g-B3C2N3: A Potential Two Dimensional Metal-free Photocatalyst for Overall Water Splitting**

Based on hybrid density functional theory (DFT) calculations, we propose a new two-dimensional (2D) B-C-N material, graphitic- (g- ), with the promising prospect of metal-free photocatalysis. We find it to be a near ultraviolet (UV) absorbing direct band gap (3.69 eV) semiconductor with robust dynamical and mechanical stability. Estimating the band positions with respect to water oxidation and hydrogen reduction potential levels along with a detailed analysis of reaction mechanism of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), we observe that g- monolayer can be efficiently used for hydrogen fuel generation over entire pH range as well as for spontaneous water splitting at basic pH range. Upon biaxial strain application, band positions get realigned along with the free energy change that is involved in HER and OER. Consequently, operational range of pH for OER gets broadened and the proposed material exhibits the ability to perform spontaneous and simultaneous oxidation and reduction even in neutral pH. The combination of pH variation and applied strain can be used as a key to control the reducing and/or oxidizing abilities precisely for diverse photocatalytic reactions to attain environmental sustainability.