The electrode characteristics and modified surface properties of V0.9Ti0.1 alloy sintered with Ni powder

Abstract

The V0.9Ti0.1 alloy absorbs a large amount of hydrogen, but it has never been used for the anode material for a NiMH battery due to the poor discharge behavior in KOH electrolyte. V0.9Ti0.1 alloy powder has been sintered with Ni powder to provide a catalytic effect on the absorption/desorption of hydrogen in KOH electrolyte. The optimal sintering condition was 5 min at 900°C and the amounts of Ni powder were varied to investigate the effects of surface modification on the discharge characteristics.All electrodes sintered with Ni powder were fully activated within 10 cycles in KOH electrolyte. The discharge capacities of the electrodes showed a maximum behavior with Ni content of the sintered alloy. The optimal amount of Ni powder showing the highest discharge capacity of 302 mA h g−1 was found to be 25 wt.%. From the results of the various analysis such as scanning electron microscopy (energy dispersive spectroscopy) and X-ray, it is found that VNi3 is formed during sintering. The VNi3 phase formed on the surface of V0.9Ti0.1 particles provides the optimum discharge capacity for the electrode. In accordance with the Brewer-Engel theory, VNi3 phases are found to be highly electrocatalytic, which is reflected in an increase of the exchange current density and a decrease of the discharging overpotential. In order to develop an anode material using metal hydride which has a large hydrogen storage capacity but is inactive for electrochemical hydrogenation, it has been suggested as a new process to modify the surface by sintering with Ni powder.