ABSTRACT
Sunlight can be transformed into useful energy via photovoltaic effect or by photolysis of water. The latter can be done by using a photoelectrochemical (PEC) cell with hematite (α-Fe2O3) as a photoanode for oxygen evolution and platinum electrode for hydrogen generation. α-Fe2O3 is a low bandgap material and thus electron-hole pairs can be generated when the oxide is illuminated with sunlight. Nonetheless, α-Fe2O3 displays low water oxidation efficiencies thus the overall solar to hydrogen conversion is often very small. The limitations of α-Fe2O3 can be due mostly to the carrier dynamics, which can be overcome by nanostructuring approach i.e. forming thin film comprising of nanostructure. One process that can be adopted to form nanostructured α-Fe2O3 film is anodic oxidation of iron. Anodic oxidation is chosen to obtain α-Fe2O3 thin film with self-ordered pores in nanoscale. The process is simple, cost-effective and rather efficient in the formation of thin film with such nanostructure. However, despite the success in surface nanostructuring, the anodic film is often hydrated and amorphous, hence requiring post-annealing treatment. Annealing results in the formation of internal oxide layer which resembles the multi layered scale oxide when iron is thermally oxidized. These internal layers, comprising of oxide of various phases, may influence the electron transport properties, lowering the overall efficiency of the PEC cell. In this chapter, a review on the recent progress in nanoporous α-Fe2O3 film formation by 241anodic process of iron and the photocurrent performance of the formed oxide will be presented, highlighting on efforts made to improve on the PEC cell efficiency.
