A Computational Investigation Of Oxygen Reduction Reaction Mechanisms On Si- And Al-doped Graphene: A Comparative Study

Abstract

In this letter, the mechanisms of the oxygen reduction reaction (ORR) on Si- and Al-doped graphene have been investigated to understand the effect of doped graphene on the ORR and predict details of ORR pathways. Density functional theory (DFT) calculations were used to achieve the true mechanism pathways of ORR on the surfaces. Also, free energy diagrams for the ORR were constructed to provide the stability of possible intermediates in the electrochemical reaction pathways. At first stage, the adsorption of O2 molecule on both surfaces was studied with two possible configurations: atop (most stable) and bridge with the Eads of -60.6 and -72.4 kcal/mol, while for bridge site they were about -48.9 and -60.4 kcal/mol, respectively. Then, the most stable configuration (atop) was selected and the pathways formed after the adsorption of four atomic hydrogen to O2 molecule for both surfaces. These mechanisms were similar in both Si- and Al- doped graphene but there was a little difference in the obtained intermediates formed in each surface. In each pathway, the O2 dissociation reaction was neglected because it was unlikely to occur due to the high activation energy (> 45 kcal/mol). The results of this study show an easy and economic way to obtain Si- and Al-doped graphene as a non-metal catalyst for ORR at the cathode electrode in fuel cells. Copyright © 2015 VBRI Press.