Rectifying effect for ion-selective electrodes with conducting polymer solid contact

Asymmetric influence of galvanostatic polarization of all-solid-state ion-selective electrodes was studied on example of a potassium-selective sensor with poly(vinyl chloride) based membrane and solid contact: typically polypyrrole doped by chloride ions. For a high thickness of the solid contact layer anodic polarization was characterized by significantly higher overpotential compared to cathodic one, thus, a “rectifying” effect of the membrane was observed. The difference in polarization influence was explained by limited availability of mobile ions on the membrane / solid contact interface. The chronopotentiometric response was discussed in terms of an equivalent circuit containing the solid contact capacitance, the membrane and charge transfer resistances. It was shown that intentional incorporation of mobile ions to the membrane or solid contact by appropriate conditioning or application of cation-exchanging solid contact material resulted in reduction or disappearance of the rectifying effect.The presence of polarization asymmetry is significant not only for application of current based electrochemical methods to ion-selective electrodes but also for newly developing area of application of lipophilic membranes to modify electrical parameters of electrolyte gated field-effect transistors.