Abstract
Aggregation in heat-treated Nafion ionomer dispersion and 117 membrane are investigated by 1H and 19F Nuclear Magnetic Resonance (NMR) spectra, spin-lattice relaxation time, and self-diffusion coefficient measurements. Results demonstrate that heat-treatment affects the average Nafion particle size in aqueous dispersions. Measurements on heat-treated Nafion 117 membrane show changes in the 1H isotropic chemical shift and no significant changes in ionic conductivity. Scanning electron microscopy (SEM) analysis of prepared cathode catalyst layer containing the heat-treated dispersions reveals that the surface of the electrode with the catalyst ink that has been pretreated at ca. 80 °C exhibits a compact and uniform morphology. The decrease of Nafion ionomer’s size results in better contact between catalyst particles and electrolyte, higher electrochemically active surface area, as well as significant improvement in the DMFC’s performance, as verified by electrochemical analysis and single cell evaluation.
Highlights
Direct methanol fuel cells (DMFCs) have been widely developed and explored in the last few decades [1,2,3]
In order to extend our finding to practical applications, we have investigated the effect of Nafion aggregation in the catalyst layer on the performance of a direct formic acid fuel cell as well as a DMFC
The results were a decrease in particle sizes and an enhancement of the long-range translational motions of the backbone chains or micelles with increasing treatment temperature
Summary
Direct methanol fuel cells (DMFCs) have been widely developed and explored in the last few decades [1,2,3]. Wang et al have investigated the effect of Nafion ionomer aggregation in solution on the structure of the cathode catalyst layer of a DMFC [12]. In order to extend our finding to practical applications, we have investigated the effect of Nafion aggregation in the catalyst layer on the performance of a direct formic acid fuel cell as well as a DMFC. In this present work, we extended the previous study [16] by examining the effect of heat-treatment on ionomer dispersion using 19F NMR, and AC Impedance spectroscopy. The structure of the cathode catalyst layer was characterized by scanning electron microscopy (SEM) and its performance was investigated through electrochemical analysis and a single cell evaluation
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