Exploring the photoactive properties of promising MXenes for water splitting

The photoactive properties and effectiveness of a selected group of ten terminated MXenes—Sc2CT2, Y2CT2 (T = Cl, Br, S, and Se), Y2CI2 and Zr2CO2—has been deeply studied by means of density functional theory (DFT). Here it is demonstrated that the studied MXenes exhibit robust energetic and dynamical stability, having all an indirect bandgap, while most of them with values within the visible spectrum, and also exhibiting suitable band alignment for the water splitting reaction. The charge density distribution of the valence band maximum (VBM) and conduction band minimum (CBM) is found to be separated across different layers with low overlaps, below 30%. Most MXenes present high charge carrier mobilities with favourable electron–hole disparities, with Sc2CBr2 also presenting directional charge carrier transport. Additionally, these materials show strong optical absorption (∼105 cm−1) in the visible spectrum, translating to promising solar-to-hydrogen (STH) efficiency theoretical limits, up to 23%. Overall, the combination of all these features positions MXenes among the optimal materials for efficient photocatalytic water splitting.