α-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, high-resolution 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 ∼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.