Numerical modeling of salt effects in weak acid–weak base diodes

Abstract

Abstract This work studies the effect of salt contamination in weak acid-base diodes by numerical modeling. In a positive salt effect some salt is added to the alkaline reservoir, while the negative salt effect appears as a suppression of the positive one by contaminating also the acidic side of the diode. First, the positive and negative salt effects were investigated for weak electrolytes and they were found to be similar to those in a traditional strong acid-base diode. Next, positive and negative salt effects were studied when the ions of the contaminating salt were different from that of the weak electrolytes. In the positive salt effect it was found that at a certain critical concentration of the added salt the current increases sharply in a nonlinear fashion. In a negative salt effect it was found that the diode current responds strongly even for small changes in the salt concentration on the acidic side. The sensitivity of a weak acid-base diode was found to be similar to that of a strong one, thus it can be also applied as a sensitive detector of nonhydrogen cations in an acidic medium. Furthermore, weak electrolytes provide milder conditions for the non-reactive parts of the diode, and their potential profiles can also be more suitable for ion detectors.