Exploring high-efficiency electrocatalysts of metal-doped two-dimensional C4N for oxygen reduction, oxygen evolution, and hydrogen evolution reactions by first-principles screening.

A single-atom catalyst is a landmark finding in the catalysis field and due to its excellent catalytic efficiency and maximum atom utilization, it is widely applied in the hydrogen evolution reaction (HER), oxygen reduction reaction (ORR), and oxygen evolution reaction (OER). Herein, 3d, 4d, and 5d single transition metal atom supported C4N catalysts (TM-C4N) are explored using density functional theory methods. First, seven thermodynamically stable TM-C4N (TM = Sc, Ti, V, Mn, Cu, Y, and Ag) are identified. Next, the calculated ΔG*H values reveal that all screened TM-C4N materials exhibit considerable catalytic performance for the HER. Besides, the ORR and OER activities of all screened TM-C4N materials are inferior to those of Pt(111) and Ru-/IrO2(110). Considering that the binding strength of *OH limits the catalytic performance of most TM-C4N, high-valent metal complexes (TM-OH-C4N) are further studied. Owing to the modification of OH, the binding strength of reaction species on most TM-OH-C4N is weakened, thereby improving the performance of the ORR and OER. In particular for Cu-OH-C4N, the overpotentials for the ORR and OER (0.61 and 0.48 V, respectively) are closest to those of Pt(111) and Ru-/IrO2(110), manifesting that it exhibits good bifunctional catalytic activity. Additionally, the variation trend of ΔE*OH on TM-C4N and TM-OH-C4N can be appropriately described by the intrinsic descriptor φ.