Solution-processed electrochemical synthesis of ZnFe 2 O 4 photoanode for photoelectrochemical water splitting

Herein, we report the synthesis of ZnO nanorod films onto FTO (fluorine-doped tin oxide) substrates using the solution-processed electrodeposition method. As-synthesized ZnO nanorod films obtained from electrodeposition were modified to form zinc ferrite (ZnFe2O4) thin films by Fe incorporation through varying molar concentrations. The formation of ZnFe2O4 films was confirmed by XRD and Raman spectroscopy. FE-SEM analysis shows a significant change in the growth morphology with an increase in Fe molar concentration. UV-Visible spectroscopy analysis showed that with an increase in Fe molar concentration, the absorption edge in ZnFe2O4 films shifts towards a higher wavelength with a reduction in the direct band gap. Finally, the PEC properties of ZnFe2O4 photoanodes were investigated for water splitting. The highest photocurrent density of ~ 353 μA/cm2 has been observed for ZnFe2O4 photoanode prepared at 2.0 M. Shift of flat band potential shift from −0.25 to −0.61 V with an increase in Fe molar concentration indicates a shift in the Fermi level towards the conduction band, which leads to an efficient charge transfer process across the electrolyte. Furthermore, increased carrier density and decreased depletion width with increased Fe molar concentration suggest easier diffusion of photo-generated charge carriers. The obtained results demonstrate that ZnFe2O4 can be a promising candidate for efficient PEC water splitting over the traditional ZnO photoanode.