Single Si-Doped Graphene as a Catalyst in Oxygen Reduction Reactions: An In Silico Study

Single Si-doped graphene C53H18Si with one carbon atom replaced by a three-coordinate silicon atom is studied by density functional theory (DFT) calculations as a catalyst for the oxygen reduction reactions (ORRs) in both acidic and alkaline media. The active sites for oxygen adsorption were determined from the distribution of the charge density difference analysis. At the equilibrium electrode potential, the most stable intermediate was found to have the structure HO*O*-C53H18Si with both oxygen atoms bound to the support, one of them being incorporated in between Si and C atoms, corresponding to the transfer of one hydrogen atom [H+ + e-]. The 2e ORR mechanism is shown to be very unlikely because the alternative 4e ORR pathway occurring via intermediates with a broken O-O bond is much more exothermic. In addition to the commonly adopted ORR mechanism, new reaction pathways have been discovered and shown to be potentially preferable over the traditional mechanism. The new proposed four-electron ORR route was predicted to proceed spontaneously in acidic media at U < 0.99 V and in alkaline media at U < 0.22.