Spontaneous full photocatalytic water splitting on 2D MoSe2/SnSe2 and WSe2/SnSe2 vdW heterostructures.

Spontaneous full photocatalytic water splitting into hydrogen and oxygen under visible light irradiation without the need for sacrificial agents is a challenging task, because suitable band gaps, low overpotentials for both half-reactions and spatially-separated catalytic sites should be fulfilled simultaneously in a photocatalytic system. Here, we propose a promising strategy to achieve this goal by constructing van der Waals (vdW) heterostructures of two-dimensional (2D) materials. Using first-principles calculations, we predict two promising photocatalysts, MoSe2/SnSe2 and WSe2/SnSe2 heterostructures, with the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) taking place separately on the MoSe2 (WSe2) and SnSe2 layers. More excitingly, the Se-vacancy of the MoSe2 (WSe2) monolayer effectively lowers the HER overpotential, making the catalytic reactions occur spontaneously under the potentials solely provided by the photo-generated electrons and holes in pure water. The unique band alignment of these hetero-structured photocatalysts leads to high solar-to-hydrogen (STH) energy conversion efficiencies up to 10.5%, which is quite promising for commercial applications. This work opens up an avenue for the design of highly-efficient photocatalysts for full water splitting.