Investigations on kinetics properties of hydrogen adsorbing/desorbing reactions for metal hydride electrodes

Abstract

As we know, the kinetics properties of hydrogen adsorbing/desorbing reactions for metal hydride electrodes are determined by the rates of the charge transfer, hydrogen transfer and hydrogen diffusion reactions. In previous studies, not only the hydrogen transfer process was always ignored, but also the values of the kinetics parameters for the charge transfer and hydrogen diffusion processes were quite different. Therefore, the purpose of this work is to investigate the key issues of the kinetics properties for hydrogen adsorbing/desorbing reactions. Firstly, the hydrogen transfer process was thoroughly studied by electrochemical impedance spectrum (EIS) method, in which it emphasized the corresponding relationship between the electrode process of hydrogen adsorbing/desorbing reactions and the time constants presented in different frequency regions of impedance spectrum. The values of the hydrogen transfer resistance were calculated as a function of depth of discharge (DOD). Meanwhile, almost all the electrochemical techniques including linear polarization curves (LP), constant potential step method (CPSM), galvanostatic intermittent titration technique (GITT), cyclic voltammetry method (CV) and EIS were used to measure the kinetics parameters for the charge transfer and hydrogen diffusion processes. Moreover, the factors causing the discrepancy of the kinetics parameters were analyzed in detail.