Wafer-scale synthesis of monolayer WSe2: A multi-functional photocatalyst for efficient overall pure water splitting

A multi-functional photocatalyst, that can combine the catalytic functions of water oxidation and proton reduction together with light harvesting capacity, is highly desired for low cost, high efficiency, and highly stable solar fuel production. Monolayer WSe2, with a direct energy gap of similar to 1.65 eV is a nearly ideal light absorber to convert sunlight to hydrogen fuels through solar water splitting. To date, however, the controlled synthesis of monolayer WSe2 on a wafer scale and the realization of overall water splitting on WSe2 have remained elusive. Here, we report the van de Waals epitaxy of crystalline monolayer WSe2 on large area amorphous SiOx substrates. We have demonstrated, for the first time, the multi-functionality of monolayer WSe2 in solar water splitting, including extraordinary capacities for efficient light harvesting, water oxidation, and proton reduction. The absorbed photon conversion efficiency exceeds 12% for a single monolayer WSe2. This work provides a viable strategy for wafer-scale synthesis of multi-functional photocatalysts for the development of efficient, low cost, and scalable solar fuel devices and systems.