Study Of Graphene Carried Pt And Alloy Free Of Pt Catalysts For PEMFs

Platinum supported by high surface carbon are generally used as both the anode and cathode catalysts in proton exchange membrane fuel cell (PEMFC) in order to increase the dispersion and utility of Pt. However, the performance of the Pt/C catalyst are very difficult to maintain during extended operation under the caustic environment due to the following reasons: (1) Pt particles show a strong tendency to shift and agglomerate since their high specific surface energy and week interaction between the metal and the support; (2) Pt dissolution; (3) loss of platinum with corrosion of the carbon support; (4) Pt surface poisoned. The durability of PEMFC has been recently recognized as one of the most important issues to be addressed before the commercialization of the PEMFC. So developing high activity,long lifetime catalysts and seeking free of Pt catalysts are an urgent needed, which is a first determining factor for the commercialization of the PEMFC.First, this paper reports synthesis of graphene (Gr) by direct reduction of tetrachloroethylene with sodium in Paraffin oil rather than by the intermediate steps of oxidized graphite (GO) and oxidized grapheme (GrO). Gr is used as a support for the subsequent deposition of Pt nanoparticles and the catalysis for the oxygen reduction (OR) on the as-prepared Pt/Gr was studied. The structure, morphology, composition and surface properties of the as-prepared catalysts Pt/Gr are characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and electrochemical measurements. It is found that Pt nanoparticles with a mean particle size of 3.1 nm are well-dispersed on the Gr. The onset potential of the OR on the Pt/Gr electrode is shifted to the positive direction by 30 mV in comparison with the electrode made of the commercial Pt/C catalysts (Johnson-Matthey Co. JM-Pt/C). The exchange current density of the OR on the Pt/Gr electrode is 1×10^-3 mA·cm^-1, which is 2.5 times as that of the electrode made of JM-Pt/C catalysts.Second, the alloy Pd-Au/MCNTs catalyst has prepared through the improvement liquid phase reducing process, namely take THF and NaBH₄ as the complexion agent and reducing agent, respectively. The experimental result indicated: the alloy with a mean particle size of 4.9 nm was well-dispersed on the MCNTs. The addition of Au in to the Pd/MCNTs catalyst can increase the electrocatalytic activity and stability. Especially, the electrocatalytic activity and stability of Pd-Au/MCNTs (THF) catalyst with the ally of Pd and Au are better than that of the Pd-Au/MCNTs catalyst, in which, Pd and Au do not from the ally.