Characterization of metal hydrides using pneumato-chemical impedance spectroscopy

Pneumato-chemical impedance spectroscopy (PIS) is a tool derived from electrochemical impedance spectroscopy (EIS). PIS can be used to analyze the kinetics of various solid-gas reactions, such as the hydriding kinetics of metals in the presence of hysteresis. Pneumato-chemical impedance diagrams are obtained from simple gas transfer experiments, using non-harmonic pressure perturbations. In single-phase domains, the global sorption mechanism consists of mainly two steps, a surface chemisorption step and a bulk hydrogen transport step, controlled by diffusion. In two-phase domains, an additional phase transformation step must be considered. Model impedances are obtained by interconnecting microscopic impedances associated with each reaction step. By fitting model impedances to the experimental ones, microscopic rate parameters such as the surface dissociation resistance, the bulk hydrogen diffusion coefficient and the phase transformation resistance can be obtained. Different results obtained on palladium, palladium–silver and LaNi5 samples (foils and powder) are presented to illustrate the potentialities of this spectroscopy.