Two-dimensional nanosheets for photoelectrochemical water splitting: Possibilities and opportunities

In view of the worldwide energy challenge in the 21st century, the technology of semiconductor-based photoelectrochemical (PEC) water splitting has received considerable attention as an alternative approach for solar energy harvesting and storage. The performance of advanced PEC devices is fundamentally related to the semiconductor photoelectrode design at the nanoscale. Among various architectures, two-dimensional (2D) nanosheets with thickness generally below 100 nm hold great promise for highly efficient PEC water splitting. Hence, this article mainly provides a comprehensive review of current research efforts that focus on the scientific and technological possibilities of using 2D nanosheets to fabricate efficient photoelectrodes for PEC water splitting, followed by a concise overview of the state-of-the-art progress of 2D nanosheets, where we also present a discussion of how to overcome the challenges that have prevented realizing the full potential of 2D nanosheets. Particular attention is paid on two major approaches. One is to align nanosheets directly on the substrate to maximize the morphological advantages of 2D nanosheets. The other is to further reduce the thickness of common 2D nanosheets to single or a few atomic layers aiming at regulating the intrinsic physical and chemical properties for PEC water splitting. Both of the approaches have led to excellent improvements on PEC performance and greatly broaden the knowledge about where and how the existing semiconductor materials can be used in solar energy-related applications. It is hence envisioned that 2D nanosheets can offer wide opportunities and perspectives on the directions toward high-efficiency solar energy conversion.