Chunxiang Lv

Hierarchical porous carbon microtubes derived from willow catkins for supercapacitor applications

With willow catkins as highly accessible carbon sources, hierarchical porous carbon microtubes (denoted as HPNCTs) have been successfully prepared by a facile carbonization and subsequent KOH activation process. The resulting materials not only inherited the natural tubular morphology of willow catkins, but also developed a hierarchical porous structure by activation, with nitrogen from the biomass being self-doped in the resulting carbon. A maximum specific surface area of 1775.7 m2 g−1 with a pore volume of 0.8516 cm3 g−1 was achieved for HPNCT-800. When evaluated as an electrode by a three-electrode system in 6 M KOH aqueous solution, the material exhibited a high gravimetric capacitance of 292 F g−1 at a current density of 1 A g−1, with a good rate capability of 83.5% retention at 10 A g−1. HPNCT-800 was further employed in a coin-type symmetric device with 1 M LiPF6 electrolyte, and exhibited a high energy density of 37.9 W h kg−1 at a power density of 700 W kg−1, with excellent cycling stability with 90.6% retention after 4000 cycles. By taking advantage of the unique structure of abundant biomass from nature, this work sheds light on the creation of advanced porous carbon materials towards energy storage applications.

A high-rate lithium–sulfur battery assisted by nitrogen-enriched mesoporous carbons decorated with ultrafine La2O3 nanoparticles

Nitrogen-enriched mesoporous carbons (NMCs) were decorated with ultrafine La2O3 nanoparticles via a simple wet impregnation method. The resulting composites with well developed mesoporous structures, high nitrogen content and uniform dispersions of La2O3 nanoparticles served as scaffolds to house sulfur for high rate lithium–sulfur batteries. Apart from their on-site trapping of polysulfides, the La2O3 nanoparticles decorated on the mesoporous carbon framework were also found to have a strong catalytic effect on sulfur reduction, offering high discharge voltages and fast electrochemical reaction kinetics. Combining the multiple effects of the well developed mesopores, nitrogen doping and La2O3 nanoparticles, the resulting ternary NMC/La2O3/S nanocomposites can deliver an initial capacity of 1043 mA h g−1 at 1 C, which remains at 799 mA h g−1 after 100 cycles. Moreover, they still maintain ultra-high rate capacities of 579 and 475 mA h g−1 at 3 C and 5 C, respectively, after 100 cycles. These encouraging results suggest that other metal oxides with suitable adsorption and catalytic abilities can be widely applied to decorate carbon frameworks for use in high rate lithium–sulfur systems.

High-power and high-energy asymmetric supercapacitors based on Li+-intercalation into a T-Nb2O5/graphene pseudocapacitive electrode

The intercalation pseudocapacitance which leads to the extraordinary charge storage properties has been confirmed as an intrinsic capacitive property of orthorhombic Nb2O5 (T-Nb2O5) nanocrystals. However, the poor electronic conductivity of T-Nb2O5 nanocrystals may limit their electrochemical utilization and high-rate performance especially for thick electrodes with high mass loadings. To address this issue, we herein reported a hydrothermal-heat treatment method to anchor T-Nb2O5 nanocrystals on conductive graphene sheets, which form a layer-by-layer integrated electrode with much shortened ion transport paths and results in excellent electrochemical capacitive properties, including high capacitance (626 C g−1), excellent rate handling and cyclic stability. Furthermore, asymmetric supercapacitors were constructed by using the high-rate response T-Nb2O5/graphene nanocomposite and mesoporous carbon as the negative and positive electrode, respectively. The asymmetric supercapacitor could deliver a high energy density of 16 W h kg−1 at an unprecedented power density of 45 kW kg−1 (discharge time of 1.2 s). The outstanding power properties of the supercapacitors are mainly attributed to the improved high-rate Li-insertion/extraction capability of the T-Nb2O5/graphene electrode and appropriate pairing of the mesoporous carbon electrode.

Self‐Assembled 3D Graphene‐Based Aerogel with Co3O4 Nanoparticles as High‐Performance Asymmetric Supercapacitor Electrode

Using graphene oxide and a cobalt salt as precursor, a three-dimensional graphene aerogel with embedded Co3 O4 nanoparticles (3D Co3 O4 -RGO aerogel) is prepared by means of a solvothermal approach and subsequent freeze-drying and thermal reduction. The obtained 3D Co3 O4 -RGO aerogel has a high specific capacitance of 660 F g(-1) at 0.5 A g(-1) and a high rate capability of 65.1 % retention at 50 A g(-1) in a three-electrode system. Furthermore, the material is used as cathode to fabricate an asymmetric supercapacitor utilizing a hierarchical porous carbon (HPC) as anode and 6 M KOH aqueous solution as electrolyte. In a voltage range of 0.0 to 1.5 V, the device exhibits a high energy density of 40.65 Wh kg(-1) and a power density of 340 W kg(-1) and shows a high cycling stability (92.92 % capacitance retention after 2000 cycles). After charging for only 30 s, three CR2032 coin-type asymmetric supercapacitors in series can drive a light-emitting-diode (LED) bulb brightly for 30 min, which remains effective even after 1 h.

Controllable synthesis of hierarchical mesoporous/microporous nitrogen-rich polymer networks for CO2 and Cr(VI) ion adsorption

A facile and scalable one-pot approach has been developed for the preparation of hierarchical meso- and microporous nitrogen-rich polymer networks by sol–gel polymerization of melamine, resorcinol and terephthaldehyde. The obtained polymer networks have a hierarchical porous structure with moderate microporous surface area and high mesoporous volume. The micropores are within the networks of highly cross-linked polymer chains, while the mesopores result from a 3-D continuous polymeric gel network formed by the reaction-induced sol–gel phase separation. The addition of hexafunctional melamine to the polymer precursor could enhance the crosslinking degree at a molecular level, thus leading to more accessible micropores within the networks. It can also increase the size of polymer clusters, leading to the formation of larger mesopores. Moreover, the nitrogen functional groups inherited from melamine and the –OH functional groups from resorcinol can also be adjusted by changing the precursor composition. These rich surface functional groups could serve as irregular sites with chemical heterogeneity available for CO2 and chromium Cr(VI) ion adsorption. High CO2 uptake up to 2.4 mmol g−1 and high chromium adsorption capacity of 126.3 mg g−1 are obtained. The outstanding advantages of the MRT networks presented here include their low price, commercially available starting compounds and the easy method of synthesis. This kind of new porous polymer with tailored physical and chemical properties has promise for further applications.

Rheological behavior of fresh cement pastes with a graphene oxide additive

Abstract The rheological properties and morphology of fresh cement pastes with different contents of graphene oxide (GO) were investigated by a rheometer and a laser confocal scanning microscope, respectively. The rheological data were fitted by the Modified-Bingham (M-B) model and Herschel-Bulkley (H-B) model. A mechanism for the effect of GO on the rheological properties is proposed. Results show that the cement particles are re-agglomerated and new flocculation structures are generated by the addition of GO. The new flocculation structures significantly alter the rheological properties of the pastes. The degree of re-agglomeration and the number of new flocculation structures increase with increasing GO content, leading to a sharp increase in the yield stress, plastic viscosity and the area of the hysteresis loop. GO can effectively reduce the degree of shear-thickening, and increase the critical shear rate and the stability of the pastes.