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

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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 CO 2 reduction reaction on rhodium and nitrogen codoped graphene, i.e., RhN x -Gra ( x = 2–4), are studied using the density functional method. The calculated formation energies show that RhN x -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 RhN x -Gra ( x = 2–4) in the rate-determining step, respectively. Thus, RhN x -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 RhN x -Gra ( x = 3, 4), respectively. For the CO 2 reduction reaction, CH 4 is the preferred product for RhN 2 -Gra with the limiting potential of −0.71 V. HCHO and CH 3 OH are competitive products for RhN 3 -Gra and the limiting potentials are −0.60 and −0.68 V, respectively. For RhN 4 -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 RhN x -Gra ( x = 2–4) have high catalytic activity and selectivity toward both the oxygen reduction reaction and CO 2 reduction reaction, in particular, for RhN x -Gra ( x = 3, 4).