Marta Zaton

Current understanding of chemical degradation mechanisms of perfluorosulfonic acid membranes and their mitigation strategies: a review

This article provides a comprehensive and up-to-date perspective of the understanding of perfluorosulfonic acid (PFSA) fuel cell membrane degradation phenomena, reviews key concepts for the mitigation of membrane degradation, appraises the effectiveness of these strategies by discussing their benefits and drawbacks, and identifies remaining challenges and research priorities for fuel cell membranes with increased longevity. Identification of stressors and improved understanding of how scavenging reactions proceed are essential for accelerated development of new fuel cell membrane materials with antioxidant properties and enhanced durability. Fuel cells convert the chemical energy of a fuel such as hydrogen into electricity and heat and have the potential to deliver environmental and economic benefits across various sectors, including transportation, power generation, industrial equipment, military power, and consumer electronics. The development of Proton Exchange Membrane Fuel Cell (PEMFC) membranes with increased durability is of crucial importance since it directly impacts fuel cell system lifetime and, therefore, large scale implementation of fuel cell technology. The PFSA proton conducting polymer (ionomer) at the heart of the membrane electrode assembly of a PEMFC is subject to chemical degradation as a result of the attack on the polymer chains by reactive oxygen species generated electrochemically in the fuel cell. For the first time, this article reviews the literature both on mechanisms by which this chemical degradation of the ionomer membrane occurs and the sites on the polymer susceptible to free radical attack, as well as how this learning and increased understanding have been used to build and develop successful mitigation strategies designed to annihilate the harmful effect of oxidative species on membrane integrity.

Mitigation of PFSA membrane chemical degradation using composite cerium oxide–PFSA nanofibres

A PFSA nanofibre-network enriched with cerium oxide nanoparticles (NFCeOx) has been developed as a trap for highly reactive oxygen species that are produced in an operating fuel cell and that lead to membrane degradation and failure. This new mitigation strategy allows the location of CeOx at the membrane electrode interface. The composite nanofibre web was deposited by electrospinning of dispersed Nafion® and CeOx nanoparticles, using a polyethylene oxide carrier polymer. Asymmetric composite Nafion® membranes were prepared by bonding the nanofibre web to one side of the membrane. In accelerated stress testing by OCV hold testing, a membrane electrode assembly with the modified membrane surface oriented to the anode gave a very stable open circuit voltage and a lifetime close to 1000 hours, while the end of life occurred at close to 100 hours for unmodified Nafion® 212. The results of characterisation by X-ray photoelectron spectroscopy, Raman spectroscopy and scanning electron microscopy of end-of-life MEAs and analysis of fuel cell effluents were used to explain the degradation processes occurring within the modified and unmodified membranes.