Mitigating cerium migration for perfluorosulfonic acid membranes using organic ligands

Improving the electrochemical stability of proton exchange membranes is a pressing priority for heavy-duty fuel cell vehicles. The lifetime of the most widely used perfluorosulfonic acid membranes is limited by reactive free radicals generated inside the system. Cerium has been found to reduce the chemical degradation of the mem-branes. However, cerium migration during fuel cell operation limits the chemical durability enhancement effect expected from the radical scavenging activity of cerium. Here we investigate a wide range of organic immobi-lizers for cerium, measuring their suitability concerning cerium retention, radical scavenging activity, and fuel cell performance. We report that partially fluorinated phosphonic acids enhance cerium retention up to 45 times and reduce fluoride emission rate by 38% compared to the commercial NafionTM XL membrane pre-impregnated with cerium. The energetics of cerium-phosphonic acid complex systems by density functional theory calcula-tions rationalizes effective cerium immobilization.

Automated summary

Improving the electrochemical stability of proton exchange membranes is crucial for heavy-duty fuel cell vehicles. Cerium has been found to reduce the chemical degradation of membranes, but its migration during fuel cell operation limits its effectiveness. It has been discovered that partially fluorinated phosphonic acids can enhance cerium retention and reduce fluoride emission rate.