Recent progress in iron oxide based photoanodes for solar water splitting

Solar assisted water splitting in a PEC is an attractive concept to store solar energy as hydrogen fuel but the effective efficiency of the process is too low for it to be a serious contender for commercialization. The most important component of the PEC to achieve efficient water splitting is a photo active anode that could effectively absorb photons and deliver holes for the oxygen evolution reaction. Hematite has many attributes that make it a good candidate material for a photoanode but it also has some deficiencies. This article reviews the state-of-the-art hematite-based photoanodes, with special emphasis on attempts made by researchers to overcome its drawbacks. The numerous research reports are categorized under distinct strategies such as nanostructuring, elemental doping, surface passivation, cocatalyst application, conducting template incorporation and heterostructures which are possible pathways to improve the performance of hematite. The scientific understandings of the operating mechanisms for each strategy are systematically presented and discussed, and the improvements achieved by different approaches are compared. Some cutting-edge strategies, such as heterojunctions, could be important and hematite based heterostructures are discussed. A developing interest in an emerging material, Fe2TiO5 is also discussed and some of the important benefits of this material are presented. Finally, the importance of scaling up the technology is discussed and attention is drawn to some possible challenges on scaling up. The paper concludes with some future technology directions and prospects for hematite-based photoanodes.