Abstract
The dynamic properties of the double layer at the AgI/solution interface are discussed in terms of the relation between Ag + interstitials in the AgI phase and the composition of the aqueous solution. Owing to the relatively short relaxation time of the space charge in AgI, the capacitance of the double layer may be regarded as a pure capacitance in the frequency range covered by the impedance measurements. Other possible components of the interfacial impedance are an ion-transfer resistance and a Warburg impedance for transport of Ag + (or I −) in solution. The latter may exhibit a complicated frequency dependence due to the roughness of the AgI surface. It is explained how in the past this complication has led to incorrect interpretation of the impedance spectrum. Experimental impedance data have been obtained by the coulostatic impulse technique. Different ways of impedance spectrum analysis are discussed, taking into account the effect of surface roughness on the mass transport impedance. It is pointed out that the analysis of the real and imaginary components of the admittance gives the best results. From the present analysis it is concluded that interfacial ion transfer is fast, and that relaxation processes are fully described by the double-layer capacitance and diffusional mass transport in solution.
Published Version
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