In order to understand microstructure formation process of the catalyst layer for a polymer electrolyte fuel cell (PEFC), we tried to evaluate the catalyst slurry properties. The catalyst slurries were prepared changing the water/ alcohol ratio of the solvent and their flow curve and packing ability were investigated. In addition the size and the adsorbed amount of the ionomer were also measured. On the other hand, the electrode was fabricated from the prepared slurry and its performance was examined.It was shown that the mean diameter of ionomer measured by dynamic light scattering and the adsorbed amount of ionomer on Pt/C particles decreased with an increase in alcohol ratio of solvent. It was also found that the packing ability of slurry became poorer when the alcohol ratio of solvent increased due to less adsorbed amount of ionomer onto Pt/C particles. From the results of the slurry and the electrode characterization, it was suggested that the adsorbed amount of ionomer and the size of free ionomer could play an important role to improve the PEFC performance.
The effect of slurry preparation for polymer electrolyte fuel cells on the electrode performance has been investigated in this work. The amount of ionomer adsorbed onto PtC powder increases when water is used as a solvent; however, the size of non-adsorbed ionomer particles increases as well, resulting in a larger gas permeation resistance. Meanwhile, increasing the ethanol-to-water mass ratio in a mixed solvent decreases the ionomer size. Therefore, an improved two-step slurry preparation procedure utilizing the irreversibility of the ionomer adsorption onto PtC powder has been investigated. In this method, (1) PtC powder is mixed with ionomer in water to maximize its adsorbed fraction, after which (2) ethanol is added to the prepared slurry to minimize the size of non-adsorbed ionomer. As compared with the conventional one-step synthesis method, the developed twostep preparation procedure enhances the electrode performance without changing its composition.
Optimization of the catalyst layer structure is necessary to realize high performance and low cost of a polymer electrolyte fuel cell (PEFC). The catalyst layer is normally composed of Pt/C powder and an ionomer. The adhesion state of ionomer to Pt/C powder not only changes the proton transport route but also influences the microstructure of the electrode, which is an important factor in controlling cell performance. In this study, in order to investigate the adhesion state of ionomer, we developed the new measurement technique of the specific surface area of catalyst layer. The measurement method was based on the gas adsorption method (N 2), and the adhesion ratio of the ionomer was determined from the ratio of the specific surface area before and after removal of the ionomer in the catalyst layer. In addition, the electrode characteristics of the catalyst layer were also measured, and the relationship between the ionomer adhesion ratio and the cell performance was discussed. As a result, it was found that the adhesion ratio of ionomer was correlated with electrode characteristics, meaning that the adhesion ratio of ionomer should be an important parameter for improving cell performance.
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