Kun Ni

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.

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) .

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.

Direct Laser Writing of Graphene Made from Chemical Vapor Deposition for Flexible, Integratable Micro‐Supercapacitors with Ultrahigh Power Output

High-performance yet flexible micro-supercapacitors (MSCs) hold great promise as miniaturized power sources for increasing demand of integrated electronic devices. Herein, this study demonstrates a scalable fabrication of multilayered graphene-based MSCs (MG-MSCs), by direct laser writing (DLW) of stacked graphene films made from industry-scale chemical vapor deposition (CVD). Combining the dry transfer of multilayered CVD graphene films, DLW allows a highly efficient fabrication of large-areal MSCs with exceptional flexibility, diverse planar geometry, and capability of customer-designed integration. The MG-MSCs exhibit simultaneously ultrahigh energy density of 23 mWh cm-3 and power density of 1860 W cm-3 in an ionogel electrolyte. Notably, such MG-MSCs demonstrate an outstanding flexible alternating current line-filtering performance in poly(vinyl alcohol) (PVA)/H2 SO4 hydrogel electrolyte, indicated by a phase angle of -76.2° at 120 Hz and a resistance-capacitance constant of 0.54 ms, due to the efficient ion transport coupled with the excellent electric conductance of the planar MG microelectrodes. MG-polyaniline (MG-PANI) hybrid MSCs fabricated by DLW of MG-PANI hybrid films show an optimized capacitance of 3.8 mF cm-2 in PVA/H2 SO4 hydrogel electrolyte; an integrated device comprising MG-MSCs line filtering, MG-PANI MSCs, and pressure/gas sensors is demonstrated.

Diameter-Sensitive Breakdown of Single-Walled Carbon Nanotubes upon KOH Activation

While potassium hydroxide (KOH) activation has been used to create pores in carbon nanotubes (CNTs) for improved energy-storage performance, the KOH activation mechanism of CNTs has been rarely investigated. In this work, the reaction between single-walled CNTs (SWCNTs) and KOH is studied in situ by thermogravimetric analysis coupled to infrared (IR) spectroscopy and gas chromatography/mass spectrometry (MS). The IR and MS results clearly demonstrate the sequential evolution of CO, hydrocarbons, CO2 , and H2 O in the activation process. By using the radial breathing mode of Raman spectroscopy, a diameter-sensitive selectivity is observed in the reaction between SWCNTs and KOH, leading to a preferential distribution of SWCNTs with diameters larger than 1 nm after activation at 900 °C and a preferential removal of SWCNTs with diameters below 1 nm upon activation.

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.

Tailoring the Structure of Carbon Nanomaterials toward High‐End Energy Applications

Carbon nanomaterials are perceived to be ideally suited candidates for high-end energy applications, owing to their unparalleled advantages including superior electric and thermal conductivity, excellent mechanical properties, and high specific surface areas. It has been demonstrated through several research contributions that the electrochemical performance of carbon nanomaterials significantly depends upon their versatile electronic structures and microstructures. These can be precisely tailored by rational defect engineering, heteroatom doping, heterostructure coupling, and pore fabrication, which largely affect the intrinsic nature of active sites and facilitate the ion/electron transfer. Herein, the recent progress in tailoring carbon nanostructures toward high-end electrocatalysis and supercapacitor applications is summarized, with an emphasis on synthesis strategies, advanced characterizations, and specific elucidation of structure-performance relationship. The challenges and opportunities for the rational design and detection of variously tailored carbon nanomaterials that can further improve the fundamental understanding and practical applications in the field of energy storage and conversion are also discussed.

Polyoxomolybdate-derived carbon-encapsulated multicomponent electrocatalysts for synergistically boosting hydrogen evolution

The hydrogen adsorption strength and activity of each catalytic site greatly influence the hydrogen evolution reaction (HER) kinetics of electrocatalysts. It remains a challenge to effectively activate catalytic sites for interfacial carbon-catalyzed electrocatalysts. Here, we report a polyoxomolybdate-derived carbon-encapsulated multicomponent catalyst with nanowire structure. The activation of catalytic sites and enhancement of HER kinetics are achieved by incorporating tiny MoO2 and Ni nanoparticles into a N-doped carbon layer (denoted as MoO2–Ni@NC). The MoO2–Ni@NC catalyst possesses a remarkable HER activity and is superior to most carbon-encapsulated electrocatalysts. In particular, it achieves a low overpotential of 58 mV at −10 mA cm−2, and a high exchange current density of 0.375 mA cm−2 with good stability (up to 80 000 s) in 0.5 M H2SO4. Theoretical analyses suggest that the N-doped carbon layer acts as an active adsorption site for hydrogen. The inner MoO2–Ni species behave as effective promoters to synergistically modulate the hydrogen adsorption strength on the interfacial carbon and enable the active sites to be more efficient. The synthesis strategy and the revealed catalytic mechanism can guide the rational design of high-efficiency carbon-encapsulated HER electrocatalysts.