Development of hydrogen storage for fuel cell generators II: utilization of calcium hydride and lithium hydride

The feasibility of using calcium hydride or lithium hydride as a hydrogen storage system for alkaline fuel cells was investigated. Both materials can provide hydrogen at a rate required for a 1 kW unit using water vapour as the reactant. The hydrogen production reaction was found to be first order with respect to water vapour pressure over the temperature range 0–60°C. Control of the H2 generation rate can be achieved by limiting the water vapour access to the hydride or by limiting the saturated water vapour pressure by electrolyte concentration. Some additional degree of control of the production rate is possible by using specific hydride morphologies. Modelling of the hydrogen generation was carried out using a diffusion limited rate determining step and by estimating boundary layer thicknesses and effective diffusivities. The exothermic behaviour of the hydrolysis reaction can cause significant temperature excursions within the hydride bed.