Inside vertical reconstruction effect enhances internal polarization field in MXenes for regulating photocatalytic water splitting

We theoretically report four photocatalyst candidates, namely, Sc2COS, Sc2CSO, Sc2COSe, and Sc2CSeO. A mirror asymmetry atom structure endows Sc2COS with the largest intrinsic built-in electric field (EF) of 7.53 × 109 V/m among these monolayers, facilitating the separation of photogenerated electron–hole pairs. Sc2CSO and Sc2CSeO with smaller EF are half-reaction water splitting photocatalysts, performing the hydrogen evolution reaction. It is highly interesting that C atoms aligned to the top S or Se atoms move down by about 0.40 Å and are vertically aligned to the bottom O atoms, named as the inside vertical reconstruction. Therefore, Sc2CSO (Sc2CSeO) transforms into Sc2COS (Sc2COSe) with larger EF, suitable for photocatalytic overall water splitting. They have great optical absorption with optical absorption coefficients up to 105 cm−1. Our work reveals the physical mechanism of EF enhancement caused by inside vertical reconstruction effect facilitates overall water splitting, which provides a feasible strategy for theoretically designing intriguing photocatalysts.