Synthesis And Performance Of New Carbon Materials-supported Non-noble Metal Compound Nanoparticles

New carbon nanomaterials have received extensive attentions in the fields of catalysis andenergy. Graphene and carbon nanotubes (CNTs) are considered as the ideal supports formetal/metal oxides, owing to their excellent properties. For instance, the high specific surfacearea of graphene is beneficial for the dispersion and stability of the supported nanoparticles(NPs), the synergistic effect between NPs and graphene provides the good performance, andthe high electrical conductivity of graphene/CNTs also make the composites outstanding inelectrochemical applications. In addition, the incorporation of NPs limits the re-agglomerationof graphene sheets and improves the stability of these composites. In this work, graphene/CNTsbased nano-materials have been prepared, including cobalt carbonitride, iron family oxides andcomplex transition metal oxides composites. Their performances in electro-catalysis,heterogeneous catalysis and Lithium-ion batteries have been studied. The main contents aresummarized as follows:1. The design and oxygen reduction reaction (ORR) performance of nitrogen-dopedgraphene supported cobalt carbonitride catalyst. Platinum has been considered as the state-of-the-art catalyst, while the application of Pt is limited due to its high cost, limited supply andunstable activity. Transition metal nitrides (TMNs) are regarded as promising substitutes for Ptcatalysts, because of their Pt-like electronic behaviors. A new catalyst, cobalt carbonitride(CoCN) nanoparticles supported on nitrogen-doped graphenes (NG), was designed andsynthesized via a high temperature ammonia nitridation method. The catalyst has a core-shellstructure with a highly active CoCN core and a protective cobalt oxide shell. The obtained ORRtests showed that the current density of CoCN@CoOx/NG (5.62mA cm-2at-0.5V) is higherthan that of h-Co3O4/NG and commercial Pt/C catalysts, the half-wave potential (-0.16V) of itis very close to that of Pt/C. The electron transfer numbers n of CoCN@CoOx/NG wascalculated to be3.74, demonstrating an efficient4e oxygen reduction process. The catalyst alsoexhibited a good methanol crossover tolerance and stability. The electrochemical tests and DFTcalculation results showed the high performance benefits from the strong synergistic effectbetween CoCN and NG and the electronic modification of cobalt oxide by CoCN from within.2. Porous hollow iron oxide nanoparticles (PHNPs) supported on carbon nanotubes (CNTs)were facilely synthesized by etching Fe@FexOy/CNT with dilute nitric acid aqueous solutionat ambient temperature without the assistance of any surfactants and ligands. The meandiameter of hollow iron oxide nanoparticles was about17nm, with a wall thickness of about4nm. The formation mechanism of PHNPs was discussed based on the characterization results from TEM, XRD and H2-TPR. The combination of nanoscale Kirkendall effect and selectiveacid etching was proposed to be responsible for the formation of CNT supported PHNPs,through a transformation from core/void/shell structures to hollow nanoparticles. The preparedFexOy/CNT nano-composites are promising in magnetic, biomedical, and catalytic fields.3. Considering the crucial size effect of nanoparticles on their performances, three methods,i.e. the direct impregnation, the homogeneous oxidative precipitation with hydrogen peroxide(H2O2HOP) and the ammonia-catalyzed hydrolysis, were applied to synthesize iron, cobalt andnickel metal oxide nanoparticles supported on graphenes. The influence of three depositionmethods on the particle size distribution was investigated. TEM, FT-IR, XRD and XPS wereused to characterize the morphology and structure of the catalysts. The highest dispersion andthe most uniform particle size distribution were obtained by the H2O2HOP method. Hydrogenperoxide favors the maximization of the oxygen-containing groups on graphenes, whichprovide sufficient absorbing and nucleation sites to give high dispersion of nanoparticles. Whileammonia accelerates the nucleation speed and results in the largest particle size andinhomogeneity. Their catalytic properties were tested with the oxidation of benzyl alcohol as aprobe reaction. The reaction activity decreased in order of: catalysts prepared by hydrogenperoxide-assisted deposition> direct impregnation> ammonia-catalyzed hydrolysis, which iswell consistent with the order of catalyst particle sizes shown in transmission electronmicroscopy images. The catalytic relevance of the particle size shows the crucial role ofdeveloping effective method for size-controlled nanocatalysts on graphenes.4. Owing to their high theoretical reversible capacity, plentiful resources and low costs,transition metal oxides (TMO) have been regarded as one of the most promising anode materialsfor Lithium-ion batteries. In this thesis, three kinds of atmosphere (NH3, H2, Ar) have beenproposed for the preparation of the composites of graphene with dual-metal TMO (MFeO,M=Co, Mn, Zn). The particle size and dispersibility of dual-metal TMOs are much better thanthat of iron oxide nanoparticles. The morphology of the samples could be further tuned byadjusting the ratio of M:Fe. The samples fabricated with the ratio of1:1exhibited the bestdispersibility. TEM characterizations showed that the NH3and H2treated samples exhibitedhollow structure, while the Ar treatment resulted in the fabrication of solid NPs. HRTEM, XRDand XPS revealed that CoFe2O(60)/NG-h sample mainly composes of NG and CoFe2O4.Electrochemical tests including galvanostatic charge-discharge and electrochemical impedancespectroscopy (EIS) were applied to investigate the comparative performance of thesecomposites. Complex metal oxide composites showed superior performance to the FeO/NG-hcomposites, revealing the role of metal component in regulating the materials performance.