Constructing inverse opal structured hematite photoanodes via electrochemical process and their application to photoelectrochemical water splitting

In this study, we constructed an inverse opal structured hematite (IOS α-Fe₂O₃) as the photoanode of a photoelectrochemical (PEC) cell for efficient solar water splitting via a simple electrochemical process. At the same time, a series of affecting factors (template particle size, electrodeposition time and annealing temperature) to construct the IOS α-Fe₂O₃ photoanode on the photoelectrochemical water splitting were considered. Optimized PEC efficiency was observed for the IOS α-Fe₂O₃ photoanode annealed at 400 °C using the 250 nm sized-polystyrene (PS) colloid template and 9 minutes of electrodeposition time for the given specific Fe precursor solution. This resulted in the highest photocurrent density compared to other crossed conditions, which significantly achieved 3.1 mA cm^-2 at 0.5 V vs. Ag/AgCl reference electrode. The synthesis of the IOS α-Fe ₂O₃via an easy-to-control electrochemical process is described for first time that opens a possibility for constructing other oxide semiconductor photoanodes (not only well-known Si, Ti and Zr) with inverse opal structure.