Problems associated with the thin-film Ag/AgCl reference electrode and a novel structure with improved durability

We have developed a novel thin-film Ag/AgCl reference electrode which shows dramatic improvement in its durability. To make the electrode resistant to heat treatment in its fabrication, a metal adhesive layer in the currently used thin-film Ag/AgCl electrodes was replaced by a polyimide layer, and a gold backbone structure was employed. Unlike the currently used structure, the entire surface of the silver layer was covered with a polyimide layer and AgCl was grown from the periphery of the pattern. The structure was resistant to baking at 300 degrees C. Whereas the currently used Ag/AgCl electrode has a very short lifespan in concentrated KCl solutions, the novel electrode showed surprising resistance in these solutions. In a KCl and AgCl saturated solution, the novel electrode gave a stable potential for approximately 8 h, while the currently used electrode functioned for only 1.5 min. A dramatic difference was also observed in the resistance to interfering materials. Although 1 mM Kl or K2S was enough to break the currently used electrode, the novel electrode was resistant to these materials and showed much smaller potential shift. In the novel Ag/AgCl structure, the rate of AgCl formation was significantly delayed and the spread of the AgCl layer was visualized. Therefore, any of the electrochemical and chemical methods of AgCl formation could be easily applied. (C) 1998 Elsevier Science S.A. All rights reserved.