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

In this study, the photoelectrochemical behavior of electrodeposited FeNiOOH/FeO/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: FeO 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/FeO/graphene system compared to its pristine FeO counterpart. Transient absorption spectroscopy measurements reveal an increased hole-lifetime in the case of the FeO/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 FeO, thus eliminating the pathway leading to the corrosion of graphene.