Their is significantly growing interests in a polymer electrolyte membrane fuel cell (PEMFC)as a promising alternative electric power generation system for stationary, backup power, and automotive applications because of high power density, low operating temperature, and reduced release of environmental pollutants relative to converntional energy conversion and storage devices [1]. In this regard, a high level of activities in materials science and engineering research for the PEMFC have been made to realize its potential applications as the advanced sustainable energy sourcecs.
For realizing the widespread commercialization of the PEMFC, there are still technical hurdles including high cost, performance loss, and insufficient durability with long-term cycles [2]. Especially in automotive condition, startup/shutdown and load-cycling cause a significant degradation of Pt nanoparticles supported on high surface area carbon. Although several types of Pt-based catalysts with enhanced catalytic activity and/or durability have emerged, they are still in development [3]. Therefore,it is still of great importance to develop efficient electro-catalysts with enhancing stability as well as sustaining catalytic acitvity under the wide ranges of operating conditions.
The development of a functional carbon supported Pt catalyst that has both high oxygen reduction activity and high durability would significantly contribute to the commercialization of automotive PEMFC. Herein we report a diazonium-functionalized graphitized carbon (DFGC) support prepared by grafting different types of end-functional groups on a GC support via simple diazonium chemistry that can improve the dispersion of Pt nanoparticles and reduce their sintering phenomena, resulting in higher electrochemical durability with enhanced catalytic activity as compared to the unmodified GC support. The membrane-electrode assembly (MEA) fabricated with the Pt/DFGC series as the cathode catalysts shows a power density higher than 1.0 W/cm2 under an automotivce operating condition at a low catalyst loading of 0.25 mgPt/cm2. The durability of the MEA was measured by electrocatalyst cycling and catalytst support cycling tests according to the procedures of DOE-FCTT accelerated stress test (AST) protocols. THe AST results reveal that the MEA series with the Pt/DFGC catalysts exhibit higher durability event at 30% lower catalyst loading compared to a commercial MEA. These results demonstrate that the catalyst design strategy based on simple diazonium chemistry is an effective way to fabricate highly durable catalysts with enhanced catalytic activity for the PEMFC, providing a design guide of a high performance MEA for automotive applications.
We also present current development status of our developed MEA for automotive applications. Our research and development focus on the fabrication of a cost-competitive MEA with high power performance and longer durability even at lower Pt amount for automotive PEMFC systems. To achieve these goals, a high level of activities have been made to develop the MEA design for high temperature and low humidified operation including the design of highly active catalyst layer, the functionalization of polymer electrolyte membrane and interfaces in the MEA, and cost-effective manufacturing process. The development of a cost-competitive MEA with high power output, long durability, and operation flexibility is expected to contribute the widespread commercialization of automotive PEMFC systems. Further development of the MEA for automotive applications would be performed by balancing high performance against long-term durability and manufacturing cost.

References

[1] M. Winter, R. J. Brodd, Chem. Rev. 104, 4245-44269 (2004)

[2] R. Borup, J. Meyers, B. Pivovar, Y. S. Kim, R. Mukundan, N. Garland, et al., Chem. Rev. 107, 3904-3951 (2007)

[3] J. Y. Kim, S. Lee, T. Y. Kim, H. T. Kim, Electrochim. Acta 134, 418-425 (2014)