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

摘要

Electrochemical properties of hydrogen storage alloy (HSA) MlNi_(3.65)Co_(0.85)Al_(0.3)Mn_(0.3) 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 I_0 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 19.1kJ mol~(-1) of the as-cast alloy to 14.2kJ 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 0.26mVh~(-1) in 200h at a current density of 25mAcm~(-2).