Pt Carried On Nitrogen Functionalized Carbon Nanotubes And PtSnCo/C Catalyst For PEMFC

Fuel cell converting chemical energy directly into electrical energy with high efficiency and low emission of pollutants may help to reduce environmental impact. Fuel cell is a practical answer to the world's pressing need for clean and efficient power. For decades, Pt-based catalysts are widely used in catalysis of oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs) and direct methanol fuel cells (DMFCs). However, the drawbacks with use of platinum, limited supply, high cost and easily poisoned by trace of carbon monoxide limit its use. Thus, a great effort has been devoted to development of new fuel cell electro-catalysts in order to increase Pt activity and reduce platinum consumption. At the same time, platinum-free catalysts have been highly esteemed.CNTs as a new form of carbon, have received researchers'attention due to their unique structural, electronic and mechanical properties. The use of CNTs as alternative supports for preparation of catalysts for low-temperature fuel cells has naturally stimulated significant interest among researchers. In recent years there has been a progress in the understanding of that the catalyst-support interaction plays a fundamental role in the performance of catalyst. However, the effective attachment of uniformly dispersed Pt nanoparticles remains a formidable challenge, due to the inertness and hydrophobic properties of the CNT surface.In part I of this paper, we successfully introduce N atoms to the graphite structure of CNTs by a simple and efficient method, leading to a certain amount of chemically active impurity sites and less surface oxygen groups. The platinum supported on nitrogen functionalized carbon nanotubes catalysts were prepared by a simple NaBH4 reduction method. We studied its electrochemical properties by electrochemistry measurement. The catalysts were characterized X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectrometry (XPS) and Fourier transform infrared spectroscopy (FTIR). The preliminary results show that:(1) As compared with the traditional Pt/FCNTs catalyst,Pt/NFCNTs have a more small mean particle size about 4nm, and Pt particles uniformly dispersed on nitrogen functionalized carbon nanotubes with no obvious agglomeration.(2) As compared with the traditional Pt/FCNTs catalyst and commercial JM-Pt/C catalyst, Pt/NFCNTs have greater electrochemical surface area and higher utilization of platinum. According to the tafel curves of oxygen reduction reaction, Equilibrium potentials of Pt/NFCNTs catalysts show a positive shift, indicate the benefit for the ORR.(3) The results of single cell test show that,the maximum power density of 1.1 W/cm~2 was achieved for both Pt/NFCNTs catalysts at 0.2 mgPt/cm~2 anode catalyst loading and 0.4 mg/cm~2 cathode catalyst loading, but the maximum power densities were only 0.6 W/cm~2 for JM-Pt/C and 0.7 W/cm~2 for Pt/FCNTs respectively at the same catalyst loading.The main problems limiting the development of DMFC are the slow anode kinetics and methanol crossover phenomenon. The excellent catalytic activity of platinum for methanol xidation, makes Pt and Pt based electrocatalyst ideal for use as an anode in direct methanol fuel cells, it is well-known that platinum is expensive and a pure platinum is readily poisoned by CO-like intermediates of methanol electro-oxidation. In the part II of this paper, Novel nano-sized PtSnCo/C trimetallic catalyst (20%w) have been prepared through borohydride reduction and subsequent hydrothermal treatment in glycol liquid phase. The structure and composition of the as-prepared electrocatalyst was assessed by XRD and EDS. We evaluated the electrocatalytic activity and stability of PtSnCo/C catalyst in methanol and sulfuric acid by anodic linear sweep voltammetry coupled with cyclic voltammetrys analysis. And pre-adsorbed CO monolayer stripping was used to investigate its anti-poisoning property. It was found that the PtSnCo/C catalyst not only showed the better electrocatalytic activity than the commercial JM-PtRu/C but also more stability for methanol oxidation, and more resistance to CO poisonings, as compared to PtSn/C catalyst and the commercial JM-Pt/C catalyst. It indicates that the addition of Co to PtSnCo/C enhanced its electrocatalytic activity and stability for methanol oxidation.