Photoelectrochemical properties of AFe2O4 (A = Co, Cu, Zn) ferrospinels for water photo-reduction

• Crystalline ferrospinels were prepared by co-precipitation.
• They are stable and efficient photo-catalysts under visible irradiation.
• ZnFe2O4 exhibited the highest hydrogen evolution rate ∼197 µmol/g s.
• All the spinels were found to be indirect band gap materials.
• They were n-type semi-conductors with indirect optical transition between ∼1.3 and 1.7 eV.

The photo-electrochemical characterization of the ferrospinel AFe2O4 (with A = Co, Cu and Zn), prepared by co-precipitation, has been investigated for the hydrogen production under visible light. They are n-type semi-conductors with indirect optical transition observed in the region between ∼1.3 and 1.7 eV. Mott-Schottky and electrochemical impedance spectroscopy techniques were used both in the dark and under illumination for investigating their photo-electrochemical (PEC) characteristics. The analysis of the frequency spectra for the real and imaginary parts of the complex impedance allow to obtain the equivalent electrical analogs for the PEC cell operating in the dark and under illumination. Electronic equivalent circuits were also proposed. Under the reaction conditions, the rate of hydrogen evolution after one hour of irradiation attains ∼197, 132 and 131 µmol g−1 s−1 with a quantum efficiency ι(H2) of 0.13, 0.09 and 0.08% for ZnFe2O4, CoFe2O4 and CuFe2O4, respectively.

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