Electrode Capacitance in Silver-Halide Solid Electrolyte Cells I. Room Temperature Graphite and Platinum Electrodes

Potentiostatic hronocoulometry on polarized graphite electrodes on AgI and AgBr solid electrolytes at room temperature shows an ideally fast, almost voltage-independent, double layer charging process for both electrolytes. Results on the more highly conductive electrolyte 2 [ (CH3)4NI] 9 13 AgI are similar to AgI, but with moderate capacitance dispersion in the subsecond time range. For all three electrolytes, the results uggest charging by a com-pact, purely electrostatic, interracial Ag+-ion layer separated from the graph-ite surface by a strongly adsorbed anion layer. For platinum electrodes on AgI and AgBr, a variety of types of platinum and surface pretreatments gave the common result of a slow, broadly dispersed charging process. The Pt results are consistent with a previously proposed interface model in which charging involves both cation and anion motion, and suggests that slow charging results from the relatively immobile anions. The relationship between various types of double layer capacitance in solid electrolytes is discussed