Mitigation of Chemical Membrane Degradation in Fuel Cells: Understanding the Effect of Cell Voltage and Iron Ion Redox Cycle

Abstract

Chemical membrane degradation through the Fenton's reaction is one of the main lifetime-limiting factors for polymer-electrolyte fuel cells. In this work, a comprehensive, transient membrane degradation model is developed to capture and elucidate the complex in situ degradation mechanism. A redox cycle of iron ions is discovered within the membrane electrolyte assembly, which sustains the Fe(II) concentration and results in the most severe chemical degradation at open circuit voltage. The cycle strength is critically reduced at lower cell voltages, which leads to an exponential decrease in Fe(II) concentration and associated membrane degradation rate. When the cell voltage is held below 0.7 V, a tenfold reduction in cumulative fluoride release is achieved, which suggests that intermediate cell voltage operation would efficiently mitigate chemical membrane degradation and extend the fuel cell lifetime.

Progression in the Morphology of Fuel Cell Membranes upon Conjoint Chemical and Mechanical Degradation

“…The oxygen map could also potentially indicate the presence of terminal carboxylic acid groups appearing due to side chain degradation induced main chain cleavage at advanced stages of chemical degradation. 10,11 Overall, the two hollow areas identified in these images are likely to have experienced an advanced stage of chemical degradation, involving both side chain and main chain decomposition, thus creating small essentially void features that may potentially grow further into macroscopic damage features such as micro-cracks and pinholes normally observed by SEM based failure analysis of EOL membranes.…”

“…Radical species such as •OOH and •OH generated through chemical and electrochemical routes have been observed to attack the side chain of the ionomer and release fluoride ions from the ionomer matrix. [8][9][10][11] The second type of stress encountered in an operating fuel cell is the mechanical stress, which originates due to compression, humidity cycling, and inhomogeneous features of the membrane electrode assembly through the mechanisms of fatigue and creep. [12][13][14][15][16] Thermal stress mainly acts as an accelerator of chemical and mechanical degradation provided that the temperature is kept within the design specifications of the membrane.…”

In-Situ Modeling of Chemical Membrane Degradation and Mitigation in Ceria-Supported Fuel Cells

“…The influences of the Ce 3+ /Ce 4+ redox system on chemical degradation by hydroxyl radical (·OH) attack are analyzed in terms of the reaction-transport phenomena of the Ce 3+ /Ce 4+ couple in the MEA. The baseline chemical degradation algorithms developed and validated in our previous work 24,25 are modified and applied for this purpose. The algorithms provide a comprehensive description of the in situ molecular degradation of PFSA ionomer membranes and the role of Fenton's reagent (iron ion and hydrogen peroxide) in the degradation process.…”

“…22,23 The hydroxyl radical formed is highly reactive and can attack the ionomer membrane in terms of side chain cleavage and unzipping 18,20,21,24,25 which is responsible for the deteriorated physicochemical properties observed in degraded membranes. Radical scavenging is therefore proposed to mitigate the chemical damage by quenching the radicals before they attack the ionomer membrane.…”

3D Failure Analysis of Pure Mechanical and Pure Chemical Degradation in Fuel Cell Membranes

“…The research topics range from fundamental studies on understanding the membrane behavior in fuel cells [5][6][7][8][9][10][11][12][13][14][15][16][17][18] to its lifetime prediction under operational conditions [19][20][21][22][23][24] as well as developing practical solutions for its durability enhancement. [25][26][27][28][29] * Electrochemical Society Student Member. * * Electrochemical Society Member.…”