Potential Effects in Electrochemical Oxidation of Carbon Monoxide Catalyzed by Rh-N-Doped Graphene

In this work, the electrochemical CO oxidation (CO-OR) reaction catalyzed by Rh-N-doped graphene (Rh-N₄-C) was studied via first-principles calculations with both the fix potential method (FPM) and the charge neutral method (CNM). The commonly used CNM assumes a zero net charge in the system and ignores the effect of the applied potential to the total charge, which could be important in real electrochemical reactions, while FPM includes such fixed potential effects by automatically adjusting the total charge of the system to match the applied electrode potential. We made a comprehensive comparison between these two methods to explore the fixed potential effects in the CO-OR reaction. Both methods predicted that Rh-N₄-C has a relatively low overpotential for the CO-OR, smaller than that of the Pt electrode. It is found that the molecule adsorption energy can be effectively modified by the applied voltage, instead of being a constant with the CNM. The fix potential effects on the reaction energy are analyzed and the observed trends can be well understood by a capacitor model. The difference in the potential of zero charge before and after a reaction step is found to play a key role in determining the potential effects. These results could be helpful to the design of catalysts for CO oxidation, as well as to the understanding of the potential effects on the catalytic process in real electrochemical reactions.