Designing triple-layer photocatalytic systems based on direct Z-scheme photocatalytic systems: Towards higher solar-to-hydrogen efficiency

Direct Z-scheme photocatalytic systems, with their strong photocatalytic redox capabilities and efficient separation of photogenerated carriers, are beneficial for enhancing photocatalytic efficiency. However, the low solar-to-hydrogen (STH) efficiency of the entire photocatalytic system is caused by the recombination of half of the photogenerated carriers at the interface. Based on this, we first propose monolayer-MoSeTe/SnSe2 and monolayer-WSeTe/SnSe2 heterostructures as direct Z-scheme photocatalytic systems for overall water splitting, with theoretical estimated STH efficiencies of 10.14% and 9.18%, respectively. To enhance the STH efficiency of the proposed direct Z-scheme systems, triple-layer photocatalytic systems are designed based on the proposed direct Z-scheme systems: bilayer-MoSeTe/SnSe2 and bilayer-WSeTe/SnSe2 heterostructures, with STH efficiencies of 11.94% and 10.78%, respectively. Compared to the monolayer-MoSeTe/SnSe2 and monolayer-WSeTe/SnSe2 heterostructures, the triple-layer photocatalytic systems possess higher efficiencies of carrier utilization and the STH efficiencies increased by 17.75% and 17.43%, respectively. Among them, the STH efficiencies of monolayer-MoSeTe/SnSe2, bilayer-MoSeTe/SnSe2 and bilayer-WSeTe/SnSe2 heterostructures exceed the threshold of 10% required for commercial applications. By introducing Te vacancies on the surfaces of Janus TMDCs, all four proposed van der Waals heterostructures can spontaneously perform hydrogen evolution reaction and oxygen evolution reaction processes in a neutral environment under illumination. Thus, our research provides a new strategy for designing highly-efficient photocatalytic systems.