Mathematical modeling of heat and mass transfer in metal hydride hydrogen storage systems: A comprehensive review

Metal hydrides (MHs) are among the most promising materials for safe, compact, and reversible hydrogen storage, but their deployment is constrained by slow kinetics and thermal management challenges. Since MH performance is strongly governed by coupled heat and mass transfer processes, mathematical modeling has become essential for optimizing and designing storage systems. This review addresses a critical gap since the last comprehensive review in 2016 by synthesizing state-of-the-art mathematical modeling approaches for heat, mass, and momentum transfer in MH reactors. Starting from effective medium theory, we formulate macroscopic conservation equations and critically compare local thermal equilibrium (LTE) and non-equilibrium (LTNE) models. LTE models are computationally efficient but may underpredict wall heat fluxes, while LTNE models enhance accuracy at higher computational cost. We analyze empirical equilibrium pressure relations, reaction kinetics, reactor geometries, boundary conditions, and thermal management strategies, including phase change materials (PCMs) and heat transfer fluids (HTF). While metal foam integration can enhance charging rates by up to 65 %, phase change materials (PCMs) can reduce hydrogen absorption time by 60.2 % in metal hydride reactors. By consolidating theoretical and numerical perspectives, and comparing the trade-offs between various modeling approaches, this review identifies limitations and outlines future research directions to accelerate the design and deployment of efficient solid-state hydrogen storage technologies.