Application:

1
Application of Electrochemical Impedance
Spectroscopy (EIS) as a Characterization Tool for
PEM Fuel Cell Gas Diffusion Electrode Derek
Cheng1,2, Siyu Ye2, and Elod Gyenge1 1University
of British Columbia - Department of Chemical and
Biological Engineering. 2Ballard Power Systems
Inc.
Objective To measure the voltammogram and
impedance spectra of the Oxygen Reduction
Reaction (ORR) on Gas Diffusion Electrode (GDE)
as a function of GDE structure and additive
composition (i.e. Teflon and Nafion content). The
reaction is carried out in oxygen saturated 0.1M
H2SO4 electrolyte at 293K.
Application A novel, non-destructive method
which provides characterization of the
three-phase interface in both catalyst and
diffusion layers, between gas, liquid, and solid
(i.e. porous carbon matrix and/or supported
catalyst/polymer electrolyte).
Experimental Setup
Principles of EIS
The ability of a circuit element to resist
current flow when a potential is applied is
called the electrical resistance. For an ideal
resistor, the relationship between voltage,
current, and resistance is given by Ohms Law (R
E/I).
Extending this to the general case, when a small
sinusoidal potential E(t) E0exp (j?t) is
applied to an electrochemical cell, the current
response I(t) I0exp(j?t-j?) is also sinusoidal
with the same frequency, but shifted in phase.
This leads to the definition of the Complex
Impedance Z(?) E/I Z0(Cos ? j Sin ?), where
kinetics parameters of an electrochemical system
can be estimated by studying the impedance
response of the electrochemical system as a
function of frequency.
Rs (electrolyte resistance)
?
Rct (charge transfer resistance)
Result
Mercury Intrusion Porosimetry (MIP)
Scanning Electron Microscopy (SEM)
Electrochemical Impedance Spectroscopy (EIS)
Cyclic Voltammetry (CV)

• Summary
• The Oxygen electro-reduction on the carbon fiber
  paper (a 2-electron process) was a strong
  function of Teflon and Nafion content as revealed
  by both CV and EIS. Hence, oxygen
  electroreduction could be used as an
  electrochemical sensor for the non-destructive
  analysis of the gas diffusion layer properties.
• Good correlation was shown between EIS and other
  electrochemical and structural measurement
  techniques, such as CV, MIP, and SEM.
• Effect of Teflon and Nafion content was studied
  and found to have significant effect on the
  oxygen reduction reaction on carbon fiber paper.
• Catalyst composition, between 25 to 50 Nafion
  content, did not seem to have significant effect
  on CV and impedance sweep.

• Future Work
• Further studies of catalyst layer composition
  Pt/C support ratio, ionomer content.
• Quantitative interpretation of the data and
  mathematical modeling.
• Scanning electrochemical impedance spectroscopy.

• Acknowledgement
• The following individuals are acknowledged for
  their contribution to this work
• Joanna Kolodziej, P.Eng. (SEM support)
• Gina Yin-Chi Chu (MIP support)
• Kelly Maclean (Sample preparation)