Enhanced Power Performance of Membrane Electrode Assemblybased on Modified Catalyst Support for PEMFC

Abstract

The cost reduction and durability enhancement of membrane electrode assembly (MEA) are of primary concerns toward commercialization of fuel cell electric vehicle (FCEV). The electrochemical corrosion of carbon supports is one of the major catalyst degradation modes occurring during loading cycling and startup-shutdown operation for FCEV, and causes a significant influence on the performance loss of MEA.Herein we present the fabrication of durable catalyst supports by the non-covalent modification of the GC support. A simple non-covalent functionalization of the GC support with the pyrene molecules was shown to enhance the dispersion and uniform distribution of Pt nanoparticles with preserving the integrity and electronic structure of carbons [1]. Electrochemical analysis demonstrated that the Pt/modified GC shows improved electrochemical durability with enhanced catalytic activity than the Pt/GC and commercial Pt/GC catalysts. Our study demonstrates that the durability of the Pt/C catalyst depends on the uniformity of Pt nanoparticles dispersion and the capability of corrosion resistance, which can be enhanced by the non-covalent modification of GC.For automotive application, the development of MEA with high power performance and high durability is of much interest. In order to investigate the practical impact of the Pt/modified GC catalyst, we designed two types of MEA employing the Pt/modified GC (Modified GC-MEA) and the Pt/GC (GC-MEA) as the cathode catalysts. The cell voltage of the modified GC-MEA under low humidified condition is higher than that of the GC-MEA in the overall region of current density studied (Fig. 1(a)). The absence of a significant mass transport limitation at high current densities for the modified GC-MEA indicates that the Pt/modified GC provides a Pt surface area large enough for preventing the local oxygen transport limitation. We hypothesized that the possible interaction between modified GC surfaces and ionomer would have an influence on ionomer distribution in the catalyst layer. As shown in Figure 1(b), the modified GC-MEA exhibits lower O2 gain than the GC-MEA under low humidified condition. Lower O2 transport resistance for the modified GC-MEA was ascribed to better O2 gas diffusion in the cathode catalyst layer. To assess the durability of the modified GC-MEA, we conducted the catalyst support durability test, following the standard test protocols suggested by DOE. The voltage loss after 5,000 cycles was about 24 mV for the modified GC-MEA, which was similar to that of the GC-MEA. Our results suggest that the non-covalent functionalization of the GC with the pyrene molecules is an effective way to fabricate highly active and durable catalysts for PEMFC, which can substantially enhance the power performance of MEA under low humidified condition without sacrificing the electrochemical stability of the GC support, providing a design guide of highly durable MEA for automotive applications. [1] H.S. Oh, H. Kim, Adv. Funct. Mater. 21 (2011) 3954-3960. Figure 1