Thermal integration of a metal hydride storage unit and a PEM fuel cell stack

A metal hydride (MH) storage unit and a polymer electrolyte membrane (PEM) fuel cell (FC) stack were thermally integrated through a common water circulation loop. The low temperature waste heat dissipated from the fuel cell stack was used to enhance and ensure the release of hydrogen from the storage unit. A water-heated MH-tank can be made more compact than an air-heated MH-tank with external heating fins, due to more direct heat transfer between MH-alloy and heating/cooling media. A water-heated MH-tank will therefore have the potential for better kinetics for absorption and desorption of hydrogen.The fuel cell stack and metal hydride storage unit were characterised and a control strategy was developed for fast start-up of the fuel cell stack. The main priority for the strategy was to maintain the metal hydride temperature at room temperature, while increasing the FC temperature to the specified operating temperature. The preferred strategy for this system was to increase the fuel cell temperature to at least 40 °C before starting to heat the metal hydride storage unit to 30 C. Without thermal integration, it was not possible to utilize the full hydrogen storage capacity of the metal hydride storage unit due to cooling of the tank.