Catalyst and Electrode Advances for High Performing PEM and AEM Fuel Cells

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Recent advances in polymer electrolyte membrane fuel cells have brought the technology extremely close to finally fulfilling its promise as a high efficiency, sustainable energy source for transportation applications1,2. An overwhelming amount of work in this area has focused on the proton exchange membrane fuel cell (PEMFC), where high performance has been achieved. However, proton-based systems still suffer from very high materials cost of both the membrane and catalysts, and the need to drive costs down by reducing material loading generally leads to accelerated degradation of otherwise stable systems as well as increased sensitivity to water due to the reduced water capacity with thinning catalyst layer thickness. To overcome these limitations, our group has developed an air-assisted cylindrical liquid jets spraying system that allows for the precise control of the catalyst layer microstructure, leading to high-performance catalyst-coated membranes. The system design and influence of operating parameters on PEMFC performance will be shown. On the materials side, our team has produced Ni-rich PtNi alloys and Pt3Ni alloy nanocages that have shown very highly activity for the oxygen reduction reaction (ORR) and excellent stability at PEMFC cathode conditions. This poster will show the structure and chemistry of the Pt-Ni catalysts as well as their in-situ and ex-situ performance. The Pt-Ni nanocage PEMFCs have shown behavior that well exceeds the DOE targets for activity and comes very close to the DOE targets for durability. From both an activity and durability perspective, these Pt-Ni nanocage catalysts considerably outperform state-of-the-art commercial Pt/C catalysts. Another low-temperature alternative to the PEMFC that has been widely discussed in recent years is the anion exchange membrane fuel cell (AEMFC). The AEMFC has an effective pKa much higher than the PEMFC, and this basic environment has several possible advantages over the acid system, including a less corrosive environment for the catalyst and catalyst support, which opens up the periodic table with regards to possible materials to be employed. Also, it is well known that the kinetics for the ORR are more facile in alkaline media than acid media3, though the converse is true for the hydrogen oxidation reaction, which necessitates the study for advanced Pt catalysts such as PtRu4. Our recent work has shown that the internal water dynamics in the AEMFC is likely more complex than the PEMFC. In this poster, the influence of the membrane, ionomer and gas diffusion layer as well as the flow rate and dew points of the anode and cathode gases on anion exchange membrane fuel cell performance will be shown. After cell optimization, a peak power density of 1.2 W/cm2 has been reproducibly achieved with radiation-grafted ETFE membranes and ionomers.