Photocatalytic hydrogen production

The photocatalytic production of hydrogen represents a fascinating way to convert and store solar energy in the form of chemical energy, i.e. as hydrogen, the cleanest and most promising energy vector for the future. Hydrogen can be produced either by the photocatalytic direct splitting of water into H2 and O2, or, more efficiently, in the presence of sacrificial reagents which more readily combine with the holes photoproduced in the conduction band of a semiconducting material, e.g. in the so-called photoreforming of organics, in either liquid or gas phase. The main challenge in this field is the electronic structure engineering of photocatalytic materials, which should not only be able to harvest solar radiation producing electron-hole couples, but also ensure efficient charge separation to achieve electron-hole transfer reactions, finally leading to solar energy driven thermodynamically up-hill processes. The fundamentals of photocatalytic hydrogen production from water solutions will be outlined, together with the mechanistic aspects of water photosplitting and photoreforming of organics. Recent achievements in the development of innovative photocatalytic materials will be presented, based on the engineering of their electronic structure, on solid solutions produced by different techniques, on the modification of the surface properties by noble metals or co-catalysts to achieve increased charge separation. Both standard and sophisticated techniques, such as time-resolved luminescence, have been employed to systematically characterize such materials, in relation to their photoactivity. Innovative technologies, including radio frequency magnetron sputtering and flame spray pyrolysis, together with electrochemical growth of different architectures on different supports, have been explored with the final aim of producing photocatalytic materials in integrated form within devices for pure hydrogen production from water solutions