ELECTRODE AND MEMBRANE POLARIZATION. Interim Report for 1958
A kinetic model for the electrical behavior of elec trode-solution interfaces is set up using the usual equations of motion for ions in a viscous medium, and a linear dependence of the reaction rates on changes in the concentrations and voltages occurring at the electo describe the properties of ideal polarized electrodes. Various equivalent circuits can be derived which depend on the sequence of reactions postulated aa taking place at the electrode. The parameters of these equivalent circuits can lie simply related to the concentratioas and diffusivities of the reacting species, and the standard free energy change associated with the reaction barrier by applying the transition state reaction rate theory. Laboratory measurements were made on a variety of metal aad semiconducting electrodes, and theoretical equivalent circuits were fit to the data. Good fits were achieved with most of these cases and with others obtained from the literature. A rather remarkable uniformity of results with different electrodes under varying conditions is found. The explanation of this result remains an open question. There is little evidence that the reactions actually taking place at the electrodes are the ones usually postulated. The ion equations of motion used in the electrode-electrolyte interface problem are also used in the study of polarization in membranes. The membrane model consists of zones of alternating transference properties in series. The ion flow in the separate zones are coupled through the continuity conditions at the interface between the zones. The frequency dependence of the impedance of this model is associated with the buildup of concentration gradients at these boundaries. When large differences in the transference properties of the zones exist, the polarization effects can be very important. The impedance can vary with frequency by a factor of two or more. There is no simple equivalent circuit that represents this impedance, but it has been evaluated numerically for several cases. Experimental studies on the electrical impedances of ion exchange resins and pure clay systems have been made, and they revealed large frequency effects, some greater than 50%. These effects are spread out over a greater range than those in the theoretical model, but this is to be expected because of the wide distribution of zone lengths existing in a natural system. When a limited comparison is made between the experiimportance of having alternating zones of different transference properties is emphasized by measurements on mixtures of anion and crition exchange resins. (auth)
- Research Organization:
- Massachusetts Inst. of Tech., Cambridge
- DOE Contract Number:
- AT(05-1)-718
- NSA Number:
- NSA-13-016921
- OSTI ID:
- 4240304
- Report Number(s):
- RME-3157
- Resource Relation:
- Other Information: Orig. Receipt Date: 31-DEC-59
- Country of Publication:
- United States
- Language:
- English
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