Thermodynamic evaluation of a PEMFC waste heat cascade utilization system considering the thermal management of the metal hydride hydrogen storage tank

This study proposes a proton exchange membrane fuel cell (PEMFC) waste-heat cascade utilization system considering the thermal management of a metal hydride hydrogen storage tank (MHT), aiming to improve the utilization efficiency of PEMFC waste heat while supporting integrated hydrogen supply. To address the mismatch in temperature level and heat flux between the PEMFC and the MHT, a thermoelectric generator (TEG) is introduced to establish a thermal coupling pathway. Through this coupling, the waste heat from the PEMFC is redistributed. Specifically, part of the heat is stably utilized to drive the endothermic hydrogen desorption process of the MHT via TEG coupling, while the remaining heat is directed to an organic Rankine cycle (ORC) for thermoelectric conversion. A coupled thermodynamic and exergy analysis model—including the PEMFC, ORC, TEG, and MHT—was established to evaluate the effects of current density, stack temperature, PEMFC cooling-water temperature difference, and MHT inlet cooling-water temperature. The results show that current density is the dominant factor influencing MHT desorption behavior, determining the desorption rate, duration, and heat demand; moderate increases in current density and stack temperature improve the power outputs of both the ORC and the TEG. Under typical operating conditions, the proposed system increases exergy efficiency by about 10% compared with a standalone PEMFC, achieving a maximum efficiency of 56.94%. These findings indicate that the system can not only effectively recover waste heat but also provide a stable heat source for MHT hydrogen desorption, offering valuable insights for the development of integrated PEMFC–metal hydride energy systems.