Surface restructuring of hematite photoanodes through ultrathin NiFeOx Catalyst: Amplified charge collection for solar water splitting and pollutant degradation

In this study, problems associated with hematite-based photoanodes are strategically solved using a ternary NiFeOx (NFO) top-layer for the first time, which is deposited using an atomic layer deposition (ALD) technique. Prior to the photoanode development, the ALD growth optimization of NiFeOx is carried out by the super-cycle combination approach and confirmed through structural analysis and high-resolution focused-ion beam transmission electron microscopy imaging. An ultrathin layer of NiFeOx (3 nm) with 25 at.% of Ni over hematite photoanodes (Sn-Fe2O3/NFO25) exhibits the highest photocurrent density at 1.23 VRHE. The roles of the surface states of hematite are elucidated through electrochemical and compositional investigations. The NiFeOx nanolayer effectively annihilates the surface states on the hematite nanorod, subsequently unraveling the inherent photovoltage. The new charge transport path is observed via interfacial analysis, where the valance band maximum VBM shuttles holes to the electrolyte at an accelerated rate. The synergistic effect of the passivation layer significantly enhances the rate of charge separation, which is also observed in photoelectrocatalytic degradation of tetracycline hydrochloride with Sn-Fe2O3/NFO25, compared with the pristine Sn-Fe2O3 photoanodes. The work puts forward a new strategy by incorporating ternary ALD systems to develop photoanodes that are effective in both water splitting and wastewater treatment technologies.

Automated summary

This study successfully addressed the issues associated with hematite-based photoanodes by strategically incorporating a ternary NiFeOx (NFO) top-layer deposited using atomic layer deposition (ALD) technique. The optimized NiFeOx layer significantly improved the photocurrent density, offering a promising approach for developing efficient photoanodes.