Single Atom-Modified TiO2-Based Catalysts for Photoelectrochemical Water Splitting: From Fundamentals to Future Prospects

Abstract

The accelerating demand for green hydrogen has intensified the development of efficient and durable photoelectrocatalysts (PECs) for sustainable water splitting. Titanium dioxide (TiO2) is a benchmark semiconductor for PEC because of its chemical stability, low cost, and highly tunable properties. However, its wide bandgap and slow charge transport limit its solar-to-hydrogen energy conversion efficiency. Single-atom catalysts (SACs) provide transformative opportunities to overcome these intrinsic limitations. This review provides a comprehensive overview of SACs-modified TiO2-based PECs, including i) fundamental principles of single-atom catalysis; ii) rational design strategies through metal selection via noble and nonnoble metals, fabrication methods and structural engineering by modification of morphology of TiO2 structures such as nanotubes, nanowires, nanofilms and metal organic frameworks, and facets engineering; and iii) advanced characterization techniques—critical to gain insights into mechanisms involved in these platforms. Hydrogen and oxygen evolution reactions driven by SACs-modified TiO2-based PECs are summarized. The limitations of these systems such as low metal loading, single-atom aggregation under operating conditions, and insufficient active sites are discussed. We also provide an outlook on future developments combining dual-single atoms and high entropy alloys in TiO2-based PECs, as promising pathways to synergistically integrate activity, stability, and atomic economy. This review provides a valuable framework for designing the next generation TiO2-based PECs for sustainable PEC water splitting.