Tianyuan Xie

Development of Highly Active Pt2Ni/CCC Catalyst for PEM Fuel Cell

Polymer electrolyte membrane fuel cells (PEMFCs) are attractive for automotive applications because of their low operating temperature (80°C), high power density at 0.6 V, portability, and relatively matured technology when compared to other lowand hightemperature fuel cells [1,2]. The membrane electrode assembly is the important component in a PEMFC which contains a Pt or Pt-alloy based electrocatalysts supported on high surface area carbon and a proton conducting polymer membrane. Studies have shown that the anode Pt loading can be reduced up to 0.05 mgPt/cm due to the faster kinetics at the anode when pure H2 fuel is used. Nearly 4-8 fold higher Pt loadings (0.2 to 0.4 mgPt/cm) are required on the cathode due to the sluggish oxygen reduction reaction (ORR) kinetics in order to achieve the necessary high power density at high cell voltages needed for automotive applications [3-6]. Considering the limited world supply of Pt and its high cost, 2015 DOE target requires Pt group metal content of ≤ 0.125 g/kW, while maintaining the MEA power density. To meet this goal, cathode Pt loadings needs to be reduced to 0.1 mgPt/cm without affecting the performance which requires at least fourfold higher mass activity of Pt-based catalysts. The specific objectives of this work are: (1) to increase the catalyst mass activity by choosing appropriate alloying metal and (2) determine the effect of different catalyst loadings on mass activity and the fuel cell performance. The catalyst support was suitably modified prior to the Pt deposition and alloying process with nickel by a methodology developed at University of South Carolina. A protective coating method was used to avoid Pt-alloy particle size growth during high temperature alloying process. Figure 1 shows the X-ray diffraction patterns of Pt/C, fresh and leached Pt2Ni/C catalysts. In order to avoid the Pt-alloy catalyst particle agglomeration at high temperature treatment, the catalyst was protected using a USC-developed coating process prior to the heat treatment. The particle sizes of Pt/C and leached Pt2Ni/C are 2.2 and 3.5 nm, respectively which confirms the efficient role of the protective coating used to control the particle growth during high temperature pyrolysis. Furthermore, the shift in the 2θ values to higher values indicates the Pt-Ni alloy formation. The mass activities of Pt/C and leached Pt2Ni/C catalysts are compared in Fig. 2. The testing was carried out under the following DOE suggested conditions [80 C/ H2/O2 (2/9.5 stoic.), 100% RH and 150 kPaabs.]. As can be seen from the figure, the alloying process drastically increased the mass activity of the Pt2Ni/C catalyst by ~3 times (0.45 A/mgPt) when compared to the fresh Pt/C catalyst (0.18 A/mgPt). Detailed experimental results and theoretical studies explaining the effect of catalyst loading on the mass activity and high current density performance under H2-air will be presented at the conference.