A model of degradation in a polymer electrolyte membrane

Author

C Jordan King

Graduation Date

2009

Document Type

Thesis

Program

Other

Program

Thesis (M.S.)--Humboldt State University, Environmental Systems: Environmental Resources Engineering, 2009

Committee Chair Name

Charles Chamberlin

Committee Chair Affiliation

HSU Faculty or Staff

Keywords

PEM, Nafion, Hydrogen fuel cell, Degradation, Humboldt State University -- Theses -- Environmental Resources Engineering

Abstract

A transient model of chemical degradation in a polymer electrolyte membrane (PEM) was developed that uses the hydrogen peroxide and iron (II) concentrations to predict the useful life of the membrane. Experimental values from the literature were used in a second order chemical kinetics rate equation to estimate the rate constant for fluoride production. The fluoride emission rate (FER) has been used as an indicator of peroxide radical induced degradation. The rate equation was combined with the conservation of momentum and species equations in a one-dimensional, through the membrane model. The equations were solved numerically using the Crank-Nicholson method of finite differences programmed in FORTRAN. At each time step the local concentration of reactants and FER was determined and algebraically correlated to the loss of cation exchange sites based on the 'unzipping' mechanism of chemical degradation. The percent degradation of initial exchange sites was used to estimate the useful life of the membrane. In order to meet the industry standard of 40,000 hours of operation, the model results show that the fixed hydrogen peroxide concentration within the membrane should be limited to approximately 340 micromoles per cubic centimeter. Furthermore, the iron (II) concentration was determined to have a strong influence on membrane life, and should be minimized to improve membrane durability.

https://scholarworks.calstate.edu/concern/theses/73666683x

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