Xiehong Cao

Preparation of Novel 3D Graphene Networks for Supercapacitor Applications

The supercapacitor is considered as a promising candidate for energy storage due to its high power performance, long life cycle, and low maintenance cost. [ 3 ] Pseudocapacitive materials, such as transition metal oxides, are being explored for use in supercapacitors with a large specifi c capacitance and high energy density. [ 4 ] However, pseudocapacitors often suffer from the low rate capability and poor stability, because the active materials are usually insulating or semiconducting, which hinders the fast electron transport required for high charge/discharge rates. As an ideal matrix, graphene is commonly used for growth of functional nanomaterials. [ 1a , 2c , 5 ] Recently, nanocomposites made by graphene and transition metal oxides have attracted wide attention in the fi eld of supercapacitors due to their synergetic effect, arising from the combination of the redox reaction of metal oxides with the high surface area/conductivity of graphene, to improve the electrochemical performance. [ 6 ]

Recent Advances in Ultrathin Two-Dimensional Nanomaterials

Since the discovery of mechanically exfoliated graphene in 2004, research on ultrathin two-dimensional (2D) nanomaterials has grown exponentially in the fields of condensed matter physics, material science, chemistry, and nanotechnology. Highlighting their compelling physical, chemical, electronic, and optical properties, as well as their various potential applications, in this Review, we summarize the state-of-art progress on the ultrathin 2D nanomaterials with a particular emphasis on their recent advances. First, we introduce the unique advances on ultrathin 2D nanomaterials, followed by the description of their composition and crystal structures. The assortments of their synthetic methods are then summarized, including insights on their advantages and limitations, alongside some recommendations on suitable characterization techniques. We also discuss in detail the utilization of these ultrathin 2D nanomaterials for wide ranges of potential applications among the electronics/optoelectronics, electrocatalysis, batteries, supercapacitors, solar cells, photocatalysis, and sensing platforms. Finally, the challenges and outlooks in this promising field are featured on the basis of its current development.

Three-dimensional graphene materials: preparation, structures and application in supercapacitors

Three-dimensional (3D) graphene materials (3DGMs) are of great importance due to their unique properties and practical applications. A number of 3DGMs with novel structures have been developed in recent years. This review presents the current progress of 3DGMs. After introducing the preparation strategies of 3DGMs, we summarize the reported 3DGMs based on their different structures, and then focus on the description of their preparation methods, properties and applications. Lastly, the applications of 3D graphene-based materials in supercapacitors are described.

Preparation of MoS2-coated three-dimensional graphene networks for high-performance anode material in lithium-ion batteries.

A novel composite, MoS2 -coated three-dimensional graphene network (3DGN), referred to as MoS2 /3DGN, is synthesized by a facile CVD method. The 3DGN, composed of interconnected graphene sheets, not only serves as template for the deposition of MoS2 , but also provides good electrical contact between the current collector and deposited MoS2 . As a proof of concept, the MoS2 /3DGN composite, used as an anode material for lithium-ion batteries, shows excellent electrochemical performance, which exhibits reversible capacities of 877 and 665 mAh g(-1) during the 50(th) cycle at current densities of 100 and 500 mA g(-1) , respectively, indicating its good cycling performance. Furthermore, the MoS2 /3DGN composite also shows excellent high-current-density performance, e.g., depicts a 10(th) -cycle capacity of 466 mAh g(-1) at a high current density of 4 A g(-1).

Ni3S2 nanorods/Ni foam composite electrode with low overpotential for electrocatalytic oxygen evolution

A Ni3S2 nanorods/Ni foam composite electrode is prepared as a high-performance catalyst for the oxygen evolution reaction (OER), which exhibits excellent OER activity with a small overpotential of ∼157 mV based on the onset of catalytic current.

One-step synthesis of Ni3S2 nanorod@Ni(OH)2nanosheet core–shell nanostructures on a three-dimensional graphene network for high-performance supercapacitors

A three-dimensional graphene network (3DGN) grown on nickel foam is an excellent template for the synthesis of graphene-based composite electrodes for use in supercapacitors. Ni(OH)2nanosheets coated onto single-crystal Ni3S2nanorods grown on the surface of the 3DGN (referred to as the Ni3S2@Ni(OH)2/3DGN) are synthesized using a one-step hydrothermal reaction. SEM, TEM, XRD and Raman spectroscopy are used to investigate the morphological and structural evolution of the Ni3S2@Ni(OH)2/3DGN. Detailed electrochemical characterization shows that the Ni3S2@Ni(OH)2/3DGN exhibits high specific capacitance (1277 F g−1 at 2 mV s−1 and 1037.5 F g−1 at 5.1 A g−1) and areal capacitance (4.7 F cm−2 at 2 mV s−1 and 3.85 F cm−2 at 19.1 mA cm−2) with good cycling performance (99.1% capacitance retention after 2000 cycles).

A New Type of Porous Graphite Foams and Their Integrated Composites with Oxide/Polymer Core/Shell Nanowires for Supercapacitors: Structural Design, Fabrication, and Full Supercapacitor Demonstrations

We attempt to meet the general design requirements for high-performance supercapacitor electrodes by combining the strategies of lightweight substrate, porous nanostructure design, and conductivity modification. We fabricate a new type of 3D porous and thin graphite foams (GF) and use as the light and conductive substrates for the growth of metal oxide core/shell nanowire arrays to form integrated electrodes. The nanowire core is Co3O4, and the shell is a composite of conducting polymer (poly(3,4-ethylenedioxythiophene), PEDOT) and metal oxide (MnO2). To show the advantage of this integrated electrode design (viz., GF + Co3O4/PEDOT-MnO2 core/shell nanowire arrays), three other different less-integrated electrodes are also prepared for comparison. Full supercapacitor devices based on the GF + Co3O4/PEDOT-MnO2 as positive electrodes exhibit the best performance compared to other three counterparts due to an optimal design of structure and a synergistic effect.

Carbon Fiber Aerogel Made from Raw Cotton: A Novel, Efficient and Recyclable Sorbent for Oils and Organic Solvents

Twisted carbon fiber (TCF) aerogel with good selective sorption is produced in large scale by using raw cotton as the precursor. TCF aerogel shows highly efficient sorption of organic liquids (pump oil: up to 192 times its own weight; chloroform: up to 115 times its own weight). Moreover, it could be regenerated many times without decrease of sorption capacity by distillation, combustion or squeezing, which depends on the type of pollutants.

Transparent, Flexible, All-Reduced Graphene Oxide Thin Film Transistors

Owing to their unique thickness-dependent electronic properties, together with perfect flexibility and transparency, graphene and its relatives make fantastic material for use in both active channel and electrodes in various electronic devices. On the other hand, the electronic sensors based on graphene show high potential in detection of both chemical and biological species with high sensitivity. In this contribution, we report the fabrication of all-reduced graphene oxide (rGO) thin film transistors by a combination of solution-processed rGO electrodes with a micropatterned rGO channel, and then study their applications in biosensing. Our all-rGO devices are cost-effective, highly reproducible, and reliable. The fabricated electronic sensor is perfectly flexible with high transparency, showing good sensitivity in detecting proteins in the physiological buffer. As a proof of concept, fibronectin as low as 0.5 nM was successfully detected, which is comparable with the previously reported protein sensors based on single-layer pristine graphene obtained from mechanical cleavage. The specific detection of avidin by using biotinylated all-rGO sensor is also successfully demonstrated.

Preparation of MoS2-Polyvinylpyrrolidone Nanocomposites for Flexible Nonvolatile Rewritable Memory Devices with Reduced Graphene Oxide Electrodes

A facile method for exfoliation and dispersion of molybdenum disulfide (MoS2) with the aid of polyvinylpyrrolidone (PVP) is proposed. The resultant PVP-coated MoS2 nanosheets, i.e., MoS2-PVP nanocomposites, are well dispersed in the low-boiling ethanol solvent, facilitating their thin film preparation and the device fabrication by solution processing technique. As a proof of concept, a flexible memory diode with the configuration of reduced graphene oxide (rGO)/MoS2-PVP/Al exhibited a typical bistable electrical switching and nonvolatile rewritable memory effect with the function of flash. These experimental results prove that the electrical transition is due to the charge trapping and detrapping behavior of MoS2 in the PVP dielectric material. This study paves a way of employing two-dimensional nanomaterials as both functional materials and conducting electrodes for the future flexible data storage.