Activated carbon with optimum pore size distribution for hydrogen storage

A series of nitrogen containing activated carbons (NAC-1.5-y) with surface areas and pore volumes in the range of 526-2386 m2/g and 0.26-1.16 cm3/g, respectively were prepared by treatment of a nitrogen-rich carbon with KOH (KOH to carbon weight ratio = 1.5) at different temperatures (y) in the range of 550-700 °C. The prepared samples were used to delineate the role of pore sizes and nitrogen content in hydrogen adsorption at 77 K. The activated carbons showed high hydrogen uptake, due to increased porosity (>0.364 nm). The optimized carbon material NAC-1.5-600, with high nitrogen content (22.3 wt%) and large volume of ultra-micropore centered at 0.59 nm in size, showed hydrogen uptake of 2.94 wt% at 77 K and 1 bar. The adsorption capacity was found to be linearly dependent on ultra-micropore volume (0.5-0.7 nm), but not linearly associated with the total surface area nor the total pore volume. Nonetheless, the surface area of larger pore material (NAC-1.5-700) was found to be favorable for hydrogen adsorption at high partial pressure. The data obtained indicated that the occurrence of nitrogen, oxygen and hydrogen-containing species has hardly any effect on hydrogen uptake at 77 K.