Simulation and analysis of hydrogen desorption dynamics in a PEMFC-metal hydride system for H-bike

The hydrogen desorption dynamics of a metal hydride (MH) tank thermally coupled with a proton exchange membrane fuel cell (PEMFC) for hydrogen-powered assistant bicycle (H-bike) applications were examined. A multiphysics simulation model was created to incorporate temperature distribution, pressure changes under flow-limited conditions, and desorption reaction kinetics. The model was validated through experimental comparisons of internal temperature, tank pressure, and hydrogen flow rate, showing strong agreement with the measured results. The simulation showed that radial temperature gradients, resulting from the low thermal conductivity of MH materials, influenced local desorption rates. Additionally, pressure differentials between the tank and equilibrium pressures were found to be crucial, especially under restricted flow conditions. Furthermore, the benefit of PEMFC exhaust heat recovery was quantified. Utilizing the exhaust heat from a PEMFC operating at 65 W increased hydrogen release by 14.7 times compared to natural convection. The recovered heat corresponds to an average absorbed thermal power of approximately 10.4 W, equivalent to 9.78% of the total chemical energy content of the released hydrogen. These findings highlight the potential of recovering PEMFC exhaust heat to enhance hydrogen desorption efficiency in PEMFC-MH systems, without requiring additional energy input, thereby providing a compact and efficient solution for mobile fuel cell applications.