A review on recent advances in the design and structure-activity correlation of TiO2-based photocatalysts for solar hydrogen production

Abstract

The major issues that determine the efficiency of photocatalyst composite materials for solar hydrogen production, with or without sacrificial agent, are efficient visible light harvesting properties, efficient separation of charge carriers and their utilization at redox sites, and stability. Significant efforts have been made in the past few decades to modify the above characteristics by integrating the constituent components of composite with different approaches. The present review attempts to enumerate the recent advances, predominantly, in the area TiO2-based photocatalyst composites for solar hydrogen production. First we provide the recent progress in the material integration aspects by describing the integration of TiO2 with different category of materials, including noble/3d metals, metal oxides/sulphides/selenides, other low bandgap semiconductors, C-based materials, dye sensitization. How the material integration helps in tailoring the electronic and optical properties for activity tuning in solar H2 production is also presented. The critical changes in the physico-chemical and electronic properties of composites with respect to preparation methods, morphology, crystallographic facet, particle size, dopant, calcination temperature, and its structure-activity relation to solar hydrogen production were addressed in detail. We also discuss the importance of fabrication of photocatalyst in thin film form and performing solar hydrogen production in different reactor set up for enhancing the photocatalytic performance, while addressing the device scalability. Despite significant advancements has been made in this field, the solar-to-hydrogen conversion efficiency is still need to be improved to implement it for practical applications. Direct conversion of water into hydrogen by overall water splitting, renewable H2 production with waste water or by using a biomass component by employing suitable photocatalyst are some possible ways to improve the energy efficiency and continuous research in the above directions are highly desired.