Diffuse charge effects in fuel cell membranes
Author(s)
Biesheuvel, P. M.; Franco, Alejandro A.; Bazant, Martin Z.
DownloadBazant_Diffuse Charge.pdf (543.2Kb)
PUBLISHER_POLICY
Publisher Policy
Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use.
Terms of use
Metadata
Show full item recordAbstract
It is commonly assumed that electrolyte membranes in fuel cells are electrically neutral, except in unsteady situations, when the double-layer capacitance is heuristically included in equivalent circuit calculations. Indeed, the standard model for electron transfer kinetics at the membrane/electrode interface is the Butler–Volmer equation, where the interfacial overpotential is based on the total potential difference between the electrode and bulk electrolyte. Here, we develop an analytical theory for a solid-state proton-conducting membrane that accounts for diffuse charge in the electrostatic polarization layers and illustrate its use for a steady-state hydrogen concentration cell. The theory predicts that the total membrane charge is nonzero, except at a certain hydrogen pressure, which is a thermodynamic constant of the fuel cell membrane. Diffuse layer polarization introduces the Frumkin correction for reaction rates, where the overpotential is based on the potential difference across only the compact (Stern) part of the polarization layer. In the Helmholtz limit of a relatively thin diffuse layer, we recover well-known results for a neutral membrane; otherwise, we predict significant effects of diffuse charge on the electron-transfer rate. Our analysis also takes into account the excluded volume of solvated protons, moving in a uniform charge density of fixed anions.
Date issued
2008-12Department
Massachusetts Institute of Technology. Department of Chemical EngineeringJournal
Journal of the Electrochemical Society
Publisher
Electrochemical Society
Citation
Biesheuvel, P. Maarten, Alejandro A. Franco, and Martin Z. Bazant. “Diffuse Charge Effects in Fuel Cell Membranes.” Journal of The Electrochemical Society 156.2 (2009): B225-B233. ©2008 The Electrochemical Society
Version: Final published version
ISSN
0013-4651