Abstract
A rotating disk electrode (RDE) along with cyclic voltammetry (CV) and linear sweep voltammetry (LSV), were used to investigate the impact of two model compounds representing degradation products of Nafion and 3M perfluorinated sulfonic acid membranes on the electrochemical surface area (ECA) and oxygen reduction reaction (ORR) activity of polycrystalline Pt, nano-structured thin film (NSTF) Pt (3M), and Pt/Vulcan carbon (Pt/Vu) (TKK) electrodes. ORR kinetic currents (measured at 0.9 V and transport corrected) were found to decrease linearly with the log of concentration for both model compounds on all Pt surfaces studied. Model compound adsorption effects on ECA were more abstruse due to competitive organic anion adsorption on Pt surfaces superimposing with the hydrogen underpotential deposition (HUPD) region.
Highlights
Previous studies showed that several chemical decomposition products were generated when perfluorinated sulfonic acid (PFSA) membranes were exposed to peroxides and hydroxyl radicals.[13,15] In addition to the release of HF from either membrane type, two compounds in particular, both in the form of a diacid, perfluoro(2-methyl-3-oxa-5-sulfonic pentanoic) acid (DA-Naf) and perfluoro(4-sulfonic butanoic) acid (DA-3M), have been identified as the main degradation compounds of Nafion (Nafion is a registered trademark of DuPont) and 3M commercial PFSA membranes respectively.[14,16]
In order to gain a broad understanding of Pt electrocatalysts, polycrystalline Pt, NSTF, and Pt/Vu catalysts were studied in a range of model compound concentrations that could realistically be found during fuel cell operation.[17]
NSTF electrodes were prepared by applying 10 μL of a catalyst ink (4.5 mL water, 0.5 mL IPA, bath sonicated in ice for 20 min, horn sonicated in ice for 1 min, and dried at 40◦C) to a glassy carbon surface at a Pt loading of 40 μg/cm[2]
Summary
Previous studies showed that several chemical decomposition products were generated when perfluorinated sulfonic acid (PFSA) membranes were exposed to peroxides and hydroxyl radicals.[13,15] In addition to the release of HF from either membrane type, two compounds in particular, both in the form of a diacid, perfluoro(2-methyl-3-oxa-5-sulfonic pentanoic) acid (DA-Naf) and perfluoro(4-sulfonic butanoic) acid (DA-3M) (shown in Figure 1), have been identified as the main degradation compounds of Nafion (Nafion is a registered trademark of DuPont) and 3M commercial PFSA membranes respectively.[14,16]. For all Pt electrode surfaces studied, it can be seen from Figures 2-3 that the presence and concentration of model compounds DA-Naf and DA-3M have a direct impact on both the Pt CV and the ORR polarization curves.
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