Solar Generated Hydrogen: 2D Heterostructures for Photocatalysts

Photocatalytic water splitting offers a promising approach for sustainable hydrogen production; however, its practical application is limited by the inherent limitations of traditional bulk semiconductors, such as restricted visible-light absorption, rapid charge-carrier recombination, and insufficient operational stability. In recent years, atomically thin two-dimensional (2D) materials and their heterostructures have emerged as a highly advanced nanoscale framework for photocatalysis, attributed to their large surface-to-volume ratios, configurable electronic structures, and charge-transfer characteristics, which are dominated by interfaces. This review provides a mechanistic and materials-oriented perspective on solar-driven hydrogen generation using 2D heterostructured photocatalysts, highlighting the influence of nanoscale dimensionality and interfacial engineering on the structure-performance-property relationship and their implication for rational photocatalyst design. Initially, the review summarizes the fundamental principles of water-splitting photocatalysis and the essential requirements for enhanced efficiency, which highlights the important categories of 2D materials, including transition metal dichalcogenides, graphitic carbon nitride, phosphorene, and MXenes, and their suitability for heterostructure construction and outlines their optoelectronic advantages. Specific attention is placed on interface-engineering approaches, including van der Waals heterojunctions, type-II band alignment, Z-scheme and S-scheme designs, and interface-induced bandgap modulation, which offer effective charge stabilization while maintaining significant redox capability. The role of solar-to-hydrogen (STH) efficiency as a performance metric at the system level is conducted with a critical focus on heterostructure design. Additionally, the emerging computational and data-driven approaches, including density functional theory, high-throughput screening, and machine learning-assisted materials discovery, are also considered as effective tools for accelerating the rational design and optimization of high-performance 2D photocatalysis. The review concludes with significant challenges such as scalable production, photocorrosion resistance, and inadequate mechanistic insights while highlighting future opportunities in device integration, in situ characterization, and solar-to-fuel conversion. Collectively, this review highlights the essential role of nanoscale interface engineering in 2D heterostructured photocatalysts for enabling effective, stable, and scalable solar-driven hydrogen production, highlighting their potential for sustainable hydrogen production technologies.