The catalytic oxidation properties for BH4− and electrochemical properties of the Ag-decorated AB5-type hydrogen storage alloy

Abstract

Anode catalysts for direct borohydride fuel cells (DBFCs) are one of the key factors controlling the performance of such cells. Hydrogen storage alloys are efficient and inexpensive DBFC anode catalysts. However, when hydrogen storage alloys are used as DBFC anode catalysts, their catalytic oxidation capacity is weakened due to their easy passivation in alkaline electrolytes. In order to improve the catalytic oxidation ability of AB5-type hydrogen storage alloy, Ag-decorated AB5-type alloy catalysts with different Ag contents were prepared by vibration ball milling method in this study. The microstructures, catalytic properties on BH4− and electrochemical properties of pure Ag, AB5-type and Ag-decorated AB5-type alloy samples were studied in detail. The results show that the Ag-decorated AB5-type alloys are composed of a single LaNi5 phase. Some of Ag powders cover the surface of the AB5-type alloy particles. Among the Ag-decorated AB5-type alloys, the Ag-decorated AB5-type alloy with an Ag content of 2 wt.% exhibits the best electrochemical performance and catalytic performance for BH4−. Its maximum discharge time in 6 M KOH solution is 303 min, which is 43 min longer than that of the AB5-type alloy. The number of electrons transferred by the Ag-decorated AB5-type alloy with 2 wt.% is the largest, reaching 1.45. The improvement of the electrochemical and catalytic properties of the alloy is mainly attributed to the proper Ag powders coating on the surface of the AB5-type alloy particles, which protects the electrode from oxidation and corrosion, and enhances the conductivity of the alloy electrode.