Electrochemical properties of rare-earth based hydrogen storage alloy for replacing Pt as the anode electrocatalyst in AFC

Electrochemical properties of hydrogen storage alloy (HSA) MlNi3.65Co0.85Al0.3Mn0.3 with different modifications as the anode electrocatalyst in alkaline fuel cell (AFC) were investigated. Three modification methods, including ball-milling, surface treatment by immersing the alloy in a hot alkaline solution containing reductant and chemically coating with Pd, were applied to improve the electrochemical properties of the alloys. As a result of the ball-milling and surface modifications, the specific surface area increased and a nickel (Ni)-rich and Pd-rich layer was formed on the surface of HSA. The exchange current density i0 of HSA reached 176 mA g−1, which was two times higher than that of the as-cast HSA, and the apparent activation enthalpy of the modified alloy dropped down from 19.1 kJ mol−1 of the as-cast alloy to 14.2 kJ mol−1. The electrocatalytic ability of the optimized AFC HSA anode was found to be relatively good, with a current density of 50 mA cm−2 at 0.866 V (versus Hg/HgO) and a current density of 197 mA cm−2 at 0.5 V. The working stability of the HSA anode was also examined, where the degradation rate of anode potential was 0.26 mV h−1 in 200 h at a current density of 25 mA cm−2.