Photocatalytic water splitting under visible light with particulate semiconductor catalysts

Photocatalytic water splitting (PWS) is the most promising technology to produce H-2 energy directly from renewable water and solar light. PWS has made a remarkable progress last decades under ultra-violet (UV) light, but there are many technical challenges remaining for PWS under visible light. Several approaches are taken in search of photocatalysts efficient for PWS under visible light: (i) to find new single phase materials, (ii) to decorate UV-active photocatalysts with a photosensitizer absorbing visible light, (iii) to tune the band gap energy by modifying cations or anions of UV-active photocatalysts with substitutional doping, and (iv) to fabricate multi-component photocatalysts by forming composites or solid solutions. This article discusses the above approaches based on our experimental results as well as data available in the literature. At the moment, the greatest challenge to the progress of visible light PWS is the low efficiency of light utilization. Finding new photocatalytic materials with unique structure and phase is still the key to the success. In addition, the synthesis of these materials with high crystallinity and high surface area is also important, because these properties exert great impact on the activity of the material of the same structure and phase. Finally, smart combination and modification of known materials could also be fruitful.