Transition metal-embedded two-dimensional C₃N as a highly active electrocatalyst for oxygen evolution and reduction reactions

Searching for highly efficient, stable and cost-effective catalysts for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is vital to resolve energy security and environmental problems. Herein, by means of computational screening based on the density functional theory (DFT), we studied a wide range of transition metal (TM) atoms embedded into the double carbon vacancy of C₃N monolayers (V_CC), denoted as TM-V_CC (TM = Mn, Fe, Co, Ni, Cu, Ru, Rh, Pd, Ir and Pt), as efficient single-atom catalysts (SACs) for OER and ORR. The calculated results showed that all the considered TM-V_CC composites exhibited a metallic feature that ensured efficient charge transfer during reactions. The interaction strength between intermediates and TM-V_CC has direct correlation with the d-band center of TM, which can be tuned by changing the TM atoms with different numbers of d electrons. The best catalyst for OER was Rh-V_CC with an overpotential (η^OER) of 0.35 V, followed by Co-V_CC (0.43 V). For the ORR process, Rh-V_CC exhibited the lowest ORR overpotential (η^ORR) of 0.27 V, followed by Co-V_CC (0.42 V). The results suggested that the performances of the newly predicted Rh-V_CC and Co-V_CC SACs are comparable to those of the noble-metal benchmark catalysts for OER and ORR. Ab initio molecular dynamic simulations indicated that Rh-V_CC and Co-V_CC SACs could remain stable under 300 K and possessed high energy barriers to prevent the isolated Rh and Co atoms from clustering. Our results highlight a new family of efficient and stable catalysts with a single atom anchored on carbon nitride-based materials, which provides a useful guideline for catalyst design and practical applications.