Sc2CCl2/WX2 (X = Se, Te) van der Waals heterostructures for photocatalytic hydrogen and oxygen evolutions with direct Z-schemes

The Sc2CCl2/WSe2 and Sc2CCl2/WTe2 heterostructures are identified for efficient photocatalytic overall water splitting with direct Z-schemes, although the conduct band minimum for the Sc2CCl2 monolayer and the valence band maximums of the WSe2 and WTe2 ones do not match the redox potential conditions. The photocatalytic direct Z-schemes are constructed for the two heterostructures according to the built-in electric fields and band alignments. The solar-to-hydrogen efficiency ηSTH, together with the Gibbs free energies are evaluated to understand the photocatalytic activities and feasibilities. The maximum ηSTH can reach 20.70% with the Sc2CCl2/WTe2 heterostructure and higher than 7.35% with the Sc2CCl2/WSe2 one. Interestingly, the biaxial tensile strains remarkably boost the ηSTH of the Sc2CCl2/WSe2 heterostructure but weakly impact that of the Sc2CCl2/WTe2 one, while the compressive strains substantially reduce the ηSTH of the Sc2CCl2/WSe2 heterostructure but raise that of the Sc2CCl2/WTe2 one. Moreover, the Gibbs free energies indicate the considered hydrogen and oxygen evolution reactions have thermodynamic feasibilities.