Phenomenological theory of electro-osmotic effect and water management in polymer electrolyte proton-conducting membranes
- Forschungszentrum Juelich GmbH (Germany). Inst. fuer Werkstoffe und Verfahren der Energietechnik
- Russian Academy of Sciences, Moscow (Russian Federation). A.N. Frumkin Inst. of Electrochemistry
Partial dehydration of the proton-conducting membrane under working conditions is one of the major problems in low-temperature fuel cell technology. In this paper a model, which accounts for the electro-osmotically induced drag of water from anode to cathode and the counterflow in a hydraulic pressure gradient is proposed. A balance of these flows determines a gradient of water content across the membrane, which causes a decline of the current-voltage performance. Phenomenological transport equations coupled with the capillary pressure isotherm are used, involving the conductivity, permeability, and electro-osmotic drag coefficients dependent on the local water content. The effects of membrane parameters on current-voltage performance are investigated. A universal feature of the obtained current-voltage plots is the existence of a critical current at which the potential drop across the membrane increases dramatically due to the dehydration of membrane layers close to the anode. For a membrane with zero residual conductivity in its dry parts, the critical current is a limiting current. Well below the critical current the effect of dehydration is negligible and the current-voltage plot obeys Ohm`s law. The shape of the capillary pressure isotherm determines the nonohmic corrections. A comparison of the results of this study to those of the pertinent diffusion-type models reveals qualitatively different features, the convection model is found to be closer to experimental observations.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 653525
- Journal Information:
- Journal of the Electrochemical Society, Vol. 145, Issue 8; Other Information: PBD: Aug 1998
- Country of Publication:
- United States
- Language:
- English
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