3M ionomer/carbon/Pt interactions were also explored through differential scanning calorimetry (DSC). Using these methods, a series of samples with and without ionomer addition were analyzed to explore the different interactions between components (Pt/Carbon, and Carbon/ionomer).
Preliminary DSC results are shown in Figure 1 for the 3M ionomer, ionomer/Pt, ionomer/Vulcan-carbon and the catalyst layer (CL) samples, where the CL is composed of ionomer/Vulcan-carbon/Pt. The 3M ionomer and ionomer/Vulcan-carbon samples, on the other hand, exhibit a weak and broad endothermic peak between 50 and 120°C. This process has been associated with the combination of structural changes in ionic cluster, and water volatilization in PFSA ionomers.1Both experiments with Pt present showed an exothermic feature around 95°C and 135°C for the ionomer/Pt and the CL samples, respectively.
The adsorption behavior of 3M ionomer on the carbon and catalyst samples was explored using 19F NMR. Figure 2 shows an NMR spectrum of the 3M PFSA ionomer in water solution after base correction. This figure also includes the chemical shifts and peak assignments. The strongest peak at -76.55 ppm corresponds to the internal reference (trifluoro acetic acid, CF3COOH) in solution. The ratio of the most prominent 3M ionomer peak (-124.13 ppm) associated with the CF2 group in the backbone and the internal reference peak was used for the analytical study, a similar approach to previous studies of Nafion.2–4