Photoelectrochemical characterization of the synthetic crednerite CuMnO2
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High quality crednerite CuMnO2 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 Mn3+ ion. Thermal analysis showed that it converts reversibly to spinel Cu x Mn3−x O4 at ~420 °C in air and further heating reform the crednerite above 940 °C. CuMnO2 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 VSCE. The electrochemical oxygen insertion/desinsertion is evidenced from the intensity–potential characteristics. The flat band potential (V fb = −0.26 VSCE) and the holes density (N A = 5.12 × 1018 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-3d 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.
KeywordsCrednerite p-Type semiconductor Photoelectrochemical Nyquist plot
We thank Dr A. Louafi for helpful discussion regarding the EIS interpretation and Dr M. Kebir for assistance in obtaining the X-ray powder data. Financial support was provided by the Faculty of Chemistry (Algiers).
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