Combined experimental and simulation study on H2 storage in oxygen and nitrogen co-doped activated carbon derived from biomass waste: superior pore size and surface chemistry development

In this study, heteroatom (O, N)-doped activated carbon (AC) is produced using urea and KOH activation from abundant and cost-effective biomass waste for H2 storage. The O and N co-doped AC exhibits the highest specific surface area and H2 storage capacity (2.62 wt%), increasing by 47% from unmodified AC at -196 °C and 1 bar. Surface modification helps develop superior pore sizes and volumes. However, the original AC is superior at lower pressures (<0.3 bar) because of its suitable pore width. This observation is then explained by molecular simulations. Optimal pore widths are 0.65 nm at <0.3 bar and 0.95-1.5 nm at pressures in moderate range (0.3-15 bar). Superior pore sizes are observed in the range of 0.8-1.3 nm at 1 bar, enhancing performance with co-doped AC to achieve uptake superior to that of other ACs described in the literature. However, above 15 bar, pore volume dominates capacity over pore width. Among the O and N groups, pyridinic-N oxide is the most substantial, playing a vital role at low and moderate pressures. These findings propose a strategy for superior H2 storage in porous carbons under various pressure conditions.