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Membranes 2012, 2(2), 237-252; doi:10.3390/membranes2020237
Article

Impedance Spectroscopic Investigation of Proton Conductivity in Nafion Using Transient Electrochemical Atomic Force Microscopy (AFM)

1
,
2
,
2
 and
1,*
1 Institute of Physical Chemistry, University of Stuttgart, Pfaffenwaldring 55, Stuttgart D-70569, Germany 2 Institute of Technical Thermodynamics, German Aerospace Center, Pfaffenwaldring 38-40, Stuttgart D-70569, Germany
* Author to whom correspondence should be addressed.
Received: 25 April 2012 / Revised: 25 May 2012 / Accepted: 29 May 2012 / Published: 6 June 2012
(This article belongs to the Special Issue Membranes for Electrochemical Energy Applications)
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Abstract

Spatially resolved impedance spectroscopy of a Nafion polyelectrolyte membrane is performed employing a conductive and Pt-coated tip of an atomic force microscope as a point-like contact and electrode. The experiment is conducted by perturbing the system by a rectangular voltage step and measuring the incurred current, followed by Fourier transformation and plotting the impedance against the frequency in a conventional Bode diagram. To test the potential and limitations of this novel method, we present a feasibility study using an identical hydrogen atmosphere at a well-defined relative humidity on both sides of the membrane. It is demonstrated that good quality impedance spectra are obtained in a frequency range of 0.2–1,000 Hz. The extracted polarization curves exhibit a maximum current which cannot be explained by typical diffusion effects. Simulation based on equivalent circuits requires a Nernst element for restricted diffusion in the membrane which suggests that this effect is based on the potential dependence of the electrolyte resistance in the high overpotential region.
Keywords: Nafion membrane; electrochemical AFM; impedance spectroscopy; single pore proton flux Nafion membrane; electrochemical AFM; impedance spectroscopy; single pore proton flux
This is an open access article distributed under the Creative Commons Attribution License (CC BY 3.0).
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Hink, S.; Wagner, N.; Bessler, W.G.; Roduner, E. Impedance Spectroscopic Investigation of Proton Conductivity in Nafion Using Transient Electrochemical Atomic Force Microscopy (AFM). Membranes 2012, 2, 237-252.

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