Oxygen reduction reaction catalyzed by C₂N nanosheet doped with a phosphorous atom: Insights from DFT calculations

Oxygen reduction reaction (ORR) is among the most key processes in energy conversion and storage devices like fuel cells (FCs) and batteries. Nevertheless, the slow kinetics of the ORR at the cathode electrode remains as an important challenge. In the present study, phosphorus (P)-doped C₂N monolayer is proposed as an effective and platinum-free electrocatalyst for the ORR in an acidic medium using first-principles calculations. The computed adsorption energies and charge transfers indicate that the catalytic process occurs at the P atom. Different ORR mechanisms on the P-embedded C₂N are thoroughly investigated. It is found that the electrochemical reduction of O₂ proceeds via a direct four-electron mechanism on the P-modified C₂N. Also, the ORR process on this electrocatalyst can involve both hydrogenation and dissociation pathways to yield two water molecules. Results indicate that the rate-determining step for both pathways is the generation of the first H₂O molecule, requiring an activation energy of 1.12 (dissociation) and 1.21 eV (hydrogenation). The findings presented in this study might be important for the practical development of novel and low-priced metal-free electrocatalysts in FCs.