Oxygen reduction reaction catalyzed by CN 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 CN 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 CN are thoroughly investigated. It is found that the electrochemical reduction of O proceeds via a direct four-electron mechanism on the P-modified CN. 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 HO 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.