Radical Corrosion And Defect-end-group Stabilization Of The Perfluorosulfonic Electrolyte For Fuel Cells

Proton exchange membrane fuel cell is one of the most vital substitutable power source device in this century, it is paid attention extensively in its performance. However, the cost and lifetime of PEMFCs are the barriers to commercialize it, and the chemical durability is one of the most important reasons, so many researchers are working on it. This paper reviews the available literature regarding the chemical degradation behavior, degradation mechanism and stabilization strategies of the perfluocarbon proton exchange membranes. Peroxide radicals that generated from hydrogen peroxide remains the most likely culprit for membrane chemical degradation. The leading mechanism for degradation of commercially-available PEM membranes is initiated by abstraction of a hydrogen atom from residual carboxylic acid ends on PTFE backbones and then unzipped the repeatted main chain. Incorporation of radical scavenger, such as cerium oxide, in the perfluocarbon proton exchange membranes is helpful to minish the concentration of peroxide radicals, and thus reduce membrane degradation. Reduction of the carboxylic acid ends by fluorination or reforming the defect groups to a stable struture, such as-CH, can substantially reduces the chemical degradation and increases the durability.Facile chemical stability improvement strategy for perfluorosulfonic acid was proposed by hydrothermal decarboxylation of the defect groups with the assist of counter ion and polyatomic alcohol at elevated temperature. We should choose a better solvent to participate in the reaction test between the alternative polyatomic alcohol solvent. The results showed that the solvent of ethylene glycol was more suitable than isopropyl alcohol, owned more disadvantages. At elevated temperature diminish of the carboxyl end groups was observed in the solvent of ethylene glycol and isopropyl alcohol, however, the solvent of ethylene glycol is more apparent than isopropyl alcohol in the affection. And at220℃, the carboxyl end groups of ethylene glycol was less than the carboxyl end groups of isopropyl alcohol. Thus, in the next experience, we selected ethylene glycol to be the solvent which would take part in the reaction. As above facile chemical stability improvement strategy for perfluorosulfonic acid was proposed by hydrothermal decarboxylation of the defect groups with the assist of counter ion and ethylene glycol at elevated temperature. The results demonstrated that the defect carboxyl end groups can be extensively removed and apparently diminish of the carboxyl end groups was observed at decarboxylated temperature of200-220℃. Decarboxylation of perfluorosulfonic acid significantly upgraded the chemical stability of the perfluorosulfonic electrolyte towards hydroperoxyl radicals, resulted in high concentration of the S2p and F1s remained after radical corrosion of12h. The decarboxylation of the electrolyte at elevated temperature also improved the side chain stability of the perfluorosulfonic acid. The fluoride emission rate increasing ratio decreased with the increased decarboxylation temperature, implying the low side chain cleavage of the polymer. In conclusion, it is confirmed that the facile durability improvement strategy could help increase the chemical durability of PEMs, and with the elevated temperature, the chemical stability will be strengthened.