Changes in the chemical structure and properties of a perfluorosulfonated acid membrane induced by fuel‐cell operation

Abstract

Changes in a perfluorosulfonated acid polymer membrane in membrane electrode assemblies were studied after different times under stationary conditions in fuel cells. A large series of characterizations demonstrated changes in the morphology, mechanical behavior, and thermal stability upon aging. Overall, the membrane evolution could be mainly attributed to both chemical degradation and cationic contamination. The reduction in the membrane thickness, detected by scanning electron microscopy, was ascribed to a radical unzipping mechanism and polymer chain erosion after 900 h in service. An additional monotonic decrease in the number of C tertiary F groups was observed even at 400 h. In parallel, membranes were cation-contaminated, and this led to drastic changes in the thermal and mechanical properties in the first stage of fuel-cell operation. The pollution cations were shown to have Lewis acid strengths close to 0.25 and thus strongly interacted with sulfonate anions of the membrane. The kinetic dependence of these membrane modifications and the influence of the platinum band were also examined.

A review of PEM fuel cell durability: materials degradation, local heterogeneities of aging and possible mitigation strategies

“…The nature and amount of cationic contaminants within a aged PFSA membrane can be determined by performing FTIR analyses, preferentially in transmission mode. According to Figure , which gathers a broad series of results from the literature, the position of the peaks at = 970 and 1060 cm −1 in a FTIR spectrum usually attributed to SO 3 − and COC moieties, respectively gives enough information to target the possible cations that induced a contamination of the membrane during PEMFC operation …”

Morphology and properties of perfluorosulfonic acid polymer/perfluorocarboxylic acid polymer blend membranes

“…The water uptake (WU) of the samples was determined by the weight difference between the hydrated membranes and dry membranes . The dry membrane weight ( W dry ) was measured after drying the samples at 130°C for 18 h in vacuum.…”

Effect of free radical-induced degradation on water permeation through PFSA ionomer membranes

“…Moreover, to date, water permeation studies have largely been restricted to pristine membranes and relatively few studies have attempted to measure the water uptake of degraded Nafion ® membranes. The majority of studies of water uptake of degraded membranes that have been reported are carried out at ambient temperature [35,42,43] but such conditions are not reflective of fuel cell operating conditions (40e100% RH and 60e80 C). In this report, we examine the effect of membrane degradation on water transport performed using ex-situ measurements.…”