The difference in the improvement of electrochemical hydrogen storage performance between two methods of coating copper on the surface of Co2B alloy

Abstract

The Co2B hydrogen storage alloy is synthetized by high temperature solid phase process. Copper coated Co2B alloys are prepared by ball milling and element replacement reaction respectively. The structural features of Co2B alloys and copper coated alloys are investigated using XRD and SEM analysis. It can be found that the surface of the material obtained by the element displacement reaction is coated with more copper than the material obtained by mechanical alloying process. The electrochemical hydrogen storage performance of the copper coated alloy electrodes is measured at 303 K. At initial cycle, copper coated Co2B alloy electrodes exceed the raw Co2B alloy in discharge capacity. The alloy obtained by element replacement reaction has the highest capacity of 718.4 mAh/g, what’s more, the cycle life of copper coated Co2B alloy electrodes is higher than that of raw Co2B alloy. The capacity retention ratio and charge-transfer resistance (Rct) of the copper covered Co2B alloy electrodes decrease because of copper coating. The excellent electrochemical hydrogen storage performance of two copper coated Co2B alloy electrodes can be put down to the addition of copper, which increases the conductivity of the alloy electrode and reduce the area of the alloy electrode exposed to the electrolyte, slows down the oxidation of boron and its dissolution into the electrolyte. Copper coated on the surface of the alloy plays a favorable effect on electrochemical properties of Co2B alloy. The displacement reaction method is better than the ball-milling method in coating the surface of Co2B alloy to improve its electrochemical hydrogen storage performance.