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Electrolyte diodes with weak acids and bases. I. Theory and an approximate analytical solution
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View: Figures


Image of FIG. 1.
FIG. 1.

Scheme of an electrolyte diode experiment. The alkaline and the acidic (HA) reservoirs are connected by a capillary filled with a hydrogel to prevent advection. Constant concentrations are maintained in these reservoirs by feeding them continuously with fresh electrolyte solutions. The steady-state voltage-current characteristics measured in this setup depends on the polarity like in a semiconductor diode. In the case of a reverse-biased electrolyte diode (when the acidic reservoir is positive as in this figure) usually the gel can be divided into three different zones: an alkaline (length ), an acidic (length ), and a middle weakly acidic (length ) zone.

Image of FIG. 2.
FIG. 2.

Analytical approximation of the current-voltage characteristic of a weak acid-weak base (a) and a strong acid-strong base diode (b), where acid and base concentrations were at both ends of a -long gel cylinder. The continuous line shows the validity range of the approximation, i.e., where the gel can be divided into three regions. The dashed line shows the potential range where there is no middle (weakly acidic) zone in the gel. (The three-zone approximation for a reverse-biased diode can be applied when the absolute value of the applied voltage is more than in the case of weak acids and bases and in the case of strong acids and bases.)

Image of FIG. 3.
FIG. 3.

Analytical approximation of the concentration profiles and the voltage profile along the gel for voltage difference in a weak acid-weak base diode [(a), (b), and (c)] [ in the left and in the right reservoir] and in a strong acid-strong base diode [(A), (B), and (C)] ( in the left and HCl in the right reservoir). The characteristic length of the gel was , and the weakly acidic fixed group concentration was , whereas the dissociation constant of the fixed groups was .)


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Electrolyte diodes with weak acids and bases. I. Theory and an approximate analytical solution