Modeling the Effect of Chemical Membrane Degradation on PEMFC Performance

Abstract

A transient, isothermal, two-dimensional model coupling cell performance and chemical membrane degradation in a polymer electrolyte membrane fuel cell (PEMFC) is developed. The model is based on the conservation of and thermodynamic equilibrium between charged and neutral species, including radicals. The model is validated against experimental polarization behavior and chemical degradation under an open circuit voltage (OCV) hold test at 368.15 K. The four-step chemical degradation of a PFSAbased membrane is assumed to start by an attack by hydroxyl radical at the terminal ether bond in the side chain. The source of the attacking hydroxyl radical is an indirect hydrogen peroxide formation and the subsequent decomposition at Fenton's reagent in the membrane. Simulation of degradation rate (defined as the loss of cell voltage with time at a fixed cell operating condition and at a point of time with a known degradation history) under an OCV-hold test agree qualitatively with the degradation rates reported in the literature.

Holistic approach to chemical degradation of Nafion membranes in fuel cells: modelling and predictions

“…On the basis of the degradation mechanisms discussed above several modelling approaches comprising membrane degradation phenomena [29][30][31][32][33][34][35][36] have been published. The model by Xie and Hayden 29 does not concentrate on the formation of radical species; yet it is possible to distinguish between two possibilities for initiation of PFSA degradation -either at the weak end groups of the main chain or at the side chains.…”

“…The kinetic framework 33 was expanded in a later publication by Wong and Kjeang. 34 An analogue model was presented recently by Singh et al, 35 being extended by regarding the temperature dependence of the Fenton reaction and an iron redox cycle, which is established by the reaction of ferric ions with hydrogen radicals.…”

“…An excellent discussion of various degradation phenomena can be found in the reviews by Borup et al, 6 Kusoglu and Weber 7 as well as Zatoń et al 5 Many mechanisms and the corresponding chemical equations [9][10][11][12][13] and kinetic details [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] have been reported. Based on that, several chemical degradation models [29][30][31][32][33][34][35][36] have been already presented. This knowledge, however, is spread in physically, chemically and technologically oriented context.…”

“…This powerful model allows monitoring and prediction of experimentally accessible data like time traces of chemical species involved 33 and fluoride emission rates (FERs). [35][36][37] Furthermore, we discuss the implications of iron containing ORR catalysts [38][39][40] for membrane degradation and the use of cerium agents [41][42][43][44][45][46][47] as radical scavengers to protect the chemical integrity of the membrane.…”

Effects of Fuel Cell Operating Conditions on Proton Exchange Membrane Durability at Open‐Circuit Voltage

“…The OCV lifetime of the MEAs is in the order of 1,100 h at 64 °C (estimated from the fitting line), >372 h at 72 °C, >339 h at 80 °C, and >168 h at 95 °C (See Table ). Membrane degradation under fuel cell operating conditions is generally due to a combination of chemical, mechanical and thermal stressors, but chemical degradation plays a key role under OCV . Danilczuk et al.…”