Study on the correlation between the microstructure, electrochemical performance and electrocatalytic performance of BH4− in La–Mg/Y–Ni hydrogen storage alloys

Abstract

Direct borohydride fuel cells (DBFC) are favored by researchers because of their advantages of high potential, high power density and safety. However, in the actual application process of the DBFC, when BH₄⁻ in borohydride fuel oxidizes under the action of the anode catalyst, a hydrolysis side reaction occurs, which will produce a lot of hydrogen and reduce the fuel efficiency. The hydrogen storage alloy has the ability to absorb and release hydrogen, which can inhibit hydrolysis and improve fuel conversion as an anode catalyst. However, the ability of hydrogen storage alloy to inhibit hydrolysis is closely related to the electrochemical properties of hydrogen storage alloy. In order to study the relationship between electrochemical properties and catalytic properties of hydrogen storage alloy, La–Mg/Y–Ni hydrogen storage alloy with a superlattice structure of Mg and Y instead of La was designed. Alloy composition for La_0.75Mg_0.25Ni_2.485Co_0.525Mn_0.28Al_0.21 (Mg alloy), La_0.3Mg_0.25Y_0.45Ni_2.485Co_0.525Mn_0.28Al_0.21 (Mg–Y alloy) and La_0.3 Y_0.7Ni_2.485Co_0.525Mn_0.28Al_0.21 alloy (Y alloy) of three kinds of hydrogen storage alloys were prepared. It was found that all three alloys had a multiphase structure. Among them, Mg–Y alloy shows a more refined microstructure. And Mg–Y alloy has the best high rate discharge performance at 600 mA/g current density and hydrogen diffusion coefficient. At the same time, when Mg–Y alloy is used as an anode catalyst, the number of transferred electrons is the highest, which is 1.440. The refined microstructure of Mg–Y alloy determines its optimal hydrogen diffusion ability, and the optimal hydrogen diffusion ability in turn promotes its excellent catalytic performance for BH₄⁻.