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In this work the dependence of limiting current on gas pressure and temperature was measured to separate the oxygen transport resistance into its components: molecular diffusion resistance in the gas diffusion layer (GDL) and resistance in the catalyst layer (CL), which comprises Knudsen diffusion resistance and oxygen permeation resistance through ionomer. The effect of microporous layer (MPL) modification by laser perforation on the oxygen transport resistances was investigated. The resistance in CL contributed a significant portion, about one quarter, to the total oxygen transport resistance. A trend of decreasing CL resistance with increasing temperature was observed. This temperature effect was mainly attributable to the oxygen permeation in CL ionomer. The MPL modification had little influence on the total transport resistance as well as its individual component for the cells under dry operation, while the perforated MPL significantly reduced the transport resistance when water starts to condense in electrode. This finding indicated that the MPL plays important roles in the cathode water management.

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At AFCC continuous effort has been made to improve the power density of fuel cell stack for automotive application in the past decade*. The unique challenges in durability posed by the need for much higher power generation per catalyst loading, kW/mg-Pt is still a major driver and a minimum viable stack functionality for mass production. This presentation will focus on one of the ways to meet the above criterion using mature Pt/C technology (10 to 50 wt% Pt on a high surface area carbon) for oxygen reduction in the cathode. The catalysts were custom made by Tanaka Kikinzoku Kogyo K.K to maximize and stabilize the Pt nanoparticles activity during their life cycle. The graph shows the linear dependency of a mix of the above catalysts characteristics such as Pt surface area (CO Chemisorption), Pt crystallite size (XRD), and catalyst surface area (N2 BET) as a function of Pt wt% on Carbon. With more in-depth analyses, preliminary optimization of catalyst layer for each of the above catalysts will be performed and the results will be discussed. These activities would facilitate the understanding of the effect of catalyst characteristics, catalyst structure (ionomer, catalyst layer thickness, EPSA, etc.), and electrode Pt loading (0.25 and 0.15 mg-Pt/cm2) on the high current density performance up to 3 A/cm2. Identifying the above parameters would leverage further development in maximizing the fuel cell functionalities and improving the stack durability.   *Reference:AFCC accomplishments, http://www.afcc-auto.com/company/about-us/ Figure 1