An investigation of the effect of applied potential on the impedance response of hydrogen storage alloys of the AB₅ (MmNi_3.7Co_0.6A_l0.4Mn_0.3) and AB₂ (Ti_1.6V_2.2Zr_1.6Ni_4.2Cr_0.7) types produced by induction melting is presented. The crystallite size of the alloys was in the range of 40-60 nm as estimated by X-ray diffraction analysis. The experimental impedance spectra for the alloys as depending on potential were compared to the prediction of a generalized model of the hydrogen reaction. In the model, it has been assumed that the radius of diffusion coincides with the crystallite size of the alloys. An equivalent electrical circuit has been proposed on the basis of the transfer function of the kinetic model. By comparing the values of the equivalent circuit parameters calculated by fitting the experimental impedance spectra to the kinetic and transport equations for these parameters derived on the basis of the physical model, the parameters of the hydrogen reaction were estimated. The parameter values are discussed in terms of the influence of the structure of the alloys on their electrochemical performance in prospective nickel-hydrogen batteries.

Keywords: Metal hydride Electrode; Impedance Spectroscopy; Kinetic Model; Spherical Diffusion;