Chuanbao Cao

Hierarchical Porous Nitrogen-Doped Carbon Nanosheets Derived from Silk for Ultrahigh-Capacity Battery Anodes and Supercapacitors

Hierarchical porous nitrogen-doped carbon (HPNC) nanosheets (NS) have been prepared via simultaneous activation and graphitization of biomass-derived natural silk. The as-obtained HPNC-NS show favorable features for electrochemical energy storage such as high specific surface area (SBET: 2494 m(2)/g), high volume of hierarchical pores (2.28 cm(3)/g), nanosheet structures, rich N-doping (4.7%), and defects. With respect to the multiple synergistic effects of these features, a lithium-ion battery anode and a two-electrode-based supercapacitor have been prepared. A reversible lithium storage capacity of 1865 mA h/g has been reported, which is the highest for N-doped carbon anode materials to the best of our knowledge. The HPNC-NS supercapacitors electrode in ionic liquid electrolytes exhibit a capacitance of 242 F/g and energy density of 102 W h/kg (48 W h/L), with high cycling life stability (9% loss after 10,000 cycles). Thus, a high-performance Li-ion battery and supercapacitors were successfully assembled for the same electrode material, which was obtained through a one-step and facile large-scale synthesis route. It is promising for next-generation hybrid energy storage and renewable delivery devices.

Ultrathin nickel hydroxide and oxide nanosheets: synthesis, characterizations and excellent supercapacitor performances.

High-quality ultrathin two-dimensional nanosheets of α-Ni(OH)2 are synthesized at large scale via microwave-assisted liquid-phase growth under low-temperature atmospheric conditions. After heat treatment, non-layered NiO nanosheets are obtained while maintaining their original frame structure. The well-defined and freestanding nanosheets exhibit a micron-sized planar area and ultrathin thickness (<2 nm), suggesting an ultrahigh surface atom ratio with unique surface and electronic structure. The ultrathin 2D nanostructure can make most atoms exposed outside with high activity thus facilitate the surface-dependent electrochemical reaction processes. The ultrathin α-Ni(OH)2 and NiO nanosheets exhibit enhanced supercapacitor performances. Particularly, the α-Ni(OH)2 nanosheets exhibit a maximum specific capacitance of 4172.5 F g−1 at a current density of 1 A g−1. Even at higher rate of 16 A g−1, the specific capacitance is still maintained at 2680 F g−1 with 98.5% retention after 2000 cycles. Even more important, we develop a facile and scalable method to produce high-quality ultrathin transition metal hydroxide and oxide nanosheets and make a possibility in commercial applications.

Multifunctional g-C3N4 nanofibers: A template-free fabrication and enhanced optical, electrochemical, and photocatalyst properties

We have developed a facile, scale up, and efficient method for the preparation of graphitic-C3N4 nanofibers (GCNNFs) as electrodes for supercapacitors and photocatalysts. The as-synthesized GCNNFs have 1D structure with higher concentration of nitrogen that is favorable for higher conductivity and electrochemical performance. Secondly, the high surface area of GCNNF provides a large electrode-electrolyte contact area, sufficient light harvesting and mass transfer, as well as increased redox potential. Thus, the GCNNF supercapacitor electrode shows high capacitance of 263.75 F g(-1) and excellent cyclic stability in 0.1 M Na2SO4 aqueous electrolyte with the capacitance retention of 93.6% after 2000 cycles at 1 A g(-1) current density. GCNNFs exhibit high capacitance of 208 F g(-1) even at 10 A g(-1), with the appreciable capacitance retention of 89.5%, which proves its better rate capability. Moreover, the GCNNF shows enhanced photocatalytic activity in the photodegradation of RhB in comparison to the bulk graphitic-C3N4 (GCN). The degradation rate constant of GCNNF photocatalyst is almost 4 times higher than GCN. The enhanced photocatalytic activity of GCNNF is mainly due to the higher surface area, appropriate bandgap, and fewer defects in GCNNF as compared to GCN. As an economical precursor (melamine) and harmless, facile, and template-free synthesis method with excellent performance both in supercapacitors and in photodegradation, GCNNF is a strong candidate for energy storage and environment protection applications.

Deposition of diamond‐like carbon films by electrolysis of methanol solution

By electrolysis of the methanol solution, an attempt was made to deposit diamondlike carbon (DLC) films on silicon substrate at temperature of less than 60 °C. Substrates were negatively biased with a dc potential of 0 to −3000 V. IR spectra showed that the O–H, C–H, and C–O vibration bands of electrolyte decreased remarkably after electrolysis and a new peak characterized as the C=C bond appeared. The deposited films were characterized as DLC films by Raman spectroscopy.

Hollow core–shell η-Fe2O3 microspheres with excellent lithium-storage and gas-sensing properties

Hollow core-shell eta-Fe(2)O(3) microspheres exhibit not only superior electrochemical performance as lithium storage electrodes but also excellent sensitivities to trace levels of gases.

Two-dimensional ultrathin ZnCo2O4 nanosheets: general formation and lithium storage application

Two-dimensional (2D) multicomponent transition-metal oxide nanosheets are the most promising candidate in low-cost and eco-friendly energy storage/conversion applications. Their surface-enhanced properties and synergic effects are fascinating, yet still underdeveloped. Here, we first report the high-quality ultrathin 2D nanosheets of ZnCo2O4 synthesized on a large scale via microwave-assisted liquid-phase growth coupled with a post annealing procedure. The well-defined and freestanding nanosheets exhibit a micron-sized planar area and ultrathin thickness, suggesting a high surface atom ratio with an unique surface and electronic structure, thus facilitating the charge transfer to enhance the overall performances in electrochemical reaction. When used as anode materials for lithium ion batteries, the ultrathin ZnCo2O4 nanosheets exhibit a high reversible lithium storage capacity of 930–980 mA h g−1 at 200 mA g−1 current density in 200 cycles with an excellent cycling stability and good high-rate capability. Even more importantly, we have extended the facile method for the formation of other analogue nanosheets including binary and ternary transition metal oxides (NiO, Co3O4, NiCo2O4, and CuCo2O4) and make a possibility in exploring more unique properties and promising commercial applications.

From Rice Bran to High Energy Density Supercapacitors: A New Route to Control Porous Structure of 3D Carbon

Controlled micro/mesopores interconnected structures of three-dimensional (3D) carbon with high specific surface areas (SSA) are successfully prepared by carbonization and activation of biomass (raw rice brans) through KOH. The highest SSA of 2475 m2 g−1 with optimized pore volume of 1.21 cm3 g−1 (40% for mesopores) is achieved for KOH/RBC = 4 mass ratio, than others. The as-prepared 3D porous carbon-based electrode materials for supercapacitors exhibit high specific capacitance specifically at large current densities of 10 A g−1 and 100 A g−1 i.e., 265 F g−1 and 182 F g−1 in 6 M KOH electrolyte, respectively. Moreover, a high power density ca. 1223 W kg−1 (550 W L−1) and energy density 70 W h kg−1 (32 W h L−1) are achieved on the base of active material loading (~10 mg cm2) in the ionic liquid. The findings can open a new avenue to use abundant agricultural by-products as ideal materials with promising applications in high-performance energy-storage devices.

Enhancing visible-light photoelectrochemical water splitting through transition-metal doped TiO2 nanorod arrays

Extending the photoresponse from the ultraviolet (UV) to the visible light region, while maintaining a high photocatalytic activity has been an important challenge for TiO2. We demonstrate the use of transition-metal doping treatment as a facile and effective strategy to substantially improve the performance of TiO2 nanorods in the visible light region for photoelectrochemical (PEC) water splitting. The effect of Fe, Mn and Co as dopants on the PEC performance of the TiO2 nanorods was investigated, wherein the Fe doping is the most effective route to enhance the photoactivity of TiO2. The photocurrent density of Fe–TiO2 sample significantly increases with bias voltage and reaches 2.92 mA cm−2 at 0.25 V vs. Ag/AgCl, which is five times higher than that of the undoped TiO2. Even under visible light illumination (>420 nm), the photocurrent density of Fe–TiO2 is as high as 0.96 mA cm−2 at 0.25 V vs. Ag/AgCl. Incident-photon-to-current-conversion (IPCE) efficiency (up to ∼18%) measurements reveal that the Fe–TiO2 nanorod sample significantly improve the photoresponse not only in the UV region, but also in the visible light region. Fe doping not only enhances the visible light absorption of TiO2 nanorods by creating impurity states near the conduction band, but also obviously increases carrier density of TiO2, leading to effective carrier separation and transportation and relatively long electron lifetime. Because of their relatively high photocatalytic activity, the Fe–TiO2 nanorods can serve as a promising candidate in various areas, such as solar water splitting, dye-sensitized solar cells, and photocatalysis.

Surface-enabled superior lithium storage of high-quality ultrathin NiO nanosheets

Two-dimensional nanomaterials hold great potential for next-generation energy storage and conversion devices. Here, we report a large-scale synthesis of high-quality ultrathin NiO nanosheets. The well-defined nanosheets show a graphene-like morphology with large planar area, ultrathin thickness (<2 nm), and high percentage of surface atoms. In comparison with the bulk material, the NiO nanosheets exhibit unique surface and electronic structure with considerable under-coordinated surface nickel atoms and crystal lattice volume expansion. The detected local coordination geometry and the electronic states endow the ultrathin NiO nanosheets with great potential in surface-dependent electrochemical reactions and catalytic processes. When used as anode materials for lithium-ion batteries, the ultrathin NiO nanosheets exhibit a high reversible lithium storage capacity of 715.2 mA h g−1 at 200 mA g−1 current density in 130 cycles with an excellent cycling stability and rate capability. In particular, the large-area ultrathin 2D nanostructure can shorten lithium ion diffusion paths and provide a large exposed surface for more lithium-insertion channels. The large-scale and cost-efficient synthesis and the excellent electrochemical performance highlight the high-quality ultrathin 2D NiO nanosheets as a competitive anode material for lithium-ion batteries.

A novel three-dimensional tubular scaffold prepared from silk fibroin by electrospinning

Effects of electrospinning parameters (including voltage, collection distance, solution concentration and flow rate) on the morphology and diameter distribution of regenerated SF (silk fibroin) fiber were investigated. Afterward, SF tubular scaffold composed of homogenous fibers was fabricated at voltage of 18kV, collection distance of 18cm, concentration of 37%, and flow rate of 0.15mL/min. After methanol treatment, SF tubular scaffold showed tensile strength of 3.57MPa and porosity of 80.85%. It is satisfied that our work offers a simple method to fabricate seamless and porous tubular scaffold from SF without any additives and organic solvents. Furthermore, the results suggest that this tubular scaffold shows promising applications in small-diameter vascular graft.