ON THE FORMATION OF "Ag₂O₃" ON SILVER ELECTRODES

Abstract

"Ag 2 O 3 " was examined electrochemically in eutectic KOH−H 2 O at −40 °C by coulombic measurements of quantities formed, open circuit potential decays, variation of potential as a function of anodic current density, and temperature coefficients of decomposition rates. It can be formed directly from Ag 2 O on Ag at current density (c.d.) > 15 μA/cm 2 , with a maximum thickness during the first oxidation cycle (25 layers, assuming a surface roughness factor of one) occurring at 65 μA/cm 2 . Potential decay (−∂E/∂ log t ≡ b) curves have protracted linear regions where 0.045 < b < 0.078, sometimes higher. One-tenth of a layer of adsorbed species superimposed on the higher oxide exists on the surface during O 2 evolution. Reduction curves show a minimum in the potential decay of the higher oxide preceding the formation of Ag 2 O. The "Ag 2 O 3 " decomposes in approximately 1 h at −40 °C to either AgO or Ag 2 O. The activation energy for its thermal decomposition is 12.0 ± 2.0 kcal/mole. Under most experimental conditions studied the results indicated that the material is not true Ag 2 O 3 but it is probably better described as Ag 2 O[O] where [O] is trapped oxygen.The evidence does point to the probable existence of a thin layer, which may be true Ag 2 O 3 , on the surface in a steady state which is maintained at high anodic current density ( > 100 μA/cm 2 at −40°).