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

Abstract

AgCoO2 prepared by co-precipitation at low temperature (~ 80 °C) is characterized by physical and photo-electrochemical techniques. The X-ray diffraction shows broad peaks with a particle size of ~ 20 nm and a specific surface area of ∼ 28 m2 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: σ = σo exp{− 0.24 eV/kT (Ω-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 VSCE. The capacitance measurement (C−2 - E) indicates p type conduction, with a flat band potential (Efb) of 0.26 VSCE and a holes density (NA) of 7.38 × 1019 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° 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 VSCE), less cathodic than that of H2O/H2 (~ −0.5 VSCE). H2 evolution rate of 79 µmol 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.