Nonlinear "salt-effect" in an electrolyte diode. Theory and experiments+

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Abstract

The electrolyte diode is an open chemical system, where simultaneous concentration and electric potential gradients are maintained in a gel medium. In the experimental apparatus a small gel cylinder connects an alkaline and an acidic chamber ted continuously by 0.1 M KOH and O.I M HCI solutions, in forward direction, when the alkaline reservoir is positively biased. K-4 and CI" ions migrate into the gel where they form a 0.1 M KC1 solution. The impedance is low in this case. On the other hand a reverse polarity creates a thin layer of electrolyte-free water with a high impedance. The low backward current can he increased by adding some salt (e.g. KCI) either to the alkaline or to the acidic feedstream. Here we study the effect of KC1 when it is added to the KOH solution. This salt-effect is highly nonlinear, however. Increasing the salt concentration in the alkaline feedstream first causes only a small change in the backward characteristic hut in the vicinity of a critical value a very steep increase of the current can be observed. Most of these experimental findings agree qualitatively with theoretical predictions based on the NernstPlanck equations. Nevertheless, on quantitative level some interesting deviations are also observed.

Original languageEnglish
Pages (from-to)279-286
Number of pages8
JournalACH - Models in Chemistry
Volume135
Issue number3
Publication statusPublished - Dec 1 1998

ASJC Scopus subject areas

  • Chemistry(all)

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