A Novel Interdigitated Electrode Design and Methodology for the Measurement of Ionic Conductivity of Ionomer Thin Film on Carbon Substrate

In this work, we introduce a new design of the interdigitated electrode (IDE) for the measurement of conductivity of ionomer thin film on the planar carbon surface, which is relevant to many electrochemical systems including fuel cells. The design is an advancement over commonly used SiO2 substrate based IDE, previously employed for Nafion thin film conductivities. Electrochemical impedance spectroscopy technique was applied to measure the conductivity of 55 nm thick Nafion film on carbon surface. Through complementary modeling work using equivalent circuit, we identify that the competition between the double layer capacitances at ionomer/carbon and ionomer/electrode interfaces can mask the conventionally observed high-to-medium impedance arc observed for Nafion films on SiO2 substrate. This problem can be circumvented by using electrochemically active Pt electrode in hydrogen environment. Hence, this systematic study describes a method to determine the thin film conductivity on carbon substrate.