Mesoporous Nitrogen Doped Carbon Supported Platinum PEM Fuel Cell Electrocatalyst Made From Ionic Liquids

A multitude of new and improved catalyst materials and concepts for membrane fuel cells were developed over the last decade. The requirements of these catalysts are low cost, high activity and durability. For example, platinum based catalyst concepts such as Pt monolayer catalysts, 2] Pt skin catalysts, Pt multimetallic catalysts, and dealloyed bimetallic Pt core-shell nanoparticle catalysts show promising activities based on Pt mass and Pt surface area for the oxygen reduction reaction (ORR). Furthermore, non-noble metal catalyst concepts could reduce the costs, but they currently still do not meet the activity targets for commercial fuel cell electrocatalysts. To improve the durability of fuel cell catalysts, also the support material is becoming more important. Oxidation resistance of the support material is one point of concern. Alternatives to pure carbon blacks (e.g. Vulcan XC 72R) were evaluated for the oxygen reduction, such as carbon nanotubes, 24] silicon carbide derived carbons, hollow spherical carbons, nitrogen modified carbons, or titanium-based materials. Especially nitrogen doped carbons show interesting properties like high conductivity, mesoporosity and the opportunity to adjust the nitrogen content in the support material. In this communication, we report the synthesis of a mesoporous nitrogen doped carbon supported platinum catalyst (Pt/ meso-BMP) based on an ionic liquid as nitrogen/carbon precursor and the evaluation of the catalytic system for ORR. Further, we analyzed the long-term behavior of this new catalyst and compared it with commercial high surface area carbon (HSAC) supported platinum catalyst. The mesoporous nitrogen doped carbon supported platinum nanoparticle fuel cell electrocatalyst (Pt/meso-BMP) was prepared by a two-step synthesis, as shown in Figure 1. In the first step, the mesoporous nitrogen doped carbon material (meso-BMP) was synthesized corresponding to the reference 35] by using N-butyl-3-methylpyridinedicyanamide (BMPdca) as ionic liquid compound. As evaluated by X-ray photoelectron spectroscopy (XPS) and elemental analysis (EA) the nitrogen content of 14.2 wt. % (XPS)/17.2 wt. % (EA) is very high. The variation of the values can be explained by the surface specificity of XPS measurements. In the second step, platinum nanoparticles were deposited on the meso-BMP substrate. The deposition of Pt occurred by a wet impregnation–freeze-drying method and followed by thermal annealing in a reductive atmosphere. Shown in Figure 2 are the XRD profiles for meso-BMP and Pt/meso-BMP. The as synthesized meso-BMP support material exhibits broad XRD reflections at 2 q= 26.1 and 42.98 corresponding to the inter (002) and intra (101) lattice planes of graphitized carbon. The reference powder diffraction patterns of (111), (200), and (220) lattice planes for pure face centered Figure 1. Synthesis route for mesoporous nitrogen doped carbon supported platinum nanoparticle catalyst.