Rhodium and Nitrogen Codoped Graphene as a Bifunctional Electrocatalyst for the Oxygen Reduction Reaction and CO2 Reduction Reaction: Mechanism Insights

Developing cost-effective and highly active heteroatom-doped carbon-based bifunctional electrocatalysts for advanced energy conversion and storage devices has attracted worldwide attention. In this work, the reaction mechanisms for the oxygen reduction reaction and CO2 reduction reaction on rhodium and nitrogen codoped graphene, i.e., RhNx-Gra (x = 2-4), are studied using the density functional method. The calculated formation energies show that RhNx-Gra (x = 2-4) is thermodynamically stable. For the oxygen reduction reaction, the energy barriers are 1.08, 0.54, and 0.24 eV for RhNx-Gra (x = 2-4) in the rate determining step, respectively. Thus, RhNx-Gra (x = 3, 4) have lower energy barriers compared to 0,80 eV for pure Pt. The working potentials are calculated to be 0.33 and 0.34 V for RhNx-Gra (x = 3, 4), respectively. For the CO2 reduction reaction, CH4 is the preferred product for RhN2-Gra with the limiting potential of 0.71 V. HCHO and CH3OH are competitive products for RhN3-Gra and the limiting potentials are -0.60 and -0.68 V, respectively. For RhN4-Gra, HCOOH is the most favorable product with the limiting potential of -0.39 V and small overpotential of 0.14 V. These results suggest that RhNx-Gra (x = 2-4) have high catalytic activity and selectivity toward both the oxygen reduction reaction and CO2 reduction reaction, in particular, for RhNx-Gra (x = 3, 4).