Visible-light-driven photocatalytic water splitting on nanostructured semiconducting materials

In view of the unlimited resource of solar energy and the abundance of water on earth, producing hydrogen through photocatalytic splitting of water under solar irradiation has the great potential to offer a low cost, environmentally friendly green fuel that does not contribute to greenhouse gas emissions. Since the pioneering work of Fujisima and Honda in 1972, tremendous research on semiconductor photocatalysis has yielded better understanding of the processes involved in photocatalytic water splitting, as well as notable enhancement of energy conversion efficiency for solar hydrogen generation. However, the solar-to-hydrogen energy conversion efficiency is still too low to be viable for practical applications, primarily due to the limitation of electronic band structure of semiconductor photocatalysts and rapid recombination of photogenerated charges. Thus, ideal photocatalysts are the key for the realisation of high efficiency hydrogen generation system. Fortunately, various kinds of effective semiconductors have been developed as good candidates for photocatalytic hydrogen generation, and high-efficiency photocatalysis systems in lab scale have also been constructed. This paper provides an overview of the common approaches that have been used in the search for high efficiency photocatalysts (i.e., photocatalyst itself and co-catalyst) and matched reaction systems of sacrificial reagents for water splitting, especially under visible light irradiation. From this review, one can also observe that nanotechnology plays an important role in the design of novel nanostructured or heterogeneous photocatalysts for the establishment of high-efficiency photocatalytic solar hydrogen system. These may offer a general guide to those who are interested in tackling the challenges.