Adsorption equilibrium of hydrogen adsorption on activated carbon, multi-walled carbon nanotubes and graphene sheets

Abstract

For obtaining the technical data to develop storage medium with appropriate structure for hydrogen storage system, behavior of hydrogen adsorption on carbon based adsorbents with different micro structures was comparatively studied. Activated carbon (SAC-02), multi-walled carbon nanotubes (MWCNTs) and graphene sheets (GS), which respectively have a specific surface area about 1916 m2/g, 155 m2/g and 221 m2/g, were selected to test adsorption equilibrium at temperature from 77.15 K to 113.15 K and pressure up to 6 MPa. Toth equation was applied to estimate the absolute adsorption amounts, and isosteric heat and limit isosteric heat of hydrogen adsorption were used to investigate the influence of structures variation for hydrogen storage. This study shows that the GS exhibits a higher potential in hydrogen storage though it is a mesoporous adsorbent, and the relative errors of predicted results from Toth equation were less than 2.1%, The value of the isosteric heat of hydrogen adsorption on GS is about 4.01–5.88 kJ/mol, which is higher than 3.67–3.96 kJ/mol for hydrogen adsorption on the SAC-02 and 2.47–4.36 kJ/mol for hydrogen adsorption on the MWCNTs, respectively. It also reveals that adsorbents with fold structure would be more beneficial to adsorbing hydrogen than the adsorbents with pore structure or flat plane, and a higher specific surface area is necessary when the GS was applied to hydrogen storage system.