Sensitivity Based Order Reduction of a Chemical Membrane Degradation Model for Low-Temperature Proton Exchange Membrane Fuel Cells

Abstract

The chemical degradation of the perfluorinated sulfonic acid (PFSA) ion-exchange membrane as a result of an attack from a radical species, originating as a by-product of the oxygen reduction reaction, represents a significant limiting factor in a wider adoption of low-temperature proton exchange membrane fuel cells (LT-PEMFCs). The efficient mathematical modeling of these processes is therefore a crucial step in the further development of proton exchange membrane fuel cells. Starting with an extensive kinetic modeling framework, describing the whole range of chemical processes leading to the membrane degradation, we use the mathematical method of sensitivity analysis to systematically reduce the number of both chemical species and reactions needed to efficiently and accurately describe the chemical degradation of the membrane. The analysis suggests the elimination of chemical reactions among the radical species, which is supported by the physicochemical consideration of the modeled reactions, while the degradation of Nafion backbone can be significantly simplified by lumping several individual species concentrations. The resulting reduced model features only 12 species coupled by 8 chemical reactions, compared to 19 species coupled by 23 reactions in the original model. The time complexity of the model, analyzed on the basis of its stiffness, however, is not significantly improved in the process. Nevertheless, the significant reduction in the model system size and number of parameters represents an important step in the development of a computationally efficient coupled model of various fuel cell degradation processes. Additionally, the demonstrated application of sensitivity analysis method shows a great potential for further use in the optimization of models of operation and degradation of fuel cell components.

Towards Integration of Two-Dimensional Hexagonal Boron Nitride (2D h-BN) in Energy Conversion and Storage Devices

“…The undesired oxidation, decreasing the active sites for reduction of oxygen at the cathode, and carbon monoxide poisoning of the cathode catalyst are other methanol crossover challenges [142][143][144][145]. Nafion, as the most common PEM used in DMFCs, suf-fers from the methanol crossover despite its supreme proton conductivity and outstanding chemical, thermal, and mechanical stability [146][147][148]. One attempt to decrease the methanol crossover in Nafion is to use 2D h-BN as reinforcement.…”

Operando Imaging of Ce Radical Scavengers in a Practical Polymer Electrolyte Fuel Cell by 3D Fluorescence CT–XAFS and Depth-Profiling Nano-XAFS–SEM/EDS Techniques

“…It has been reported that Ce 3+ and Mn 2+ or these oxide nanoparticles, whose cations can undergo fast reversible redox reactions and quench radicals by donating or accepting electrons under aqueous conditions, are very effective at protecting PEMs from chemical degradation, − and hence, PEM stabilization has been achieved by incorporation of radical scavenger species by a variety of methods. − The presence of Ce 3+ scavengers leads to a 20-fold reduction in the MEA degradation rate and a nearly 1000-fold reduction in fluoride reduction. Compared with Ce 3+ mitigation, equivalent levels of Mn 2+ doping are 5–10 times less effective .…”

The principle of detailed balancing, the iron-catalyzed disproportionation of hydrogen peroxide, and the Fenton reaction

“…There are many publications that include this pair of reactions in the proposed mechanism, assigning second-order kinetics to both steps. 19,30,31,60,[69][70][71][72][73][74][75][76][77][81][82][83][86][87][88][89]91,92,94,96,[136][137][138][139][140][141][142][143][144][145][146][147][148][149][150][151][152][153][154] The H + in the second step is bracketed to indicate that it is required for the stoichiometry but does not appear in the rate law. This reaction pair corresponds to a reversible equilibrium, but it violates the principle of detailed balancing because the rate expressions in the forward and reverse directions are second order, which disagrees with the form of the equilibrium expression.…”