Production and physical-chemical characterization of walnut shell-derived activated carbons for hydrogen storage application

A series of activated carbons have been produced from walnut shells by pyrolysis and physical activation in an oxidizing atmosphere. The effects of the activation time on the porosity formation and physicochemical characteristics, then hydrogen storage properties, were investigated. The synthesized samples reveal highly microporous structures with large specific surface area values that strongly influence the hydrogen adsorption capacity. The highest values of specific surface area (1163 m2 /g), total pore volume (0.491 cm3 /g), and micropore volume (0.450 cm3 /g) were obtained with an activation time of 90 min, allowing hydrogen uptake at 77 K of 1.7 and 2.6 wt% at a pressure of 1 and 80 bar respectively. Adsorption-desorption cycles were performed to test the reversibility and reproducibility of the process. The results confirm the key role of ultra-micropores (<0.7 nm) and suggest walnut shell-derived activated carbons as promising and cost-effective materials for hydrogen storage.