Unraveling Z-scheme carrier separation in ReS2/XC (X = Si, Ge) Van der Waals heterostructures for high-efficiency photocatalytic water splitting

To overcome the high carrier recombination, weak redox ability, and narrow light absorption of single-component photocatalysts, the geometry, electronic properties, mechanism, and light absorption of ReS 2 /XC van der Waals heterostructures were systematically studied. The ReS 2 /XC heterojunction is structurally stable, featuring an indirect bandgap with staggered alignment. Hole-electron recombination occurs between the XC and ReS 2 layers, forming a built-in electric field that promotes Z -scheme charge transfer: strongly reductive electrons remain on the XC side and strongly oxidative holes on the ReS 2 side. The Z-scheme heterojunctions tolerate pH variation well (0–7), with redox potentials straddling water reactivity potentials. Gibbs free energy calculations identify the XC side (especially SiC) as the most active site for hydrogen evolution. Both heterojunctions exhibit high absorption coefficients (up to 10 6 cm −1 ) in visible and ultraviolet regions, significantly outperforming their individual components. Thus, the ReS 2 /XC heterojunction is a stable and efficient Z -scheme photocatalyst for water splitting.