1403
Impact of PFSA Ionomer Specifically Adsorbed Onto Pt Surface on PEFC Electrode Kinetics Towards Oxygen Reduction Reaction

Sunday, 29 May 2022: 08:20
West Meeting Room 212 (Vancouver Convention Center)
W. Y. Choi, H. Choi (Hanyang University), S. W. Choi (Gwangju Institute of Science and Technology), M. Lee (Korea Institute of Energy Research), Y. J. Park (Hanyang University), Y. G. Yoon (Korea Institute of Energy Research), S. C. Yi (Hanyang University), and C. Y. Jung (Korea Institute of Energy Research)
The specific adsorption of PFSA ionomer onto the Pt catalytic surfaces is a major hurdle for obtaining facilitated electrode kinetics performance for oxygen reduction reaction (ORR) (1, 2). The electrostatic attractive interaction between the terminal sulfonate groups (negatively charged) and Pt surfaces (positively charged) reduces the ORR electrode kinetics by blocking the active sites located on the surfaces of Pt catalyst (3). Unfortunately, it is not clearly demonstrated until now that how the Pt surfaces poisoned by ionomer affect negatively on the Pt efficiency. Cyclic voltammetry (CV) is one of the most widespread techniques for measuring the effective electrochemically surface area (ECSA) of the PEFC electrode (4); however, the CV analysis based on the humidified N2 alone is not accurate enough to exclude the hydrogen evolution or cross-over hydrogen oxidation peaks. In this work, we demonstrate calculate the poisoned Pt rate by dry proton accessibility test and liquid proton accessibility test for measuring absorbed and effectively utilized catalyst surface respectively. The commercially available 20 wt.% Pt/Vulcan and 20 wt.% Pt/HSC catalysts, where most of Pt nanoparticles located in the exterior and interior surfaces of the carbon support(5), respectively, were employed to investigate the effect of ionomer distribution as well as Pt catalytic poisoning by ionomer on the PEFC performance. The MEA samples are fabricated with a variation of ionomer-to-carbon ratios from 0.3, 0.5 and 0.7. The STEM analysis was conducted to confirm the location of the Pt in the Vulcan and high surface area carbon (HSC) supports, either on the external or interior surfaces. Finally, the CV analysis with N2-purged DI water cycling and Tafel analysis with pressurized H2 and O2 feedings at 150 kPag were conducted to draw out the accurate values for ECSA and Pt specific activity towards ORR. Major findings provided here, such as Pt location, ionomer coverage and distribution, and ORR activity on MEA level, may give in-depth insights for understanding the key roles of responsibilities of carbon supports.

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See more of: I03 - Membrane and Ionomer 1
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