Chemical and Ionic Conductivity Degradation of Ultra-Thin Ionomer Film by X-ray Beam Exposure

Abstract

X-ray based techniques have been adopted as a diagnostic tool for both ex-situ and in-situ material characterization techniques in PEMFC. Possible damage of Nafion due to X-ray irradiation is a concern especially for thin films. To investigate the X-ray irradiation effect on ultra-thin Nafion film structure and properties, supported 10 nm films were prepared on SiO 2 /Si substrate with inter-digitated gold arrays (IDA) and exposed to X-ray radiation at three X-ray power sources: 300, 200 and 100 W for 45 mins. Proton conductivity of each film was measured by electrochemical impedance spectroscopy before and after X-ray exposure. We determine that X-ray radiation damages the polymer by preferential removal of sulfur species from the film that results in a clear loss of proton conductivity. Damage by 300, 200, and 100 W radiation over 45 minutes removes 78, 74 and 54% of the sulfur present, respectively, yielding a loss of 99, 97 and 95% in the proton conductivity of the film. It is suggested that Nafion degradation takes place by not only the removal of the sulfonic group, but also by the removal of a fraction of fluorine consistent with cleavage at the ether group of its side chain.

Polymer electrolyte fuel cell performance degradation at different synchrotron beam intensities

“…The analysis of the product water of the CC irradiated cells revealed a 5 to 38 times higher release rate of sulfate ions during and after the irradiation experiments of the cells. Variable sampling condition and duration do not allow for correlation between the sulfate release rates to the beam intensities, but a dose dependency can be expected (Paul et al, 2013). Cathode catalyst poisoning by the sulfate species reversibly reduces the oxygen reduction reaction activity of the electrocatalyst (Kabasawa et al, 2008) and was postulated by Schneider et al (2010).…”

Interesting Facets of Surface, Interfacial, and Bulk Characteristics of Perfluorinated Ionomer Films

“…To test the hypothesis that X-rays can damage Nafion films, resulting in sulfonic groups loss, we designed an experiment to measure the proton conduction of 10 nm Nafion films before and after X-ray exposure in an XPS system. 120 The sulfur and fluorine signals were monitored during the exposure over 90 min, and steady losses in these signal were observed as shown in Figure 22 (left). After 50 min of exposure to the X-rays, the proton conduction of the samples was measured again, and the results are shown in Figure 22 (right).…”

“…At the time, there were no studies on X-ray damage to Nafion except for an obscure article. To test the hypothesis that X-rays can damage Nafion films, resulting in sulfonic groups loss, we designed an experiment to measure the proton conduction of 10 nm Nafion films before and after X-ray exposure in an XPS system . The sulfur and fluorine signals were monitored during the exposure over 90 min, and steady losses in these signal were observed as shown in Figure (left).…”

Proton-Exchange Membrane Fuel Cells with Low-Pt Content

“…Many ex situ techniques such as X-ray scattering, neutron and X-ray reflectivity, TEM, XPS, AFM, and FTIR were employed to study this effect [57,[71][72][73][74][75][76][77][78]. Some effects include a formation of multilamellar nanostructure and reduced transport properties such as lower water uptake and uptake rate [59,72,[74][75][76][77][79][80][81][82]. These effects are highly dependent on treatment condition, substrate type, and operating environments [76,83].…”