Photoanodes based on TiO2 and α-Fe2O3 for solar water splitting – superior role of 1D nanoarchitectures and of combined heterostructures

Decades of experimental research on TiO₂ (titania) and α-Fe₂O₃ (hematite) have pointed out that these two semiconductors are promising candidates as anodes for photoelectrochemical water splitting, mainly owing to their stability in a wide range of (photo-/electro)chemical conditions, their natural abundance and non-toxicity, and a low production cost. In spite of these remarkable aspects, limited charge transfer kinetics (intrinsic of both oxides) still hampers the development of efficient TiO₂– and α-Fe₂O₃-based PEC devices that could fulfill the requirements for large-scale applications. In the review paper recently published in Chemical Society Reviews we show that key to overcoming such a limitation in a PEC arrangement is the use of one-dimensional (1D) oxide nanostructures (i.e., nanotubes, nanorods, nanowires): 1D-nanoarchitectures offer the possibility of decoupling the direction of light absorption and charge-carrier collection, and establish a preferential percolation pathway for charges (i.e., h⁺ transfer to the electrolyte and e^– vertical diffusion towards the back-contact). In particular, we describe a range of synthetic methods and modifying concepts (including doping, decoration with co-catalysts and heterojunction engineering) of 1D-photoanodes based on titania and hematite, illustrating possibilities and potentials. In addition to the modification of these two oxides, we also illustrate recent achievements and outlooks regarding the use of α-Fe₂O₃-TiO₂ systems that combine the complementary features and functionalities of the two counterparts in terms of light absorption, charge transport and, for open circuit photocatalysis, in terms of energetic engineering.

Kment, S.; Riboni, F.; Pausova, S.; Wang, L.; Wang,L.; Han, H.; Hubicka, Z.; Krysa, J.; Schmuki, P.; Zboril, R. Photoanodes based on TiO₂ and α-Fe₂O₃ for solar water splitting – superior role of 1D nanoarchitectures and of combined heterostructures. Chem. Soc. Rev. 2017, DOI: 10.1039/c6cs00015k