Sacrificial hydrogen production over TiO2-based photocatalysts: Polyols, carboxylic acids, and saccharides

Photocatalytic generation of H-2 from water over titanium dioxide (TiO2) has received a great deal of interest for developing a renewable and clean energy source. It is initiated by charge-separation in TiO2 upon photoexcitation. The electron reduces water to generate H-2 while the hole oxidizes hydroxide to generate hydroxyl radicals. However, water-splitting into O-2 and H-2 is not easy because of the large up-hill reaction and rapid reverse reaction. It is well known that the use of electron-donating sacrificial agents (hole scavengers) remarkably accelerates TiO2-photocatalyzed H-2 evolution in which the hydroxyl radical is consumed by the sacrificial agents. Thus, sacrificial H-2 production over a TiO2 photocatalyst is a convenient method to generate H-2 from biomass and waste. This paper reviews the sacrificial H-2 production from polyols, carboxylic acids, and saccharides, focusing on the chemical yield of H-2 production.