| Low-temperature fuel cell, being one kind of green energy conversion equipment, hasbeen widly applied in various fields, such as military, transportation, communication, clearpower station, aerospace, electro-automobile, and portable power source. However, as theenvironmental and energy issues being worse today, further research and improvement onfuel cell (such as on its cost, working performance, and energy convert-efficiency) still bevery important and meaningful in the present. As the catalytic reaction center, the catalyticmaterial (including metal catalyst and catalyst support) on electrode of fuel cell is one ofthe most important components of fuel cell, and its properties directly affect theperformance and energy convert-efficiency of fuel cell. Particularly, the catalyst supportsplay significant role on nanoparticle size, distribution, and stability of metal catalysts. It iswell known that carbon black is the most conventional fuel cell catalyst support with highspecific surface area, but contributes mostly with micropores of less than1nm, whichleads to the limited accessibility and low activity of catalysts. Therefore, the developmentof novel, effective-cost, large surface area, high-performance and stable catalyst supportsare urgently required.Considering their conductive and stable three-dimensional structures, conductingpolymers can be used as suitable supports for low-temperature fuel cell catalysts.Compared with conventional carbon material supports, conducting polymer used as fuelcell catalyst support possesses several advantages:1) Generally, conducting polymer growsthree dimensionally by chemical or electrochemical method. Hence, it will provide highlyporous and rough structure, which can generate a large surface area for metal catalystnanoparticle deposition;2) The properties of conducting polymer can be easily changed orimproved by introducing kinds of functional groups into the main chains;3) Due to theirreversible redox behavior and special π-conjugated structures, conducting polymer canprevent the oxidation corrosion suffered by carbon materials and maintain high stability under fuel cell operational conditions;4) Some conducting polymer are not only electronconducting, but also proton conducting materials, so they can replace Nafion in the catalystlayer of fuel cell electrode and provide enhanced performance. Moreover, the introducedconducting polymer can provide a low ohmic drop for the electron transfer between themetal catalyst and the substrates, and also improves the interfacial properties between theelectrode and the electrolyte. And also, there may be some synergic effect between themetal nanoparticles and the polymer matrixes, which can enhance the electrocatalyticactivity as well as the poison-tolerant ability of metal catalysts. Therefore, conductingpolymers as a novel kind of catalyst supports after carbon materials develop a new field forresearch on fuel cell catalyst supports. In this paper, we prepared a series of novelconducting polymers, and used these polymers to support Pt/Pd metal catalysts, and theirelectrocatalytic properties toward methanol, ethanol, and formic acid oxidation werecarefully investigated. These studies of new electrocatalysts may provide a new idea aswell as a basic theoretical reference for future prospecting of catalyst support materials.The main research work in this paper is listed in the following:(1) A novel conducting polymer, poly(5-aminoindole)(PAIn), has beenelectrosynthesized in0.5M H2SO4aqueous solution containing0.02M5-aminoindole(AIn). As-synthesized PAIn shows good electrochemical activity and stability in aqueoussolution.1H NMR, UV-visible and emission spectral analyses confirmed the formation ofthe polymer with conjugated chain structure and that the polymerization mainly occurred atC(2) and C(3) positions with–NH2and–NH–remaining intact. The PAIn modified carboncloth (CC) was used as support for Pt particle electrodeposition. Compared with pure Ptparticles, the Pt/PAIn/CC catalyst shows higher catalytic activity and strongerpoisoning-tolerance for formic acid electrooxidation.(2) AIn and3,4-ethylenedioxythiophene (EDOT) were copolymerizedelectrochemically on a carbon cloth (CC) electrode in aqueous sulfuric acid solution.As-prepared copolymer was characterized by CV, SEM, UV-vis and FT-IR spectra, throughwhich the electrochemical properties, structure, and composition of as-obtained copolymerwere determined. The electrochemical activity and stability of as-formed copolymer aresignificantly improved in comparison with PAIn, due to the incorporation of EDOT units into the conjugated chain. The copolymer film modified CC was used as substrate for Ptparticle deposition (Pt/copolymer/CC), and then its catalytic activity towards formic acidelectrooxidation was studied. Experimental results indicate that the catalytic activity ofPt/copolymer/CC towards formic acid electrooxidation is enhanced in comparison withthat of Pt/homopolymer/CC, which can be attributed to the homogeneous distribution of Ptnanoparticles on copolymer/CC substrate and the improved electrochemical activity of thecopolymer film.(3) AIn was electropolymerized on graphene (GE) modified glass carbon (GC)electrode in0.5M H2SO4aqueous solution containing0.01M AIn. Because of thecatalytic effect of GE, the polymerization efficiency of AIn and the electrochemicalactivity of as-formed PAIn were significantly improved on GE/GC electrode. The preparedPAIn/GE/GC electrode was used as substrate for Pt particle electrodeposition. SEM, EDXand Raman spectral were used to characterize the prepared electrodes. Electrocatalyticexperiments demonstrate that the Pt/PAIn/GE/GC electrode possesses high catalyticactivity towards methanol electrooxidation in alkaline medium, due to the good dispersionof Pt particles on PAIn/GE/GC and the electronic interactions between the metal particlesand the polymer matrixes. Thus, PAIn can be a promising alternative for polymeric catalystsupport in direct alcohol fuel cells.(4) A series of novel Pt-Pd/polyfluorenes (PFs) composite catalysts were facilelyprepared based on Pt/Pd precursor and PFs with hydroxyl and carboxyl substitution at theC-9position by electrochemical method and their electrocatalytic performance towardformic acid oxidation were studied. Electrocatalytic experiments demonstrate that thePt-Pd nanoparticles immobilized on poly(9-fluorenecarboxylic acid)(PFCA)-decoratedglassy carbon (GC) electrode (Pt-Pd/PFCA/GC) show larger electrochemical active surfacearea, higher catalytic activity and stability toward formic acid oxidation than that of otherPt-Pd/PFs/GC, Pt-Pd/GC, as well as the commercial JM20%Pt/C/GC electrodes, whichcan be attributed to the small-sized and well-dispersed Pt-Pd nanoparticles on PFCA matrixand the special electronic interaction between the metal nanoparticles and the polymersubstrate. Moreover, the electron-withdrawing carboxyl substitution rather than theelectron-donating hydroxyl on the polymer main chain is of great benefit to the removal of poison CO as well as the enhancement of catalytic activity of Pt-Pd toward formic acidoxidation.(5) Pd-PEDOT/GE composite catalyst was prepared by “one pot” method. In thesystem, EDOT was oxidized and polymerized to PEDOT, and PdCl42–was simultaneouslyreduced to Pd nanoparticles. And then, NaBH4was added to reduce GO to GE and theadditional PdCl42–to Pd. The obtained composite catalyst was characterized by SEM, TEM,EDX, XRD, Raman, and FTIR spectra. The as-prepared Pd-PEDOT/GE catalysts showimproved electrochemical activity as compared to Pd-PEDOT catalyst. Electrocatalyticexperiments demonstrate that the Pd-PEDOT/GE catalysts perform much higherelectrocatalytic activity, anti-poisoning ability and stability toward ethanol oxidation incomparison with that of the Pd-PEDOT and commercial Pd/C catalysts, which areattributed to the excellently uniform dispersion of Pd nanoparticles on/in PEDOTnanospheres and GE as well as the electronic interactions between Pd nanoparticles andPEDOT. |
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