Integrating Metal Hydride‐Based Hydrogen Storage Tanks With PEM Fuel Cell Stacks for Enhanced Energy Efficiency in Underwater Applications

ABSTRACT This study presents a comprehensive modeling and integration approach for coupling metal hydride‐based hydrogen storage systems with PEM fuel cell stacks, specifically tailored for high‐demand underwater applications. The focus is on optimizing the hydrogen desorption process from LaNi 5 ‐based metal hydride tanks by utilizing waste heat from PEM fuel cells. A 360 kW PEM fuel cell system, comprising six 60 kW stacks, is designed, with hydrogen flow rate requirements calculated based on stack parameters and operating conditions. The effect of varying voltage, current density, and cell count on hydrogen consumption and waste heat generation is analyzed across five case scenarios. Results show that, for a single 60 kW PEM fuel cell stack, reducing the cell voltage from 0.60 to 0.50 V increases hydrogen demand from 3.82 to 4.57 kg/h, while fuel cell heat generation rises significantly from 78.1 to 98.9 kW, corresponding to an increase of over 30%. For the 360 kW MH–PEMFC integrated overall system operating at 0.60 V, a total hydrogen consumption of 22.9 kg/h is obtained, with a fuel cell efficiency of 43.4% and an overall system efficiency of 70.9%, and the thermal coupling ratio is 0.48. These results highlight the trade‐off between operating voltage, thermal load, and system efficiency in PEM fuel cell systems. To address the resulting thermal loads, a seawater‐compatible two‐stage heat exchanger configuration is proposed to manage the thermal needs of both hydrogen desorption and fuel cell cooling under underwater conditions. A complete process flow diagram is developed to illustrate the system's hydrogen, oxygen, heat, and water flows, emphasizing modularity, redundancy, and adaptability. The findings demonstrate that integrated heat recovery from fuel cells can effectively sustain hydrogen desorption while enhancing system reliability and efficiency in submarine energy storage applications.