Zhong-Shuai Wu

Graphene Anchored with Co3O4 Nanoparticles as Anode of Lithium Ion Batteries with Enhanced Reversible Capacity and Cyclic Performance

We report a facile strategy to synthesize the nanocomposite of Co(3)O(4) nanoparticles anchored on conducting graphene as an advanced anode material for high-performance lithium-ion batteries. The Co(3)O(4) nanoparticles obtained are 10-30 nm in size and homogeneously anchor on graphene sheets as spacers to keep the neighboring sheets separated. This Co(3)O(4)/graphene nanocomposite displays superior Li-battery performance with large reversible capacity, excellent cyclic performance, and good rate capability, highlighting the importance of the anchoring of nanoparticles on graphene sheets for maximum utilization of electrochemically active Co(3)O(4) nanoparticles and graphene for energy storage applications in high-performance lithium-ion batteries.

Graphene Anchored with Co 3 O 4 Nanoparticles as Anode of Lithium Ion Batteries with Enhanced Reversible Capacity and Cyclic Performance

We report a facile strategy to synthesize the nanocomposite of Co(3)O(4) nanoparticles anchored on conducting graphene as an advanced anode material for high-performance lithium-ion batteries. The Co(3)O(4) nanoparticles obtained are 10-30 nm in size and homogeneously anchor on graphene sheets as spacers to keep the neighboring sheets separated. This Co(3)O(4)/graphene nanocomposite displays superior Li-battery performance with large reversible capacity, excellent cyclic performance, and good rate capability, highlighting the importance of the anchoring of nanoparticles on graphene sheets for maximum utilization of electrochemically active Co(3)O(4) nanoparticles and graphene for energy storage applications in high-performance lithium-ion batteries.

3D nitrogen-doped graphene aerogel-supported Fe3O4 nanoparticles as efficient electrocatalysts for the oxygen reduction reaction.

Three-dimensional (3D) N-doped graphene aerogel (N-GA)-supported Fe(3)O(4) nanoparticles (Fe(3)O(4)/N-GAs) as efficient cathode catalysts for the oxygen reduction reaction (ORR) are reported. The graphene hybrids exhibit an interconnected macroporous framework of graphene sheets with uniform dispersion of Fe(3)O(4) nanoparticles (NPs). In studying the effects of the carbon support on the Fe(3)O(4) NPs for the ORR, we found that Fe(3)O(4)/N-GAs show a more positive onset potential, higher cathodic density, lower H(2)O(2) yield, and higher electron transfer number for the ORR in alkaline media than Fe(3)O(4) NPs supported on N-doped carbon black or N-doped graphene sheets, highlighting the importance of the 3D macropores and high specific surface area of the GA support for improving the ORR performance. Furthermore, Fe(3)O(4)/N-GAs show better durability than the commercial Pt/C catalyst.

Doped Graphene Sheets As Anode Materials with Superhigh Rate and Large Capacity for Lithium Ion Batteries

One great challenge in the development of lithium ion batteries is to simultaneously achieve high power and large energy capacity at fast charge and discharge rates for several minutes to seconds. Here we show that nitrogen- or boron-doped graphene can be used as a promising anode for high-power and high-energy lithium ion batteries under high-rate charge and discharge conditions. The doped graphene shows a high reversible capacity of >1040 mAh g(-1) at a low rate of 50 mA g(-1). More importantly, it can be quickly charged and discharged in a very short time of 1 h to several tens of seconds together with high-rate capability and excellent long-term cyclability. For example, a very high capacity of ∼199 and 235 mAh g(-1) was obtained for the N-doped graphene and B-doped graphene at 25 A g(-1) (about 30 s to full charge). We believe that the unique two-dimensional structure, disordered surface morphology, heteroatomic defects, better electrode/electrolyte wettability, increased intersheet distance, improved electrical conductivity, and thermal stability of the doped graphene are beneficial to rapid surface Li(+) absorption and ultrafast Li(+) diffusion and electron transport, and thus make the doped materials superior to those of pristine chemically derived graphene and other carbonaceous materials.

Fabrication of Graphene/Polyaniline Composite Paper via In Situ Anodic Electropolymerization for High- Performance Flexible Electrode

Freestanding and flexible graphene/polyaniline composite paper was prepared by an in situ anodic electropolymerization of polyaniline film on graphene paper. This graphene-based composite paper electrode, consisting of graphene/polyaniline composite sheets as building blocks, shows a favorable tensile strength of 12.6 MPa and a stable large electrochemical capacitance (233 F g(-1) and 135 F cm(-3) for gravimetric and volumetric capacitances), which outperforms many other currently available carbon-based flexible electrodes and is hence particularly promising for flexible supercapacitors.

High-energy MnO2 nanowire/graphene and graphene asymmetric electrochemical capacitors

In order to achieve high energy and power densities, we developed a high-voltage asymmetric electrochemical capacitor (EC) based on graphene as negative electrode and a MnO(2) nanowire/graphene composite (MGC) as positive electrode in a neutral aqueous Na(2)SO(4) solution as electrolyte. MGC was prepared by solution-phase assembly of graphene sheets and α-MnO(2) nanowires. Such aqueous electrolyte-based asymmetric ECs can be cycled reversibly in the high-voltage region of 0-2.0 V and exhibit a superior energy density of 30.4 Wh kg(-1), which is much higher than those of symmetric ECs based on graphene//graphene (2.8 Wh kg(-1)) and MGC//MGC (5.2 Wh kg(-1)). Moreover, they present a high power density (5000 W kg(-1) at 7.0 Wh kg(-1)) and acceptable cycling performance of ∼79% retention after 1000 cycles. These findings open up the possibility of graphene-based composites for applications in safe aqueous electrolyte-based high-voltage asymmetric ECs with high energy and power densities.

Three-Dimensional Nitrogen and Boron Co-doped Graphene for High-Performance All-Solid-State Supercapacitors

carbide-derived carbon, [ 12 ] carbon nanotubes (CNTs), [ 14–17 ] and graphene, [ 6 , 7 , 10 , 18 , 19 ] possess notable features including high surface area, high electrical conductivity, and good chemical stability, and therefore they have been widely explored as thinfi lm electrode materials for ASSSs. However, the fabrication of ASSSs generally involves complex solution processing, highpressure pressing, high-temperature sintering, and sputtering techniques. [ 11 , 12 , 14–17 ] Moreover, polymer binders and conductive additives are required to enhance the adhesion between electrode materials and substrates as well as to improve the conductivity of the electrode, which unavoidably leads to decreased energy density of the devices. [ 6 , 20 ] Therefore, several challenges remain in developing ASSSs, such as to: i) explore high-performance electrode materials, ii) enhance the interfacial compatibility between electrode and solid-state electrolyte, and iii) simplify the device fabrication process. Graphene aerogels (GAs) represent a new class of ultralight and porous carbon materials that are associated with high

Three-Dimensional Graphene-Based Macro- and Mesoporous Frameworks for High-Performance Electrochemical Capacitive Energy Storage

Three-dimensional graphene-based frameworks (3D-GFs) with hierarchical macro- and meso-porous structures are presented. The interconnected macropores are derived from hydrothermally assembled 3D graphene aerogels (GAs), while the mesopores are generated by the silica networks uniformly grown on the surface of graphene. The resulting 3D-GFs exhibit narrow mesopore size distribution (2-3.5 nm), high surface area, and low mass density. These intriguing features render 3D-GFs a promising template for creating various 3D porous materials. Specifically, 3D GA-based mesoporous carbons (GA-MC) and metal oxide hybrids (GA-Co(3)O(4), GA-RuO(2)) can be successfully constructed via a nanocasting technology. Benefiting from the integration of meso- and macroporous structures, 3D GA-MC manifests outstanding specific capacitance (226 F g(-1)), high rate capability, and excellent cycling stability (no capacitance loss after 5000 cycles) when it is applied in electrochemical capacitors.

Mesoporous Metal–Nitrogen-Doped Carbon Electrocatalysts for Highly Efficient Oxygen Reduction Reaction

A family of mesoporous nonprecious metal (NPM) catalysts for oxygen reduction reaction (ORR) in acidic media, including cobalt-nitrogen-doped carbon (C-N-Co) and iron-nitrogen-doped carbon (C-N-Fe), was prepared from vitamin B12 (VB12) and the polyaniline-Fe (PANI-Fe) complex, respectively. Silica nanoparticles, ordered mesoporous silica SBA-15, and montmorillonite were used as templates for achieving mesoporous structures. The most active mesoporous catalyst was fabricated from VB12 and silica nanoparticles and exhibited a remarkable ORR activity in acidic medium (half-wave potential of 0.79 V, only ∼58 mV deviation from Pt/C), high selectivity (electron-transfer number >3.95), and excellent electrochemical stability (only 9 mV negative shift of half-wave potential after 10,000 potential cycles). The unprecedented performance of these NPM catalysts in ORR was attributed to their well-defined porous structures with a narrow mesopore size distribution, high Brunauer-Emmett-Teller surface area (up to 572 m(2)/g), and homogeneous distribution of abundant metal-Nx active sites.

Graphene-based in-plane micro-supercapacitors with high power and energy densities

Micro-supercapacitors are important on-chip micro-power sources for miniaturized electronic devices. Although the performance of micro-supercapacitors has been significantly advanced by fabricating nanostructured materials, developing thin-film manufacture technologies and device architectures, their power or energy densities remain far from those of electrolytic capacitors or lithium thin-film batteries. Here we demonstrate graphene-based in-plane interdigital micro-supercapacitors on arbitrary substrates. The resulting micro-supercapacitors deliver an area capacitance of 80.7 μF cm−2 and a stack capacitance of 17.9 F cm−3. Further, they show a power density of 495 W cm−3 that is higher than electrolytic capacitors, and an energy density of 2.5 mWh cm−3 that is comparable to lithium thin-film batteries, in association with superior cycling stability. Such microdevices allow for operations at ultrahigh rate up to 1,000 V s−1, three orders of magnitude higher than that of conventional supercapacitors. Micro-supercapacitors with an in-plane geometry have great promise for numerous miniaturized or flexible electronic applications.