Mechanistic insights into hydrogen storage in MoSe₂-Ni(OH)₂-g-C₃N₄ via optimized weak chemisorption

In this work, a series of MoSe₂-Ni(OH)₂-g-C₃N₄ (MNG) composites were synthesized via a combination of hydrothermal and wet-impregnation methods and systematically studied for their hydrogen storage capacity under moderate conditions. Hydrogen desorption results show that pristine MoSe₂ and Ni(OH)₂ exhibit the lowest performance, releasing respectively 0.8 and 0.3 wt% H₂ at 423 K. Incorporation of g-C₃N₄ significantly improves performance with capacities rising to 2.1 wt% (MNG5), 3.0 wt% (MNG25) and 2.5 wt% (MNG50). MNG25 shows the best performance, desorbing 3.2 wt% H₂ at 473 K within 60 min under isothermal conditions, achieving nearly four fold enhancement over pristine samples. Upon hydrogenation under moderate conditions, the MNG composites exhibit significant desorption capacity and kinetics, demonstrating the strong effect of elevated activation temperature. DTG desorption profiles further confirm the storage improvement across MNG compositions, the main desorption peak shifts from 435 K (MoSe₂) to 418–416 K for MNG compositions. Kinetic analysis supports these trends, showing a reduction in activation energy from 34.2 kJ/mol (binding energy 32.9 kJ/mol) for MoSe₂ to 26.9 kJ/mol (binding energy 26.9 kJ/mol) for the most active MNG composite. These results highlight the interaction among g-C₃N₄, Ni(OH)_2, and MoSe₂, which promotes strong physisorption with optimized weak chemisorption assistance, leading to accelerated kinetics, reduced desorption temperatures, and superior hydrogen storage capability.