The Role of Transition Metal Doping in Enhancing Hydrogen Storage Capacity in Porous Carbon Materials

Porous carbon materials with high specific surface area are potential hydrogen storage materials. However, due to the weak van der Waals forces between the material and H2, hydrogen can generally be stored only at a cryogenic temperature under high hydrogen pressure. To solve this problem, in this work, ZIF-8-derived porous carbon material (PCM) modified with transition metals (PCM-TMs, TM: Mn, Fe, Ni) was prepared to investigate the role of TM doping. The developed PCM-TMs have a high specific surface area (up to 1363 m2/g) and pore volume (up to 0.89 cm3/g). Experimental results show that PCM-TMs exhibit higher hydrogen storage capacity, usable capacity, and hydrogen uptake capacity per specific surface area compared to PCM. In addition, PCM-TMs have a higher isosteric heat of adsorption (Qst) than PCM, which suggests that TM doping enhances the interaction between H2 and carbon materials. Theoretical calculations further indicate that this interaction is a nearly weak chemisorption force (~9.27kJ/mol). Notably, Mn-doped porous carbon material (PCM-Mn) exhibits a hydrogen storage capacity of ~3.45wt.% (20.44g/L) at 77K under 35 bar-H2. Even at 253K under 50 bar-H2, the capacity can reach ~1.41wt.% (8.34g/L). The hydrogen uptake capacity per specific surface area for PCM-Mn reaches 1.03×10-3wt.% / m2·g-1 at 253K under 50 bar-H2, which is 1.5 times larger than that of PCM. Under proper operating conditions, such as loading at 77K and 35 bar-H2, and discharging at 253K and 2 bar-H2, PCM-Mn can achieve a usable capacity of at least 19.30g/L. The hydrogenation kinetics curves reveal that PCM-Mn can store 1.39wt.%-H2 (8.25g/L) under 12MPa H2 at 298K, while it is only 0.88wt.% (5.53g/L) for PCM at the same condition. This work provides valuable insight into improving the hydrogen storage performance of hydrogen storage materials of physisorption. [Display omitted] •Transition metals (TMs) doping can significantly strengthen the interaction between carbon materials and H2.•The interaction is close to weak chemisorption (theoretically calculated value of 9.27kJ/mol).•The hydrogen storage capacity, usable capacity, and H2 adsorption capacity per SSA can be increased by TMs doping.•PCM-Mn can store ~3.45wt.% -H2 (20.44g/L) at 77K and 35 bar-H2, and remain 1.34wt.% (8.25g/L) even at 298K and 13MPa.•If loading at 77K and 35 bar-H2, and discharging at 253K and 2 bar-H2, PCM-Mn can achieve a usable capacity of 19.30g/L.