(353f) The Fabrication of Cu2o/g-C3N4/WS2 Triple-Layered Photocathode for Photoelectrochemical Hydrogen Evolution

Xintian Xu, Yuanzhi Zhu, Xiaobin Fan, Guoliang Zhang, Wenchao Peng*

School of Chemical Engineering & Technology, Tianjin University, Tianjin 300072, China.

wenchao.peng@tju.edu.cn

Hydrogen is being vigorously pursued as a future energy carrier due to the fossil energy depletion. Photoelectrochemical (PEC) water splitting is an emerging hydrogen production technology by utilizing the solar light. This technology integrates in the same device both solar energy collection and water electrolysis. Both photo-active semiconductor and catalysts for hydrogen evolution reaction (HER) are necessary in this device. Cu₂O is a direct P-type semiconductor with a narrow band gap (~2.0 eV), which can be activated by the visible light. Moreover, Cu is a kind of earth abundant element, and the synthesis of Cu₂O is facile. Cu₂O is therefore one of the most promising low-cost photoactive semiconductor reported until now. However, the activity of bare Cu₂O is still poor, and it is not stable towards chemical oxidants and light corrosion. Combing with other semiconductors (e.g. TiO₂, ZnO) could improve the activity and stability of Cu₂O effectively.

As we know, Pt and other precious metals are the most efficient catalysts for hydrogen evolution reaction (HER). However, these metals are rare and expensive to apply. Transition-metal dichalcogenides (TMDs), such as Molybdenum disulfide (MoS₂), tungsten disulphide (WS₂), are emerging HER catalysts that could be used as a substitute for noble metals in HER.

In this study, a novel Cu₂O/g-C₃N₄/WS₂ triple-layered photocathode was designed for the PEC hydrogen evolution. Cu₂O was electrodeposited on the FTO glass as the active layer for the light harvesting. A metal-free g-C₃N₄ was exfoliated and covered on the surface of Cu₂O as protection layer. G-C₃N₄ could also form p-n junction with Cu₂O to increase the activity. 1T-WS₂was obtained by lithium intercalation and used as HER catalyst for the further modification of the photocathode.

The obtained photocathode was then used for PEC HER test in the Na₂SO₄/H₂SO₄ solution (λâ?¥420nm, 100 mW/cm²). With the irradiation, electron-hole pair will be generated in the p-type Cu₂O, and the excited electron could be then extracted through the g-C₃N₄ protective layer to produce hydrogen on the WS₂. The efficient extraction of excited electrons by this triple-layered photocathode leads to photocurrents of up to -6 mA/cm^-2 at -0.4 V versus RHE (pH 6.0). The corresponding overpotential is -0.23 V (versus RHE) for the H₂ evolution. In sharp contrast, nearly no H₂ evolution happened under dark conditions. This photocathode is facile to synthesis and has great potential for developing low-cost PEC water-splitting device.