Ternary Composites Using Graphitic Carbon Nitride/Tin Disulfide/Reduced Graphene Oxide (mpg-C3N4/Sns2/RGO) for Visible Driven Photoelectrochemical Water Splitting

Photoelectrochemical (PEC) water splitting is the potent technology to solve the global issues of energy crisis and environmental pollution. It converts solar energy to chemical energy stored in the form of hydrogen. In practical application, no single material can meet all the requirements for PEC water splitting. Two-dimensional (2D) nanostructures have been developed as potential materials for application in photoelectrochemical (PEC) water splitting due to their unique structure and fascinating properties. However, the light harvesting ability of bulk or nanosized materials are always limited due to the low light transmittance and high reflection at the grain boundaries. Also, the photo generated charge carriers inside the semiconductor with atomistic thickness will reach the surface faster relative to bulk materials due to the shortened transport distance. SnS 2 is a two-dimensional (2D) transition metal dichalcogenide with a layered cadmium iodide (CdI 2 ) structure. It has a narrow band gap of 2.18-2.44 eV. It is inexpensive, nontoxic and chemically stable in acidic and neutral solutions. A metal free semiconductor, known as graphitic carbon nitride (g-C 3 N 4 ) also possesses a layered 2D structure and has been reported to have potential applications in photocatalysis. It exhibits various interesting properties, including visible-light absorption with a band gap of 2.7 eV. However, g-C 3 N 4 suffers from low electrical conductivity which can be enhanced by the use of reduced graphene oxide (RGO). RGO has been extensively used by combining with various semiconductors to develop efficient photocatalysts. In the present work, ternary composites consisting of 2D nanomaterials of SnS 2 , reduced graphene oxide (RGO), and mesoporous graphitic carbon nitride (mpg-C 3 N 4 ) were synthesized by using hydrothermal method. The presence of SnS 2 , mpg-C 3 N 4 and RGO was confirmed by XRD, UV-Vis spectroscopy, and TEM. The single SnS 2 nanosheet acquires a hexagonal structure with a lateral size of 20-50 nm. Generally, these SnS 2 nanosheets tend to agglomerate which is prevented by RGO nanosheets. Due to the intimate face-to-face interactions offered by the 2D structured constituents, the obtained composite showed excellent performance as photoanode. The ternary composite showed photocurrent density of 1.4 mA/cm 2 at 1.2 V versus RHE, which is over 28 times higher than that of the pure SnS 2 material and almost 5 times more than C 3 N 4 -SnS 2 composite. The superior photocatalytic activity of the mpg-C 3 N 4 /SnS 2 /RGO composite is attributed to enhanced separation of the photogenerated electron-hole pairs, as well as increased visible-light absorption. [1] J. Di, J. Xia, H. Li, Z. Liu, Freestanding atomically-thin two-dimensional materials beyond graphene meeting photocatalysis: Opportunities and challenges, Nano Energy. 35 (2017) 79-91. [2] Y. Sun, H. Cheng, S. Gao, Z. Sun, Q. Liu, Q. Leu, F. Lei, T. Yao, J. He, S. Wei, Y. Xie, Freestanding tin disulfide single-layers realizing efficient visible-light water splitting, Angew. Chemie - Int. Ed. 51 (2012) 8727-8731. [3] Z. Zhang, J. Huang, M. Zhang, Q. Yuan, B. Dong, Ultrathin hexagonal SnS 2 nanosheets coupled with g-C 3 N 4 nanosheets as 2D/2D heterojunction photocatalysts toward high photocatalytic activity, Appl. Catal. B Environ. 163 (2015) 298-305. [4] M.S.A. Sher Shah, A.R. Park, A. Rauf, S.H. Hong, Y. Choi, J. Park, J. Kim, W.-J. Kim, P.J. Yoo, Highly interdigitated and porous architected ternary composite of SnS 2 , g-C 3 N 4 , and reduced graphene oxide (rGO) as high performance lithium ion battery anodes, RSC Adv. 7 (2017) 3125-3135. Figure 1