ELECTROCATALYTIC HYDRIDE-FORMING COMPOUNDS FOR RECHARGEABLE BATTERIES

A new class of highly electroactive hydride-forming compounds is described as well as simple metallurgical methods of producing these materials. The new type of metal alloys consist of two different crystallographic phases. The bulk phase is responsible for hydrogen storage and is formed by the stable multicomponent "standard alloy" of the AB5 type. The second phase homogeneously decorates the surface of the bulk phase and ensures a high electrocatalytic activity. In composing this second phase no precious metals are required, but carefully selected combinations of transition metals can be used. Very high overall exchange currents and discharge efficiencies are obtained, even at low temperatures. Cycle life and storage capacities are comparable with the values found for the standard alloy. Substituting small amounts of B-metals with highly electrocatalytic elements was also found to be effective in improving the electroactivity of AB5 compounds. However, a drawback of this method is that significant improvements are obtained only when precious metals are incorporated. Double-phase materials must therefore be considered as more serious candidates for use in future nickel/metal-hydride batteries with high charge/discharge capability.