Abstract: Hydrogen adsorption and absorption in metals and oxides are relevant to a wide range of energy- and environment-related applications, including hydrogen storage, high-temperature superconductivity, and catalytic processes. Because hydrogen is the lightest atom and possesses spins, it is often argued that quantum effects play an important role in its dynamics.
In this study, we investigate hydrogen diffusion in TiO₂ and Pd using nuclear reaction analysis combined with channeling techniques and electrical resistance measurements. In TiO₂, we find that hydrogen diffusion is faster in the anatase phase than in the rutile phase, which we discuss in terms of the localized nature of electron polarons. In Pd, we measure the temperature dependence of hydrogen hopping from tetrahedral to octahedral sites and analyze the results within the framework of Kondo theory. Furthermore, we have recently developed a spin-polarized hydrogen beam, which enables us to study spin-orientation effects on hydrogen adsorption on Ni surfaces. We discuss the observed spin-dependent adsorption behavior in terms of exchange interaction associated with electron repulsion.