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Carbon nano fiber membrane as a carrier for direct methanol fuel cell anode catalysts

Author: LiMiaoYu
Tutor: YangBinSheng；HanGaoYi
School: Shanxi University
Course: Inorganic Chemistry
Keywords: Carbon nanofibers Pt Nanoparticles Methanol Electrochemical oxidation
CLC: TM911.4
Type: PhD thesis
Year: 2011
Downloads: 166
Quote: 1
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Abstract

With the social and scientific and technological development, human demand for energy is growing. And with the wide application of fossil fuels, environmental pollution is getting worse, in order to improve the living environment, humans had to find an ideal alternative energy and the development of efficient energy conversion devices. Fuel cell is a continuous supply of fuel chemical energy continuously into electrical energy, due to its high energy conversion efficiency, clean pollution has become widely accepted. Among them, the direct methanol fuel cell due to its high theoretical energy density, low operating temperature, the battery structure is simple and safe to use as well as a rich source of raw material methanol, inexpensive, easy to store and carry, etc. are of concern, is the ideal portable power . However, since the anode catalyst efficiency is low, and the noble metal catalyst is expensive and limited to commercialization. Therefore, improving the catalytic oxidation of methanol anode catalyst performance, in order to reduce the cost of direct methanol fuel cells are currently the focus of research. This paper was prepared by the electrostatic spinning of polyacrylonitrile fiber membrane treatment, constructed conductive carbon nanofibers (CFMs), and carbon nano-fiber membrane as the carrier, H2PtCl6 · 6H2O as a catalyst precursor, the application of different preparation Methods Pt particles are supported on conductive carbon nano fiber membrane constructed Pt / CFMs electrode and studied the performance of catalytic oxidation of methanol. (1) and heat with electrospinning constructed smooth surface, an average diameter of about 150 nm composed of long carbon fiber conductive carbon nanofibers; using confocal Raman spectroscopy and four-electrode method of carbon nano-fiber membrane were tested Raman spectroscopy and conductivity. The results showed that: ① Preparation of a carbon nanofiber paper membrane D / G of 1.16, far below the reported temperature carbonization of the same D / G value (1000 ℃ the D / G is 1.51 when 3.41,1500 ℃) ; ② Preparation of a carbon nano-fiber membrane conductivity of about 55 S cm-1, carbonization temperature of the literature 2000 ℃ the conductivity close (carbonization temperature of 1500 and 2000 ℃, the conductivity was 14.86 and 55.41S cm-1). It may be prepared herein diameter than the carbon nanofibers reported in the literature fiber diameter (fiber diameter range :200-300 nm, an average diameter of about 250 nm) is small, because of high degree of graphitization. (2) comparison of the carbon nanofibers and commercial carbon paper (CP) physical properties. Which: ① carbon nanofiber membrane surface area, pore volume and porosity were 22.84 m2g-1, 2.94 mL g-1 and 65%, while commercial carbon paper surface area, pore volume and porosity were 4.64 m2 g -1,0.24 mL g-1 and 29%. In addition, commercial carbon paper mainly microporous diameter greater than 2μm, and the presence of carbon nano fiber membrane pore size of not greater than 2 gm (55%) of the hole, but also the distribution of diameter less than 2μm (45%) of the hole; ② carbon nanofibers the film tensile strength, compressive strength and bending strength were 12.09,16.02 and 38.67 MPa, slightly larger than the commercial carbon paper (tensile strength, compressive strength and bending strength were 11.49,15.56 and 35.85 MPa) . Description of carbon nanofibers prepared to meet the mechanical strength of the membrane electrode. (3) commercial Pt / C catalysts were supported on carbon nanofibers and carbon paper to build commercial Pt / C-CFMs and Pt / C-CP electrode, and examine their effect on the catalytic oxidation of methanol. The results showed that the electrode Pt / C-CP compared electrode Pt / C-CFMs only has a high catalytic activity, but also has better stability. In addition, the dynamic tests show that the electrode Pt / C-CP compared to the electrode Pt / C-CFMs catalytic oxidation of methanol exchange current larger, and charge transfer resistance is small. This is because the Pt / C catalyst can be better dispersed in the pores of the carbon nanofibers, the carbon nanofibers and the continuous Pt / C particles have better contact, to improve the utilization of the catalyst. Thus, the higher the conductivity, the carbon nanofibers and the continuous accumulation of specific pore structure characteristics, the carbon nanofibers are expected to become an effective catalyst support material. (4) Carbon nanofiber membrane carrier, H2PtCl6 · 6H2O as a catalyst precursor, using cyclic voltammetry, formaldehyde liquid phase reduction method, gas phase reduction method (the reducing agent is formaldehyde and formic acid vapor, respectively), and ethylene glycol reduction method Different methods Pt supported on the electrically conductive particles are carbon nanofiber membrane constructed Pt / CFMs electrode and to study the performance of the catalytic oxidation of methanol. The results show that the commercial Pt / C catalyst, electrode Pt / CFMs has high catalytic activity, good resistance to poisoning intermediates capacity and better long-term stability. Moreover, dynamic tests have shown that the electrode Pt / C-CFMs compared electrode Pt / CFMs catalytic oxidation of methanol exchange current larger charge transfer resistance is small. These can be attributed to the carbon nanofibers have a high conductivity, platinum particles in close contact with the carbon fibers to improve the utilization of the Pt catalyst. (5) Considering the different constructed of Pt / CFMs electrode catalytic oxidation of methanol, found: electrostatic spinning technology and heat treatment technology combines the method of carbon nano fiber membrane as the carrier, by physical adsorption - formaldehyde gas phase reduction France constructed Pt / CFMs electrodes for electro-catalytic oxidation of methanol with high catalytic activity, better resistance to poisoning intermediates capacity and better stability, not only simple preparation process, but also with solvent savings, low emissions of pollutants characteristics, it is expected to be a new method of preparation of noble metal catalysts.

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