Facile preparation of nanostructured α-Fe2O3 thin films with enhanced photoelectrochemical water splitting activity

Abstract

We report on the use of a facile electrospray technique for the synthesis of α-Fe₂O₃ thin films on a FTO substrate for photoelectrochemical (PEC) water splitting. The effect of synthesis parameters such as substrate temperature, discharge potential and post-heat treatment on morphology, particle size and PEC performance of α-Fe₂O₃ films were investigated. With an increase in substrate temperature, the surface morphology of the α-Fe₂O₃ film was altered from a packed worm-like surface to highly porous nanostructures. XRD analysis revealed that the (110) grain orientation of the film was transformed to the (104) grain orientation at 300 °C, due to the oxidation of the precursor at the surface of the substrate. Raman spectroscopy and XPS analysis indicated the presence of highly pure α-Fe₂O₃ in the film. By changing the discharge potential, the size of particles in the film was reduced to a minimum of 23 nm. Under optimized conditions the nanostructured α-Fe₂O₃ films showed a water splitting photocurrent of ∼0.6 mA cm⁻² at 1.23 V versus RHE under standard illumination conditions (AM 1.5 G 100 mW cm⁻²), and an incident photon to current efficiency (IPCE) of 13% at 350 nm (at 1.4 V versus RHE) which are among the best results obtained for undoped α-Fe₂O₃ photoanodes. This enhanced PEC performance can be attributed to the efficient charge separation at the α-Fe₂O₃-electrolyte interface due to the larger interfacial area of small-sized particles in the film. This study thus provides a simple route for the synthesis of highly active α-Fe₂O₃ thin films that can be extended to metal doped films such as Ti-doped α-Fe₂O₃.