Open-cathode PEMFC heat utilisation to enhance hydrogen supply rate of metal hydride canisters

Abstract

In this paper, the hydrogen supply to an open-cathode PEM fuel cell (FC) by using metal hydride (MH) storage and thermal coupling between these two components are investigated theoretically. One of the challenges in using MH hydrogen storage canisters is their limited hydrogen supply rate as the hydrogen release from MH is an endothermic reaction. Therefore, in order to meet the required hydrogen supply rate, high amounts of MH should be employed that usually suggests storage of hydrogen to be higher than necessary for the application, adding to the size, weight and cost of the system. On the other hand, the exhaust heat (i.e. that is usually wasted if not utilised for this purpose) from open-cathode FCs is a low-grade heat. However, this heat can be transferred to MH canisters through convection to heat them up and increase their hydrogen release rate. A mathematical model is used to simulate the heat transfer between PEMFC exhaust heat and MH storage. This enables the prediction of the required MH for different FC power levels with and without heat supply to the MH storage. A 2.5-kW open-cathode FC is used to measure the exhaust air temperature at different output powers. It was found that in the absence of heat supply from the FC to the MH canisters, significantly higher number of MH canisters are required to achieve the required rate of hydrogen supply to the FC for sustained operation (specially at high power outputs). However, using the exhaust hot air from the FC to supply heat to the MH storage, can reduce the number of the MH canisters required by around 40% to 70% for power output levels ranging from 500 W to 2000 W.