Cyclic voltammetry and electrochemical impedance of MmNi 3.6Co 0.7Mn 0.4Al 0.3 alloy electrode before and after treatment with a hot alkaline solution containing reducing agent

Abstract

The hydrogen storage alloy (MmNi 3.6Co 0.7Mn 0.4Al 0.3, Mm=Ce-rich mischmetal) electrodes were treated in an alkaline solution containing a reducing agent (KBH 4 or NaH 2PO 2). Cyclic voltammetry (CV) and electrochemical impedance spectra (EIS) were applied to characterize the electrochemical properties of the alloy electrodes before and after surface treatment. The results show that the charging efficiency and electrochemical reaction activity of metal hydride (MH) electrode were markedly improved by the treating. The reaction of the untreated MH electrode was chiefly controlled by the charge transfer process at the interface of electrode/electrolyte, or by the mixture of the charge transfer and hydrogen diffusion processes, but the reaction of the treated electrode was mainly controlled by hydrogen atom's diffusion in the alloy bulk. The results of EIS measurements indicate that the charge transfer resistance of MH electrode was reduced and its specific surface area augmented after treatment.