PtS2/GeC van der Waals heterostructure: a promising direct Z-scheme photocatalyst with high solar-to-hydrogen energy conversion efficiency for overall water splitting under acidic, alkaline, and neutral conditions and in large-strain regions

In this study, first-principles calculations were used to investigate in detail the structural, electronic, optical, and photocatalytic properties of PtS₂/GeC heterostructures. The calculations demonstrate that the PtS₂/GeC heterostructure has favorable stability with an inherent type-II (staggered) band alignment and a much smaller indirect bandgap of 0.83 eV than those of 2.59 and 2.80 eV for constructional PtS₂ and GeC monolayers, respectively. The GeC layer transfers 0.11 |e| to the PtS₂ layer and leads to a 1.3 eV potential drop, both resulting in a built-in electric field E_in from the GeC side to the PtS₂ side. Both the E_in and band edge bending make the direct Z-scheme PtS₂/GeC heterostructure a promising photocatalyst with the oxidation and reduction reactions achieved respectively on the PtS₂ and GeC layers with high catalytic activity. The PtS₂/GeC heterostructure has a higher solar-to-hydrogen (STH) energy conversion efficiency of 56.69% than that of a few previously reported photocatalytic materials. The PtS₂/GeC heterostructure's ability to absorb solar light in the visible and infrared spectrum can be significantly enhanced by tensile strain. Therefore, the newly designed direct Z-scheme PtS₂/GeC heterostructure is a promising photocatalyst with high STH efficiency for overall water splitting under acidic, alkaline, and neutral conditions and in large-strain regions.