Yiming Chen

Microwave-assisted in situ synthesis of reduced graphene oxide/Mn3O4 composites for supercapacitor applications

Reduced graphene oxide/Mn3O4 (GM) composites were prepared by a simple and convenient strategy, that is, microwave irradiation of the hydrothermal product of reduced graphene oxide–Mn(NO3)2 mixtures. Mn3O4 nanoparticles with sizes of 20–50 nm were uniformly distributed on the surface of reduced graphene oxides. The GM composites exhibited good electrochemical performance with a specific capacitance of 344.8 F g−1 at the discharge current density of 1 A g−1 using 5 M NaOH as the electrolyte. The energy density of the GM composites was as high as 47.8 W h kg−1 with a power density of 1000 W kg−1. After 5000 cycles of charge/discharge experiments, a high level retaining specific capacitance of 342.1 F g−1 was obtained with 99.2% retention of the initial capacitance at 1 A g−1 and the equivalent series resistance of the GM composites system was much lower than that of pure Mn3O4. Therefore, the GM composites with large capacitance, good cycling performance and reversibility can be used as a promising electrode material for supercapacitor applications.

Study on carbon nanocomposite counterelectrode for dye-sensitized solar cells

Carbon nanocomposite electrodes were prepared by adding carbon nanotubes (CNTs) into carbon black as counterelectrodes of dye-sensitized solar cells(DSSCs). The morphology and structure of carbon nanocomposite electrodes were studied by scanning electron microscopy. The influence of CNTs on the electrochemical performance of carbon nanocomposite electrodes is investigated by cyclic voltammetry and electrochemical impedance spectroscopy. Carbon nano composite electrodes with CNTs exhibit a highly interconnected network structure with high electrical conductivity and good catalytic activity. The influence of different CNTs content in carbon nanocomposite electrodes on the open-circuit voltage, short-circuit current, and filling factor of DSSCs is also investigated. DSSCs with 10% CNTs content exhibit the best photovoltaic performance in our experiments.

Nanocomposite LiFePO 4 ·Li 3 V 2 (PO 4 ) 3 /C synthesized by freeze-drying assisted sol-gel method and its magnetic and electrochemical properties

Nano-sized LiFePO4·Li3V2(PO4)3/C was synthesized via a sol-gel route combining with freeze-drying. X-ray diffraction results show that this composite mainly consists of olivine LiFePO4 and monoclinic Li3V2(PO4)3 phases with small amounts of V-doped LiFePO4 and Fe-doped Li3V2(PO4)3. The magnetic properties of LiFePO4·Li3V2(PO4)3/C are significantly different from LiFePO4/C. Trace quantities of ferromagnetic impurities and Fe2P are verified in LiFePO4/C and LiFePO4·Li3V2(PO4)3/C by magnetic tests, respectively. LiFe-PO4·Li3V2(PO4)3/C possesses relatively better rate capacities and cyclic stabilities, especially at high charge-discharge rates. The initial discharge capacities are 136.4 and 130.0 mA h g−1, and the capacity retentions are more than 98% after 100 cycles at 2 C and 5 C, respectively, remarkably better than those of LiFePO4/C. The excellent electrochemical performances are ascribed to the mutual doping of V3+ and Fe2+, complementary advantages of LiFePO4 and Li3V2(PO4)3 phases, the residual high-ordered carbon and Fe2P with outstanding electric conductivity in the nanocomposite.摘要本文采用冷冻干燥与溶胶-凝胶相结合的方法制备了纳米复合材料LiFePO4·Li3V2(PO4)3/C. XRD结果表明该复合材料主要由橄榄石型LiFePO4和单斜晶系Li3V2(PO4)3相组成, 同时包含少量的V掺杂LiFePO4和Fe掺杂Li3V2(PO4)3. 磁学测试结果表明, LiFePO4·Li3V2(PO4)3/C的磁学特性显著区别于LiFePO4/C, 并且痕量的铁磁性杂质和Fe2P杂质分别存在于LiFePO4/C和LiFePO4·Li3V2(PO4)3/C中. LiFePO4·Li3V2-(PO4)3/C具有相对优良的循环稳定性, 尤其是在大倍率条件下. 在2 C和5 C时, 首次放电容量分别为136.4和130.0 mA h g-1, 100周循环后保持率在98%以上, 优于LiFePO4/C的电化学性能. LiFePO4·Li3V2(PO4)3/C电化学性能的改善归因于V3+和Fe2+的相互掺杂, LiFePO4和Li3V2-(PO4)3相的优势互补, 残留的高有序碳以及导电性优异的Fe2P.

The Mossbauer spectra of carbon nanotubes synthesize using ferrite catalyst

The ferrite powder with honeycombed structure obtained by chemical combustion was used as catalyst to synthesize multi-walled carbon nanotubes by chemical vapor deposition. The magnetic components and characters of the the carbon nanotubes synthesized were investigated by X-ray diffraction (XRD), Mossbauer spectra and vibrating-sample magnetometer (VSM). The ferric components of the carbon nanotubes samples can be identified by Mossbauer spectra. The Mossbauer spectra of carbon nanotubes sample after purification contains two ferromagnetic sextet components corresponding to α-Fe species and Fe3C (cementite) species. While the Mossbauer spectra of the carbon nanotubes sample before purification contains three ferromagnetic sextet components corresponding to α-Fe species, Fe3C species and γ-Fe2O3. The saturation magnetization intensity Ms of carbon nanotubes sample after purification is decreased from 46.61 to 2.94 emu/g, but the coercive force increasd and reached 328Oe.