Kangwen Qiu

Hierarchical TiO2 nanobelts@MnO2 ultrathin nanoflakes core–shell array electrode materials for supercapacitors

Hierarchical TiO2 nanobelts@MnO2 ultrathin nanoflakes core–shell arrays (TiO2@MnO2 NBAs) have been fabricated on a Ti foil substrate by hydrothermal approach and further investigated as the electrode for a supercapacitor. Their electrochemical properties were examined using cyclic voltammetry (CV), galvanostatic charge–discharge, and electrochemical impedance spectroscopy (EIS) in a three-electrode cell. The experimental observations clearly show that the fabricated TiO2@MnO2 NBAs electrode possesses superior rate capability and outstanding cycling performance due to its rationally designed nanostructure. A specific capacitance as high as 557.6 F g−1 is obtained at a scan rate of 200 mV s−1 (454.2 F g−1 at a current density of 200 mA g−1) in 1 M Na2SO4 aqueous solution. The energy density and power density measured at 2 A g−1 are 7.5 Wh kg−1 and 1 kW kg−1 respectively, demonstrating its good rate capability. In addition, the composite TiO2@MnO2 NBAs electrode shows excellent long-term cyclic stability. The fabrication method presented here is facile, cost-effective and scalable, which may open a new pathway for real device applications.

Mesoporous CuCo2O4 nanograsses as multi-functional electrodes for supercapacitors and electro-catalysts

Hierarchical, mesoporous CuCo2O4 nanograsses have been synthesized on copper foam using a simple and cost-effective hydrothermal approach followed by a post-annealing treatment. The electrodes made from the novel nanoarchitecture exhibit multi-functional electrochemical performance. They deliver an excellent specific capacitance of 796 F g−1 at a current density of 2 A g−1 in a 2 M KOH aqueous solution and a long-term cyclic stability of 94.7% capacitance retention after 5000 cycles. When applied to electro-catalytic oxidation of methanol, the current density of the CuCo2O4/Cu foam electrode in 1 M KOH mixed with 0.5 M methanol is maintained up to 27.6 A g−1. The superior electrochemical performances are mainly due to the unique one dimensional porous acicular architecture with a very large surface area and porosity grown on a highly conductive Cu substrate, offering faster ion/electron transfer, an improved reactivity and an enhanced structural stability. The fabrication strategy presented here is simple, cost-effective and scalable, which can open new avenues for large-scale applications of the novel materials in energy storage.

Self-assembled graphene@PANI nanoworm composites with enhanced supercapacitor performance

Self-assembled hierarchical graphene@polyaniline (PANI) nanoworm composites have been fabricated using graphene oxide (GO) and aniline as the starting materials. The worm-like PANI nanostructures were successfully obtained via a simple polymerization route. The graphene-wrapped hierarchical PANI nanoworm structures could be prepared using a three-step process by dispersing the PANI nanoworms sequentially into the relevant solution. The morphologies and microstructures of the samples were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. Electrochemical properties were also characterized by cyclic voltammetry (CV) and galvanostatic charge–discharge. The results indicated that the integration of graphene and the worm-like PANI nanocomposites possessed excellent electrochemical properties. These hierarchical worm-like graphene@PANI nanostructures could afford an interconnected network with a lot of well-defined nanopores, and further provided more active sites and excellent electron transfer path for improving the electric conductivity as well as good mechanical properties. Supercapacitor devices based on these self-assembled nanocomposites showed high electrochemical capacitance (488.2 F g−1) at a discharge rate of 0.5 A g−1, which also could effectively improve electrochemical stability and rate performances.

Hierarchical Core/Shell NiCo2O4@NiCo2O4 Nanocactus Arrays with Dual-functionalities for High Performance Supercapacitors and Li-ion Batteries

We report the synthesis of three dimensional (3D) NiCo2O4@NiCo2O4 nanocactus arrays grown directly on a Ni current collector using a facile solution method followed by electrodeposition. They possess a unique 3D hierarchical core-shell structure with large surface area and dual-functionalities that can serve as electrodes for both supercapacitors (SCs) and lithium-ion batteries (LIBs). As the SC electrode, they deliver a remarkable specific capacitance of 1264 F g−1 at a current density of 2 A g−1 and ~93.4% of capacitance retention after 5000 cycles at 2 A g−1. When used as the anode for LIBs, a high reversible capacity of 925 mA h g−1 is achieved at a rate of 120 mA g−1 with excellent cyclic stability and rate capability. The ameliorating features of the NiCo2O4 core/shell structure grown directly on highly conductive Ni foam, such as hierarchical mesopores, numerous hairy needles and a large surface area, are responsible for the fast electron/ion transfer and large active sites which commonly contribute to the excellent electrochemical performance of both the SC and LIB electrodes.

Facile Synthesis of Graphene-Like Copper Oxide Nanofilms with Enhanced Electrochemical and Photocatalytic Properties in Energy and Environmental Applications

Novel graphene-like CuO nanofilms are grown on a copper foam substrate by in situ anodization for multifunctional applications as supercapacitor electrodes and photocatalysts for the degradation of dye pollutants. The as-prepared CuO consists of interconnected, highly crystalline, conductive CuO nanosheets with hierarchical open mesopores and a large surface area. The CuO nanofilms supported on a copper foam are employed as freestanding, binder-free electrodes for supercapacitors, which exhibit wonderful electrochemical performance with a large specific capacitance (919 F g(-1) at 1 A g(-1)), an excellent cycling stability (7% capacitance loss after 5000 cycles), and a good rate capability (748 F g(-1) at 30 A g(-1)). The porous CuO nanofilms also demonstrate excellent photocatalytic activities for degradation of methylene blue, with a degradation rate 99% much higher than 54% of the commercial CuO powders after 60 min. This excellent energy storage and photocatalytic performance of the graphene-like CuO nanofilms can open a new avenue for large-scale applications in energy and environmental fields.

Hierarchical porous CuO nanostructures with tunable properties for high performance supercapacitors

We report a novel, low-cost strategy to synthesize copper oxide (CuO) nanostructures as high-performance supercapacitor electrodes using an alkaline solution oxidation method. The structure, morphological features, surface area and pore size distribution of the products are tuned using different types of surfactants. The CuO electrode obtained from sodium dodecyl sulfate (SDS) presents the best electrochemical performance due to the synergies arising from the large surface area and pore volume created by the ultrathin nanoleaves constituting the flower-shape nanostructure. The electrode delivers a remarkable specific capacitance of 520 F g−1 at 1 A g−1 and a high rate capacitance of 405 F g−1 at 60 A g−1 with more than 95% Coulombic efficiency after 3500 cycles.

Solution growth of NiO nanosheets supported on Ni foam as high-performance electrodes for supercapacitors

Well-aligned nickel oxide (NiO) nanosheets with the thickness of a few nanometers supported on a flexible substrate (Ni foam) have been fabricated by a hydrothermal approach together with a post-annealing treatment. The three-dimensional NiO nanosheets were further used as electrode materials to fabricate supercapacitors, with high specific capacitance of 943.5, 791.2, 613.5, 480, and 457.5 F g-1 at current densities of 5, 10, 15, 20, and 25 A g-1, respectively. The NiO nanosheets combined well with the substrate. When the electrode material was bended, it can still retain 91.1% of the initial capacitance after 1,200 charging/discharging cycles. Compared with Co3O4 and NiO nanostructures, the specific capacitance of NiO nanosheets is much better. These characteristics suggest that NiO nanosheet electrodes are promising for energy storage application with high power demands.

Cost-effective CuO nanotube electrodes for energy storage and non-enzymatic glucose detection

A facile strategy is developed for the in situ synthesis of low-cost, freestanding, binder-free CuO nanotube electrodes on a conducting Cu foil, totally eliminating non-active materials and extra processing steps. The synergy arising from the ameliorating structure, such as high porosity, large surface area and the ability for fast electron transport, make CuO nanotube electrodes ideal multi-functional electrochemical devices with excellent pseudocapacitive performance and a remarkable sensitivity to glucose for use as non-enzymatic biosensors (NGBs). The electrodes deliver remarkable specific capacitances of 442 and 358 F g−1 at current densities of 1 and 20 A g−1, respectively. The capacitance loss after 5000 cycles is only 4.6% at 1 A g−1, reflecting the excellent cyclic stability of the supercapacitor. The biosensor made from CuO nanotubes presents an extremely rapid and accurate response to glucose in blood in a wide, linear range of 100 μM to 3 mM, with a sensitivity of 2231 μA mM−1 cm−2. These interesting discoveries may open up the potential for the further development of new, multi-functional electrodes possessing both excellent energy storage and biosensory capabilities.

Seed-assisted synthesis of Co3O4@α-Fe2O3 core–shell nanoneedle arrays for lithium-ion battery anode with high capacity

A novel hierarchical Co3O4@α-Fe2O3 core–shell nanoneedle array (Co3O4@α-Fe2O3 NAs) on nickel foam substrate is synthesized successfully by a stepwise, seed-assisted, hydrothermal approach. This composite nanostructure serving as an anode material for lithium-ion batteries (LIBs) is advantageous in providing large interfacial area for lithium insertion/extraction and short diffusion pathways for electronic and ionic transport. The results show that a high initial discharge capacity of 1963 mA h g−1 at 120 mA g−1 was obtained by using these hierarchical Co3O4@α-Fe2O3 NAs heterostructures as an anode, and is retained at 1045 mA h g−1 after 100 cycles, better than that of pure Co3O4 nanoneedle arrays (Co3O4 NAs) and α-Fe2O3 film grown under similar conditions, indicating a positive synergistic effect of the material and structural hybridization on the enhancement of the electrochemical properties. The fabrication strategy presented here is facile, cost-effective, and scalable, which opens new avenues for the design of optimal composite electrode materials with improved performance.

Hierarchical multi-villous nickel–cobalt oxide nanocyclobenzene arrays: morphology control and electrochemical supercapacitive behaviors

Binary metal oxides have been regarded as ideal potential anode materials which display electrochemical performances which surpass those of single metal oxides, in terms of reversible capacity, structural stability and electronic conductivity. In this work, hierarchical multi-villous NiCo2O4 nanocyclobenzene arrays (NCAs) on nickel foam have been fabricated by a simple hydrothermal approach combined with a post-annealing treatment. Such unique nanoarchitectures exhibit a remarkable electrochemical performance, with high capacitance and a desirable cycle lifespan at high rates. When evaluated as an electrode material for supercapacitors, the NCAs supported on nickel foam are able to deliver a high specific capacitance of 1545 F g−1 at a current density of 5 A g−1 in 2 M KOH aqueous solution. In addition, the composite electrode shows excellent mechanical behavior and long-term cyclic stability (93.7% capacitance retention after 5000 cycles). All in all, the fabrication strategy presented herein is simple, cost-effective and scalable, which opens new avenues for the large scale application of these novel materials in energy storage.