This study aimed at improving the hydrogen storage capacities of mesoporous carbons by chemical modifications. The type of chemical specie was first investigated, using 5 mass% of nickel, copper, cobalt, iron, lithium, and lanthanum. Different experimental routes of incorporation of nickel were then compared.
Ordered mesoporous carbon (CMK-3) was used as the carbon support. Then, 5 wt% of doping chemical was introduced by incipient wetness impregnation. Isotherms of hydrogen adsorption were measured at 77 K and 298 K up to 8 MPa by a volumetric system. The results varied notably from one material to the other. At ambient temperature, the introduction of the above-listed species had positive influence on hydrogen storage, in comparison with pristine carbon. Particularly, nickel-doping increased hydrogen uptake by up to 18% at room temperature. Hydrogen spillover was enlightened as the additional adsorption mechanism that caused hydrogen storage enhancements.
Further investigations were conducted to optimize the dispersion of metal in the porosity of CMK-3. For that purpose, three different experimental routes were used to incorporate nickel into the carbon material, namely, incipient wetness impregnation, impregnation in ethanol followed by sonication, and also by adding the metal salt during the synthesis of the ordered mesoporous carbon. Hydrogen isotherms were measured at 77K and 298K and up to 8 MPa. The results showed that hydrogen was adsorbed in larger amounts at 298 K with the impregnation methods. Therefore, hydrogen spillover was shown to be only possible with an active (i.e. accessible) metal surface.