Shin-Ming Li

Design and tailoring of a hierarchical graphene-carbon nanotube architecture for supercapacitors

Stacking of individual graphene sheets (GS) is effectively inhibited by introducing one-dimensional carbon nanotubes (CNTs) to form a 3-D hierarchical structure which significantly enhances the electrochemical capacitive performances of GS-based composites. From SEM images, inserting proper quantity of CNTs as nanospacers can effectively impede the stacking of GS and enlarge the space between GS sheets, leading to obtain a highly porous nanostructure. The specific capacitance of GS-CNTs-9-1 (∼326.5 F g−1 at 20 mV s−1) is much higher than that of GS material (∼83 F g−1). Furthermore, the energy and power densities of GS-CNTs-9-1 are respectively as high as 21.74 Wh kg−1 and 78.29 kW kg−1, revealing that the hierarchical graphene-CNT architecture provides remarkable effects on enhancing the capacitive performance of GS-based composites. Therefore, the GS-CNT composites are promising carbon materials for supercapacitors.

Lightweight and flexible reduced graphene oxide/water-borne polyurethane composites with high electrical conductivity and excellent electromagnetic interference shielding performance.

In this study, we developed a simple and powerful method to fabricate flexible and lightweight graphene-based composites that provide high electromagnetic interference (EMI) shielding performance. Electrospun waterborne polyurethane (WPU) that featured sulfonate functional groups was used as the polymer matrix, which was light and flexible. First, graphene oxide (GO)/WPU composites were prepared through layer-by-layer (L-b-L) assembly of two oppositely charged suspensions of GO, the cationic surfactant (didodecyldimethylammonium bromide, DDAB)-adsorbed GO and intrinsic negatively charged GO, depositing on the negatively charged WPU fibers. After the L-b-L assembly cycles, the GO bilayers wrapped the WPU fiber matrix completely and revealed fine connections guided by the electrospun WPU fibers. Then, we used hydroiodic acid (HI) to obtain highly reduced GO (r-GO)/WPU composites, which exhibited substantially enhanced electrical conductivity (approximately 16.8 S/m) and, moreover, showed a high EMI-shielding effectiveness (approximately 34 dB) over the frequency range from 8.2 to 12.4 GHz.

Effect of Molecular Chain Length on the Mechanical and Thermal Properties of Amine-Functionalized Graphene Oxide/Polyimide Composite Films Prepared by In Situ Polymerization

This study fabricates amine (NH(2))-functionalized graphene oxide (GO)/polyimide(PI) composite films with high performance using in situ polymerization. Linear poly(oxyalkylene)amines with two different molecular weights 400 and 2000 (D400 and D2000) have been grafted onto the GO surfaces, forming two types of NH(2)-functionalized GO (D400-GO/D2000-GO). NH(2)-functionalized GO, especially D400-GO, demonstrated better reinforcing efficiency in mechanical and thermal properties. The observed property enhancement are due to large aspect ratio of GO sheets, the uniform dispersion of the GO within the PI matrix, and strong interfacial adhesion due to the chemical bonding between GO and the polymeric matrix. The Youngs modulus of the composite films with 0.3 wt % D400-GO loading is 7.4 times greater than that of neat PI, and tensile strength is 240% higher than that of neat PI. Compared to neat PI, 0.3 wt % D400-GO/PI film exhibits approximately 23.96 °C increase in glass transition temperature (T(g)). The coefficient of thermal expansion below T(g) is significantly decreased from 102.6 μm/°C (neat PI) to 53.81 μm/°C (decreasing 48%) for the D400-GO/PI composites with low D400-GO content (0.1 wt %). This work not only provides a method to develop the GO-based polyimide composites with superior performances but also conceptually provides a chance to modulate the interfacial interaction between GO and the polymer through designing the chain length of grafting molecules on NH(2)-functionalized GO.

Effect of Covalent Modification of Graphene Nanosheets on the Electrical Property and Electromagnetic Interference Shielding Performance of a Water-Borne Polyurethane Composite

Flexible and lightweight graphene nanosheet (GN)/waterborne polyurethane (WPU) composites which exhibit high electrical conductivity and electromagnetic shielding performance were prepared. Covalently modifying GNs with aminoethyl methacrylate (AEMA; AEMA-GNs) through free radical polymerization effectively inhibited the restacking and aggregation of the GNs because of the -NH3(+) functional groups grafted on the AEMA-GNs. Moreover, the AEMA-GNs exhibited high compatibility with a WPU matrix with grafted sulfonated functional groups because of the electrostatic attraction, which caused the AEMA-GNs to homogeneously disperse in the WPU matrix. This homogeneous distribution enabled the GNs to form electrically conductive networks. Furthermore, AEMA-GNs with different amounts of AEMA segments were introduced into the WPU matrix, and the effects of the surface chemistry of the GNs on the electrical conductivity and EMI shielding performance of composites were investigated. AEMA-GN/WPU composites with a GN loading of 5 vol % exhibited remarkable electrical conductivity (approximately 43.64 S/m) and EMI shielding effectiveness (38 dB) over the frequency of 8.2 to 12.4 GHz.

Effects of Multiwalled Carbon Nanotubes Functionalization on the Morphology and Mechanical and Thermal Properties of Carbon Fiber/Vinyl Ester Composites

Multiwalled carbon nanotube (MWCNT)/carbon fiber (CF)/vinyl ester (VE) laminate composites have been fabricated in this study. Pristine MWCNTs were treated with acid solution, which formed numerous oxygen-containing functional groups onto their surface, resulting in COOH-MWCNTs. Thereafter, acrylic functional groups were grafted onto the COOH-MWCNTs to generate acryl-MWCNTs. Three types of MWCNTs (pristine MWCNTs, COOH-MWCNTs, and acryl-MWCNTs) were used to reinforce the CF/VE-based composites. The dispersion of MWCNTs in the VE matrix and the interfacial interaction between MWCNTs and the VE matrix were investigated. Thereafter, the individual reinforcement efficiencies of these MWCNTs are compared. The flexural strength of the MWCNT/CF/VE composite with 1.0 phr acryl-MWCNTs content is 29.8% greater than that of neat CF/VE composites, and the flexural modulus of the MWCNT/CF/VE composite is 9.9% higher than that of neat CF/VE composites. Compared with neat CF/VE composites, 1.0 phr acryl-MWCNT/CF/VE composites exhibit an approximately 19.9 °C increase in glass transition temperature (Tg). The coefficients of thermal expansion significantly decreased from 47.2 ppm/°C of the neat CF/VE composites to 35.6 ppm/°C of the acryl-MWCNTs/CF/VE composites with 1 phr acryl-MWCNT content. This study provides a method for developing acryl-MWCNT/CF/VE composites with good dispersion of MWCNTs in VE matrix and strong interfacial interaction between the MWCNTs and VE matrix for enhancing the stress transfer from VE matrix to CF reinforcement.

Effect of Octa(aminophenyl) Polyhedral Oligomeric Silsesquioxane Functionalized Graphene Oxide on the Mechanical and Dielectric Properties of Polyimide Composites

An effective method is proposed to prepare octa(aminophenyl) silsesquioxane (OAPS) functionalized graphene oxide (GO) reinforced polyimide (PI) composites with a low dielectric constant and ultrastrong mechanical properties. The amine-functionalized surface of OAPS-GO is a versatile starting platform for in situ polymerization, which promotes the uniform dispersion of OAPS-GO in the PI matrix. Compared with GO/PI composites, the strong interfacial interaction between OAPS-GO and the PI matrix through covalent bonds facilitates a load transfer from the PI matrix to the OAPS-GO. The OAPS-GO/PI composite film with 3.0 wt % OAPS-GO exhibited an 11.2-fold increase in tensile strength, and a 10.4-fold enhancement in tensile modulus compared with neat PI. The dielectric constant (D(k)) decreased with the increasing content of 2D porous OAPS-GO, and a D(k) value of 1.9 was achieved.

A highly electrically conductive graphene–silver nanowire hybrid nanomaterial for transparent conductive films

Uniform and high-quality graphene oxide thin films were prepared using a dip-coating approach and were reduced to highly electrically conductive graphene nanosheet (GN) transparent conductive films (TCFs) using hydriodic acid. Silver nanowires (AgNWs), which were modified using thiophenol and exhibited a high aspect ratio and high electrical conductivity, were deposited on the surfaces of the GN TCFs through π–π interactions between the aromatic functional groups on the AgNWs and GNs to form high-performance GN/AgNW TCFs. The GN/AgNW hybrid nanomaterial films exhibited a sheet resistance of 71 Ω □−1 and 85% light transmittance.

Fabrication of a silver nanowire-reduced graphene oxide-based electrochemical biosensor and its enhanced sensitivity in the simultaneous determination of ascorbic acid, dopamine, and uric acid

Silver nanowire/reduced graphene oxide nanocomposites (AgNW/rGO) are synthesized using a two-step process: preparation of silver nanowire/graphene oxide (AgNW/GO) and the microwave-assisted hydrothermal (MAH) method. The nanocomposites are characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) analyses. Ascorbic acid (AA), dopamine (DA), and uric acid (UA) are determined simultaneously on the AgNW/rGO-modified screen-printed carbon electrodes (SPCEs) by cyclic voltammetry (CV) and linear sweep voltammetry (LSV). The results reveal that AgNW/rGO-modified SPCEs exhibit well-resolved oxidation peaks with a negative shift in peak potential and enhanced peak currents in the simultaneous determination of AA, DA and UA in comparison with the pure rGO-modified SPCEs, demonstrating the superior catalytic activity of AgNW/rGO composites. AgNW/rGO-modified SPCEs show the linear response of AA, DA and UA in the concentration range of 45–1550, 40–450 and 35–300 μM with a detection limit of 0.81, 0.26 and 0.30 μM (S/N = 3), respectively. The covalent bonds between AgNWs and rGOs are expected to suppress the random attachment of AgNWs and facilitate the electron transfer and reactant transport by constructing a porous and continuous electrically conductive network. The excellent sensitivity of AgNW/rGO composites makes them become promising electrode materials in the field of electrochemical biosensors.

Electrochemical composite deposition of porous cactus-like manganese oxide/reduced graphene oxide–carbon nanotube hybrids for high-power asymmetric supercapacitors

This paper proposes a simple, one-step, two-electrode electrochemical composite deposition for fabricating amorphous manganese oxide/graphene–carbon nanotube (a-MnOx/rGO–CNT) hybrids. The a-MnOx/rGO–CNT hybrids were simultaneously deposited onto steel substrates by using dodecylbenzene-sulfonic acid and controlling the cell voltage. The cell voltage affected the deposition rates of manganese oxide (driven by the concentration gradient) and carbon materials (driven by the potential gradient). The mass ratio of a-MnOx to rGO–CNT, controlled by the cell voltage, affected the morphology, microstructure, and capacitive behavior of a-MnOx/rGO–CNT. Under the optimal cell voltage (=1.25 V), an a-MnOx/rGO–CNT electrode exhibited a cactus-like a-MnOx nanostructure, an even dispersion of a-MnOx within the rGO–CNT, and a highly porous structure, yielding the highest outer charge (296.5 C g−1 cm−2) among all a-MnOx/rGO–CNT electrodes. In addition, a-MnOx/rG-CNT1.25V exhibited a high specific capacitance (440 F g−1 at 5 mV s−1) and excellent capacitance retention (60% at 1000 mV s−1). An asymmetric supercapacitor consisting of a commercial activated carbon negative electrode and an a-MnOx/rGO–CNT1.25V positive electrode provided a high specific energy (SE) of 18 W h kg−1 at a specific power (SP) of 1 kW kg−1. The SE of this asymmetric supercapacitor reached 5.1 W h kg−1 at a very high SP of 32 kW kg−1.

A novel approach to prepare graphene oxide/soluble polyimide composite films with a low dielectric constant and high mechanical properties

This paper proposes an effective and simple approach to fabricate high-performance graphene oxide (GO)/soluble polyimide (SPI) composite films through a novel and effective process. In this method, GO is dispersed in a dissolved SPI (R-SPI) polymeric matrix with curing state, preventing the reduction of crosslinking reactions of the polymeric matrix, and resulting in substantial improvements in the mechanical and dielectric properties of the composite. The GO/R-SPI composite film contains only 1.0 wt% GO; it possesses high tensile strength (up to 288.6 MPa) and Youngs modulus (7.58 GPa), which represent an increase of 260% in tensile strength and 402% in Youngs modulus, compared with the neat SPI film (80.3 MPa and 1.51 GPa, respectively). The dielectric constant (Dk) decreases with an increase in the GO content; the Dk of the GO/R-SPI composite film can be as low as 2.1 (compared with 2.8 for the neat SPI film). This novel fabricating method provides a path for developing high-performance GO/R-SPI composite materials as next-generation low-k dielectric materials.