Power vs. capacity performances of thermally integrated MH-PCM hydrogen storage solutions: current status and development perspectives

The present work focuses on two particular performance indicators for hydrogen storage solutions based on the thermal integration of metal hydrides (MH) with phase-change materials (PCMs): i) the (specific) discharge power and ii) the system-level volumetric capacity. The paper first condenses available literature data from modelling and experimental activities, and then analyses a basic numerical benchmark of a low-temperature MH-PCM system. Findings from the literature review show that, due to the interrelation between efficient thermal management and hydrogen desorption rate, the selected performance indicators are not independent one from another. It is also confirmed that simultaneously achieving high-power (flexibility) and specific capacity (compactness) is a challenging goal for such kind of hydrogen storage systems. The parametric analysis of the numerical benchmark system suggests that, for a given MH operating pressure-temperature envelope, special care should be given in the PCM accurate characterisation and selection, as well as in the quantification of the optimal trade-off between the PCM volume and desorption kinetics performance. Furthermore it is found that the geometrical distribution of the MH and PCM volumes have a larger than expected impact on the specific discharge power.