Carbon-Based Membrane Materials to a Silver/Silver Chloride Reference Electrode

Carbon-based membrane materials made of natural charcoal and pencil lead were attempted as an ion-exchange membrane to a silver-silver chloride reference electrode in sulfuric acid, hydrofluoric acid, sodium sulfate, boric-borate buffer, and potassium hydroxide solutions. During the immersion in ultrapure water, the potential shift towards the positive potential direction revealed that the KCl reference solution is diluted through the membranes. Electrochemical impedance spectroscopy showed that the pencil lead membrane is more electrochemically resistive than the charcoal membrane in all the pH solutions. The relatively high resistance of the pencil lead compared to the charcoal membrane is thought to be due to its pore structure and the presence of clay as an ingredient of pencil lead. The charcoal membrane could be a more suitable material than the pencil lead as a salt bridge to the reference electrode in aqueous solutions.