Computational study based prediction of new photocatalysts for water splitting by systematic manipulation of MXene surfaces†

The compositional and structural flexibility of functionalised two-dimensional metal carbonitrides or MXenes has been exploited through a combinatorial search for new materials that can act as catalysts for photo-assisted water splitting by absorbing sunlight with energy in the infra-red region. Detailed calculations on 47 Janus MXenes where two surfaces are of asymmetric nature are carried out by first-principles density functional theory. A screening procedure is adopted to arrive at potential candidates. Our calculations predict four new materials whose surfaces can activate both hydrogen and oxygen evolution reactions upon splitting water, two out of which are infra-red active, and the rest are visible light-active. To explain our results, we have performed a detailed microscopic analysis to find out the interrelations of the structural model of surface functionalisation, the chemistry of the surfaces, the electronic structure, and the alignment of bands with respect to the reaction potentials. Apart from these four compounds, we find thirteen other compounds that are suitable for either hydrogen evolution or oxygen reduction reactions. This study lays out a guideline towards systematic discovery of potential new catalysts for water splitting under sunlight irradiation.