Emerging cocatalysts in TiO2-based photocatalysts for light-driven catalytic hydrogen evolution: Progress and perspectives

• Cocatalysts in TiO2-based photocatalysts are highlighted for solar hydrogen production. • Design strategies of cocatalysts in TiO2-based photocatalysts are presented systematically. • Enhancements are attributed to manipulating the charge separation and surface reactions. • Challenges and perspectives of cocatalysts in TiO2-based photocatalysts are proposed. TiO 2 -based photocatalysts have been maintained as the most prominent candidate for solar-driven hydrogen (H 2 ) evolution over the past decades. However, poor separation of generated electron-hole pairs has been considered the bottle-neck issue, restricting the TiO 2 activity. Coupling a TiO 2 photocatalyst to cocatalyst(s) turns out to be the ideal strategy to suppress the charge recombination and offer robust active centres, boosting the H 2 evolution performance. This review aims at providing the frontier investigations of cocatalysts-integrated TiO 2 for photo-induced H 2 evolution. Four types of cutting-edge development of cocatalysts, including metal (noble metal, non-noble metal, bimetallic), metal sulfides and metal phosphides, 2D-MXenes, and dual materials-based cocatalysts, have been successfully highlighted and discussed. The systematically provided cocatalysts, which remarkably promote the charge separation and facilitate the surface reactions, bring out a roadmap to inspire the preparation of superior TiO 2 -based materials for H 2 evolution shortly. We expect this review could provide enriched information to tailor the TiO 2 supported active sites of cocatalysts for highly photo-induced H 2 evolution.