In-situ quantitative measurement of phase-sensitive hydrogen diffusion in metals

• We develop in-situ scanning Kelvin probe force microscopy which enables hydrogen loading toward a metal specimen. • The diffusion coefficients of hydrogen in magnesium and TiFe alloys are determined at the submicron scale. • The alloying elements drastically reduce the diffusion barrier of hydrogen in the TiFe alloys. 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 kinetics 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 measurement 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 coefficient. 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. By integrating scanning Kelvin probe microscope with hydrogen loading sample stage, we developed an in-situ method for evaluating the diffusion behavior of hydrogen in multiphase alloys at the submicron scale. The temporal and spatial variations of surface potential in hydrogenated metals were obtained, enabling precise estimation of the diffusion coefficients of hydrogen in individual phases.