Effect of Metal Modification of Activated Carbon on the Hydrogen Adsorption Capacity

This study investigates the hydrogen adsorption performance of activated carbon (AC) derived from rice husks and modified with magnesium and nickel salts. Adsorption isotherms were recorded at 25 °C and 50 °C up to 80 bar, simulating practical storage conditions. The unmodified AC exhibited the highest hydrogen uptake (0.62 wt% at 25 °C), attributed to its high surface area and dominant ultramicroporosity (<0.9 nm). Modifications with Mg and Ni reduced adsorption capacity, likely due to partial pore blockage and decreased surface functionality, as confirmed by FTIR, Raman, and XRD analyses. Despite this, all samples demonstrated stable cyclic adsorption-desorption behavior and consistent isotherm profiles. Hysteresis observed in the modified samples suggests capillary condensation within mesopores. Thermodynamic analysis confirmed the exothermic nature of hydrogen adsorption. Among the modified materials, ACM10 (Mg-modified) exhibited the best performance (0.54 wt%), highlighting the importance of optimizing the metal content. The obtained results indicate that the micropore size distribution and accessible surface functionality critically govern the hydrogen storage capacity, suggesting that unmodified AC is a promising candidate for low-temperature hydrogen storage systems.