Hydrogen adsorption on activated carbons prepared from olive waste: effect of activation conditions on uptakes and adsorption energies

Two series of activated carbon samples have been prepared from olive waste, using ZnCl2 and H3PO4 as chemical activation agents. The porous structure characteristics of all samples are determined by nitrogen adsorption at −196 °C. Hydrogen adsorption at −196 °C is followed using both manometry and calorimetry. The results show that the highest areas are observed for the samples prepared with larger diameter of precursors and that the hydrogen uptake is strongly influenced by the available BET area. Furthermore, the adsorption energies do not vary significantly for any activation protocol and therefore seem to play only a minor role to the hydrogen adsorption behavior. However, the chemical activation does have a strong role on hydrogen uptake. Samples prepared with H3PO4 show a greater hydrogen uptake per unit area such that comparable uptakes are observed for the samples prepared with larger diameter of precursor even though the sample prepared with ZnCl2 shows a 30 % higher BET area. This work highlights the non-trivial role of each activation protocol on hydrogen uptake.