Yongsong Luo

Seed-assisted synthesis of highly ordered TiO2@α-Fe2O3 core/shell arrays on carbon textiles for lithium-ion battery applications

Highly ordered TiO2@α-Fe2O3 core/shell arrays on carbon textiles (TFAs) have been fabricated by a stepwise, seed-assisted, hydrothermal approach and further investigated as the anode materials for Li-ion batteries (LIBs). This composite TFA anode exhibits superior high-rate capability and outstanding cycling performance. The specific capacity of the TFAs is much higher than that of pristine carbon textiles (CTs) and TiO2 nanorod arrays on carbon textiles (TRAs), indicating a positive synergistic effect of the material and structural hybridization on the enhancement of the electrochemical properties. This composite nanostructure not only provides large interfacial area for lithium insertion/extraction but should also be beneficial in reducing the diffusion pathways for electronic and ionic transport, leading to the improved capacity retention on cycling even at high discharge–charge rates. It is worth emphasizing that the CT substrates also present many potential virtues for LIBs as flexible electronic devices owing to the stretchable, lightweight and biodegradable properties. The fabrication strategy presented here is facile, cost-effective, and scalable, which opens new avenues for the design of optimal composite electrode materials for high performance LIBs.

Self-assembly of well-ordered whisker-like manganese oxide arrays on carbon fiber paper and its application as electrode material for supercapacitors

Self-assembled well-ordered whisker-like manganese dioxide (MnO2) arrays on carbon fiber paper (MOWAs) were synthesized via a simple in situ redox replacement reaction between potassium permanganate (KMnO4) and carbon fiber paper (CFP) without any other oxidant or reductant addition. The CFP serves as not only a sacrificial reductant and converts aqueous permanganate (MnO4−) to insoluble MnO2 in this reaction, but also a substrate material and guarantees MnO2 deposition on the surface. The electrochemical properties were examined by cyclic voltammograms (CV), galvanostatic charge/discharge, and electrochemical impedance spectroscopy (EIS) in a three-electrode cell. According to the CV results, the ordered MOWAs yield high-capacitance performance with specific capacitance up to 274.1 F g−1 and excellent long cycle-life property with 95% of its specific capacitance kept after 5000 cycles at the current density of 0.1 A g−1. The high-performance hybrid composites result from a synergistic effect of large surface area and high degree of ordering of the ultrathin layer of MnO2 nanowhisker arrays, combined with the flexible CFP substrate and can offer great promise in large-scale energy storage device applications.

Controlled synthesis of hierarchical graphene-wrapped TiO2@Co3O4 coaxial nanobelt arrays for high-performance lithium storage

As one of the most important research areas in lithium-ion batteries (LIBs), well-designed nanostructures have been regarded as key for solving problems such as lithium ion diffusion, the collection and transport of electrons, and the large volume changes during cycling processes. Here, hierarchical graphene-wrapped TiO2@Co3O4 coaxial nanobelt arrays (G-TiO2@Co3O4 NBs) have been fabricated and further investigated as the electrode materials for LIBs. The results show that the yielded G-TiO2@Co3O4 NBs possess a high reversible capacity, an outstanding cycling performance, and superior rate capability compared to TiO2 and TiO2@Co3O4 nanobelt array (TiO2@Co3O4 NBs) electrodes. The core–shell TiO2@Co3O4 NBs may contain many cavities and provide more extra spaces for lithium ion storage. The introduction of graphene into nanocomposite electrodes is favorable for increasing their electrical conductivity and flexibility. The integration of hierarchical core–shell nanobelt arrays and conducting graphene may induce a positive synergistic effect and contribute to the enhanced electrochemical performances of the electrode. The fabrication strategy presented here is facile, cost-effective, and can offer a new pathway for large-scale energy storage device applications.

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.

Scalable synthesis of graphene-wrapped Li4Ti5O12 dandelion-like microspheres for lithium-ion batteries with excellent rate capability and long-cycle life

A three-dimensional dandelion-like Li4Ti5O12@graphene microsphere electrode is designed by using a simple and scalable solution fabrication process. The graphene nanosheets are incorporated into the porous dandelion-like Li4Ti5O12 microspheres homogenously, which provide a highly conductive network for electron transportation. When tested as an anode for Li-ion batteries, the dandelion-like Li4Ti5O12@graphene composite with 3 wt% graphene exhibits excellent rate capabilities and superior cycle life between 0.01 and 3.0 V. The capacities of Li4Ti5O12@graphene (3 wt%) reach 206 mA h g−1 after 500 cycles between 0.01 and 3.0 V and 166 mA h g−1 after 100 cycles between 0.7 and 3.0 V at a current density of 0.12 A g−1, respectively. In addition, Li4Ti5O12-based anode materials at lower voltage can offer a higher cell voltage and discharge capacity for lithium-ion batteries. Hence, it is significant to study the electrochemical behaviors of the Li4Ti5O12-based anode in a wide voltage range of 0.01–3.0 V. This facile and scalable method for Li4Ti5O12@graphene composites represents an effective strategy to develop advanced electrochemical energy storage systems with long cycle life and high rate performance.

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 CuS microspheres integrated with carbon nanotubes for high-performance supercapacitors.

Carbon nanotubes (CNTs) incorporated porous 3-dimensional (3D) CuS microspheres have been successfully synthesized via a simple refluxing method assisted by PVP. The composites are composed of flower-shaped CuS secondary microspheres, which in turn are assembled with primary nanosheets of 15–30 nm in thickness and fully integrated with CNT. The composites possess a large specific surface area of 189.6 m2 g−1 and a high conductivity of 0.471 S cm−1. As electrode materials for supercapacitors, the nanocomposites show excellent cyclability and rate capability and deliver an average reversible capacitance as high as 1960 F g−1 at a current density of 10 mA cm−2 over 10000 cycles. The high electrochemical performance can be attributed to the synergistic effect of CNTs and the unique microstructure of CuS. The CNTs serve as not only a conductive agent to accelerate the transfer of electrons in the composites, but also as a buffer matrix to restrain the volume change and stabilize the electrode structure during the charge/discharge process. The porous structure of CuS also helps to stabilize the electrode structure and facilitates the transport for electrons.