Perfluorosulfonic acid (PFSA) materials have been used in polymer electrolyte membrane fuel cells (PEMFCs) as electrolyte materials due to their mechanical durability and high proton conductivity. To understand the molecular physicochemical properties, local dynamics studies using double quantum filtered ssNMR spectroscopy have been recently developed and validated.[1] The local dynamics information has been separated and analyzed in terms of fluorine interactions with respect to different temperatures and hydration levels. The polymer side chain is proven to be more locally mobile which is reflected by the lower apparent dipolar coupling constant (Dapp) compared to the backbone. This observation agrees with the micro-phase separation morphology development. In the current study, the dynamics investigation of different PFSA materials has been conducted at various conditions. In operando membrane performance analyses have been obtained in parallel at Ballard Power Systems. PFSA membranes are prepared into membrane electrode assembly (MEA) form, with catalyst layers and gas diffusion layers. From the cyclic voltammetry measurements of the MEAs, the H2 crossover values have been extracted. There is a strong correlation between the H2 permeability and the PFSA side chain local dynamics from the NMR analysis. As the side chain mobility increases (lower Dapp), an increase in the H2 permeability is observed. The link between the fundamental dynamics study and the PFSA performance analysis provides insight into gas transport mechanisms in this type of material.[2]

Understanding polymer dynamics in perfluorosulfonic acid membranes via solid-state NMR

255th National Meeting (2018)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.