Photoelectrochemical characterization of the synthetic crednerite CuMnO2

High quality crednerite CuMnO2 was prepared by solid state reaction at 950 degrees 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 CuxMn3-xO4 at similar to 420 degrees C in air and further heating reform the crednerite above 940 degrees 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 mu A cm(-2) and a corrosion potential of similar to-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 x 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-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 degrees 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.