The surface structure and the electrochemical properties of hydrogen-absorbing alloys treated with an HCl aqueous solution

The surface structure and the electrochemical properties of hydrogen-absorbing alloys treated with an HCl aqueous solution were investigated. This process was observed to form a porous layer rich in nickel on the alloy surface because HCl partially dissolved some of the other elements from the alloy. Therefore, the discharge capacity increased by increasing the reaction surface area. However, the overvoltage of an excessively treated alloy increased along with the depth of discharge as the surface layer of the alloy oxidized and thickened. The effects of treatment on alloys were found to be determined by the hydrogen ion amounts in the acid solution per unit mass of the alloy, regardless of the concentration and volume of the solution. The optimal hydrogen ion amount for a treatment solution was found to be 0.1 mol/kg.