The redox reaction of Mn in Li2MnO3 was studied by X-ray absorption spectroscopy and ab initio multiplet calculation. Associated with the de-intercalation of Li-ion, small but clear spectral changes were observed in Mn-L2,3 X-ray absorption near edge structure (XANES). The systematic ab initio multiplet calculations of Mn-L2,3 XANES revealed that the spectral changes in the experiment could not simply be ascribed to the change of the valency from Mn4+ to Mn5+ but can be explained well by the changes of local atomic structures around Mn4+ due to the Li de-intercalation. Our results suggest that the electronic state of oxygen should change during charging in Li2MnO3.

We develop platinum–iron–nickel (PtFeNi) trimetallic alloy catalysts having a chemically ordered L10-type superlattice structure. The PtFeNi catalyst annealed at 800 °C possesses a superlattice structure and exhibits oxygen reduction reaction (ORR) activity that is much higher than that of the disordered PtFeNi catalysts and a commercial Pt catalyst supported on carbon black. Moreover, the ORR specific activities in the PtFeNi trimetallic systems are enhanced more than those in the PtFe and PtNi bimetallic systems. Analyses of in situ X-ray absorption spectroscopy reveals Pt–Pt bond distances in the PtFeNi annealed at 800 °C (2.70–2.72 Å) are shorter than those in a commercial Pt (2.77 Å), leading to a suitable balance of oxygen species chemisorption energies on the Pt atoms. In addition, high durability of the PtFeNi catalyst with a superlattice structure is demonstrated. Therefore, tuning the atomic structures of Pt-alloy catalysts by the formation of a superlattice structure and trimetallic system effectively enhances both ORR activity and durability.

X-ray absorption near edge structure (XANES) analysis is an element-specific method for proving electronic state mostly in the field of applied physics, such as battery and catalysis reactions, where the valence change plays an important role. In particular, many results have been reported for the analysis of positive electrode materials of Li-ion batteries, where multiple transition materials contribute to the reactions. However, XANES analysis has been limited to identifying the valence state simply in comparison with reference materials. When the shape of XANES spectra shows complicated changes, we were not able to identify the valence states or estimate the valence quantitatively, resulting in insufficient reaction analysis. To overcome such issues, we propose a valence state evaluation method using K- and L-edge XANES analysis with first-principles simulations. By using this method, we demonstrated that the complicated reaction mechanism of Li(Ni1/3Co1/3Mn1/3)O2 can be successfully analyzed for distinguishing each contribution of Ni, Co, Mn, and O to the redox reactions during charge operation. In addition to the XANES analysis, we applied resonant photoelectron spectroscopy (RPES) and diffraction anomalous fine structure spectroscopy (DAFS) with first-principles calculations to the reaction analysis of Co and Mn, which shows no or very little contribution to the redox. The combination of RPES and first-principles calculations successfully enables us to confirm the contribution of Co at high potential regions by electively observing Co 3d orbitals. Through the DAFS analysis, we deeply analyzed the spectral features of Mn K-edges and concluded that the observed spectral shape change for Mn does not originate from the valence change but from the change in distribution of wave functions around Mn upon Li extraction.

We report the results of high‐resolution transmission electron‐micrograph (TEM) observation, electron diffraction, and neutron diffraction (ND) measurements, which are sensitive to oxygen‐vacancies, for Ta‐oxide‐based oxygen‐reduction electrocatalysts used for polymer electrolyte fuel cells (PEFCs). Both TEM and ND results indicate that highly active tantalum oxide (Ta2O5) phase have an incommensurate long‐period structure with oxygen vacancies in the oxides, forming three‐dimensionally ordered region in the crystal. Such corrective oxygen‐vacancies might be effective to create better electronic or surface structural features for oxygen reduction reaction.

This paper describes the development and the characterization of a Li + optical sensor (optode) based on a Li + selective fluoroionophore (KBL-01-Si), immobilized to a mesoporous silica thin film. KBL-01-Si was synthesized by the formation of a urethane bond between the hydroxyl terminated alkoxy chain of KBL-01 and 3-isocyanatopropyl-triethoxysilane. Li + optodes with different amounts of KBL-01-Si fluoroionophore were fabricated by changing the grafting time of KBL-01-Si to mesoporous silica thin films with two different pore sizes. When the concentration of KBL-01-Si immobilized to the pore surface of the mesoporous silica thin films was low, response curves following a theoretical 1 : 1 complex formation equilibrium with binding constants for Li + (log K) between 4.38 and 5.04 were observed. At higher concentrations of immobilized fluoroionophore, the response curves deviated from the fitting curve based on a theoretical chemical equilibrium, and the dynamic response was extended over a broad range from 10 26 to 1 M. In addition, it was observed by XPS depth profiling that KBL-01-Si was mainly localized on pore surface areas close to the channel entrances. These results indicate that not only the design of the fluoroionophore, but also the matrix for immobilization, and the microscale distribution of the fluoroionophore affect the characteristics of an ion sensor.