and XAS measurements. The prepared S-Cu/Cu2O samples exhibit excellent electrochemical performance with high specific capacity of 669 mAh·g−1 at 1 A·g−1, even 450 mAh·g−1 at 10 A·g−1. When the materials are composed as pseudo capacity-type cathode//battery-like anode (MnO2//S-Cu/Cu2O), and (+) battery-type//battery-type (-) (Ni-Cu hydroxide/Cu(OH)2/CF//S-Cu/Cu2O) hybrid capacitors, they show the energy density of 47.7 and 147.3 Wh·kg−1 at the power density of 636.2 and 800 kW·kg−1, respectively. Otherwise, the flexible MnO2//S-Cu/Cu2O hybrid capacitor is assembled, which also exhibits good performance at different bending conditions. This work can provide a simple method to prepare the electrode materials via in situ anion modification for high-energy density battery-like energy storage systems.

Recommendations to standardize reporting, execution, and interpretation of X-ray Absorption Spectroscopy measurements

Recommendations to standardize reporting, execution, and interpretation of X-ray Absorption Spectroscopy measurements

High-vacancy-type titanium oxycarbide for large-capacity lithium-ion storage

Electrochemical processes involving the ion insertion/desertion are usually accompanied by composition variation and structural evolution of electrode materials. Here we propose a meaningful lattice regulation by inserting lithium ions to unlock an active crystalline plane from which high energy storage performance can be obtained. A rock-salt titanium oxycarbide featuring 12% titanium vacancies (Ti0.88□0.12C0.63O0.37) in high active (011) crystalline plane bears excellent electrochemical activity that enables additional reversible lithium insertion, providing a high initial specific capacity of 390 mAh g−1 at 0.05 A g−1. EPR, XAS, PDF and TEM measurements confirm abundant titanium vacancies, electrochemical studies combined with computational calculations demonstrate high activity of (011) crystalline plane as domain channels for lithium-ion insertion, and ex-situ XRD investigations disclose structural evolution during lithium-ion insertion/desertion. Notably, the repeated lithium-ion insertion/desertion promotes new exposure of (011) crystalline planes, leading to a capacity “negative fading” from the initial 120 to 325 mAh g−1 after 1100 cycles at 0.5 A g−1. The study presents the inner relationship between material microstructural transformation and electrochemical properties, providing a new perspective for mechanism re-understanding and structure development of ion-storage electrode materials.

Dimensionality driven exchange coupling effect in cuprate-manganite superlattices

The coupling and competition between various degrees of freedom at the interface of transition metal oxide heterointerfaces greatly enrich their physical properties and expand their relevant application scope. It has been reported that dimensionality is an effective method to regulate the properties of oxide heterostructure. The structure of SCO film exhibits a planar-type-to-chain-type transformation with the change of thickness. In this work, the high-quality SCO/LCMO superlattices are deposited by a pulsed laser deposition system. And the interfacial exchange coupling effect is effectively manipulated by controlling the dimensionality of SCO layer. X-ray absorption spectrum (XAS) measurement shows that the charge transfer occurs at the heterointerface. When the SCO layer is thin, the interfacial superexchange coupling supported by charge transfer generates a weak magnetic moment to pin the ferromagnetic LCMO layer. As the SCO layer thickens, the charge transfer will decrease. Meanwhile, the long-range antiferromagnetic order in thicken SCO layer can interact with LCMO layer, resulting in the exchange bias effect. This experiment confirms the important role of dimensionality in modulating the properties in multifunctional oxide heterostructure.

Investigation of local structure and phase recovery in an irradiated Nd2Zr2O7 pyrochlore

SHI irradiation-induced order–disorder transition in an Nd2Zr2O7 pyrochlore is observed by XRD and XAS measurements. The recrystallization of the irradiated phase was observed as a result of thermal annealing.

X-ray and Nuclear Spectroscopies to Reveal the Element-Specific Oxidation States and Electronic Spin States for Nanoparticulated Manganese Cyanidoferrates and Analogs

In this publication, the potential non-gadolinium magnetic resonant imaging agent—nanoparticulate K2Mn[Fe(CN)6]—its comparison sample KFe[Co(CN)6], as well as their reference samples were measured and analyzed using Mn, Co and Fe L-edge X-ray absorption spectroscopy (L XAS). From the information obtained, we conclude that K2Mn[Fe (CN)6] has a high spin (hs)-Mn(II) and a low spin (ls)-Fe(II), while KFe[Co(CN)6] has an hs-Fe(II) and an ls-Co(III). In these Prussian blue (PB) analog structures, the L XAS analysis also led to the conclusion that the hs-Mn(II) in K2Mn[Fe(CN)6] or the hs-Fe(II) in KFe[Co(CN)6] bonds to the N in the [M(CN)6]4−/3− ions (where M = Fe(II) or Co(III)), while the ls-Fe(II) in K2Mn[Fe(CN)6] or the ls-Co(III) in KFe[Co(CN)6] bonds to the C in the [M(CN)6]4−/3− ion, suggesting the complexed metalloligand [Mn(II) or Fe(II)] occupies the N-bound site in PB. Then, nuclear resonant vibrational spectroscopy (NRVS) was used to confirm the results from the L XAS measurements: the Mn(II), Eu(III), Gd(III), Fe(II) cations complexed by [M(CN)6]n−-metalloligand all take the N-bound site in PB-like structures. Our NRVS studies also prove that iron in the K2Mn[Fe(CN)6] compound has a 2+ oxidation state and is surrounded by the C donor atoms in the [M(CN)6]n− ions.

Operando X-Ray Absorption Spectroscopy of Solid Electrolyte Interphase Formation on Silicon Anodes

Lithium-ion batteries (LIBs) are key to the transition from fossil fuels towards increased use of renewable energy sources. However, more widespread deployment requires improvements in energy density, cost and cycle-lifetime. Various cathode and anode materials are under consideration for next-generation LIBs, and the interfacial stability of these materials in contact with the electrolyte is a critical consideration. Interface-sensitive operando characterization techniques are thus urgently needed to reveal the reactions occurring in working batteries.1,2 The solid electrolyte interphase (SEI) that forms on Li-ion battery anodes is critical to their long-term performance, however observing SEI formation processes at the buried electrode-electrolyte interface is a significant challenge. Here we show that operando soft X-ray absorption spectroscopy in total electron yield mode can resolve the chemical evolution of the SEI during electrochemical formation in a Li-ion cell, with nm-scale interface sensitivity. O, F, and Si K-edge spectra, acquired as a function of potential, reveal when key reactions occur on high-capacity amorphous Si anodes cycled with and without fluoroethylene carbonate (FEC).3 Cross-referencing to cycling data, complementary bulk sensitive fluoresecent yield (FY) XAS measurements, and density functional theory (DFT) calculated spectra enables identification of the electrolyte and SEI species, and the dominant mechanisms of SEI formation. Without FEC present, LiF formation is detected at 0.6 V vs. Li/Li+ prior to significant lithiation of the a-Si, whilst at lower potentials the SEI grows in thickness with an increased contribution from organic components containing -C(=O)O- species. The observed sequential formation of inorganic and organic components is implicated in layering of the SEI. With FEC as an additive we see the onset of SEI formation at much higher potentials (1.0 V vs. Li/Li+), and attribute the improved cycle life seen with this additive to the rapid healing of SEI defects formed during delithiation. Operando TEY-XAS offers new insights into the formation mechanisms of electrode-electrolyte interphases and their stability for a wide variety of electrode materials and electrolyte formulations. References Wu et al. Phys. Chem. Chem. Phys. 2015, 17, 30229.Weatherup et al. Top. Catal. 2018, 61, 2085.Swallow et al. Nature Commun. 2022, 13, 6070.

Polymer template assisted construction of spherical Co3O4@meso-SiO2 yolk-shell nanoreactors for catalytic combustion of volatile organic compounds

Co3O4@SiO2 yolk-shell materials containing Co3O4 nanoparticles protected against aggregation and easily accessible for gaseous reactants inside a mesoporous SiO2 shell were developed for the catalytic combustion of volatile organic compounds (VOCs). Spherical polymer templates with an appropriate cation adsorption capacity were used as scaffolding for the construction of these structures by the bottom-up strategy. An application of polystyrene led to accumulation of introduced cobalt phase within the SiO2 layer and favored the formation of catalytically inactive Co silicate species. On the other hand, poly(maleic anhydride-co-divinylbenzene) modified with diethylenetriamine gave improved penetration of the composite interior by Co2+ cations and highly dispersed Co3O4 nanoparticles after calcination. The latter materials appeared excellent nanoreactors for the catalytic combustion of toluene. The real role of the active phase was determined by characterization of the developed catalysts with XRD, N2 adsorption, SEM-EDS, TEM, UV–Vis-DR, FT-IR, H2-TPR, isothermal oxidation-reduction analyses, XPS, XAS and electrochemical measurements.

Investigation of Rh/NR3 catalytic systems in sequential stages of reductive hydroformylation engaging in situ X-ray absorption spectroscopy

Nowadays reductive hydroformylation over Rh/NR3 catalysts is of great interest to both industry and academia, however, some of its aspects remain controversial or unclear, including those which might turn essential for developing new active catalysts and optimization of parameters. In this work, we studied in depth separately both stages of the process – hydroformylation of olefins and hydrogenation of aldehydes, – and estimated the role of the amine structure in them. Also, for the first time, we investigated Rh/NR3 catalytic system under the reaction conditions by in situ XAS method to gain the additional structural information, and observed the correlation of the obtained data with the results of catalytic experiments. Catalytic and in situ XAS measurements shown that tertiary amines suppress Rh clusterization, forming species of lower nuclearity. These Rh/amine species may include both charged and uncharged ones. The addition of amines, which are effective promotors of the hydrogenation step, decelerates hydroformylation, presumably, through the formation of amine containing Rh complexes.

Structural and Chemical Properties of NiOx Thin Films: Oxygen Vacancy Formation in O2 Atmosphere.

NiOx films on Si(111) were put in contact with oxygen at elevated temperatures. During heating and cooling in oxygen atmosphere Near Ambient Pressure (NAP)-XPS and -XAS and work function (WF) measurements reveal the creation and replenishing of oxygen vacancies in dependence of temperature. Oxygen vacancies manifest themselves as a distinct O1s feature at 528.9 eV on the low binding energy side of the main NiO peak as well as by a distinct deviation of the Ni2p3/2 spectral features from the typical NiO spectra. DFT calculations reveal that the presence of oxygen vacancies leads to a charge redistribution and altered bond lengths of the atoms surrounding the vacancies causing the observed spectral changes. Furthermore, we observed that a broadening of the lowest energy peak in the O K-edge spectra can be attributed to oxygen vacancies. In the presence of oxygen vacancies, the WF is lowered by 0.1 eV.

Relating Near-Surface Ti Electrode Structure with Electrochemical Nitrate Reduction Performance Via Synchrotron X-Ray Characterization

The global nitrogen cycle has been severely skewed since the widespread adoption of the Haber-Bosch process to produce ammonia (NH3). Currently, removal of reactive nitrogen (inorganic forms besides N2) from the environment lags behind its production and emission to the environment. Nitrate is one of the most prevalent waterborne nitrogen pollutants and, in its excess, threatens the health of ecosystems. Enabling a sustainable food-energy-water nexus requires feeding a growing population while minimizing environmental impacts. Therefore, selective electrochemical nitrate reduction (NO3RR) to NH3 can couple water purification and NH3 production, helping offset the energy- and carbon-intensive Haber Bosch process. NH3 recovery from emissions could contribute over 20 million tons N per year by 2050 (~ 10% of projected N demand).Noble and transition metal catalysts including single metals (e.g., Pt, Rh, Ru, Ir, Pd, Cu, Ag, Au)[1,2] and alloys (e.g., CuNi)[3] have been studied for NO3RR. Notably, under acidic conditions, polycrystalline titanium has been demonstrated to display robust and efficient NO3RR.[4] Ti is corrosion-resistant, a poor hydrogen evolution catalyst, and a readily available, abundant metal. However, under acidic and reducing conditions, Ti forms a water-stable hydride (TiHx, 0<x≤2).[5] It remains unclear how the degree of surface hydride formation – which alters the physical and electronic properties of the electrode surface – impacts NO3RR performance. Thus, rationally implementing Ti-catalyzed NO3RR requires improved understanding of how near-surface Ti-hydride forms and influences NO3RR activity and selectivity.In this work, we show that near-surface Ti-hydride formation is a function of the duration and magnitude of applied NO3RR potential. A combination of ex situ grazing-incidence X-ray diffraction (GIXRD – probes long-range, crystalline order) and X-ray absorption spectroscopy (XAS – probes short-range, atom-specific probe into local coordination environments) enabled quantitative near-surface characterization of Ti-hydride electrodes. Through electrochemical testing and density functional theory calculations, we investigated the role near-surface Ti-hydride may play in electrochemical nitrate conversion. Our results preliminary suggest that near-surface hydride content plays a relatively minor role in steering NO3RR performance compared to applied potential and electrolyte effects. In addition, we are performing ongoing in situ GIXRD and XAS measurements to interrogate the transient nature and interplay of near-surface hydride formation and NO3RR. Put in context, our results help prioritize how Ti-catalyzed NO3RR processes can be optimized for electrified ammonia production and wastewater remediation.[1] G. E. Dima, A. C. A. de Vooys, M. T. M. Koper, Journal of Electroanalytical Chemistry 2003, 554–555, 15–23.[2] G. E. Dima, G. L. Beltramo, M. T. M. Koper, Electrochimica Acta 2005, 50, 4318–4326.[3] Y. Wang, A. Xu, Z. Wang, L. Huang, J. Li, F. Li, J. Wicks, M. Luo, D.-H. Nam, C.-S. Tan, Y. Ding, J. Wu, Y. Lum, C.-T. Dinh, D. Sinton, G. Zheng, E. H. Sargent, J. Am. Chem. Soc. 2020, 142, 5702–5708.[4] J. M. McEnaney, S. J. Blair, A. C. Nielander, J. A. Schwalbe, D. M. Koshy, M. Cargnello, T. F. Jaramillo, ACS Sustainable Chem. Eng. 2020, 8, 2672–2681.[5] Y. Liu, Z. H. Ren, J. Liu, R. F. Schaller, E. Asselin, J. Electrochem. Soc. 2019, 166, C3096–C3105.

Structural Diversity, XAS and Magnetism of Copper(II)-Nickel(II) Heterometallic Complexes Based on the [Ni(NCS)6]4- Unit.

The new heterometallic compounds, [{Cu(pn)2}2Ni(NCS)6]n·2nH2O (1), [{CuII(trien)}2Ni(NCS)6CuI(NCS)]n (2) and [Cu(tren)(NCS)]4[Ni(NCS)6] (3) (pn = 1,2-diaminopropane, trien = triethylenetetramine and tren = tris(2-aminoethylo)amine), were obtained and characterized by X-ray analysis, IR spectra, XAS and magnetic measurements. Compounds 1, 2 and 3 show the structural diversity of 2D, 1D and 0D compounds, respectively. Depending on the polyamine used, different coordination polyhedron for Cu(II) was found, i.e., distorted octahedral (1), square pyramidal (2) and trigonal bipyramidal (3), whereas coordination polyhedron for nickel(II) was always octahedral. It provides an approach for tailoring magnetic properties by proper selection of auxiliary ligands determining the topology. In 1, thiocyanate ligands form bridges between the copper and nickel ions, creating 2D layers of sql topology with weak ferromagnetic interactions. Compound 2 is a mixed-valence copper coordination polymer and shows the rare ladder topology of 1D chains decorated with [CuII(tren)]2+ antennas as the side chains attached to nickel(II). The ladder rails are formed by alternately arranged Ni(II) and Cu(I) ions connected by N2 thiocyanate anions and rungs made by N3 thiocyanate. For the Cu(I) ions, the tetrahedral thiocyanate environment mixed N/S donor atoms was found, confirming significant coordination spheres rearrangement occurring at the copper precursor together with the reduction in some Cu(II) to Cu(I). Such topology enables significant simplification of the magnetic properties modeling by assuming magnetic coupling inside {NiIICuII2} trinuclear units separated by diamagnetic [Cu(NCS)(SCN)3]3- linkers. Compound 3 shows three discrete mononuclear units connected by N-H…N and N-H…S hydrogen bonds. Analysis of XAS proves that the average ligand character and the covalency of the unoccupied metal d-based orbitals for copper(II) and nickel(II) increase in the following order: 1 → 2 → 3. In 1 and 2, a weak ferromagnetic coupling between copper(II) and nickel(II) was found, but in 2, additional and stronger antiferromagnetic interaction between copper(II) ions prevailed. Compound 3, as an ionic pair, shows, as expected, a spin-only magnetic moment.

Operando X-Ray Absorption Spectroscopic Study of Pt-Based Nanowire Catalysts Under Oxygen Reduction Reaction

Polymer electrolyte fuel cells (PEFCs) are attracting attention as an environmentally friendly electrochemical device that uses hydrogen as a fuel. The application of PEFC has been limited by the consumption of platinum due to the sluggish kinetics of the cathode reaction and limiting platinum reserves. It has been noted that the interaction between the cathode catalyst and the oxygen intermediate species results in an overpotential in the ORR process. Therefore, it is very important to evaluate the interaction between the oxygen species and the catalyst based on the electronic structure. Pt nanowires are known to be highly active as ORR catalysts because they tend to expose more active planes for ORR, such as (111) planes1. Pt oxides formed on Pt nanowires with such 1D anisotropy are different from conventional nanoparticle catalysts in terms of structure and electronic structure2. However, this has not been fully clarified yet under oxygen reduction conditions. In this study, we analyzed the oxidation state of Pt nanowire catalysts in the ORR by operando analysis and analyzed the electronic and local structures.Synthesis of Pt nanowire catalyst : Oleylamine (5 mL) was used as a solvent and Pt(acac)2, Ni(acac)2, W(CO)6 and CTAC (hexadecyltrimethylammonium chloride) were added and sonicated for 1 hour. The product was dissolved and allowed to react in an oil bath at 160°C for 2 hours. The product particles were collected by centrifugation, and the washing and centrifugation were repeated three times with a mixture of cyclohexane: ethanol = 1:9. The nanowires were then loaded on Vulcan XC-72. ORR activity evaluation and XAS measurement: The rotating disk electrode (RDE) method was used for electrochemical measurements. A tripolar cell was used for the measurements. catalyst ink containing Pt nanowires was prepared and applied to a glassy carbon electrode for the RDE to prepare the electrode. A catalyst-coated electrode was used as the working electrode, a platinum mesh as the counter electrode, and a reversible hydrogen electrode (RHE) as the reference electrode. The electrolyte was 0.1 M HClO4. The cell temperature was controlled at 25 oC. XAS measurements were performed using a home-made measuring cell and the same electrochemical measurement conditions as for the RDE.The morphology and structure of the prepared Pt nanowires were observed by electron microscopy. As shown in Figure 1, the nanowires were uniformly distributed on the carbon and no significant aggregation was observed. The average diameter of the nanowires was 2.0 nm.To analyze the local structure of the Pt nanowire catalyst, the Pt-Pt bond length was estimated from EXAFS. Figure 2 shows the fitting results of the Pt-Pt bond lengths of Pt nanowire and Pt nanoparticle (TEC10V30E, TKK) catalysts in the range 0.5-1.1 V vs. RHE. With increasing potential, the Pt-Pt bond lengths of both catalysts gradually increased, but the Pt nanowire catalyst maintained a short Pt-Pt bond, and this nanowire characteristic structure may be the reason for its higher ORR activity than the nanoparticle. Acknowledgements: This work was supported by the project (JPNP20003) and a NEDO FC-Platform project commissioned by the New Energy and Industrial Technology Development Organization (NEDO).

Operando X-Ray Absorption Spectroscopy of Pt Catalyst in Polymer Electrolyte Fuel Cell Under High Temperature and Low Humidification

For the widespread use of fuel cell vehicles, it is necessary to improve the performance and durability of the cathode catalyst of polymer electrolyte fuel cells (PEFCs). In particular, high-temperature operation of PEFCs is attracting attention for application to commercial vehicles for heavy-duty application. Operation at higher temperatures than the conventional one (60-80°C) is expected to enhance oxygen reduction kinetics and mass transfer and reduce specific adsorption of ionomers. Despite such advantages, due to the thermal effect, the oxide formation on Pt surface is expected to be enhanced and decrease the activity of the catalyst. However, the quantitative relationship between catalyst behavior and the electronic structure of Pt under high temperature operation has not yet been elucidated. Here, we developed an MEA cell for high temperature and high pressure conditions and analyzed the oxidation state and local structure of Pt on Pt/C catalysts at different temperatures by operando XAS measurements.MEAs were prepared with Pd/C as anode catalyst, Pt/C as cathode catalyst. XAS measurements of the Pt LIII absorption edge were made at 80°C, 105°C, and 120°C with 100% H2 flowing to the anode and Air flowing to the cathode, and spectra were collected by the transmission mode. The area values of the XANES spectra were calculated to compare the relationship of Pt oxide formation with operating temperature and the local structural model of Pt oxide at high temperature by EXAFS.Comparison of operando XANES results of cathode catalyst Pt/C under conventional operating temperature (80°C), 105°C, and 120°C showed a marked difference, especially at 80°C and 120°C. In addition, the XANES area values increased as the operating temperature was increased. This is thought to be due to the fact that Pt oxide formation is accelerated at higher temperatures. Next, comparing the EXAFS analysis results at each temperature, the Pt-O bond peak is stronger at 120°C, indicating that Pt oxidation is more advanced than at 80°C. The 120°C results can be explained by a mixed model of β-PtO2 and Pt metal. Pt-O bond coordination number analysis shows that β-PtO2, in which oxygen is latent inside Pt, is formed more frequently at high temperatures. From this result, it was found that the structure of Pt oxide is different in high-temperature systems, and that catalyst design must take this into account. Fig ure 1. Pt LIII-edge XANES spectra Area vs. Applied voltage for pure H2 at the cathode of Pt/C. MEA temperature: blue circle is 80°C, black circle is 105°C, red circle is 120°C. Fig ure 2. Pt LIII-edge EXAFS Pt-O bond coordination Number vs. Applied voltage for pure H2 at the cathode of Pt/C. MEA temperature: blue triangle is 80°C, black triangle is 105°C, red triangle is 120°C. Acknowledgement This work was supported by a NEDO FC-Platform project commissioned by the New Energy and Industrial Technology Development Organization (NEDO) Reference s : [1] Hideto I.; Koichi I.; Masashi M.; Yoshimi K.; Kazuo K.; Yasuhiko I., J . Am . Chem . Soc ., 2009, 131 (17), 6293-6300. Figure 1