Ming-Yu Yen

Preparation of Covalently Functionalized Graphene Using Residual Oxygen-Containing Functional Groups

When fabricated by thermal exfoliation, graphene can be covalently functionalized more easily by applying a direct ring-opening reaction between the residual epoxide functional groups on the graphene and the amine-bearing molecules. Investigation by X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and transmission electron microscopy (TEM) all confirm that these molecules were covalently grafted to the surface of graphene. The resulting dispersion in an organic solvent demonstrated a long-term homogeneous stability of the products. Furthermore, comparison with traditional free radical functionalization shows the extent of the defects characterized by TEM and Raman spectroscopy and reveals that direct functionalization enables graphene to be covalently functionalized on the surface without causing any further damage to the surface structure. Thermogravmetric analysis (TGA) shows that the nondestroyed graphene structure provides greater thermal stability not only for the grafted molecules but also, more importantly, for the graphene itself, compared to the free-radical grafting method.

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.

Polypropylene-grafted multi-walled carbon nanotube reinforced polypropylene composite bipolar plates in polymer electrolyte membrane fuel cells

Polypropylene-grafted multi-walled carbon nanotubes (MWCNTs/PP-g-MA) were prepared via a ring-opening reaction between polypropylene grafted maleic anhydride (PP-g-MA) and animated MWCNTs by a solution process. The prepared MWCNTs/PP-g-MA were introduced to the PP nanocomposite bipolar plates, to achieve a high compatibility and good adhesion between MWCNTs and the immiscible PP matrix through PP-g-MA chains. Replacement of amine-terminated groups by PP-g-MA on the MWCNTs leads to covalent grafting of longer copolymer chains to the MWCNTs, and to improve the dispersion of MWCNTs in the PP matrix. The resulting PP nanocomposite bipolar plates with 1, 2, and 4 wt% of MWCNTs/PP-g-MA demonstrates not only improved flexural strengths by 56.3, 68.5, and 70.9%, but also enhanced bulk electrical conductivities by 282, 425, and 473%, respectively, over those of the neat composite bipolar plates. The contact resistance of the MWCNTs/PP-g-MA/PP nanocomposite bipolar plate is 9.1 mOhm cm2, which is lower than the D.O.E. target ∼10 mOhm cm2 in the year 2010. The maximum current density and power density of the single cell test for the nanocomposite bipolar plate with 4 wt% MWCNTs/PP-g-MA are 1.41 A cm−2 and 0.586 W cm−2, respectively, which are 12.4 and 4.56% slightly lower than those of graphite plates. Comparing with pristine MWCNTs/PP nanocomposite bipolar plates, MWCNTs/PP-g-MA/PP nanocomposite bipolar plates are suitable for bipolar plates of polymer electrolyte membrane fuel cells.

Direct synthesis of platelet graphitic-nanofibres as a highly porous counter-electrode in dye-sensitized solar cells

We synthesized platelet graphitic-nanofibres (GNFs) directly onto FTO glass and applied this forest of platelet GNFs as a highly porous structural counter-electrode in dye-sensitized solar cells (DSSCs). We investigated the electrochemical properties of counter-electrodes made from the highly porous structural GNFs and the photoconversion performance of the cells made with these electrodes.

Electrical, mechanical and thermal properties of high performance polymer nanocomposite bipolar plates for fuel cells

Abstract: Proton exchange membrane fuel cells (PEMFC) have received attention owing to their low operating temperature and quick start-up. Fuel cells have high material costs, low power density and short lifetime, which are major barriers to their use. In order to become commercially viable, PEMFC bipolar plates must be cheaper, lighter, and more compact. Here, carbon nanotubes (CNTs) are assessed as a reinforcement for either thermoplastic or thermoset-based nanocomposite bipolar plates, because of such properties as superior mechanical strength, high electrical and thermal properties, and light weight. CNTs have strong intrinsic van der Waals forces with each other, which hold together in ropes and bundles, resulting in very low solubility in most solvents. Therefore, homogeneous dispersion of CNTs in the matrix is key. How to achieve homogeneous dispersion of CNTs by chemical modification is discussed. Owing to the formation of effective 3D electrical conducting networks better properties are obtained such as high mechanical strength, improved electrical conductivity and cell performance when the functionalized CNT is incorporated in a bipolar plate. Functionalized CNT reinforcement is a promising method to manufacture alternative high performance bipolar plates for PEM fuel cell applications.