Chih-Chun Teng

Platinum nanoparticles/graphene composite catalyst as a novel composite counter electrode for high performance dye-sensitized solar cells

We herein describe our use of a water–ethylene method to prepare a composite material consisting of platinum nanoparticles and graphene. Results obtained using XPS and XRD show that the degree of reduction of graphene was increased by the incorporation of Pt, and in addition, the increased concentration of defects was confirmed by the D/G ratio of the Raman spectra obtained. In comparison with Pt films, results obtained using CV and EIS showed that the electrocatalytic ability of the composite material was greater, and afforded a higher charge transfer rate, an improved exchange current density, and a decreased internal resistance. SEM images showed that the morphology of PtNP/GR counter electrodes is characterized by a smooth surface, however, resulting in a lower resistance to diffusion, thereby improving the total redox reaction rate that occurs at the counter electrode. PtNP/GR electrodes have a number of advantages over other electrodes that consist solely of graphene or Pt films, including a high rate of charge transfer, a low internal resistance, and a low resistance to diffusion. In our study, we showed that DSSCs that incorporate platinum-grafted graphene had a conversion efficiency of 6.35%, which is 20% higher than that of devices with platinized FTO.

Preparation and properties of a graphene reinforced nanocomposite conducting plate

This study presents a novel nanocomposite conducting plate (CP) reinforced by graphene at a low weight fraction percentage, and compares the properties of this novel nanocomposite CP with those containing various weight fractions of multi-wall carbon nanotubes (MWCNT) (0.2, 0.5, and 1 phr). Adding only 0.2 phr of graphene as reinforcement remarkably enhanced the thermal, mechanical, and electrical properties of the nanocomposite CP. The coefficient of thermal expansion (CTE) of nanocomposite CP below the glass transition temperature (Tg) decreased from 49.7 μm−1 m °C−1 to 26.9 μm−1 m °C−1 and the CTE above Tg decreased from 119.2 μm−1 m°C−1 to 55.2 μm−1 m °C−1. Thermal conductivity increased from 18.4 W m−1 K−1 to 27.2 W m−1 K−1. The flexural strength increased from to 28.0 MPa to 49.2 MPa. The in-plane electrical conductivity increased from 155.7 S cm−1 to 286.4 S cm−1. The enhancement percentages of these properties are 47.8%, 75.7%, and 83.9%, respectively, which are much higher than that of the original composite CP. These results indicate that using graphene as reinforcement in the preparation of nanocomposite CP is effective in terms of cost and performance, because of the low cost the raw material, graphite, and the fact that a lower loading of graphene than of MWCNT can yield the same performance. Moreover, this novel multi-functional nanocomposite CP has wide potential for use in proton exchange membrane fuel cells (PEMFCs), direct methanol fuel cells (DMFCs), the dye-sensitized solar cells (DSSCs) counter electrode, and vanadium redox battery (VRB) applications.

Metal-free, nitrogen-doped graphene used as a novel catalyst for dye-sensitized solar cell counter electrodes

Nitrogen-doped graphene (NGR) was incorporated as a catalyst and used as a counter electrode in dye-sensitized solar cells (DSSCs). The NGR electrodes showed a number of advantages over other electrodes that consisted solely of graphene or Pt films, including high charge transfer rates, low resistance to diffusion, and low internal resistance.

Morphology and properties of aminosilane grafted MWCNT/polyimide nanocomposites

This investigation presents a novel method for modifying multiwalled carbon nanotubes (MWCNTs). The morphology, electrical resistivity, and percolation threshold of MWCNT/Polyimide nanocomposites were studied. Acid-modified MWCNTs reacted with (3-aminopropyl)triethoxysilane by ionic bonding, and were then mixed with polyamic acid via imidization. TEM microphotographs reveal that silane-grafted MWCNTs were connected to each other. The electrical resistivity of silane-grafted MWCNT/polyimide decreased substantially below than that of acid-treated MWCNTs when the silane-modified MWCNT content was lower than 2.4 wt%. The percolation threshold of the MWCNT/polyimide composites is 1.0wt% for silane-modified MWCNT and exceeds 7.0 wt% for acid-modified MWCNT. The acid-modified MWCNT/polyimide composites possess slightly higher glass transition temperatures than that of pure polyimide. The glass transition temperature of the polyimide increased significantly with silane-modified MWCNT content. Tensile properties of the polyimide have been improved with the MWCNTs content.

Highly transparent and conductive thin films fabricated with nano-silver/double-walled carbon nanotube composites

This study develops a technique for enhancing the electrical conductivity and optical transmittance of transparent double-walled carbon nanotube (DWNT) film. Silver nanoparticles were modified with a NH(2)(CH(2))(2)SH self-assembled monolayer terminated by amino groups and subsequent surface condensation that reacted with functionalized DWNTs. Ag nanoparticles were grafted on the surface of the DWNTs. The low sheet resistance of the resulting thin conductive film on a polyethylene terephthalate (PET) substrate was due to the increased contact areas between DWNTs and work function by grafting Ag nanoparticles on the DWNT surfaces. Increasing the contact area between DWNTs and work function improved the conductivity of the DWNT-Ag thin films. The prepared DWNT-Ag thin films had a sheet resistance of 53.4 Ω/sq with 90.5% optical transmittance at a 550 nm wavelength. After treatment with HNO(3) and annealing at 150 °C for 30 min, a lower sheet resistance of 45.8 Ω/sq and a higher transmittance of 90.4% could be attained. The value of the DC conductivity to optical conductivity (σ(DC)/σ(OP)) ratio is 121.3.

Preparation and characterization of nano-inorganic materials coated multi-walled carbon nanotubes/epoxy composites for thermal interface materials

Recent developments of nanofabrication have enabled the miniaturization of electronic devices, allowing more electronic devices to be combined into a single device with a high performance. However, the complex devices have led to the escalation of power dissipation as well as the increasing heat flux at the interface between devices. Electronic devices were damaged by much heat accumulation, since the reliability of deives is dependent on the junction temperature. For example a small operating temperature difference (in the order of 10~15°C) can result in a two times reduction in the lifetime of a device. Carbon nanotubes with large aspect ratio and unique thermal properties can be as thermal dissipating filler for some nanocomposites. However, carbon nanotubes with high electrical conductivity will induce short leakage at the same time. For overcoming this problem, the objective of this research is to propose the surface modification technology by inorganic materials on the carbon nanotubes for thermal interfacial materials (TIM) applications. This research is to develop the surface modification technology by depositing alumina nanoparticles on the surface of the multi-walled carbon nanotubes (MWCNTs). TIMs were prepared from epoxy resin and various content of alumina @ MWCNTs (1~5phrs) and then their volume resistivity with different loading alumina @ MWCNTs content can maintain round 1015 ohm*cm. The thermal conductivity of a TIM with 5phrs alumina @ MWCNTs was 1.01W/mK (increased 677% compared to neat epoxy resin with 0.13W/m*K).

Thermal conductivity and morphology of non-covalent functionalized graphene/epoxy nanocomposites

High thermal conductive graphene reinforced epoxy composites were prepared. The dispersion and interface between epoxy and graphene are improved by Pyrene-end poly(glycidyl methacrylate) (Py-PGMA). Py-PGMA was synthesized by atomic transfer radical polymerization (ATRP) which was absorbed onto graphene by the non-covalent surface functionalization. Additionally, the Py-PGMA content on graphene is 26 wt% by thermogravimetric analysis (TGA). The functionalized graphene provides the reactivity with epoxy forming chemical linkage, which improved the interfacial interaction, result in enhanced thermal conductivity of epoxy composites. The thermal conductivity of 3phr functionalized graphene based epoxy composite is 0.51 W/mK, which is significantly higher than that of neat epoxy (0.18 W/mK) and 3phr multi-walled carbon nanotubes (MWCNTs)/epoxy (0.36 W/mK). The 2D structure of graphene provides more thermal transfer pathway and lower thermal resistance than that of ID MWCNTs. Thermal conductivity of graphene/epoxy and MWCNTs/epoxy were compared in this study.