Computational screening of Group VⅢ@C5N4 single-atom electrocatalysts for overall water splitting

•TM@C5N4 SAC catalysts feature Group VⅢ atoms embedded into C5N4 monolayer.•Theoretical screening of TM@C5N4 SAC catalysts for overall water splitting.•Ir@C5N4 shows superb HER/OER activity when applying biaxial tensile strain of 2 %. Single-atom catalysts (SACs) have great potential for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) since their high atomic utilization and strong metal–support interactions. Herein, we develop TM@C5N4 (TM = Fe, Co, Ni, Ru, Rh, Pd, Os, Ir and Pt) catalysts via embedding Group VⅢ TM in holey C5N4 substrate and further evaluate their electrocatalytic activity using density functional theory (DFT) calculations. Systematical studies indicate that Fe@C5N4, Pd@C5N4 and Ir@C5N4 catalysts all exhibit excellent HER performance, which mainly because of their small ΔGH* values of 0.101 eV, -0.114 eV and 0.070 eV, respectively. In parallel, Rh@C5N4 and Ir@C5N4 possess high OER activity along with low overpotential of 0.50 V, which is superior to the commercial IrO2 catalyst (0.56 V). Obviously, Ir@C5N4 could be utilized as bifunctional electrocatalysts both HER and OER in water splitting. Furthermore, we analyze their correlative catalytic mechanisms using the molecular orbitals. Besides, biaxial strain modulation could effectively regulate the catalytic activity of HER and OER. Particularly, 2 % biaxial tensile strain could bring Ir@C5N4 superb HER/OER catalytic performance. Finally, we anticipate that this strain engineering would provide a new perspective for developing high-performance SACs for water splitting. [Display omitted] We first construct the TM@C5N4 SAC catalysts via embedding Group VIII TM into 2D C5N4 monolayer, and we then screen the optimal bifunctional catalyst of Ir@C5N4 using DFT calculations. Furthermore, it is found that strain modulation engineering can well realize improved HER/OER activity in water splitting by altering the interaction strength between intermediates and Ir@C5N4 catalyst.