As anode materials of Li-ion and Na-ion batteries, the electrochemical insertion/extraction reactions of Li and Na were investigated for a rutile-type Nb-doped TiO2 synthesized by a sol–gel method. We changed the particle and crystallite sizes of the Nb-doped rutile TiO2 powders by annealing at various temperatures between 100 and 1000 °C and prepared thick-film electrodes consisting of the powders. The anode performances were remarkably improved not only in the Li-ion battery but also in the Na-ion battery with a reduced annealing temperature of 400 from 1000 °C. We revealed that the Nb-doped TiO2 showing better high-rate performances exhibited a larger ratio of crystallite size to particle size. The size-dependent enhancement in the performance of rutile TiO2 was much more drastic than that of anatase TiO2. These results suggest that rutile’s potential diffusivity of Li and Na appeared more obviously when increasing the ratio because its diffusion coefficient is anisotropic and significantly high.

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We report results of our experimental and theoretical studies on the oxidation of Cu-Au alloy surfaces, viz., Cu3Au(111), CuAu(111), and Au3Cu(111), using hyperthermal O2 molecular beam (HOMB). We observed strong Au segregation to the top layer of the corresponding clean (111) surfaces. This forms a protective layer that hinders further oxidation into the bulk. The higher the concentration of Au in the protective layer formed, the higher the protective efficacy. As a result, of the three Cu-Au surfaces studied, Au3Cu(111) is the most stable against dissociative adsorption of O2, even with HOMB. We also found that this protective property breaks down for oxidations occurring at temperatures above 300 K.

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