Study of Polypyrrole Coating on the Performance Improvement of Ag/AgCl Chloride Ion Sensor in Highly Alkaline Concrete Environments

Ag/AgCl possesses the merits of a stable reference potential and good chemical stability, making it widely used in concrete for monitoring chloride ions. However, in the concrete circumstance, the high hydroxide ion content would significantly deteriorate the sensitivity and stability of the Ag/AgCl electrode in detecting chloride ions. Herein, in this work, a highly sensitive and stable Ag/AgCl electrode is proposed by employing a protective coating layer based on polypyrrole (PPy). Using a facile coating process, a uniform PPy layer is coated on the surface of an Ag piece, effectively precluding hydroxide ions from reacting with AgCl. The modified Ag/AgCl electrode exhibits high sensitivity to chloride ions over a wide range (10⁻⁵–5 mol/L), fast response time (0.01 s), and distinguished long-term stability (90 days). Moreover, the feasibility of the proposed Ag/AgCl electrode in monitoring chloride ions of concrete has been validated, suggesting its great practicability in concrete structures.