Preparation and Hydrogen Absorption Kinetics Study of Hybrid Molding Metal Hydride Beds

Hydrogen absorption kinetics in metal hydride beds is constrained by coupled heat and mass transfer, which often leads to a slow refueling response and reduced storage system efficiency. In this work, hybrid molding by mixing silicone gel with various thermally conductive additives was used to prepare TiMn-based metal hydride beds with tailored porosity and thermal conductivity. Three experimental groups were prepared: 5 wt.% silicone gel and 5 wt.% single-walled carbon nanotubes (Group A), 5 wt.% silicone gel only (Group B), and 5 wt.% silicone gel and 5 wt.% silicone sheets (Group C). Hydrogen absorption kinetics at 30 °C and 50 bar were measured experimentally and simulated using a coupled heat-mass transfer model in COMSOL Multiphysics. The physical property results showed that Group A exhibited approximately threefold higher porosity (0.527) compared with the other two groups, while its thermal conductivity (2.476 W·m−1·K−1) was the lowest among them (3.189 W·m−1·K−1 for Group B and 3.246 W·m−1·K−1 for Group C). These property differences led to distinct hydrogen absorption rate-limiting behaviors. Group A dominated in the diffusion-controlled stage (hydrogen uptake between 0.5 and 1.15 wt.%) due to enhanced hydrogen transport through its macroporous network, while Group C exhibited faster kinetics in the later stage (above 1.15 wt.%), where thermal conductivity governed the absorption driving force. Numerical simulations reproduced the experimental kinetic curves and confirmed the transition of rate-limiting mechanisms. This work reveals that the rate-limiting factors of hydrogen absorption in hybrid molding hydride beds vary across different stages, and that independent optimization of porosity and thermal conductivity is required to achieve rapid kinetics across the entire absorption process.