alpha-Fe2O3 nanorods decorated with NiMnO3 co-catalyst as photoanode for enhanced oxygen evolution reaction in photoelectrochemical water splitting

Abstract

An efficient hematite nanorods (HNRs) decorated with NiMnO3 co-catalyst photoanode (NiMnO3-HNRs) is explored for the first time by preparing through a simple two-step hydrothermal method using inexpensive precursors. In the first hydrothermal step, flower-like arranged HNRs have been synthesized, and in the second hydrothermal step, the pure phase of NiMnO3 as an oxygen evolution reaction (OER) co-catalyst is decorated on the HNRs surface. NiMnO3-HNRs photoanode has been characterized by scanning electron microscopy, highresolution transmission electron microscopy, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, UV-vis spectroscopy, and photoluminescence spectroscopy. The interlinked dynamic concurrence of different valence states of Ni and Mn in NiMnO3, caused by the incorporation of Ni in the Mn-O based catalyst, facilitates the photogenerated charge-carriers transfer in HNRs surface. It is the reason why NiMnO3-HNRs shows higher photocurrent density as compared to MnO2-HNRs and HNRs. The NiMnO3-HNRs photoanode presented an enhanced photocurrent density of 2.96 mA cm(-2) at 1.23 V vs. RHE applied potential, which is superior photocurrent density to MnO2-HNRs (0.76 mA cm(-2)), and pristine HNRs photoanode (0.16 mA cm(-2)). Furthermore, the NiMnO3-HNRs photoanode is stable in alkaline medium and shows only a similar to 3 % reduction in the photocurrent value in 8 h. A significant cathodic shift in onset potential corresponding to OER photocurrent, from 1.03 V vs. RHE to 0.66 V vs. RHE, is observed due to the combined effect of enhanced OER activity and efficient electron-hole separation on NiMnO3-HNRs surface. NiMnO3 co-catalyst suppresses the photogenerated charge-carriers recombination on HNRs surface, intrinsically maintains good interfacial contact, and significantly decreases photoanode-electrolyte interface charge-transfer resistance.