Electrochemical measurements in high impedance systems

Electrochemical impedance spectroscopy (EIS) is commonly introduced as the ideal technique for studying electrode reaction kinetics in high resistance systems. However, the primary difficulty when carrying electrochemical measurements in high impedance systems is the limitation of the instrumentation available. Frequency Response Analyzers (FRA's) generally have input impedances of 10⁶ ohms which is insufficient in this case. Problems can also arise with potentiostatic measurements when a meaningful and a stable electrode potential often cannot be determine. The impedance response can also become complex to interpret in systems where the capacitive properties of the medium can obscure useful electrode kinetic information. This paper reports on the experience gained at UMIST in EIS and cites work carried out in glycol-ether water mixtures, on thick epoxy coatings, in deionised water and in an ethanolic automotive fuel