Metal/Metal Oxide Hybrid Nanomaterials:Synthesis And Electrochemical Properties

Due to the unique nano-structural properties, novel metal and metal oxide hybrid nanomaterials as anodes for lithium-ion batteries and catalysts for fuel cells are expected to exhibit excellent electrochemical performance, and therefore have been considered to be one of the most promising candidates as the electrode materials for the next generation of power batteries.In this dissertation, we propose various synthetic methods to obtain a rich variety of novel metal and metal oxide hybrid nanomaterials, including hydrothermal method, chemical vapor deposition (CVD), RF-sputtering, electrochemical deposition, and wet chemical method. By using hydrothermal method and subsequent calcination, Co2SnO4@C core-shell nanoparticles, Zn2SnO4@C core-shell nanorods, and Co3O4@SnO2@C core-shell nanorods have been prepared. By using electrochemical deposition and RF-sputtering methods, CoO-Cu nanorod arrays and CoO-NiSi nanowire arrays have been fabricated. In addition, CoO-graphene nanosheets, Pt-Cu/C alloy nanocrystals, Rh-Pd/C alloy nanodendrites, and Pd-Cu/C alloy nanoparticles have also been generated by using wet chemical method. Owing to their unique nano-structural properties, the above-mentioned hybrid nanomaterials exhibit excellent electrochemical performance. The main innovative results are displayed as follows:(1) Co2SnO4@C core-shell nanostructures and Zn2SnO4@C core-shell nanorods have been synthesized through a simple glucose hydrothermal and subsequent carbonization approach. These core-shell nanostructures remarkably improved the cyclic performance compared to pure Co2SnO4and Zn2SnO4nanocrystals, which can be attributed to the uniform and continuous carbon buffering matrix.(2) Co3O4@SnO2@C core-shell nanorods have been fabricated through a facile hydrothermal and subsequent carbonization approaches. These core-shell nanorods exhibited good cycling and enhanced power rate performances, which can be ascribed to the synergetic effect between CO3O4and SnO2, as well as the structural stability and improved electronic conductivity of the carbon matrix.(3) Nanostructured hybrid CoO/Cu and CoO/NiSiX core-shell nanowire array electrodes have been synthesized through chemical deposition and RF-sputtering. When applied as the anode material for lithium-ion batteries, the electrochemical performance of the nanostructured hybrid electrode is much better than planar electrode, which can be attributed to the large accessible surface area and improved electronic/ionic conductivity of the nanostructured electrodes.(4) Highly loaded CoO/graphene nanocomposites have been synthesized through a thermal decomposition process in a mixture containing Co(acac)3and graphene with oleylamine (OAm) as both solvent and reducing agent. The as-prepared highly loaded CoO/graphene nanocomposites were evaluated as anodes for lithium-ion batteries, which exhibited superior electrochemical performances including large reversible capacity, excellent cyclic performance, and high rate capability. We believed that the robust composite structures, large quantity of accessible active sites, and synergistic effects between CoO NCs and graphene may be responsible for the significantly enhanced performance.(5) Pt-Cu alloy concave nanocubes and Rh-Pd alloy nanodendrites with high-index facets in high qualities and yields have been synthesized through a facile oil-phase method under kinetic control. When supported on carbon, the alloy nanocrystals showed enhanced electrocatalytic activity and durability for methanol oxidation reaction (MOR) and oxygen reduction reaction (ORR) relative to the commercial Pt/C due to a combination of composition and facet effects.(6) CuPd alloy nanoparticles with average sizes varying from6-23nm have been synthesized by the coreduction of Pd(acac)2and Cu(acac)2with OAm as both the solvent and reductant and TOPO as a stabilizer. The amounts of CTAB in the reaction solution were a key to the successful size-control of alloy nanoparticles. In addition, TOPO played a key role in controlling nucleation and growth of Cu and Pd into CuPd alloy nanoparticles. These alloy nanoparticles are expected to exhibit the good performance as catalysts for formic acid oxidation.