Hydrogen diffusion in metallic and nanostructured materials

The diffusion mechanisms of hydrogen in metallic and nanostructured materials have been studied systematically by different nuclear magnetic resonance techniques. The present paper reviews three examples of our recent work: (i) The hydrogen-stabilized Laves-phase compound C15-HfTi2H4, with rather complex mechanisms of hydrogen diffusion. Long-range diffusion and localized motion coexist on different time scales in this compound. (ii) Nanostructured vanadium-hydrides n-VHx, in which the dynamical properties of hydrogen are fundamentally changed compared to that in a crystalline compound. The diffusion parameters of hydrogen in the grain boundary regions could be determined independently of the hydrogen motion inside the crystalline grains. (iii) Hydrogen in nanostructured hydrogen-graphite-systems n-CHx, where the NMR spectra reveal two types of hydrogen coordinations. The relaxation data indicate high hydrogen mobilities at ambient temperatures