Study of Ionic Conductivity Profiles of the Air Cathode of a PEMFC by AC Impedance Spectroscopy

Abstract

A characterization of the ionic conduction of the active layer of a polymer electrolyte membrane fuel cell (PEMFC) cathode by ac impedance measurement at open-circuit potential conditions was conducted. Porous electrode theory was used to derive a compact equation, ∂2normalΦ̑2/∂y2+∂lnffalse(yfalse)/∂y×∂normalΦ̑2/∂y−R/ffalse(yfalse)false(1+jnormalΩfalse)normalΦ̑2=0, to solve for the impedance response of a cathode at open-circuit potential conditions. This equation includes a parameter R, the ratio of an ionic resistance (evaluated at the active layer/membrane interface), to the total charge-transfer resistance of the active layer. The influence of an assumed ionic conductivity distribution profile ffalse(yfalse) on the error in the estimation of total double-layer capacitance of the active layer from the −1/false(ZnormalImωfalse) vs. ZnormalRe plot was also investigated in this work. The increase of ionic conductivity in the active layer of an air cathode with an increase in the ionomer loading was revealed from both impedance data and surface area measurements. A nonlinear parameter estimation method was used to extract the ionic resistance from the high-frequency region of the impedance data at open-circuit potential conditions. The assumed ionic conductivity distribution profile in the active layer was found to vary with ionomer loadings. © 2003 The Electrochemical Society. All rights reserved.

WO3-based electrochromic system with hybrid organic–inorganic gel electrolytes

“…7 and the measured conductivity values (4,2-5,1) Â 10 À3 X À1 cm À1 have proved to be relatively stable in that frequency range. Similar results for ionic conductive hybrid materials have been, reported, inter alia, in [28,29].…”

The Control and Effect of Pore Size Distribution in AEMFC Catalyst Layers

“…46 However, C dl found for the CCMs deposited over 4-hour (CCMs 1 and 4) were half of CCMs deposited over 1-hour (CCMs 2, 3, and 5) (see Table III). This data suggests an alteration to ionomer morphology in the 4-hour CCMs, 1 and 4, caused by long periods of time at temperature between ultra-thin layers.…”

Analysis of electrochemical impedance spectroscopy in proton exchange membrane fuel cells

“…For the airfed cathode, besides the increasing Tafel slope observed from the high-frequency impedance loop, a second impedance loop began to grow adding an extra Tafel slope. In an earlier paper, Guo et al (2003) developed an impedance model for a PEMFC cathode with a non-uniform ionic conductivity. Porous electrode theory was used to derive the governing equation for the impedance response of the cathode at open-circuit conditions.…”