Tuning MXenes Towards Their Use in Photocatalytic Water Splitting

Abstract

Finding appropriate photocatalysts for solar-driven water (H2O) splitting to generate hydrogen (H2) fuel is a challenging task, particularly when guided by conventional trial-and-error experimental methods. Here, density functional theory (DFT) is used to explore the MXenes photocatalytic properties, an emerging family of two-dimensional (2D) transition metal carbides and nitrides with chemical formula Mn+1XnTx, known to be semiconductors when having Tx terminations. More than 4,000 MXene structures have been screened, considering different compositional (M, X, Tx, and n) and structural (stacking and termination position) factors, to find suitable MXenes with a bandgap in the visible region and band edges that align with the water-splitting half-reaction potentials. Results from bandgap analysis show how, in general, MXenes with n = 1 and transition metals from group III present the most cases with bandgap and promising sizes, with C-MXenes being superior to N-MXenes. From band alignment calculations of candidate systems with a bandgap larger than 1.23 eV, the minimum required for a water-splitting process, Sc2CT2, Y2CT2 (Tx = Cl, Br, S, and Se) and Y2CI2 are highlighted as adequate photocatalysts.