Sodium alanate hydrogen storage system for automotive fuel cells

Suitability of Ti-catalyzed sodium alanate as a reversible hydrogen storage system for automotive poly mer-electrolyte fuel cells has been assessed under the constraint that it must meet certain performance criteria with respect to the amount of recoverable H-2 needed for vehicle driving range, minimum full-flow of H-2 needed to satisfy vehicular power demands, maximum refueling time and minimum H-2 delivery pressure. It is assumed that the thermal energy for desorbing hydrogen is supplied by the fluid that cools the high-temperature membrane fuel cell stack operating at 120 degrees C. It is found that a ten-fold enhancement in published desorption kinetics is needed to attain 90% reversible H-2 storage capacity while satisfying the minimum full-flow requirement of 0.02g H-2/kWe. The catalyzed medium needs a metal foam support to facilitate heat removal necessary for 0.5-1.5 kg/min H-2 refueling rate. The faster the refueling rate, the higher is the peak heat transfer rate and the lower is the amount of recoverable H-2. For a system with 5.6 kg recoverable H-2, the peak heat transfer rate during refueling can exceed 1 MW. The overall specific energy and energy density of the storage medium are functions of the packing density of the metal hydride powder. The minimum acceptable hydrogen delivery pressure from the storage device determines the hydrogen storage capacity but otherwise has small influence on sorption kinetics. Published by Elsevier Ltd on behalf of the International Association for Hydrogen Energy.