Development of gel electrolyte from agar for using in Ag/AgCl electrode

Ag/AgCl reference electrode (Ag/AgCl) is frequently employed among the reference electrodes due to its simplicity, low cost, and environmental-friendly with non-toxic components. Normally, Ag/AgCl reference electrode is filled with liquid electrolyte making it prone to leakage or evaporation loss and is also difficult to maintain. Gel polymer electrolyte (GPE) is an alternative for use as electrolyte in reference electrode that can provide high flexibility, low maintenance, and possibility for miniaturization. In this work, the Ag/AgCl reference electrode was constructed using agar gel for its electrolyte. Agar, glutaraldehyde (GA), and potassium chloride (KCl) were used for preparation of GPE. The prepared gel has low evaporation loss, good mechanical strength and good conductivity. It can be stored without the appearance of salt creep or fungal mold for over 6 months. A prototype reference electrode was also constructed from a pipette tip and silver wire. The silver wire was passivated with a layer of AgCl by passing an electrical current in 0.05M KCl for 10 minutes. Porous PTFE was placed at the end of the pipette tip forming the ion-conductive porous junction. This prototype Ag/AgCl reference electrode was used to test for the potential stability and the potential difference against a standard commercial Ag/AgCl electrode in 0.1M, 1M, 2M and pH 4, 7, 10 solution for the short-time stability of 5-minutes and longer-time stability of 10 hours. The fabricated reference electrode showed good precision and stability. The drift over 5-minutes stability was less than 10 hours stability and was less than 1 mV. The maximum potential difference compared to the standard commercial electrode was less than 16 mV in various solutions.