Electrochemical activation and electrocatalitic enhancement of a hydride-forming metal alloy surface-modified with Palladium, Platinum and Nickel

A. VISINTIN; B. CASTRO; S. REAL; C. WANG; M. SORIAGA

Tesalónica, Grecia

Congreso; 55rd ISE Annual Meeting; 2004

ISE

Recently, metal hydride (MHx) electrode materials used for Ni-metal hydride (Ni-MHx) secondary batteries have been studied thoroughly due to their high capacity, high rate of dischargeability, good cycling property and environmental compatibility. The activation of the alloy plays a key role in the electrodic process, since it defines the reaction rate of the hydride formation. During activation, several different processes occur, such as: i) reduction or change of the composition of the surface oxides that interfere with hydrogen, ii) reduction of particle size due to cracks produced by the volume increase, iii) changes in the chemical composition and/ or surface structure of the metal. The interest of this work is focused in the improvement of the properties of metallic alloys related to hydride formation in alkaline solutions. The effect of the addition of different metallic powders, to alloys of the AB5 type, was studied. The influence of Pt, Pd and Ni powders, on charge -discharge cycling, is presented. It was determined that the process of activation of the alloy is notably enhanced by the addition of the metallic powders. During the successive charge-discharge cycles, the capacity of the alloy increases and the overpotential diminishes, due to physicochemical changes in the reaction interface. The improvement of the activation process and of the electrocatalitic properties, due to the metallic additives, follows the order: Pt>Pd>Ni> No catalyst. The behaviour of the metal hydride electrode and the effect of the different metallic additives is anlysed in terms of a physicochemical model which has been validated by electrochemical impedance spectroscopy (EIS) measurements.