2D materials-based photoelectrochemical cells: Combination of transition metal dichalcogenides and reduced graphene oxide for efficient charge transfer

Abstract Transition metal dichalcogenides (TMDs) and their hybrids with reduced graphene oxide (rGO) have attracted great attention for use as electrocatalysts to replace Pt. However, their applications for photoelectrochemical (PEC) cells are not widely known. Herein, we report the fabrication of highly efficient photo-cathodes for PEC cells using only two-dimensional (2D) materials, MoS 2 , WS 2 (with 1T and 2H phases) and rGO sheets. Two types of hybrid films were prepared based on various combinations of the components and optimization of the thickness; multi-layered (1T MoS 2 /2H MoS 2 /2H WS 2 /rGO/ITO) and multi-component (1T MoS 2 /(2H MoS 2  + 2H WS 2  + rGO)/ITO) films. The hybrid films with the same component materials but different structures showed high efficiency when used as cathodes in PEC cells in terms of the current density under illumination: the increase by 60 and 67%, respectively, for the multi-layered and the multi-component films. Furthermore, the roles of each component were identified. The 1T MoS 2 layer contributes to catalytic activity for hydrogen evolution reaction. The hybrid of 2H MoS 2 and 2H WS 2 with different band structures facilitates more efficient carrier transport through proper band alignment than the individual MoS 2 or WS 2 sheets. The rGO sheets act as conductive interconnecting components to prevent the recombination of electrons and holes. Finally, the optimized hybrid film (1T MoS 2 /(2H MoS 2  + 2H WS 2  + rGO)/rGO/ITO), based on above roles of each component, showed highly efficient PEC performance. This study points out that the performance of PECs consisting of 2D materials is affected by the combination of 2D materials and the structure of the photoelectrode.