An effective strategy to promote hematite photoanode at low voltage bias via Zr4+/Al3+ codoping and CoOx OER co-catalyst

Highlights: • Zr⁴⁺/Al³⁺-codoped Fe₂O₃ photoanode synthesized by hydrothermal method. • CoO_x co-catalyst improves the OER kinetics via surface reworking. • Optimum photoanode exhibits 102% increase in photocurrent density than Fe₂O₃. • The charge transfer mechanism in 6% Zr + 6% Al + 15 mM Co is also proposed. -- Abstract: Herein, we report the surface treatment on Zr⁴⁺/Al³⁺ codoped α-Fe₂O₃ photoanode for high-performance photoelectrochemical water splitting. A high-temperature quenching exhibits the Zr⁴⁺/Al³⁺ codoping in α-Fe₂O₃ photoanode without damaging morphology. The presence of Zr⁴⁺/Al³⁺ codoping shows a cathodic shift in onset potential, but lack of increment in photocurrent reveals the major role of passivation and the minimum doping effect of aluminum. Additionally, CoO_x cocatalyst exhibits increment in photocurrent with the greater cathodic shift in onset potential than the pristine α-Fe₂O₃ nanorods. The CoO_x surface-reworked Zr⁴⁺/Al³⁺ codoped α-Fe₂O₃ photoanode displays the highest photocurrent of 1.5 mA/cm² at 1.23 V vs. RHE (76% increment over the pristine α-Fe₂O₃) and 0.7 mA/cm² at 1.0 V vs. RHE (102% increment over the pristine α-Fe₂O₃). The systematic characterization carried out using x-ray diffraction and scanning electron microscopy confirms that after Zr⁴⁺/Al³⁺ codoping, and surface treatment, the crystalline structure, and morphology of the photoanodes remains unchanged. X-ray photoelectron spectroscopy confirmed the existence of Zr⁴⁺/Al³⁺ codopants in the hematite nanostructure. The electrochemical properties of the photoanode suggest that Al³⁺ and Zr⁴⁺ codoping, as well as surface treatment with CoO_x, cocatalyst lowers charge transfer resistance across the FTO/hematite interface, and hematite/electrolyte interface. This designs not only lowers onset potential but also offers the blueprint for the development of an efficient catalyst for solar water oxidation.