Design and analysis of in-plane and out-of-plane heterostructures based on monolayer tri-G with enhanced photocatalytic property for water splitting.

Abstract

Photocatalytic water splitting is considered to be a promising renewable solution to the energy crisis and environmental problems as an inexhaustible clean energy source. Graphene has an ultrahigh carrier mobility, but the zero gap limits its practical application in the photocatalysis field. Graphane has a wider band gap and retains a high carrier mobility, which demonstrates its great potential in this field. However, the broad band gap results in low photocatalytic efficiency. In this work, we propose two effective ways to modulate its electronic structure, modifying the structure of graphane and constructing a heterojunction using density functional calculations. We systematically investigated four trilayer graphane (tri-G) conformers and designed in-plane (lateral) and out-of-plane (vertical) heterojunctions with tri-G and chair-G (cha-G), the two most stable graphanes, with theoretical prediction. The results show that tri-G not only has a smaller band gap, falling in the ultraviolet range, which enhances the UV-light catalytic performance, but also has tunable band edge positions, locating outside the reduction potential of hydrogen and oxidation potential of water. Furthermore, the calculated electron effective mass for the tri-G conformers is smaller than that of cha-G. What's more, the band gap, band edge position, and photocatalytic efficiency are further optimized by constructing heterojunctions. In particular, both the in-plane and out-of-plane tri-G-C/cha-G heterostructures are confirmed as direct band gap semiconductors and type-I heterostructures exhibiting special band alignment, meanwhile satisfying the requirements for water splitting. And the band gaps of the heterostructures are further reduced. In addition, metal doping is expected to further optimize their electronic structure. These results provide theoretical support and a feasible modulation strategy for developing graphane as an effective photocatalyst for water splitting.