Fabrication Of Conducting Polymer/Precious Metal Composite Materials And Their Application In Small Organic Molecules Electrocatalytic Oxidation

Low-temperature fuel cells as new-style energy devices have attracted great attention because of their high-energy conversion efficiency, low operating temperature, low pollutant emission, the simplicity of handling liquid fuel and quick startup. High efficient electrochemical oxidation of small organic molecules will be directly related to the development and application of low-temperature fuel cells. The current state of the art employs carbon-supported platinum and platinum alloys as anode and cathode catalysts in low-temperature fuel cells. However, carbon material may cause easily Pt particle aggregation and carbon corrosion occurred by electrochemical oxidation, which lower the utilization rate of Pt and the lifetime of fuel cell. Compositing of conducting polymers (CPs) with precious metal possesses some advantages, such as high anti-corrosion, good electron and proton conductivities, and synergistic effect. For the electrooxidation of small organic molecules, presently, CPs as host material of precious metals were centered on the polyaniline, polypyrrole, polythiophene and their derivatives. Electrodepositon had been proved to be one of the most useful approaches for the preparation of conducting polymer and its composites. Other CPs with excellent performances has been developed. Therefore, it would be quite significant to extend such studies to other CPs which might be more suitable as host materials of precious metals in low-temperature fuel cells. In this dissertation, we fabricated a series of novel CPs/metal composites such as Polyindoles/Pt, Polycarbazole/Pt-Ru and Poly(p-phenylene)/Pd-Au, and evaluated the electrooxidation activities of small organic molecules (for example: formic acid, methanol and isopropanol) on the different composite catalysts. Additionally, we systematically studied different parameters affecting the electrooxidation of small organic molecules and the nature of synergistic effect between CP and metal. We also prepared Pt catalyst modified with indole for the high efficient electrooxidation of formic acid. They were briefly described as follows.1. Four novel composite catalysts have been developed by the electrodeposition of Pt onto glassy carbon electrode (GC) modified with polyindoles: polyindole, poly(5-methoxyindole), poly(5-nitroindole) and poly(5-cyanoindole), which were prepared from boron trifluoride diethyl etherate and its mixed electrolyte. As-formed composite catalysts were characterized by SEM, XRD and electrochemical analysis. Compared with Pt nanoparticles deposited on the GC modified with polypyrrole, the four newly developed composite catalysts exhibited higher catalytic activity towards formic acid electrooxidation by improving selectivity of the reaction via dehydrogenation pathway and thus mostly suppressing the generation of poisonous COads species. The enhanced performance was proposed to come from the synergetic effect between Pt and polyindoles and the increase of electrochemical active surface area (EASA) of Pt on polyindoles. On the other hand, the results of the catalytic activity for methanol oxidation showed that the Pt/PIn/GC and Pt/PMI/GC exhibited higher catalytic activity and stronger poisoning-tolerance than Pt/PPy/GC.2. Polycarbazole (PCZ) was obtained by the electropolymerization of carbazole in boron trifluoride diethyl etherate + 20% ethyl ether on glassy carbon electrode (GC). The monometallic Pt and bimetallic Pt-Ru nanoparticles firstly dispersed onto PCZ (Pt/PCZ/GC, Pt-Ru/PCZ/GC) and their electro-catalytic activities towards formic acid and methanol oxidation have been investigated. PCZ had good conductibility and electrochemical activity in 0.5 M H2SO4. As-formed electrodes were characterized by SEM, EDS and electrochemical analysis. Relative to Pt and Pt-Ru deposited on the bare GC (Pt/GC, Pt-Ru/GC), Pt/PCZ/GC and Pt-Ru/PCZ/GC had a somewhat enhanced efficiency for the methanol oxidation, however, they exhibited higher catalytic activity and stronger poisoning-tolerance ability towards formic acid electro-oxidation. The enhanced performance was proposed to come from the synergetic effect between metal particles (Pt, Pt-Ru) and PCZ. At the same time, the results of the stripping voltammograms of CO show that PCZ can weaken largely the adsorption strength of CO on catalysts and electro-oxidize COads easily on catalysts. 3. We found that as-prepared poly(5-nitroindole) (PNI) in alkaline solutions had also good electrochemical activity and stability in the potential range from -0.6 to 0.5 V versus SCE. Therefore, we firstly studied the electrooxidation of methanol on Pt/poly(5-nitroindole) (Pt/PNI) in alkaline media. The effects of different parameters related to the methanol oxidation reaction kinetics, such as Pt loading, mass of PNI film, concentration of methanol and KOH, potential scan rate, have been investigated in detail. The results of the catalytic activity for methanol oxidation showed that Pt/PNI had higher catalytic activity and stronger poisoning-tolerance than Pt/GC electrode.4. Poly(p-phenylene) (PPP) films were synthesized by a low-potential electrochemical polymerization of biphenyl in pure boron trifluoride diethyl etherate. As-formed PPP film was firstly used as a catalyst support. Pd-Au nanoparticles were successfully electro-deposited on PPP films (namely, Pd-Au/PPP) and used for the electrooxidation of isopropanol in alkaline media and the electrooxidation of formic acid in acidic media. As-prepared Pd-Au/PPP composite catalyst was characterized by SEM, EDX and electrochemical methods. The results for isopropanol oxidation indicated that Pd-Au/PPP had higher catalytic activity and stronger poisoning resistance than the Pd-Au deposited on the bare electrode. On the other hand, the electrocatalytic activity of formic acid oxidation on Pd-Au/PPP composite catalyst was also enhanced relative to Pd-Au/GC.5. In order to further prove the synergistic effect of polyindole and Pt, self-assembly of Pt and indole into a novel composite catalyst on a glassy carbon electrode (GC) has been developed by a one-step electrodeposition in the presence of 3.0 mM H2PtCl6 and 0.1 mM indole. As-formed Pt-indole composite catalyst was characterized by SEM, XPS and the electrochemical methods. Compared to Pt/GC and Pt/C, the novel Pt-indole composite catalyst exhibited higher catalytic activity and stronger poisoning-tolerance for electrooxidation of formic acid. The adsorption strength of CO on Pt-indole composite catalyst was greatly weakened as demonstrated by CO stripping voltammograms. This was due to indole with an abundant amount of electrons may generate an electronic effect when it adsorbs onto Pt surface and the adsorbed indole on Pt surface will modify the Pt surface microstructure. At the same time, the effects of different parameters related to the formic acid oxidation reaction kinetics, such as Pt loading, concentration of formic acid, potential scan rate, have also been investigated in detail.