A density functional theory study on 3d metal/graphene for the removal of CO from H2 feed gas in hydrogen fuel cells

Abstract

Metal/graphene has been used as a filter membrane exterior to the hydrogen fuel cell to prevent CO poisoning. The removal of CO from H₂ feed gas is important for efficient use of the anode catalyst and would increase the lifetime of the fuel cells. In this work, the adsorptions of CO and H₂ on metal/perfect-graphene (M/G_p) and metal/defect-graphene (M/G_d) (M = Sc–Zn) are investigated using density functional theory. Our results indicated that the defect sites in graphene enhance the stability of metal on the graphene surface compared to perfect graphene. For gas molecule adsorption, however, CO and H₂ adsorption is weaker on defective graphene compared with the perfect material, due to the more localized metal d electrons in the former case. For both defective and perfect graphene, Fe/G_p(d), Co/G_p(d) and Ni/G_p(d) are more effective in separating CO from H₂ feed gas, particularly for perfect graphene. Orbital analysis suggested that the d_yz and/or d_xz orbitals of metal atoms play a major role in CO and H₂ adsorption.