Photo-electrochemical properties of p-type AgCoO2 prepared by low temperature method

AgCoO2 prepared by co-precipitation at low temperature (similar to 80 degrees C) is characterized by physical and photo-electrochemical techniques. The X-ray diffraction shows broad peaks with a particle size of similar to 20 nm and a specific surface area of similar to 28 m(2) g(-1). The forbidden band (1.33 eV) is due to Ag+ : d -> d transition, further transition at 4.50 eV is assigned to the charge transfer. The transport properties, measured up to 650 K, indicate intrinsic conductivity: sigma = sigma(o) exp{- 0.24 eV/kT (Omega-cm)(-1)}, supporting a phonon assisted conduction mechanism. An exchange current density of 1.27 mA cm(-2) in Na2SO4 (0.1 M) solution is consistent with the electrochemical stability up to 0.8 V-SCE. The capacitance measurement (C-2 - E) indicates p type conduction, with a flat band potential (E-fb) of 0.26 V-SCE and a holes density (N-A) of 7.38 x 10(19) cm(-3) due to the oxygen insertion in the layered lattice. The electrochemical impedance spectroscopy (EIS) data, recorded in the range (1 mHz - Hz), reveals a predominant bulk contribution with a low depletion angle of 3 degrees and a pseudo capacitive behavior. As application, AgCoO2 is tested for the hydrogen production upon visible illumination owing to the potential of its conduction band (-0.83 V-SCE), less cathodic than that of H2O/H-2 (similar to -0.5 V-SCE). H-2 evolution rate of 79 mu mol g(-1) min(-1) is determined at neutral pH with a quantum yield of 1.92% in presence of NO2 as hole scavenger; no Ag deposition was observed after photocatalysis.