Study On Electrocatalysts Of Fuel Cell Based On Noble Metal Nanoparticles/Carbon Nanomaterial Hybrids

Fuel cells have been one of the research hotspots in new energy sources due to high power efficiency, low pollution, abundant sources, and so on. However, the low catalytic activity and high cost of the electrocatalysts are still the key issues hindering the commercial application of fuel cell. At present, the investigation of electrocatalysts focuses on the improvement of the catalytic activity and utilization of the electrocatalysts, and the decrease of the loading mass of noble metals. To achieve this aim, it is desirable that noble metal nanoparticles (NPs) with small size are dispersed uniformly on the supports with good electronic conductivity and high specific surface area.In this dissertation, several methods for surface modification of carbon supports (carbon nanotubes (CNTs) and graphene) have been developed and noble metal NPs with small particle size have been dispersed uniformly on the functionalized carbon supports. Additionally, the electrocatalytic performances of the obtained noble metal NPs/carbon nanomaterial hybrids towards the oxidation of alcohols (methanol, ethanol), glucose and oxygen reduction have been studied in detail. The main points are summarized as follows:(1)Taking CNTs modified with poly(1-allyl-3-ethylimidazolium tetrafluoroborate)(PIL-CNTs) as support and silver NPs as sacrified template, Pt hollow nanospheres (PtHNs) with high dispersion and small particle size were successfully "grown" on CNT surface by in-situ displacement method. The electrocatalytic performance of the obtained PtHNs/PIL-CNTs for methanol oxidation in acidic solution was investigated by cyclic voltammetry (CV) and chronoamperometry (CA). Comparing with commercial E-TEK Pt/C and PtHNs adsorbed on acid-oxidized CNTs, PtHNs/PIL-CNTs electrocatalyst has the highest mass activity and best long-term stability for methanol oxidation.(2) Functionalized CNTs (AILP-CNTs) were prepared by polymerization of1-methyl-3-(prop-2-ynyl)-imidazolium bromide monomers with catalysis of PdCl2, then Pd/AILP-CNTs catalyst was synthesized by one-pot method. The results obtained by the methods of four-point and electrochemical impedance show that AILP-CNTs has better electronic conductivity and smaller charge transfer resistance than CNTs functionalized with poly(1-vinyl-3-ethylimidazolium bromide). Transmission electron microscopy (TEM) result shows that Pd NPs with an average diameter of3.5±0.5nm were uniformly dispersed on the surface of AILP-CNTs. The results from CV and CA demonstrate that Pd/AILP-CNTs catalyst has higher mass activity and stability towards glucose electrooxidation in alkali solution than Pd/CNTs.(3)With CNTs modified by acetylenic ionic liquid polymer (AILP-CNTs) as support, PdAu/AILP-CNTs electrocatalyst was prepared by NaBH4reduction method. TEM result shows that PdAu NPs with an average diameter of4.5±0.5nm were uniformly dispersed on the surface of AILP-CNTs. The results from CV and CA demonstrate that PdAu/AILP-CNTs catalyst has higher activity and electrochemical stability towards ethanol electrooxidation in alkali solution than PdAu/CNTs.(4)PCA-CNTs was prepared by the surface modification of CNTs with1-pyrenecarboxaldehyde (PCA). Using the reduction ability of the PCA’s aldehyde group, PtRu/PCA-CNTs electrocatalyst was synthesized via microwave-assisted reduction process in water. TEM result shows that Pt NPs with an average diameter of1.7±0.3nm were uniformly dispersed on the surface of PCA-CNTs. The results from CV and CA demonstrate that PtRu/PCA-CNTs catalyst has higher activity and long-term stability towards methanol electrooxidation comparing with PtRu/CNTs catalyst obtained by formaldehyde reduction method.(5) With1,10-phenanthroline hydrochloride monohydrate-functionalized graphene (PNT-GNs) as support, Pt/PNT-GNs electrocatalyst was prepared by microwave-assisted glycol reduction method. Scanning electron microscopy result shows that Pt NPs on the surface of PNT-GNs had better dispersion and smaller particle size than those on the surface of unmodified graphene. The electrocatalytic performance of Pt/PNT-GNs for oxygen reduction was investigated by rotate disk electrode and linear scanning voltammetry. The results show that Pt/PNT-GNs has better catalytic activity than Pt/GNs.(6)Using1-pyrenecarboxaldehyde as the reductant for exfoliated graphene oxide (GO), carboxylate-functionalized and high-reduced graphene nanosheets (PC--GNs) were prepared based on a one-step reduction/functionalization strategy. The obtained PC--GNs have excellent dispersibility in water and then are used as support for Pt NPs. Reduction of GO was confirmed by X-ray photoelectron spectroscopy and X-ray diffraction spectroscopy. TEM result shows that Pt NPs with an average diameter of1.3±0.2nm were uniformly dispersed on the surface of PC--GNs. The results from CV and CA demonstrate that Pt/PC--GNs catalyst has higher activity and long-term stability towards methanol electrooxidation comparing with Pt/GNs catalyst.