Wencong Zeng

A Hierarchical Carbon Derived from Sponge-Templated Activation of Graphene Oxide for High-Performance Supercapacitor Electrodes.

A hierarchical porous carbon is fabricated by introducing a polyurethane sponge to a template graphene oxide into a 3D interconnected structure, while KOH activation generates abundant micropores in its backbone. Supercapacitors assembled with this carbon achieve a high energy density of 89 W h kg(-1) (64 W h L(-1) ) and outstanding power density due to the shortened ion-transport distance in 3D.

Hierarchically micro/mesoporous activated graphene with a large surface area for high sulfur loading in Li-S batteries

A hierarchically micro/mesoporous a-MEGO with a high surface area (up to 3000 m2 g−1) and large pore volume (up to 2.14 cm3 g−1) was utilized as a superior carbon host material for high sulfur loading towards advanced Li–S batteries.

Incorporating Pyrrolic and Pyridinic Nitrogen into a Porous Carbon made from C60 Molecules to Obtain Superior Energy Storage

Nitrogen-doped porous carbon is obtained by KOH activation of C60 in an ammonia atmosphere. As an anode for Li-ion batteries, it shows a reversible capacity of up to ≈1900 mA h g-1 at 100 mA g-1 . Simulations suggest that the superior Li-ion storage may be related to the curvature of the graphenes and the presence of pyrrolic/pyridinic group dopants.

Creating Pores on Graphene Platelets by Low-Temperature KOH Activation for Enhanced Electrochemical Performance.

KOH activation of microwave exfoliated graphite oxide (MEGO) is investigated in detail at temperatures of 450-550 °C. Out of the activation temperature range conventionally used for the preparation of activated carbons (>600 °C), the reaction between KOH and MEGO platelets at relatively low temperatures allows one to trace the structural transition from quasi-two-dimensional graphene platelets to three-dimensional porous carbon. In addition, it is found that nanometer-sized pores are created in the graphene platelets at the activation temperature of around 450 °C, leading to a carbon that maintains the platelet-like morphology, yet with a specific surface area much higher than MEGO (e.g., increased from 156 to 937 m(2) g(-1) ). Such a porous yet highly conducting carbon shows a largely enhanced electrochemical activity and thus improved electrochemical performance when being used as electrodes in supercapacitors. A specific capacitance of 265 F g(-1) (185 F cm(-3) ) is obtained at a current density of 1 A g(-1) in 6 m KOH electrolyte, which remains 223 F g(-1) (156 F cm(-3) ) at the current density of 10 A g(-1) .

LiFePO4/reduced graphene oxide hybrid cathode for lithium ion battery with outstanding rate performance

A lithium iron phosphate (LFP)/reduced graphene oxide (rGO) hybrid has been prepared using a homogeneous coprecipitation method followed by heat treatment. As a cathode material for the lithium ion battery, the hybrid demonstrates a specific capacity higher than 170 mA h g−1. The excess capacity of more than the theoretical value of LFP is attributed to the reversible reduction–oxidation reaction between lithium ions and rGO nanosheets. The highly conductive rGO sheets upon which LFP particles are uniformly and closely anchored assist in the electron migration and lithium ion transfer and prevent the aggregation of LFP particles during charging and discharging, leading to an initial coulombic efficiency of more than 100% with the content of rGO between 7% and 25% in the hybrid. LFP with 15% rGO shows a high discharge capacity of 172 mA h g−1 at 0.06 C, and the capacity remains 139 mA h g−1 at 11.8 C, in addition to showing an excellent cycling stability.

Assembling carbon quantum dots to a layered carbon for high-density supercapacitor electrodes

It is found that carbon quantum dots (CQDs) self-assemble to a layer structure at ice crystals-water interface with freeze- drying. Such layers interconnect with each other, forming a free-standing CQD assembly, which has an interlayer distance of about 0.366 nm, due to the existence of curved carbon rings other than hexagons in the assembly. CQDs are fabricated by rupturing C60 by KOH activation with a production yield of ~15 wt.%. The CQDs obtained have an average height of 1.14 nm and an average lateral size of 7.48 nm, and are highly soluble in water. By packaging annealed CQD assembly to high density (1.23 g cm−3) electrodes in supercapacitors, a high volumetric capacitance of 157.4 F cm−3 and a high areal capacitance of 0.66 F cm−2 (normalized to the loading area of electrodes) are demonstrated in 6 M KOH aqueous electrolyte with a good rate capability.

Manipulating Size of Li3V2(PO4)3 with Reduced Graphene Oxide: towards High-Performance Composite Cathode for Lithium Ion Batteries

Lithium vanadium phosphate (Li3V2(PO4)3, LVP)/reduced graphene oxide (rGO) composite is prepared with a rheological method followed by heat treatment. The size and interface of LVP particles, two important merits for a cathode material, can be effectively tuned by the rGO in the composite, which plays as surfactant to assist sol-gelation and simultaneously as conductive carbon coating. As a consequence, the composite with 7.0 ± 0.4 wt.% rGO shows a capacity of 141.6 mAh g−1 at 0.075 C, and a rate capacity of 119.0 mAh g−1 at 15 C with respect to the mass of LVP/rGO composite, and an excellent cycling stability that retains 98.7% of the initial discharge capacity after 50 cycles. The improved electrochemical performance is attributed to the well-controlled rGO content that yields synergic effects between LVP and rGO. Not only do the rGO sheets reduce the size of LVP particles that favor the Li+ ion migration and the electron transfer during charging and discharging, but also contribute to the reversible lithium ions storage.

Microwave-assisted synthesis of hematite/activated graphene composites with superior performance for photocatalytic reduction of Cr(VI)

Hematite (α-Fe2O3) nanoparticles are deposited onto porous ‘activated microwave expanded graphite oxide’ (aMEGO) carbon via a simple, rapid one-pot microwave process. Under the irradiation of visible light, the α-Fe2O3/aMEGO composites exhibit significantly enhanced photocatalytic activity for the reduction of Cr(VI) to Cr(III). A maximum Cr(VI) removal rate of 95.28% is obtained for the composite containing 7.72 wt% aMEGO as compared to that of 25.26% for pure α-Fe2O3; the rate constant of the composite is nearly 9 times higher than that of pure α-Fe2O3. The crucial role of aMEGO in enhancing the photocatalytic efficiency of the composites relies not only on its large surface area, but also on the high conductivity which benefits the transport of photoexcited electrons. The enhancement in the charge separation and the suppression in the electron–hole pair recombination is evidenced by an increased photocurrent and a suppressed photoluminescence in the α-Fe2O3/aMEGO composites.

Supercapacitors: A Hierarchical Carbon Derived from Sponge‐Templated Activation of Graphene Oxide for High‐Performance Supercapacitor Electrodes (Adv. Mater. 26/2016)

H. Ji, Y. Zhu, and co-workers demonstrate a 3D hierarchically porous carbon by introducing a polyurethane sponge to template graphene oxide into a 3D interconnected structure while KOH activation generates abundant micropores in its backbone. As described on page 5222, a supercapacitor assembled with this carbon material achieves a high energy density of 89 W h kg(-1) (64 W h L(-1) ) and outstanding power density due to its shortened ion transport distance in three dimensions.

Fast pseudocapacitive reactions of three-dimensional manganese dioxide structures synthesized via self-limited redox deposition on microwave-expanded graphite oxide

Three-dimensional (3D) MnO2 structures are deposited on microwave-expanded graphite oxide (MEGO) via a self-limited redox reaction between MEGO and KMnO4. The 3D architecture consists of MnO2 sheets lying uniformly on MEGO and walls protruding from MEGO, both with thickness in the range of 1–5 nm. The loading of MnO2 and the height and density of walls in the 3D architecture can be controlled by tuning the reaction duration, leading to a balanced specific capacitance and power performance. Symmetric supercapacitors assembled using a MEGO–MnO2 composite with 24.5 wt% MnO2 can work at a voltage of up to 2 V in a 1 M Na2SO4 electrolyte, yielding an energy density of 14 W h kg−1 (13.6 W h L−1) at a power density of 250 W kg−1 (243 W L−1) or a power density of 7.67 kW kg−1 (7.44 kW L−1) at an energy density of 5.46 W h kg−1 (5.3 W h L−1). Asymmetric supercapacitors, consisting of the MEGO–MnO2 (containing 24.5 wt% MnO2) composite as the positive electrode and activated MEGO as the negative electrode in a 1 M Na2SO4 electrolyte, exhibit an energy density of 25.1 W h kg−1 at a power density of 93 W kg−1 with a working voltage of up to 1.8 V.