Abstract: Absorption and desorption processes of hydrogen in metals are facilitated by alloying elements; however, the formation of secondary phases often reduces storage capacity. The alloying effect on the hydrogen ki-netics has been examined by time-lag permeation measurement, which lacks spatial resolution and yields the averaged diffusion coefficient from multiple phases. Here, we report an advanced scanning Kelvin probe force microscopy, combined with in-situ hydrogen loading system for submicron-scale measure-ment of diffusion kinetics in metals. Successive probing of the surface during hydrogen loading detects the temporal and spatial variations in the surface potential, enabling the estimation of diffusion coeffi-cient. Not only for a single-phase magnesium but also for multiphase titanium-iron based alloys, we can obtain the diffusion coefficients of hydrogen in each phase. The estimated diffusion coefficients for TiFe alloys are higher than that for the pristine TiFe intermetallic compound, due to alloying elements that reduce the diffusion barrier and modify bond character. Our approach paves the way to the microscopic understanding of hydrogen diffusion in metals.

Key words: Hydrogen diffusion, Diffusion coefficients, TiFe alloy, Hydrogen storage, Scanning Kelvin probe force microscopy