The effects of dispersion method for ink preparation and types of catalyst on the catalyst layer’s structure and characteristics were investigated. Catalyst layers prepared by two dispersion methods, i.e., sonication and ball-milling, and two types of catalyst: Pt-HSC (High Surface Area) and Pt-Vulcan XC-72, were fabricated. Viscosity, particle size distribution of the catalyst inks, catalyst layer’s surface properties, and cell performance were measured. Experimental results with the Pt-HSC at ionomer/carbon weight ratio 0.8 show that ink dispersity strongly depends on the mixing method and large agglomerates form in the ink after sonication. The effect of the dispersion method on the ink prepared by Pt-Vulcan XC-72 at similar conditions is not noticeable. The catalyst layer’s mechanical properties, such as hardness and Young’s modulus, were found to vary widely. With an increase of catalyst layer thickness, the number of pin-holes decreased and cracks gradually increased in size. Polarization curves show that the membrane electrode assemblies (MEAs) made with 60% Pt-HSC have a better performance than those with 30% Pt-Vulcan XC-72. The performance and measured electrochemical active surface area of the MEAs made from both catalysts are slightly affected by dispersion method.
A core-shell Pt/C@NCL300 catalyst with an accessible layer was designed to recover lost ORR activity and was constructed via a one-step self-assembly process in this paper. A thin porous layer derived from Nafion was first formed on the surface of Pt/C catalyst to create a shell. This first coating successfully separated the Nafion and Pt particles in the catalysts and reducing the negative impact of Nafion on ORR activity and enhancing the fuel cell performance. The newly fabricated Pt/C@NCL300 catalyst exhibited much higher specific activity than the original Pt/C catalyst in RDE tests under the same conditions and were comparable to the activity of Pt/C electrode without Nafion poisoning. Moreover, the fuel cell with Pt/C@NCL300 catalyst exhibited a higher power density without an obvious increase in proton transport and O 2 transport resistance compared to that of a Pt/C fuel cell with a low Pt loading. This result indicates that coating the Pt/C catalyst with a layer accessible for oxygen and protons is a promising way to effectively promote Pt-based catalysts that work under normal operating conditions.
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