The use of agar gelled electrolyte for in situ electrochemical measurements on metallic cultural heritage

Electrochemical techniques, such as electrochemical impedance spectroscopy (EIS), are widely used for corrosion studies. However, their applicability to studies on metallic cultural heritage has been less spread due to the practical difficulties of performing measurements in-situ on sculptures or monuments. One interesting approach to this application is the use of gel polymer electrolytes (GP-E) to overcome the difficulties of handling liquid electrolytes on irregular leaning surfaces. In this paper, the behavior of an agar gelled electrolyte with a portable cell is evaluated for EIS measurements over three types of bronze coupons, and compared with a traditional liquid cell. The influence of the addition of agar in the reproducibility and repeatability of measurements is assessed, as well as the possible interaction of agar with the corrosion process. Results show that, although agar slightly accelerates the anodic process, it does not significantly affect the cathodic reaction and does not introduce new reactions in the corrosion mechanism. It is demonstrated that the GP-E allows obtaining reproducible and good quality EIS spectra, comparable to the liquid cell. Hence, it can be used for comparative in-situ measurements, being a very valuable tool for the evaluation of patina and coatings on metal cultural heritage.