Oxygen Layers on Silver in Alkaline Electrolytes

The Ni(OH)2 layers consist of a few molecular layers only. Thin layers do not yet possess [92] the properties of the bulk phase. The free energy of formation approaches [92] that of the bulk phase with increasing layer thickness. Thus the formation of the initial patches of hydroxide or oxide may be expected during the anodic sweep at potentials which are smaller than the reversible potential of the corresponding bulk phase if a kinetic hindrance is absent. The presence of thin layers cannot be predicted on thermodynamic grounds but has to established experimentally. Few experimental results on the equilibrium properties of thin films have been published [92], but thin films may be classified as taking an intermediate position between chemisorbed layers and phase hydroxides and oxides. 

The formation of the lowest silver oxide, Ag20, according to reaction 11 

The i—U curves measured [95] with 0.1 V/sec on silver between 0.1 V and 1.1 V in 1 M KOH, saturated with argon, show waves with peaks at about 0.35 V and 0.75 V during both the anodic and cathodic sweep. The waves were attributed to the formation or reduction respectively of two adsorption compounds of oxygen. The silver electrodes had been polished mechanically, washed in hot 1 M KOH, and reduced with a current of —1.5mA. Anodic pretreatment at C/ 1.5V, carried out before the reduction, increased the roughness of the silver surface. The current at a given potential had a larger value than without anodic pretreatment. 

The i — U curve in Fig. 33 was measured by Zhutaeva and Shumilova [97] in 1 M KOH with 0.1 V/sec. The silver electrode was kept at —0.4 V for 10 min before applying the sweep once. The curve displays five waves during the anodic sweep. There are three waves during the cathodic sweep. By choosing the limits of the potential sweep appropriately, 

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