Photoelectrochemical characterization of the synthetic crednerite CuMnO2

High quality crednerite CuMnO 2 was prepared by solid state reaction at 950 °C under argon flow. The oxide crystallizes in a monoclinically distorted delafossite structure associated to the static Jahn–Teller (J–T) effect of Mn 3+ ion. Thermal analysis showed that it converts reversibly to spinel Cu x Mn 3− x O 4 at ~420 °C in air and further heating reform the crednerite above 940 °C. CuMnO 2 is p -type, narrow semiconductor band gap with a direct optical gap of 1.31 eV. It exhibits a long-term chemical stability in basic medium (KOH 0.5 M), the semi logarithmic plot gave an exchange current density of 0.2 μA cm −2 and a corrosion potential of ~−0.1 V SCE . The electrochemical oxygen insertion/desinsertion is evidenced from the intensity–potential characteristics. The flat band potential ( V fb = −0.26 V SCE ) and the holes density ( N A = 5.12 × 10 18 cm −3 ) were determined, respectively, by extrapolating the curve C − 2 versus the potential to the intersection with C − 2 = 0 and from the slope of the Mott–Schottky plot. From photoelectrochemical measurements, the valence band formed from Cu-3 d wave function is positioned at 5.24 ± 0.02 eV below vacuum. The Nyquist representation shows straight line in the high frequency range with an angle of 65° ascribed to Warburg impedance originating from oxygen intercalation and compatible with a system under mass transfer control. The electrochemical junction is modeled by an equivalent electrical circuit thanks to the Randles model.