Two-dimensional transition metal dichalcogenide heterostructures for photoelectrochemical water splitting: Recent advances, challenges, and future directions

Photoelectrochemical (PEC) water splitting represents a promising strategy for green hydrogen production, offering a clean energy alternative to fossil fuels. Improving the efficiency of this process depends on the development of photoelectrodes with optimized band gaps, surface areas, and charge generation and transport capabilities. Among candidate materials, two-dimensional transition metal dichalcogenides (2D TMDs) have garnered significant interest owing to the unique layer-dependent tunability of their electronic and optical properties, enabling enhanced photon absorption and charge carrier dynamics. This review article provides a detailed overview of the progress in the design and application of TMD-based heterostructures for PEC water splitting. We explore how combining different TMDs and other materials in heterostructured architectures enhances charge separation, reduces recombination losses, and improves photocatalytic efficiency. The article is structured to include: (1) an introduction to PEC water splitting, (2) PEC water splitting mechanisms, (3) heterostructure classification and band alignment, (4) synthesis techniques, (5) physical and crystallographic properties of TMDs, (6) PEC performance evaluation of TMD systems, (7) operando insights, and (8) conclusions, challenges, and future directions. By critically examining current advancements and persistent challenges, this review aims to guide future research towards the scalable application of TMD heterostructures in solar-driven hydrogen production.