Liang Huang

Nickel-cobalt hydroxide nanosheets coated on NiCo2O4 nanowires grown on carbon fiber paper for high-performance pseudocapacitors.

A series of flexible nanocomposite electrodes were fabricated by facile electro-deposition of cobalt and nickel double hydroxide (DH) nanosheets on porous NiCo2O4 nanowires grown radially on carbon fiber paper (CFP) for high capacity, high energy, and power density supercapacitors. Among different stoichiometries of CoxNi1-xDH nanosheets studied, Co0.67Ni0.33 DHs/NiCo2O4/CFP hybrid nanoarchitecture showed the best cycling stability while maintaining high capacitance of ∼1.64 F/cm(2) at 2 mA/cm(2). This hybrid composite electrode also exhibited excellent rate capability; the areal capacitance decreased less than 33% as the current density was increased from 2 to 90 mA/cm(2), offering excellent specific energy density (∼33 Wh/kg) and power density (∼41.25 kW/kg) at high cycling rates (up to150 mA/cm(2)).

Hybrid Composite Ni(OH)(2)@NiCo2O4 Grown on Carbon Fiber Paper for High-Performance Supercapacitors

We have successfully fabricated and tested the electrochemical performance of supercapacitor electrodes consisting of Ni(OH)2 nanosheets coated on NiCo2O4 nanosheets grown on carbon fiber paper (CFP) current collectors. When the NiCo2O4 nanosheets are replaced by Co3O4 nanosheets, however, the energy and power density as well as the rate capability of the electrodes are significantly reduced, most likely due to the lower conductivity of Co3O4 than that of NiCo2O4. The 3D hybrid composite Ni(OH)2/NiCo2O4/CFP electrodes demonstrate a high areal capacitance of 5.2 F/cm(2) at a cycling current density of 2 mA/cm(2), with a capacitance retention of 79% as the cycling current density was increased from 2 to 50 mA/cm(2). The remarkable performance of these hybrid composite electrodes implies that supercapacitors based on them have potential for many practical applications.

Flexible Transparent Molybdenum Trioxide Nanopaper for Energy Storage.

A flexible transparent molybdenum trioxide nanopaper, assembled via ultralong molybdenum trioxide nanobelts, displays an excellent average transmittance of ≈90% in the visible region. The free-standing nanopaper electrode delivers an outstanding specific capacitance of 1198 F g(-1) and shows an excellent long-term stability performance over 20 000 cycles with a retention rate of 99.1%.

Oxygen- and Nitrogen-Enriched 3D Porous Carbon for Supercapacitors of High Volumetric Capacity.

Efficient utilization and broader commercialization of alternative energies (e.g., solar, wind, and geothermal) hinges on the performance and cost of energy storage and conversion systems. For now and in the foreseeable future, the combination of rechargeable batteries and electrochemical capacitors remains the most promising option for many energy storage applications. Porous carbonaceous materials have been widely used as an electrode for batteries and supercapacitors. To date, however, the highest specific capacitance of an electrochemical double layer capacitor is only ∼200 F/g, although a wide variety of synthetic approaches have been explored in creating optimized porous structures. Here, we report our findings in the synthesis of porous carbon through a simple, one-step process: direct carbonization of kelp in an NH3 atmosphere at 700 °C. The resulting oxygen- and nitrogen-enriched carbon has a three-dimensional structure with specific surface area greater than 1000 m(2)/g. When evaluated as an electrode for electrochemical double layer capacitors, the porous carbon structure demonstrated excellent volumetric capacitance (>360 F/cm(3)) with excellent cycling stability. This simple approach to low-cost carbonaceous materials with unique architecture and functionality could be a promising alternative to fabrication of porous carbon structures for many practical applications, including batteries and fuel cells.

Salt-Templated Synthesis of 2D Metallic MoN and Other Nitrides

Two-dimensional (2D) transition-metal nitrides just recently entered the research arena, but already offer a potential for high-rate energy storage, which is needed for portable/wearable electronics and many other applications. However, a lack of efficient and high-yield synthesis methods for 2D metal nitrides has been a major bottleneck for the manufacturing of those potentially very important materials, and only MoN, Ti4N3, and GaN have been reported so far. Here we report a scalable method that uses reduction of 2D hexagonal oxides in ammonia to produce 2D nitrides, such as MoN. MoN nanosheets with subnanometer thickness have been studied in depth. Both theoretical calculation and experiments demonstrate the metallic nature of 2D MoN. The hydrophilic restacked 2D MoN film exhibits a very high volumetric capacitance of 928 F cm-3 in sulfuric acid electrolyte with an excellent rate performance. We expect that the synthesis of metallic 2D MoN and two other nitrides (W2N and V2N) demonstrated here will provide an efficient way to expand the family of 2D materials and add many members with attractive properties.

Rapid mass production of two-dimensional metal oxides and hydroxides via the molten salts method

Because of their exotic electronic properties and abundant active sites, two-dimensional (2D) materials have potential in various fields. Pursuing a general synthesis methodology of 2D materials and advancing it from the laboratory to industry is of great importance. This type of method should be low cost, rapid and highly efficient. Here, we report the high-yield synthesis of 2D metal oxides and hydroxides via a molten salts method. We obtained a high-yield of 2D ion-intercalated metal oxides and hydroxides, such as cation-intercalated manganese oxides (Na0.55Mn2O4·1.5H2O and K0.27MnO2·0.54H2O), cation-intercalated tungsten oxides (Li2WO4 and Na2W4O13), and anion-intercalated metal hydroxides (Zn5(OH)8(NO3)2·2H2O and Cu2(OH)3NO3), with a large lateral size and nanometre thickness in a short time. Using 2D Na2W4O13 as an electrode, a high performance electrochemical supercapacitor is achieved. We anticipate that our method will enable new path to the high-yield synthesis of 2D materials for applications in energy-related fields and beyond.

Activated carbon derived from melaleuca barks for outstanding high-rate supercapacitors.

Activated carbon (AC) was prepared via carbonizing melaleuca bark in an argon atmosphere at 600 °C followed with KOH activation for high-rate supercapacitors. This AC electrode has a high capacitance of 233 F g(-1) at a scan rate of 2 mV s(-1) and an excellent rate capability of ∼80% when increasing the sweep rate from 2 to 500 mV s(-1). The symmetric supercapacitor assembled by the above electrode can deliver a high energy density of 4.2 Wh kg(-1) with a power density of 1500 W kg(-1) when operated in the voltage range of 0-1 V in 1 M H2SO4 aqueous electrolyte while maintaining great cycling stability (less than 5% capacitance loss after 10 000 cycles at sweep rate of 100 mV s(-1)). All the outstanding electrochemical performances make this AC electrode a promising candidate for potential energy storage application.

3D interconnected porous NiMoO4 nanoplate arrays on Ni foam as high-performance binder-free electrode for supercapacitors

3D interconnected NiMoO4 nanoplate arrays (NPAs) are grown on Ni foam (NPAs@Ni) via a facile hydrothermal reaction. The obtained NPAs@Ni is directly used as a binder-free integrated electrode for supercapacitors. The optimized electrode exhibits a specific capacitance as high as 3.4 F cm−2 (2138 F g−1) at a current density of 2 mA cm−2, and an excellent cyclability with 87% retention of the initial specific capacitance after 3000 cycles. The remarkable electrochemical performance can be attributed to the interconnected architecture in which the electrons and ions readily transport along the conductive 3D channels.

Highly conductive and flexible molybdenum oxide nanopaper for high volumetric supercapacitor electrode

Paper-like electrodes with high conductivity and flexibility hold great potential for assembling high-performance flexible electronic devices. In this study, a flexible conductive film was fabricated via vacuum filtration using highly conductive MoO3−x ultralong nanobelts. This film has low sheet resistance of 5.1 Ω sq−1 and exhibits a stable three-dimensional structure even under 1000 times of bending test. Significantly, this free-standing film has a high volumetric capacitance of 652 F cm−3. Moreover, a symmetric device based on this electrode demonstrates good cycling stability with a capacitance retention of 85.7% after 25000 cycles. We anticipate that this strategy can also be applied to other three-dimensional flexible porous films based on one-dimensional conductive nanostructure, which could open up new opportunities for energy storage and conversion.

Hierarchical core-shell NiCo2O4@NiMoO4 nanowires grown on carbon cloth as integrated electrode for high-performance supercapacitors

Hierarchical core-shell NiCo2O4@NiMoO4 nanowires were grown on carbon cloth (CC@NiCo2O4@NiMoO4) by a two-step hydrothermal route to fabricate a flexible binder-free electrode. The prepared CC@NiCo2O4@NiMoO4 integrated electrode was directly used as an electrode for faradaic supercapacitor. It shows a high areal capacitance of 2.917 F cm−2 at 2 mA cm−2 and excellent cycling stability with 90.6% retention over 2000 cycles at a high current density of 20 mA cm−2. The superior specific capacitance, rate and cycling performance can be ascribed to the fast transferring path for electrons and ions, synergic effect and the stability of the hierarchical core-shell structure.