X-ray Absorption Near-edge Structure Study Research Articles

Elucidating the Complex Oxidation Behavior of Aqueous H3PO3 on Pt Electrodes via In Situ Tender X-ray Absorption Near-Edge Structure Spectroscopy at the P K-Edge.

In situ tender X-ray absorption near-edge structure (XANES) spectroscopy at the P K-edge was utilized to investigate the oxidation mechanism of aqueous H3PO3 on Pt electrodes under various conditions relevant to high-temperature polymer electrolyte membrane fuel cell (HT-PEMFC) applications. XANES and electrochemical analysis were conducted under different tender X-ray irradiation doses, revealing that intense radiation induces the oxidation of aqueous H3PO3 via H2O yielding H3PO4 and H2. A broadly applicable experimental procedure was successfully developed to suppress these undesirable radiation-induced effects, enabling a more accurate determination of the aqueous H3PO3 oxidation mechanism. In situ XANES studies of aqueous 5 mol dm-3 H3PO3 on electrodes with varying Pt availability and surface roughness reveal that Pt catalyzes the oxidation of aqueous H3PO3 to H3PO4. This oxidation is enhanced upon applying a positive potential to the Pt electrode or raising the electrolyte temperature, the latter being corroborated by complementary ion-exchange chromatography measurements. Notably, all of these oxidation processes involve reactions with H2O, as further supported by XANES measurements of aqueous H3PO3 of different concentrations, showing a more pronounced oxidation in electrolytes with a higher H2O content. The significant role of water in the oxidation of H3PO3 to H3PO4 supports the reaction mechanisms proposed for various chemical processes observed in this work and provides valuable insights into potential strategies to mitigate Pt catalyst poisoning by H3PO3 during HT-PEMFC operation.

Unravelling the role of iron and manganese oxides in colouring Late Antique glass by micro-XANES and micro-XRF spectroscopies

This research aims to understand colouring technologies in 5th–7th centuries glass imported to Atlantic Britain by correlating the iron (Fe) and manganese (Mn) ratios and oxidation states with colour. Despite having a similar matrix chemical composition and concentrations of Fe and Mn oxides, these vessels display different colours (from green to yellow/amber, sometimes with purple streaks). Colour changes can be induced by controlling the reduction-oxidation reactions that occur during glass production, which are influenced by the raw materials, furnace and melt atmosphere, and recycling. To evaluate these parameters, reference glasses were prepared, following the composition of Late Antique archaeological glass recovered from Tintagel (UK) and Whithorn (UK). A corpus of archaeological and experimental glass samples was analysed using bulk Fe and Mn K-edge x-ray absorption near edge structure (XANES) spectroscopy, micro-XANES and micro x-ray fluorescence (μ-XRF) at beamline ID21, at the European Synchrotron Radiation Facility. Fe and Mn XANES spectra of the archaeological glass indicate that Fe and Mn are in a similar oxidation state in all the yellow samples, predominantly Fe3+ and Mn2+. No detectable difference in Mn and Fe oxidation state occurs in the purple streaks compared to the yellow glass bulk but μ-XRF maps of the distribution of Fe and Mn show that Mn is more concentrated in the purple streaks. This indicates that the purple colour of the streaks is mainly due to a higher Mn/Fe ratio and persistence of more oxidised manganese in the purple areas, even though it is difficult to detect. Many archaeological fragments appear pale green in transmitted light but amber in reflected light. XANES studies detected the presence of surface layers where manganese is more oxidised. This layer is believed to scatter transmitted and reflected light differently and might be responsible for the optical features of the archaeological glass.

Orbital hybridisation effects in B2 phase Cr doped Co2MnAl

We investigate here the magnetic, transport, local structural and electronic properties of Co2MnCr x Al (x = 0, 0.05, 0.1 and 0.2). Our results show that all the compounds stabilise in B2 phase and are ferromagnets. The results reveal disorder at the structural and magnetic levels. X-ray absorption near edge structure (XANES) analysis reveal signature of antisite disorder between Mn and Al atoms with equal ratio. The electronic structure calculations suggest enhancement in the half metallicity, localisation of electrons at the Fermi level and an increment in density of states with doping. The combined results of electronic structure calculations and XANES studies suggest transfer of electrons to the Co site. The results of high temperature resistivity measurements suggest the conduction electrons are undergoing transition from delocalisation to weak localisation to activated behaviour with Cr doping. The extended x-ray absorption spectroscopic analysis shows that the local structure around Mn atom is different from the global structure as obtained from the x-ray diffraction results. The behaviour of the edge region is in line with the trend as obtained from the compositional analysis. We observe link between the hybridisation of 3d like states at the Mn, Cr sites with that at the Co site and the transport properties. This could help in understanding the unusual decrement in the lattice parameter with doping. These results reveal the role of local structure in understanding the physical properties of such systems.

Phase evolution in the UO2–CeO2 system under oxidizing and reducing conditions: X-ray diffraction and spectroscopic studies

The solid-solution formation mechanism and defect dynamics in U1-xCexO2±δ solid solutions have been investigated by means of X-ray diffraction (XRD) analysis, Raman spectroscopy, and X-ray absorption near-edge structure (XANES) spectroscopy. Diffraction studies have revealed the formation of single-phase solid solutions with a fluorite-type structure at x ≤ 0.2 and a single-phase fluorite-type structure with broadened diffraction peaks, attributed to inhomogeneity in the O/M ratio, at 0.3 ≤ x ≤ 0.8 under reducing conditions. Oxidizing conditions result in the formation of single-phase solid solutions with fluorite-type structure at x ≥ 0.4. Upon the formation of Ce3+ in solid solutions at x ≤ 0.2 under reducing conditions, charge neutrality is achieved through oxygen vacancy creation and formation of higher oxidation states of uranium through a charge compensation mechanism. Lattice parameter–composition relationships for fluorite-type phases synthesized under oxidizing conditions show a decrease in lattice parameters as compared to their stoichiometric counterparts due to the oxidation of U4+ to U5+/U6+. XANES studies provide direct experimental evidence of the presence of Ce3+ in solid solutions, despite synthesis under oxidizing conditions.

Insights into enhanced activity and durability of hierarchical Fe-doped Ni(OH)2/Ni catalysts for alkaline oxygen evolution reaction: In situ XANES studies

Nature of activation and degradation of NiFe layered double hydroxide (NiFe-LDH) and hierarchical Fe-doped Ni(OH)2/Ni has been explored using in situ X-ray absorption near edge structure (XANES) spectroscopy coupled with cyclic voltammetry (CV) in a potential range of 0–0.9 V (vs. Hg/HgO). A series of NiFe-LDH samples have been prepared by electrodeposition with varying Ni/Fe molar ratios from 99:1–16:84. Fe has been doped on Ni(OH)2 and anodized Ni as Fe-Ni(OH)2 and Fe-ANi, respectively. CV and electrochemical impedance spectroscopy (EIS) analysis confirm the degradation of NiFe-LDH due to the redox irreversibility of Ni(OH)2/NiOOH. On the other hand, hierarchical Fe-doped Ni(OH)2/Ni shows not only high activity but also stability in alkaline OER. In situ XANES analysis demonstrated that the phase of Ni is maintained with Ni2+ in Fe-ANi, while the phase of Ni2+ changes to Ni3.6+ in NiFe-LDH, contributing to durable OER performance of Fe-ANi even under potential fluctuations.

Breaking the structural anisotropy of ZnO enables dendrite-free lithium-metal anode with ultra-long cycling lifespan

Crystalline materials have shown great potential for lithium-metal batteries. However, crystalline materials are prone to uncontrollable growth of lithium dendrites due to their anisotropic characteristics. Herein, we break the structural anisotropy of zinc oxide as an amorphous host to efficiently induce a uniform lithium deposition. Theoretical calculations first confirm that amorphous ZnO presents a much larger lithium adsorption energy. X-ray photoelectron spectroscopy (XPS) and X-ray absorption near-edge structure (XANES) studies reveal that amorphous zinc oxide possesses both numerous “floppy” bonds and multiple vacancies, resulting in not only an increase in lithiophilic sites but also a more uniform distribution of the electric field. As a result, amorphous zinc oxide delivers an improved Coulomb efficiency of 98.2% even after 500 cycles at 1 mA cm−2 and an ultra-long cycling lifespan over 2,500 h in symmetric cells, outperforming most representative and state-of-the-art lithium-metal anodes. This work opens a new pathway to exploring amorphous materials for lithium-metal batteries.

Operando Laboratory‐Based Multi‐Edge X‐Ray Absorption Near‐Edge Spectroscopy of Solid Catalysts

AbstractLaboratory‐based X‐ray absorption spectroscopy (XAS) and especially X‐ray absorption near‐edge structure (XANES) offers new opportunities in catalyst characterization and presents not only an alternative, but also a complementary approach to precious beamtime at synchrotron facilities. We successfully designed a laboratory‐based setup for performing operando, quasi‐simultaneous XANES analysis at multiple K‐edges, more specifically, operando XANES of mono‐, bi‐, and trimetallic CO2 hydrogenation catalysts containing Ni, Fe, and Cu. Detailed operando XANES studies of the multielement solid catalysts revealed metal‐dependent differences in the reducibility and re‐oxidation behavior and their influence on the catalytic performance in CO2 hydrogenation. The applicability of operando laboratory‐based XANES at multiple K‐edges paves the way for advanced multielement catalyst characterization complementing detailed studies at synchrotron facilities.

Operando Laboratory-Based Multi-Edge X-Ray Absorption Near-Edge Spectroscopy of Solid Catalysts.

Laboratory-based X-ray absorption spectroscopy (XAS) and especially X-ray absorption near-edge structure (XANES) offers new opportunities in catalyst characterization and presents not only an alternative, but also a complementary approach to precious beamtime at synchrotron facilities. We successfully designed a laboratory-based setup for performing operando, quasi-simultaneous XANES analysis at multiple K-edges, more specifically, operando XANES of mono-, bi-, and trimetallic CO2 hydrogenation catalysts containing Ni, Fe, and Cu. Detailed operando XANES studies of the multielement solid catalysts revealed metal-dependent differences in the reducibility and re-oxidation behavior and their influence on the catalytic performance in CO2 hydrogenation. The applicability of operando laboratory-based XANES at multiple K-edges paves the way for advanced multielement catalyst characterization complementing detailed studies at synchrotron facilities.

XANES, EXAFS, Voltammetric, and Microhardness Studies of Manganese Dioxide-Lead-Lead Dioxide Vitroceramics.

In this work we investigated the electrochemical performances and mechanical behavior of the manganese dioxide–lead dioxide–lead vitreous system. The structural and electrochemical properties of vitroceramics were investigated by the analysis of X-ray diffraction (XRD) spectra, X-ray absorption spectroscopy (XAS), and measurements of cyclic voltammetry and linear sweep voltammetry. The mechanical properties of the studied samples were determined by Vickers hardness values using the indentation method. The analysis of X-ray absorption near edge structure (XANES) data for the L3 edge of the lead and the radial distribution function data for the PbO2 and Pb model indicate the modification of Pb-O interatomic distances by the doping process. The voltammetric study reveals the vitroceramic with x = 90 mol% Pb as the most suitable for application as a lead acid battery electrode.

High ICE Hard Carbon Anodes for Lithium-Ion Batteries Enabled by a High Work Function

Hard carbons (HC) derived from biomass material are most promising anodes for lithium-ion batteries (LIBs) because of their cost effectiveness and environmental friendliness. However, the low initial Coulombic efficiency (ICE) of HC anodes reduces the energy density of full cells, which seriously impedes their practical applications. Herein, we demonstrate that the ICE of HC anodes can be significantly improved by modulating the work function of a model HC derived from cotton and deliberately treated to form C-Cl bonds on its surface. By X-ray absorption near-edge structure and density functional theory (DFT) calculation studies, it is verified that the introduction of the C-Cl bond leads to the electron transfer from C to Cl and enhances the work function of the system. In addition, this Cl-doped HC anode can inhibit the reduction of solvent molecules in the electrolyte and reduce the formation of a solid electrolyte interface (SEI) film. Consequently, the ICE is improved from 64.8 to 78.1%. This study provides an effective route to reduce the formation of the SEI film and improve the ICE of hard carbon anodes for LIBs.

Crystal structure and XANES study of Fe-substituted Barium Titanate ceramics prepared by conventional solid-state technique

The structural characterizations of Fe-substituted Barium Titanate (Fe–BaTiO3) ceramics prepared at different sintering temperatures were investigated in this work. The Fe–BaTiO3 ceramics (with 10 mol% of Fe substitution) were prepared via a conventional solid-state reaction (SSR) method. The structural data were examined by XRD (X-ray Diffraction) and XAS (X-ray Absorption Spectroscopy) techniques. The results revealed the transformation from tetragonal to hexagonal structure with increasing sintering temperature. The measured XANES (X-Ray Absorption Near-Edge Structure) data exhibited the oxidation state of Fe ion as Fe3+ in the Fe–BaTiO3. The comparison between measured and calculated XANES spectra to examine the effect of different sintering temperatures on the local structure around the Ti atom was carried out. Finally, it should be emphasized that the local structure evolution in Fe–BaTiO3 ceramics may be explored by the XANES investigations.

Evolution of transition metal charge states in correlation with the structural and magnetic properties in disordered double perovskites Ca2-xLaxFeRuO6 (0.5 ≤ x ≤ 2).

A series of disordered Ca1.5La0.5FeRuO6, CaLaFeRuO6 and La2FeRuO6 double perovskites were prepared by the solid-state reaction method and investigated by neutron powder diffraction, X-ray absorption near-edge structure (XANES) analysis at the Ru-K edge, Mössbauer spectroscopy, DC magnetization and resistivity measurements. All compounds crystallize in the orthorhombic crystal structure with the space group Pbnm down to 3 K, showing a random distribution of Fe and Ru at the B site. Thermogravimetric analysis indicates oxygen deficiency in the Ca-rich and formal oxygen hyperstoichiometry in the La-rich members of the present series. While Mössbauer spectra verify the Fe3+ state for all compositions, the XANES study reveals a variable Run+ oxidation state which decreases with increasing La content. The end member actually is a Ru3+/Ru4+ compound with possibly some cation vacancies. From magnetic susceptibility and neutron diffraction measurements, the presence of a G-type antiferromagnetic ordering was observed with a drastic increase in transition temperature from 275 K (Ca1.5La0.5FeRuO6) to 570 K (La2FeRuO6). Mössbauer spectroscopy confirms the presence of long-range ordering but, due to local variations in the exchange interactions, the magnetic states are microscopically inhomogeneous. All the samples are variable range hopping semiconductors. A complex interplay between structural features, charge states, anion or cation defects, and atomic disorder determines the magnetic properties of the present disordered 3d/4d double perovskite series.

The fate of calcium in temperate forest soils: a Ca K-edge XANES study

Calcium (Ca) plays a crucial role for plant nutrition, soil aggregation, and soil organic matter (SOM) stabilization. Turnover and ecological functions of Ca in soils depend on soil Ca speciation. For the first time, we used synchrotron-based X-ray absorption near-edge structure (XANES) spectroscopy at the Ca K-edge (4038 eV) to investigate Ca speciation in soils. We present Ca K-edge XANES spectra of standard compounds with relevance in soils (e.g. calcite, dolomite, hydroxyapatite, anorthite, clay mineral-adsorbed Ca; Ca oxalate, formate, acetate, citrate, pectate, phytate). Calcium XANES spectra with good signal-to-noise ratios were acquired in fluorescence mode for Ca concentrations between 1 and 10 mg g−1. Most standard spectra differed markedly among each other, allowing the identification of different Ca species in soils and other environmental samples as well as Ca speciation by linear combination fitting. Calcium XANES spectra obtained for samples from different horizons of twelve temperate forest soils revealed a change from dominating lithogenic Ca to clay mineral-bound and/or organically bound Ca with advancing pedogenesis. O layer Ca was almost exclusively organically bound. With increasing SOM decomposition, shares of oxalate-bound Ca decreased. Oxalate-bound Ca was absent in calcareous, but not in silicate subsoil horizons, which can be explained by microbial decomposition in the former vs. stabilization by association to pedogenic minerals in the latter soils. Synchrotron-based Ca XANES spectroscopy is a promising novel tool to investigate the fate of Ca during pedogenesis and—when performed with high spatial resolution (µ-XANES), to study aggregation and SOM stabilization mechanisms produced by Ca.

Capture and Decomposition of the Nerve Agent Simulant, DMCP, Using the Zeolitic Imidazolate Framework (ZIF-8).

Understanding mechanisms of decontamination of chemical warfare agents (CWA) is an area of intense research aimed at developing new filtration materials to protect soldiers and civilians in case of state-sponsored or terrorist attack. In this study, we employed complementary structural, chemical, and dynamic probes and in situ data collection, to elucidate the complex chemistry, capture, and decomposition of the CWA simulant, dimethyl chlorophosphonate (DMCP). Our work reveals key details of the reactive adsorption of DMCP and demonstrates the versatility of zeolitic imidazolate framework (ZIF-8) as a plausible material for CWA capture and decomposition. The in situ synchrotron-based powder X-ray diffraction (PXRD) and pair distribution function (PDF) studies, combined with Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), zinc K-edge X-ray absorption near edge structure (XANES), and Raman spectroscopies, showed that the unique structure, chemical state, and topology of ZIF-8 enable accessibility, adsorption, and hydrolysis of DMCP into the pores and revealed the importance of linker chemistry and Zn2+ sites for nerve agent decomposition. DMCP decontamination and decomposition product(s) formation were observed by thermogravimetric analysis, FT-IR spectroscopy, and phosphorus (P) K-edge XANES studies. Differential PDF analysis indicated that the average structure of ZIF-8 (at the 30 Å scale) remains unchanged after DMCP dosing and provided information on the dynamics of interactions of DMCP with the ZIF-8 framework. Using in situ PXRD and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), we showed that nearly 90% regeneration of the ZIF-8 structure and complete liberation of DMCP and decomposition products occur upon heating.

Promoting effect of 2000 ppm H2S on the dry reforming reaction of CH4 over pure CeO2, and in situ observation of the behavior of sulfur during the reaction

Biomass-derived gas and unused industrial byproducts are resources for H2 production with low CO2 emission; however, they contain > 1000 ppm H2S, which necessitates the use of H2S-tolerant catalysts. Herein, a pure CeO2 catalyst demonstrated stable and efficient H2 production via the dry reforming reaction in the presence of 2000 ppm H2S. No impurity phases and carbon deposition appeared on the catalyst after the reaction. Moreover, CeO2 catalytic activity improved with H2S concentration. The effect of H2S on CeO2 was determined by in situ infrared spectroscopy and S K-edge X-ray absorption near-edge structure studies. The re-oxidation of CeO2 by CO2, a key step of the dry reforming reaction, was accelerated by the rapid redox cycle of sulfur, which promoted CH4 activation and decreased the apparent activation energy from 125 to 101 kJ/mol. The redox cycle of S made the pure CeO2 catalyst resistant to high concentration of H2S.

Effect of Ce4+-substitution at A and B sites of Nd2Zr2O7: A study for plutonium incorporation in pyrochlores

Zirconate pyrochlores have been envisaged as promising candidates for inert matrix fuel applications and immobilization of nuclear waste. Therefore, Ce4+-substituted Nd2Zr2O7 samples with general formula [Nd1-xCex]2Zr2O7+δ (0.0 ≤ x ≤ 0.5) and Nd2[Zr1-xCex]2O7 (0.0 ≤ x ≤ 1.0) were synthesized by solid state route and thoroughly characterized by X-ray diffraction (XRD) in order to mimic plutonium incorporation at A- and B-sites of Nd2Zr2O7 pyrochlore which are crystallographically distinct. The local structure has also been probed by Raman spectroscopy and X-ray absorption near edge structure (XANES) spectroscopy. Interestingly, the substitution of Ce4+ at different sites yields distinct phase relations. Ce4+-substitution at A- (Nd3+) site retains pyrochlore-type phase up to nominal composition with x = 0.4 and F-type phase was observed for composition with x = 0.5. However, Ce4+-substitution at B- (Zr4+) site demonstrated transformation of pyrochlore-type phase to F-type phase through a biphasic phase field consisting of these two phases. Raman spectroscopic studies on Nd2[Zr1-xCex]2O7 (0.0 ≤ x ≤ 1.0) system clearly indicated existence of C-type ordering in largely F-type phases for compositions with x = 0.6 and beyond. XANES studies exhibited a change in Zr local coordination upon successive Ce4+-substitution at ‘Nd’ site and pointed towards increase in local disorder across the pyrochlore phase regime. Ce LIII edge XANES also revealed significant changes in ‘Ce’ local environment in Ce-substituted samples.

A mechanistic study of molecular CO2 interaction and adsorption on carbon implanted SnS2 thin film for photocatalytic CO2 reduction activity

Gas-phase photocatalytic reactions to convert carbon dioxide and water into oxygen and hydrocarbons are the foundation of life on earth. However, the efficiency of photosynthesis is relatively low (~1%), which leaves much room for artificial photosynthesis to reach the benchmark of the solar cells (>15%). In this work, carbon implanted SnS2 thin films (C–SnS2) were prepared to study photocatalytic activity and adsorbate-catalyst surface interactions during CO2 photoreduction. The electron density distribution in C–SnS2 and its contribution toward the photogenerated charge transfer process has been analyzed by the angle-dependent X-ray absorption near-edge structure (XANES) study. The C–SnS2 surface affinity toward the CO2 molecule was monitored by in-situ dark current and Raman spectroscopy measurements. By optimizing the dose during ion implantation, SnS2 thin film with 1 wt% carbon incorporation shows 108 times enhancement in the CO2 conversion efficiency and more than 89% product selectivity toward CH4 formation compared with the as-grown SnS2 without carbon incorporation. The improved photocatalytic activity can be ascribed to enhanced light harvesting, pronounced charge-transfer between SnS2 and carbon with improved carrier separation and the availability of highly active carbon sites that serve as favorable CO2 adsorption sites.

Crystal structure and XANES study of Sn-substituted YBa2Cu3O7-y powder prepared by solid-state synthesis method

In this research, the crystal and chemical characterizations of Sn-substituted YBa2Cu3O7-y (YBCO) powder were studied. The experimental powder samples of (Y1-xSnx)Ba2Cu3O7-y (0 ≤ x ≤ 0.2) were prepared using the solid-state synthesis method. The starting precursor powders in appropriate ratios were mixed and calcined at 880 °C for 12 h in a normal atmosphere. The calcined powders were investigated for phase content using the X-ray diffraction technique (XRD). The microstructure of the powders was investigated by scanning electron microscopy (SEM). The chemical composition was carried out by energy-dispersive X-ray analysis (EDX). In addition, the details of the oxidation state of Sn and Cu determined by X-ray absorption near-edge structure (XANES) spectroscopy was also analyzed and discussed in relation to the cationic site substitution and variation in the local structure. It was found that the indexing of the XRD pattern showed Sn-substituted YBCO main peaks, and the impurity peaks of BaSnO3 and BaCuO2 were also found in the pattern. The small solubility of Sn in YBCO matrix was the major factor which induced the formation of the latter secondary phase. SEM images of the particles indicated that they possessed an irregular shape with a particle-size range of 1–3 μm. Sn L3-edge XANES spectra indicated that the average formal valence of Sn was Sn2+/Sn4+. The Cu K-edge spectra helped confirm that the Sn ions could not substitute Cu site in YBCO structure.

Dual Graphitic-N Doping in a Six-Membered C-Ring of Graphene-Analogous Particles Enables an Efficient Electrocatalyst for the Hydrogen Evolution Reaction.

Graphene-based materials still exhibit poor electrocatalytic activities for the hydrogen evolution reaction (HER) although they are considered to be the most promising electrocatalysts. We fabricated a graphene-analogous material displaying exceptional activity towards the HER under acidic conditions with an overpotential (57 mV at 10 mA cm-2 ) and Tafel slope (44.6 mV dec-1 ) superior to previously reported graphene-based materials, and even comparable to the state-of-the art Pt/C catalyst. X-ray absorption near-edge structure (XANES) and solid-state NMR studies reveal that the distinct feature of its structure is dual graphitic-N doping in a six-membered carbon ring. Density functional theory (DFT) calculations show that the unique doped structure is beneficial for the activation of C-H bonds and to make the carbon atom bonded to two graphitic N atoms an active site for the HER.

An EXAFS and XANES Study of V, Ni, and Fe Speciation in Cokes for Anodes Used in Aluminum Production

Lower-quality petroleum coke with higher levels of sulfur and metal impurities will have to be used for the manufacturing of anodes for aluminum production in the future. The sulfur and metallic impurities affect the anode properties in the aluminum production process, but the chemical identity of the metal species in the coke is not known. In this study, industrial petroleum cokes with high sulfur levels were analyzed by X-ray absorption near edge structure (XANES) and Extended X-ray absorption fine structure (EXAFS) in order to determine the identity of the V, Ni, and Fe impurities. The XANES spectra were compared with pure-phase standards. EXAFS was used to compare the impurity metal structures with known crystal structures. It was found that V is present mainly as hexagonal V3S4. Ni is present mainly as hexagonal NiS, and Fe is present as hexagonal FeS. This knowledge of the chemical states of the metal elements in coke, which are known to affect anode performance, is the first step in understanding the mechanism of the action of these elements on anode reactivity.