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This study elucidates the factors reducing the CO2methanation reaction temperature of TiO2-supported Ru catalysts prepared via the polygonal barrel-sputtering method (Ru/TiO2(BS)) to investigate the structure-sensitivity mechanism. The smaller nanoparticles deposited in Ru/TiO2(BS) (<4 nm) were amorphous RuO2because of air exposure after the preparation, and their surfaces were changed to island-shaped structures consisting of amorphous RuO2and amorphous Ru metal by H2exposure. In this case, dissociative hydrogen was also adsorbed in abundance on the amorphous Ru metals. Such hydrogen atoms were not observed in conventional Ru/TiO2catalysts. Under the supplied CO2+ H2at a stoichiometric ratio of 1:4, these hydrogen atoms not only contributed to the generation of a unique CO intermediate (Ru–CO–Ru–H) from room temperature, but also reduced this CO adsorbate to methane even in low-temperature ranges (≤120 °C). These reaction steps were completely different from the reported mechanisms. Accordingly, the formation of amorphous Ru metals and the adsorption of hydrogen atoms on them are essential for reducing the CO2methanation temperature. These are key factors of structure-sensitivity, which would also be useful for improving activities of various catalysts.

We investigated the electrode/electrolyte interphase structure using synchrotron radiation based techniques, namely in-situ and time resolvedhard X-ray diffraction (XRD), hard X-ray photoelectron spectroscopy (HAXPES) and soft X-ray absorption fine structure spectroscopy (SXAFS). The formation and dissolution of Li2O2 upon the discharge/charge cycle were monitored by in-situ XRD, and the structure and chemical compositions at the electrode/electrolyte interphase were analyzed by HAXPES and SXAFS. In the XRD measurements, we found the Li2O2 formation during discharge and the rapid Li2O2 dissolution in the charge reaction. The combination of HAXPES and SXAFS analyses revealed that a large number of side products such as carbonates, C-F compounds, LiF, sulfones, and Li2O were generated after the discharge reaction. Furthermore, these side products were partially decomposed and/or oxidized in the charge stage. We systematically summarized the results in relation with the charge/discharge operation.

To investigate the nature of the characteristic properties (especially the wide potential window and the low background current) of boron-doped diamond electrodes, we discuss electric field effects on the electron transfer process between the diamond surface and a proton based on density functional theory (DFT) and Anderson–Newns Hamiltonian analysis. All of the necessary data for this analysis were obtained by a “finite-field DFT method” at the level of B3LYP/6-31G and natural bond orbital analysis (NBO). The diamond and graphite electrode surfaces were modeled by corresponding clusters. We investigated the differences in the electric-field response of the density of states (DOS) peak of the proton 1s orbital and the number of electrons on the proton for the cases of a diamond cluster and a graphite cluster. These differences are attributable to the differences in the overlap between the proton 1s orbital and the surface orbitals. We discuss the relationship between this electric-field effect on the DOS peak, critical points of the Q-curve and two characteristic properties of diamond electrodes, that is, low background currents and wide potential windows.

We investigated the electrode/electrolyte interphase structure using synchrotron radiation based techniques, namely in-situand time resolvedhard X-ray diffraction (XRD), hard X-ray photoelectron spectroscopy (HAXPES) and soft X-ray absorption fine structure spectroscopy (SXAFS). The formation and dissolution of Li2O2upon the discharge/charge cycle were monitored by in-situXRD, and the structure and chemical compositions at the electrode/electrolyte interphase were analyzed by HAXPES and SXAFS. In the XRD measurements, we found the Li2O2formation during discharge and the rapid Li2O2dissolution in the charge reaction. The combination of HAXPES and SXAFS analyses revealed that a large number of side products such as carbonates, C-F compounds, LiF, sulfones, and Li2O were generated after the discharge reaction. Furthermore, these side products were partially decomposed and/or oxidized in the charge stage. We systematically summarized the results in relation with the charge/discharge operation.