Theoretical screening of highly efficient multifunctional single-atom catalysts supported by pc-C3N2 monolayers for the electrocatalytic HER, OER and ORR

Abstract

Exploring highly efficient, stable, and low-cost multifunctional electrocatalysts for the hydrogen evolution reaction (HER), oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is of great significance for overall water splitting and rechargeable metal–air batteries. In this work, a series of single transition metal (TM = Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Os, Ir, Pt, and Au) atoms anchored on the cavities of 2D phthalo-carbonitride (pc-C₃N₂) monolayers (TM@C₃N₂) as single-atom catalysts (SACs) were systematically investigated for their HER, OER, and ORR performance through first-principles calculations. The results indicate that TM@C₃N₂ SACs show excellent thermodynamic and electrochemical stability as well as good electrical conductivity. Among these candidates, Co@C₃N₂ and Rh@C₃N₂ are predicted to be the promising HER/OER bifunctional electrocatalysts for overall water splitting with a lower hydrogen adsorption Gibbs free energy (ΔG_H*) of −0.12 to −0.19 eV and an OER overpotential of 0.38–0.50 V. However, Co@C₃N₂, Ni@C₃N₂, Rh@C₃N₂ and Ir@C₃N₂ are potential OER/ORR bifunctional electrocatalysts for rechargeable metal–air batteries with ultralow OER overpotentials of 0.31–0.50 V and ORR overpotentials of 0.24–0.63 V. In addition, Rh@C₃N₂ is a promising trifunctional electrocatalyst for the HER/OER/ORR with relatively low overpotentials. The electronic origin of the enhanced HER/OER/ORR activity of TM@C₃N₂ catalysts can be well understood by the d-band center model. This study provides a new type of multifunctional SAC based on 2D pc-C₃N₂ materials and may find application in the fields of energy conversion and storage.