New Electrocatalyst for PEM Fuel Cell Application Based on Platinum Supported on Mwcnts and Few Graphene Layers

Abstract

Carbon blacks supporting Pt, currently widely used as electrocatalysts in Polymer Electrolyte Membrane Fuel Cells (PEMFC) are thermochemically unstable in PEMFC operating conditions. This is especially true at the cathode side where, on top of relatively elevated temperature (80°C) and acidic conditions, both the potential and the relative humidity may be high. The resulting carbon oxidation is partially responsible for the PEMFC performance decrease observed over time. Hence, long term durability still needs to be improved in order to consider PEMFC as credible alternatives to conventional power sources for automotive, stationary or portable applications. Much effort have been directed to identify and synthesize alternative carbon materials as catalyst supports for PEMFCs. One strategy to decrease carbon support corrosion is to use carbon with high extent of graphitization, which is supposed to decrease defect sites on the carbon structure, where carbon oxidation starts [1], [2]. However high graphitic content of carbon can be a brake for particle nucleation and dispersion. Among the different forms of carbon, graphene and carbon nanotubes have attracted tremendous interest materials for various energy applications [3], [4]. We will show how the combination of their high surface area, high conductivity and high chemical stability makes these 1D and 2D materials promising candidates for cathode catalyst support in PEMFCs. In this work, platinum and bimetallic (PtM, M=Co or Ni) nanoparticles catalysts have been prepared on N-doped Multi-Walled Carbon Nanotubes (MWCNTs) (home synthetized and commercial) and Few Graphene Layers (FGLs) using three synthetic routes: polyol route [5], impregnation and reduction under H2 [6] and SBH reduction [7]. The Platinum loading, the dispersion and size of metallic nanoparticles were analyzed by UV, XRD, SEM. Our materials showed good dispersion on nanostructured support and size of metallic particles reached 2 nm (figure 1). We investigated the properties of 2D FGLs/1D MWCNTs Pt and PtM catalysts for electrocatalysis of oxygen reduction. By comparing the electrochemical properties of these hybrid materials with a commercial Pt/C catalyst using carbon blacks as carbon support, it is found that this hybrid material demonstrated an enhancement of electro-catalyst performances in RDE tests. Moreover accelerated stress tests in half cell and fuel-cell setup demonstrated that the use of this hybrid FGLs/MWCNTs support can be promising in effectively reducing the carbon corrosion and then increase lifetime of the cell. This work is funded by the FP7 NANOCAT European program (SP1-JTI-FCH.2012.1.5) and French region Midi-Pyrénées. REFERENCES [1] Xin Wang , Wenzhen Li , Zhongwei Chen , Mahesh Waje , Yushan Yan, “Durability investigation of carbon nanotube as catalyst support for proton exchange membrane fuel cell”, Journal of Power Sources, 2006, 158, pp 154–159 [2] D. Bom, R. Andrews, D. Jacques, J. Anthony, B. Chen, M. S. Meier, John P. Selegue , “Thermogravimetric Analysis of the Oxidation of Multiwalled Carbon Nanotubes: Evidence for the Role of Defect Sites in Carbon Nanotube Chemistry”, Nano Letters, 2002, 2, pp 615-619 [3] Yingwen Cheng, Songtao Lu, Hongbo Zhang, Chakrapani V. Varanasi⊥, and Jie Liu, “Synergistic Effects from Graphene and Carbon Nanotubes Enable Flexible and Robust Electrodes for High-Performance Supercapacitors”, Nano Letters, 2012, 12 (8), pp 4206–4211 [4] Zhou, X., Qiao, J., Yang, L. and Zhang, J ”A Review of Graphene-Based Nanostructural Materials for Both Catalyst Supports and Metal-Free Catalysts in PEM Fuel Cell Oxygen Reduction Reactions”, Adv. Energy Mater., Vol. 4, (2014) p.1301523 [5] Yongjie Li, Wei Gao, Lijie Ci, Chunming Wang, Pulickel M. Ajayan “Catalytic performance of Pt nanoparticles on reduced graphene oxide for methanol electro-oxidation”, Carbon (2010), 48, 1124-1130. [6] S. M. Choi, M. H. Seo, H. J. Kim, W. B. Kim, “Synthesis and characterization of graphene-supported metal nanoparticles by impregnation method with heat treatment in H2 atmosphere”, Synthetic Metals 161 (2011) 21–22, 2405–2411. [7] D. Wang et al., Nature Materials, “Synthesis and characterization of Cocore–Ptshell electrocatalyst prepared by spontaneous replacement reaction for oxygen reduction reaction” 2013, 12, 81-87. Figure 1