Document Type


Subject Area(s)

Chemical Engineering


The metal hydride (MHx) electrode is the negative electrode in one of the most advanced secondary batteries (i.e.,nickel/metal hydride). The objective of this study is to obtain insight on the mechanism of the hydriding/dehydridingreaction in the battery by using the electrochemical impedance spectroscopy (EIS) technique. An equivalent circuit for the MHx electrode reaction is proposed. The rate capability of charge and discharge of the MHx electrode is determined by thekinetics of the charge-transfer reaction at the alloy surface, which is mainly represented by the EIS responses in the lowfrequency region. Transient and pseudo-steady-state analyses (cyclic voltammetry and potential vs. current density behavior)qualitatively and quantitatively support the EIS results. EIS studies on electrodes with (i) three types of bindingadditives, (ii) varying amounts of active material, and (iii) two types of alloys as active materials demonstrate the usefulnessof this technique for developing electrodes with the optimum composition and structure.