Study on the analysis of hydrocarbon-type membrane degradation and its enhancement of long-term stability for polymer electrolyte fuel cells

Abstract

Polymer electrolyte fuel cells (PEFCs) have been recognized for the last few decades as the environmen-tally friendly energy conversion device for stationary, automotive, and portable systems. In PEFCs, the poly-mer electrolyte membrane is a key material function as the proton conduction from anode to cathode and ef-fective separation of both sides of reactants. As a polymer electrolyte membrane, Nafion has been most com-monly used in PEFCs due to its advantages including high proton conductivity, good chemical/thermal stability, and dimensional stability. However, it also has several drawbacks such as high cost, limited operation tempera-ture, and high fuel crossover. To solve these problems, there have been various efforts to develop alternative non-perfluorinated polymer electrolyte membranes and most of them are sulfonated hydrocarbon-type (HC-type) aromatic polymer membranes. Unfortunately, these alternative membranes also have some barriers for commercialization of the PEFCs such as low chemical and mechanical stability. From these point of view, this dissertation covered degradation analysis of the HC-type membrane and several strategies for enhancement of its durability.Degradation of HC-type membrane is occurred in two routes. One is chemical degradation by the radi-cal attack and the other is physical degradation by the low dimensional stability in condition of severe humidi-ty change. In case of HC-type membrane, electron-rich ether and aromatic groups are more likely to be oxi-dized than C-F bonds of perfluorinated membrane. Even if these unwanted chemical reactions appear to be occurring during the cell operation, studies about chemical stability and degradation mechanism under fuel cell operation are few. Also, the high ion exchange capacity of HC-type membrane results in much water uptake and such membranes exhibit poor dimensional stability because of polymer expansion by hydration. Finally, the cell with HC-type membrane showed poor long-term ...