To Eliminate Electrical Double Layers Towards Intrinsic Through-Plane Conductivity for Fully Hydrated Nafion Membrane

Abstract

It is important to measure proton conductivity for Nafion membrane, generally restricted by electrical double layers (EDLs) from Pt electrodes. This paper used equivalent circuit to reflect current response in CV and EIS measurements, optimizing Pt electrodes structure and dimension towards intrinsic through-plane conductivity for fully hydrated Nafion membrane. Our results show the small Pt wire electrodes and large Pt strip electrodes cannot achieve intrinsic conductivity because their solid surface present EDLs obstacles. In contrast, the large Pt mesh electrodes can eliminate EDLs to obtain intrinsic conductivity under both CV and EIS measurements. Our analysis shows that the CV and EIS can drive porous Pt mesh electrodes to initiate continuous oscillation and long-range proton transportation process, presenting quasi-capacitances completely. This provides key clue to make strict Laplace analysis, thus we make significant theoretical breakthrough to verify ideal and reversible Ohm’s law in CV measurement. Furthermore, we clarify the quasi-capacitances unify CV in time-domain measurement and EIS in frequency-domain measurement, obtaining intrinsic through-plane conductivity independently. All these progresses show the equivalent circuit can establish methodology with CV and EIS measurements to indicate ideal measuring system, thus revealing electrical response on materials and contact interfaces essentially.

Keywords: conducting membrane, CV, Electrochemical Impedance Spectroscopy(EIS), proton conductivity, electrical double layers(EDLs), equivalent circuit