Analysis of Porous Electrodes with Sparingly Soluble Reactants: IV . Application to Particulate Bed Electrode: System

Abstract

Experiments were conducted to characterize critical processes which determine performance of totally immersed, porous, secondary electrodes having sparingly soluble reactants. Particulate beds comprised of silver spheres, 37.7 -+-4.2 ~m in diameter, were used as Ag/AgC1 electrodes in 1N KC1. Silver chloride product distribution and facial potential as functions of time during galvanostatic charging are compared to predictions of a recently developed mathematical model. Good accord is shown over the tested time range, 1-19 rain, and exterior current density 50 mA cm-~. Time for onset of pore blockage with failure to accumulate charge, about 18 rain, and the reaction penetration, mostly less than 0.03 era, are predicted with reasonable accuracy. A characteristic minimum in polarization occurs during galvanostatic discharge due to reduction in pore blockage at the beginning of discharge, increase in KC1 concentration in the depth of the electrode, and increase in effective matrix electronic conductivity with silver deposition. A final rise in polarization occurs when silver chloride is depleted. Theory is used to show how governing rate processes are shifted by the occurrence of blockages of the first and second kinds.) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 128.6.218.72 Downloaded on 2015-06-06 to IP Vol. 123, No. 9 ANALYSIS OF POROUS ELECTRODES Basis of parameter selection Measured Approximate measured value Measured Measured Estimated from photomicrographs Approximate, measured value, Ref. (13)Calculated from porosity and sphere diameter, Ref. (15) Calculated from porosity and sphere diameter, Ref. (15) Calculated from estimated diffusion coefficient, Ref. (12), and diffusion path, Ref. (13) Best value fitting data From Ref. (12) where A is specific surface area in era-1 and from assumption of 0.9 coverage factor, Fig. 8 Assumed functional dependence and mode change at 0.9, Fig. 8 Geometrical reasoning, e.g., Ref. (21)9 A parabolic decrease with distance is a~sumed for the porosity change at depths from 0 to 0.45 mm as an approximation based o• photomicrographs. 9 * Surface is calculated according to ReL (15) from the porosity and sphere radius for depths from 0 to 0.45 ram.) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 128.6.218.72 Downloaded on 2015-06-06 to IP

Potentiometric Response of Ag/AgCl Chloride Sensors in Model Alkaline Medium

“…e surface properties (morphology and microstructure) of the AgCl layer will affect the surface chemistry of the sensors. e level of surface chemistry alterations was found to be directly linked to the thickness, morphology, and microstructure of the AgCl layer, which were dependent on the anodization regime used for the sensor preparation [19][20][21][22]. For instance, chemical recombination and/or the presence of oxygen or carbon-based impurities on the sensors' surface would be responsible for a deviation of the sensors' response from the one expected for a purely Ag/AgCl interface [17].…”

Analysis of Porous Electrodes with Sparingly Soluble Reactants: V . Single Pore Studies: System

“…Equation [4] results from integrating along an assumed diffusion path between the active salt and metal surfaces. On examination of SEM photographs of our own (11) as well as those by Katan et al (5,6) and in interpretating our theoretical calculations and comparison to experiment, it became apparent that all of the exposed area, 0 for the metal or (1 --0) for the salt, is not active, As 0, for example, goes over 0.5 some of the area becomes inactive. The concept of an effective area was introduced such that a ring of fixed distance around the salt crystals was assumed to define 0elf for 0 > 0.5.…”

“…The electrolytic oxidation of thiocyanate ion in thiocyanate melt was reported by several authors (i-4) to result in the formation of a polymeric substance, parathiocyanogen (SCN)x; others (5,6) found the reaction to yield sulfur and cyanogen. The oxidation product is an orange-yellow deposit sticking to the surface of the anode.…”

“…with real battery plates (2), electrodes formed from uniform powder (3,4) or uniform-size spheres (5,6), and idealized single pores (7)(8)(9).…”

“…Applying the results to the validation of a mathematical model is usually less desirable due to uncertainties in the physical parameters of the electrode such as porosities and tortuosities. In the earlier study of a particulate bed Ag electrode (5), the porosity and the specific surface area of the electrode were only approximately known. When comparing the mathematical model calculations with experimental results, a tortuosity factor of 0.5 was assumed, and the exchange current density was used as a fitting parameter.…”