Effects of the phase transition on the photoelectrochemical properties of CuFe2O4 composite photoelectrode

In this study, CuFe₂O₄ was grown using various Cu:Fe source molar ratios. The morphological, structural, electrical, and photoelectrochemical properties of CuFe₂O₄ photoelectrodes with different structural phases based on molar ratios were analyzed. XRD and XPS were performed to systematically analyze the relationship between the structural and photoelectrochemical properties of the photoelectrode. XRD analysis revealed the phase transformation of CuFe₂O₄ from cubic to tetragonal phase and back to cubic phase as the Cu:Fe source molar ratio was varied. The crystallinity of Cu-rich cubic-CuFe₂O₄ was found to be superior to that of tetragonal-CuFe₂O₄. XPS analysis showed that the Cu-rich cubic-CuFe₂O₄ sample has higher Cu and Fe binding energies and more oxygen vacancies than the tetragonal-CuFe₂O₄ sample, which helps reduce carrier recombination. Additionally, cubic-CuFe₂O₄ samples prepared in Cu-rich conditions demonstrated high flat-band potential and low charge transfer resistance values. As a result, the cubic-CuFe₂O₄ photoelectrode sample under the Cu-rich condition exhibited a relatively high photocurrent density value. The highest photocurrent density value (-0.38 mA/cm² at −0.55 V_SCE) was obtained with cubic-CuFe₂O₄ samples prepared under the Cu:Fe 3:1 condition.