Hydrogen storage capacities in nanoporous M2(m-dobdc) metal-organic frameworks at near ambient temperatures

Green hydrogen presents a cleaner alternative to petroleum-based energy, with onboard storage challenges addressed by Metal-Organic frameworks (MOFs). This study evaluates M2(m- dobdc) MOFs (M = Mn, Fe, Co, and Ni) for H2-storage using Grand Canonical Monte Carlo simulations (GCMC) at five distinct temperatures (77 K, 160 K, 198 K, 233 K, and 298 K) and pressures 1–100 bar. The Fe2(m-dobdc) MOF achieves a promising volumetric H2 storage capacity of 51.2 g/L under cryogenic conditions, meeting the target of the Department of Energy, United States of America (USDOE), while the calculated value of the gravimetric uptake is 4.2 wt.%, which approaches to the USDOE 2025 target of 5.5 wt.%. M2(m-dobdc) MOFs series reflect exceptional volumetric uptake capacities at room temperature, ranging from 11.0-12.3 g/L, while gravimetric capacities are moderate, indicating key challenges in physisorption-based nanoporous materials when operating at ambient conditions. Density functional theory (DFT) calculations reveal the heat of H2 adsorption (Qst) ranging from -15 to -18 kJ/mol in this M2(m-dobdc) MOFs series, confirming the reversible physisorption phenomenon. Our results highlight the potential of M2(m-dobdc) MOFs for mobile H2-storage applications, with deliverable volumetric capacities ranging from 36.3 g/L to 40.8 g/L and gravimetric uptake ranging from 2.7 to 3.4 wt.% under a temperature-pressure swing range (77 K/100 bar to 160 K/5 bar). The present investigation indicates that the M2(m-dobdc) MOFs have shown the advances of the USDOE target and a promise to meet the practical onboard hydrogen storage requirements in automobile applications. Their balanced gravimetric-volumetric capacities make them promising candidates for near-future implementation in green energy systems.