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XANES
About: XANES is a research topic. Over the lifetime, 7737 publications have been published within this topic receiving 188032 citations.
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TL;DR: In situ XAS measurements on a bifunctional manganese oxide catalyst with high electrochemical activity for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) demonstrate that the OER activity scales with film thickness, which suggests that the films have porous structure, which does not restrict electrocatalysis to the top geometric layer of the film.
Abstract: In situ X-ray absorption spectroscopy (XAS) is a powerful technique that can be applied to electrochemical systems, with the ability to elucidate the chemical nature of electrocatalysts under reaction conditions. In this study, we perform in situ XAS measurements on a bifunctional manganese oxide (MnOx) catalyst with high electrochemical activity for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER). Using X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS), we find that exposure to an ORR-relevant potential of 0.7 V vs RHE produces a disordered Mn3II,III,IIIO4 phase with negligible contributions from other phases. After the potential is increased to a highly anodic value of 1.8 V vs RHE, relevant to the OER, we observe an oxidation of approximately 80% of the catalytic thin film to form a mixed MnIII,IV oxide, while the remaining 20% of the film consists of a less oxidized phase, likely corresponding to unchanged Mn3II,III,IIIO4. XAS...
467 citations
TL;DR: In this article, the effect of nitrogen doping on the structure of graphene has been systematically investigated by various characterization techniques such as SEM, TEM, BET, Raman and XRD analysis were used to distinguish the difference of the microstructures; and FT-IR, XPS, especially XANES were performed to elucidate the bonding information such as C-N.
463 citations
TL;DR: In this paper, a host-guest chemistry strategy was proposed to construct Fe-mIm nanocluster (NC) (guest)@zeolite imidazole framework-8 (ZIF-8) precursors that can be transformed into Fe-N/C electrocatalysts with controllable structures.
Abstract: Even though Fe-N/C electrocatalysts with abundant Fe-Nx active sites have been developed as one of the most promising alternatives to precious metal materials for oxygen reduction reaction (ORR), further improvement of their performance requires precise control over Fe-Nx sites at the molecular level and deep understanding of the catalytic mechanism associated with each particular structure. Herein, we report a host–guest chemistry strategy to construct Fe-mIm nanocluster (NC) (guest)@zeolite imidazole framework-8 (ZIF-8) (host) precursors that can be transformed into Fe-N/C electrocatalysts with controllable structures. The ZIF-8 host network exhibits a significant host–guest relationship dependent confinement effect for the Fe-mIm NCs during the pyrolysis process, resulting in different types of Fe-Nx sites with two- to five-coordinated configurations on the porous carbon matrix confirmed by X-ray absorption near edge structure (XANES) and Fourier transform (FT) extended X-ray absorption fine structure ...
436 citations
TL;DR: The dramatic improvement in resolution and detailed structure for the x-ray-absorption near-edge structure (XANES) at the Dy {ital L}{sub III} edge is presented.
Abstract: A novel method to measure x-ray-absorption spectra without the inner-shell lifetime broadening is presented. It is based on a high-resolution spectrometer which can be used to analyze the fluorescence photon energy with better resolution than the natural linewidth. The dramatic improvement in resolution and detailed structure for the x-ray-absorption near-edge structure (XANES) at the Dy ${\mathit{L}}_{\mathrm{III}}$ edge is presented. This new technique reveals structure which is totally invisible using conventional XANES.
420 citations
TL;DR: In this paper, mixed Fe−Ni oxide electrocatalysts for the oxygen evolution reaction in alkaline electrolytes were synthesized using three different approaches: evaporation induced self-assembly, hard templating, and dip-coating.
Abstract: Mixed Fe−Ni oxide electrocatalysts for the oxygen evolution reaction in alkaline electrolytes were synthesized using three different approaches: evaporation induced self-assembly, hard templating, and dip-coating. For each synthesis method, a peak in oxygen evolution activity was observed near 10 mol % Fe content, where the mixed metal oxide was substantially more active than the parent metal oxide electrocatalysts. X-ray diffraction (XRD) analysis showed the formation of a mixed NiO/NiFe2O4 phase at low Fe concentrations, and formation of Fe2O3 at compositions above 25 mol % Fe. Raman vibrational spectroscopy confirmed the formation of NiFe2O4, and did not detect Fe2O3 in the electrocatalysts containing up to 20 mol % Fe. X-ray absorption near edge structure (XANES) showed the Fe in the mixed oxides to be predominantly in the +3 oxidation state. Extended X-ray absorption fine structure (EXAFS) showed changes in the Fe coordination shells under electrochemical oxygen evolution conditions. Temperature programmed reaction spectroscopy showed the mixed oxide surfaces also have superior oxidation activity for methanol oxidation, and that the reactivity of the mixed oxide surface is substantially different than that of the parent metal oxide surfaces. Overall, the NiFe2O4 phase is implicated in having a significant role in improving the oxygen evolution activity of the mixed metal oxide systems.
403 citations