Photochemical properties of rhenium disulfide/graphene heterojunctions with different stacking structures

Abstract

Energy and pollution are crucial problems. Photocatalysis technology is a way to solve the problem by electrolysis of aquatic hydrogen and degradation of organic pollutants. Preparing photocatalysts with fantastic photocatalytic activity and high photocarrier separation efficiency is a key technique. In recent years, two-dimensional (2D) nanomaterials have attracted much attention because of their unique structures and excellent properties, which are different from the traditional materials’. The 2D nanomaterials demonstrate in-plane covalent bonds and out-of-plane van der Waals interactions. Therefore, two 2D materials can form van der Waals heterojunctions by van der Waals forces, which are also known as nanocomposites. However, there is an interesting problem in the study of van der Waals heterojunctions in the field of photochemistry, which has not been paid attention to no studied. Specifically, that problem is whether the photochemical properties of the van der Waals heterojunctions are affected by the different stacking structures after the relationship between the upper and lower positions has been adjusted. In this paper, the van der Waals heterojunction films with different stacking structures ReS<sub>2</sub>-Gra (ReS<sub>2</sub> on the top) and Gra-ReS<sub>2</sub> (graphene on the top) are prepared by liquid phase exfoliation combined with electrophoretic deposition method. The heterojunctions are utilized as photoelectrodes in photochemical reactions, and the findings are as follows. i) Different stacking structures will affect the photoelectric chemical characteristics of heterojunctions: comparing with the ReS<sub>2</sub>-Gra photoelectrode, the photocurrent of the Gra-ReS<sub>2</sub> photoelectrode increased by 54% under the same conditions. We think that the main reason is due to the fact that graphene has a zero-band gap structure and holds a wider spectral absorption range. ii) The construction of the heterojunction significantly enhances the photochemical properties of the photoelectrode materials, resulting in a larger and rapidly photocurrent response. The photocurrent response of the Gra-ReS<sub>2</sub> photoelectrode (2.47 μA) is twice that of the pure ReS<sub>2</sub> photoelectrode (1.16 μA). Based on the experimental results of this paper, a possible mechanism for effective separation and prolonged recombination of the photo-induced electro-hole pairs in ReS<sub>2</sub>/graphene heterojunction is proposed. This work not only puts forward new ideas for preparing the van der Waals heterojunctions, but also lays a theoretical foundation for further studying the solar energy conversion devices.