Deyang Zhang

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.

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.

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.

Self-assembly of mesoporous ZnCo2O4 nanomaterials: density functional theory calculation and flexible all-solid-state energy storage

Ternary spinel metal oxide ZnCo2O4 with Co2+ at the tetrahedral sites (8a) in the spinel Co3O4 replaced by Zn2+ is promising in energy storage and an economical way to fabricate low-toxicity nanostructured ZnCo2O4 is described. Theoretical calculation confirms the rationality of the experimental scheme and elucidates the underlying reason for the increased band gap. The high electrochemical activity and excellent stability of the ZnCo2O4 NFs//ZnCo2O4 NW symmetrical device suggest large potential for energy storage applications. The fabricated device boasts a capacity of 220.6 F g−1 at a current density of 2 A g−1 and long-term cycling stability with 67.5% of the capacitance retained after 8000 cycles. The maximum energy density of 60.04 W h kg−1 at a power density of 1.4 kW kg−1 and a power density of 7 kW kg−1 at an energy density of 23.72 W h kg−1 are achieved at an operating voltage of 1.4 V. This combined experimental and theoretical study provides insights into the design and controllable preparation of nanomaterials for energy storage applications.

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.

High-performance asymmetrical supercapacitor composed of rGO-enveloped nickel phosphite hollow spheres and N/S co-doped rGO aerogel

An asymmetrical supercapacitor (ASC), comprising reduced graphene oxide (rGO)-encapsulated nickel phosphite hollow microspheres (NPOH-0.5@rGO) as positive electrode, and porous nitrogen/sulfur co-doped rGO aerogel (NS-3D rGO) as negative electrode has been prepared. The NPOH-0.5@rGO electrode combines the advantages of the NPOH hollow microspheres and the conductive rGO layers giving rise to a large specific capacitance, high cycling reversibility, and excellent rate performance. The NS-3D rGO electrode with abundant porosity and active sites promotes electrolyte infiltration and broadens the working voltage range. The ASC (NPOH-0.5@rGO//NS-3D rGO) shows a maximum voltage of up to 1.4 V, outstanding cycling ability (capacitance retention of 95.5% after 10,000 cycles), and excellent rate capability (capacitance retention of 77% as the current density is increased ten times). The ASC can light up an light-emitting diodes (LED) for more than 20 min after charging for 20 s. The fabrication technique and device architecture can be extended to other active oxide and carbon-based materials for next-generation high-performance electrochemical storage devices.

Amorphous red phosphorus anchored on carbon nanotubes as high performance electrodes for lithium ion batteries

Red phosphorus-carbon nanotube (P@CNT) composites were synthesized as anodes for advanced lithium ion batteries via a facile solution-based method at room temperature. In these composites, the entangled P@CNT nanostructure reduced the aggregation of both components and allowed their complete utilization in a synergetic manner. The highly conductive and porous CNT framework, along with the nanoscale red P particles intimately anchored on the CNT surface, conferred the composite with excellent ion/electron transport properties. Volume expansion within the red P particles was mitigated by their amorphous and nanoscale features, which can be well buffered by the soft CNTs, therefore maintaining an integrated electrode structure during cycling. When used as an anode in lithium ion batteries, the composite exhibited a reversible capacity of 960 mAh·g−1 (based on the overall weight of the composite) after 120 cycles at 200 mA·g−1. The composite also delivered excellent high-rate capability with capacities of 886, 847, and 784 mAh·g−1 at current densities of 2,000, 4,000, and 10,000 mA·g−1, respectively, which reveals its potential as a high performance anode for lithium ion batteries.