Hybrid FeNiOOH/α-Fe₂O₃/Graphene Photoelectrodes with Advanced Water Oxidation Performance

In this study, the photoelectrochemical behavior of electrodeposited FeNiOOH/Fe₂O₃/graphene nanohybrid electrodes is investigated, which has precisely controlled structure and composition. The photoelectrode assembly is designed in a bioinspired manner where each component has its own function: Fe₂O₃ is responsible for the absorption of light, the graphene framework for proper charge carrier transport, while the FeNiOOH overlayer for facile water oxidation. The effect of each component on the photoelectrochemical behavior is studied by linear sweep photovoltammetry, incident photon-to-charge carrier conversion efficiency measurements, and long-term photoelectrolysis. 2.6 times higher photocurrents are obtained for the best-performing FeNiOOH/Fe₂O₃/graphene system compared to its pristine Fe₂O₃ counterpart. Transient absorption spectroscopy measurements reveal an increased hole-lifetime in the case of the Fe₂O₃/graphene samples. Long-term photoelectrolysis measurements in combination with Raman spectroscopy, however, prove that the underlying nanocarbon framework is corroded by the photogenerated holes. This issue is tackled by the electrodeposition of a thin FeNiOOH overlayer, which rapidly accepts the photogenerated holes from Fe₂O₃, thus eliminating the pathway leading to the corrosion of graphene.