Qiaobao Zhang

A hydrolysis-hydrothermal route for the synthesis of ultrathin LiAlO2-inlaid LiNi0.5Co0.2Mn0.3O2 as a high-performance cathode material for lithium ion batteries

We present a novel hydrolysis-hydrothermal approach to using lithium residues on the surface of LiNi0.5Co0.2Mn0.3O2 as raw materials to synthesize ultrathin LiAlO2-inlaid LiNi0.5Co0.2Mn0.3O2 cathode materials, for the first time. High-resolution transmission electron microscopy (HRTEM) and fast Fourier transform (FFT) analysis indicate that the spherical particles of LiNi0.5Co0.2Mn0.3O2 are completely coated by crystalline LiAlO2 with an average thickness of 4 nm; cross-section SEM and corresponding EDS results confirm that partial Al3+ ions are doped into the bulk LiNi0.5Co0.2Mn0.3O2 with gradient distribution. Electrochemical tests show that the modified materials exhibit excellent reversible capacity, enhanced cyclability and rate properties, combining with higher Li ion diffusion coefficient and better differential capacity profiles compared with those of the pristine material. Particularly, the 2 mol% LiAlO2-inlaid sample maintains 202 mA h g−1 with 91% capacity retention after 100 high-voltage cycles (with 4.6 V charge cut-off) at 1 C. The enhanced electrochemical performance can be ascribed to the removal of lithium residues and the unique LiAlO2-inlaid architecture. The removal of lithium residues are believed to decrease side reactions between Li2O and the electrolyte, while the unique LiAlO2-inlaid architecture can buffer the volume change of core and shell during cycles, enhance the composites lithium ion diffusion ability and inherit the advantages of LiAlO2 coating and doping.

High-Performance Energy Storage and Conversion Materials Derived from a Single Metal–Organic Framework/Graphene Aerogel Composite

Metal oxides and carbon-based materials are the most promising electrode materials for a wide range of low-cost and highly efficient energy storage and conversion devices. Creating unique nanostructures of metal oxides and carbon materials is imperative to the development of a new generation of electrodes with high energy and power density. Here we report our findings in the development of a novel graphene aerogel assisted method for preparation of metal oxide nanoparticles (NPs) derived from bulk MOFs (Co-based MOF, Co(mIM)2 (mIM = 2-methylimidazole). The presence of cobalt oxide (CoOx) hollow NPs with a uniform size of 35 nm monodispersed in N-doped graphene aerogels (NG-A) was confirmed by microscopic analyses. The evolved structure (denoted as CoOx/NG-A) served as a robust Pt-free electrocatalyst with excellent activity for the oxygen reduction reaction (ORR) in an alkaline electrolyte solution. In addition, when Co was removed, the resulting nitrogen-rich porous carbon-graphene composite electrode (denoted as C/NG-A) displayed exceptional capacitance and rate capability in a supercapacitor. Further, this method is readily applicable to creation of functional metal oxide hollow nanoparticles on the surface of other carbon materials such as graphene and carbon nanotubes, providing a good opportunity to tune their physical or chemical activities.

Hierarchical Mesoporous Zinc–Nickel–Cobalt Ternary Oxide Nanowire Arrays on Nickel Foam as High-Performance Electrodes for Supercapacitors

Nickel foam supported hierarchical mesoporous Zn-Ni-Co ternary oxide (ZNCO) nanowire arrays are synthesized by a simple two-step approach including a hydrothermal method and subsequent calcination process and directly utilized for supercapacitive investigation for the first time. The nickel foam supported hierarchical mesoporous ZNCO nanowire arrays possess an ultrahigh specific capacitance value of 2481.8 F g(-1) at 1 A g(-1) and excellent rate capability of about 91.9% capacitance retention at 5 A g(-1). More importantly, an asymmetric supercapacitor with a high energy density (35.6 Wh kg(-1)) and remarkable cycle stability performance (94% capacitance retention over 3000 cycles) is assembled successfully by employing the ZNCO electrode as positive electrode and activated carbon as negative electrode. The remarkable electrochemical behaviors demonstrate that the nickel foam supported hierarchical mesoporous ZNCO nanowire array electrodes are highly desirable for application as advanced supercapacitor electrodes.

Facile large-scale synthesis of vertically aligned CuO nanowires on nickel foam: growth mechanism and remarkable electrochemical performance

Large-scale vertically aligned single crystalline CuO nanowires grown directly on nickel foam have been successfully fabricated by facile thermal oxidation of e-beam evaporated Cu thin films in static air. A growth mechanism based on stress-driven grain-boundary diffusion associated with surface diffusion of Cu atoms/ions is proposed to explain the formation of CuO nanowires on nickel foam. The resulting CuO nanowires are directly used as binder- and conductive-agent-free electrodes for lithium ion batteries and demonstrate remarkable electrochemical performance with excellent capacity retention and high rate capability on cycling. It can deliver a stable reversible capacity of 692 mA h g−1 after 50 cycles at a current density of 100 mA g−1 and maintain a high reversible capacity of 445 mA h g−1 over 600 cycles with 95.7% capacity retention even at a high current density of 1000 mA g−1. Such superior electrochemical performance of the electrodes made by directly growing electro-active aligned CuO nanowires on conductive 3D nickel foam makes them have very promising applications in high-performance lithium ion batteries.

A tailored double perovskite nanofiber catalyst enables ultrafast oxygen evolution

Rechargeable metal–air batteries and water splitting are highly competitive options for a sustainable energy future, but their commercialization is hindered by the absence of cost-effective, highly efficient and stable catalysts for the oxygen evolution reaction. Here we report the rational design and synthesis of a double perovskite PrBa0.5Sr0.5Co1.5Fe0.5O5+δ nanofiber as a highly efficient and robust catalyst for the oxygen evolution reaction. Co-doping of strontium and iron into PrBaCo2O5+δ is found to be very effective in enhancing intrinsic activity (normalized by the geometrical surface area, ∼4.7 times), as validated by electrochemical measurements and first-principles calculations. Further, the nanofiber morphology enhances its mass activity remarkably (by ∼20 times) as the diameter is reduced to ∼20 nm, attributed to the increased surface area and an unexpected intrinsic activity enhancement due possibly to a favourable eg electron filling associated with partial surface reduction, as unravelled from chemical titration and electron energy-loss spectroscopy.

Growth of Hierarchical 3D Mesoporous NiSix/NiCo2O4 Core/Shell Heterostructures on Nickel Foam for Lithium‐Ion Batteries

We demonstrate the facile and well-controlled design and fabrication of heterostructured and hierarchical 3D mesoporous NiSix /NiCo2 O4 core/shell nanowire arrays on nickel foam through a facile chemical vapor deposition (CVD) technique combined with a simple but powerful chemical bath deposition (CBD) technique. The smart hybridization of NiCo2 O4 and NiSix nanostructures results in an intriguing mesoporous hierarchical core/shell nanowire-array architecture. The nanowire arrays demonstrate enhanced electrochemical performance as binder- and conductive-agent-free electrodes for lithium ion batteries (LIBs) with excellent capacity retention and high rate capability on cycling. The electrodes can maintain a high reversible capacity of 1693 mA h g(-1) after 50 cycles at 20 mA g(-1) . Given the outstanding performance and simple, efficient, cost-effective fabrication, we believe that these 3D NiSix /NiCo2 O4 core/shell heterostructured arrays have great potential application in high-performance LIBs.

Harnessing the concurrent reaction dynamics in active Si and Ge to achieve high performance lithium-ion batteries

Advanced composite electrodes containing multiple active components are often used in lithium-ion batteries for practical applications. The performance of such heterogeneous composite electrodes can in principle be enhanced by tailoring the concurrent reaction dynamics in multiple active components for promoting their collective beneficial effects. However, the potential of this design principle has remained uncharted to date. Here we develop a composite anode of Cu/Si/Ge nanowire arrays, where each nanowire consists of a core of Cu segments and a Si/Ge bilayer shell. This unique electrode architecture exhibited a markedly improved electrochemical performance over the reference Cu/Si systems, demonstrating a stable capacity retention (81% after 3000 cycles at 2C) and doubled specific capacity at a rate of 16C (1C = 2 A g−1). By using in situ transmission electron microscopy and electrochemical testing, we unravel a novel reaction mechanism of dynamic co-lithiation/co-delithiation in the active Si and Ge bilayer, which is shown to effectively alleviate the electrochemically induced mechanical degradation and thus greatly enhance the long-cycle stability of the electrode. Our findings offer insights into a rational design of high-performance lithium-ion batteries via exploiting the concurrent reaction dynamics in the multiple active components of composite electrodes.

Approaching the ideal elastic strain limit in silicon nanowires

Single-crystalline silicon nanowires can be reversibly stretched above 10% elastic strain at room temperature. Achieving high elasticity for silicon (Si) nanowires, one of the most important and versatile building blocks in nanoelectronics, would enable their application in flexible electronics and bio-nano interfaces. We show that vapor-liquid-solid–grown single-crystalline Si nanowires with diameters of ~100 nm can be repeatedly stretched above 10% elastic strain at room temperature, approaching the theoretical elastic limit of silicon (17 to 20%). A few samples even reached ~16% tensile strain, with estimated fracture stress up to ~20 GPa. The deformations were fully reversible and hysteresis-free under loading-unloading tests with varied strain rates, and the failures still occurred in brittle fracture, with no visible sign of plasticity. The ability to achieve this “deep ultra-strength” for Si nanowires can be attributed mainly to their pristine, defect-scarce, nanosized single-crystalline structure and atomically smooth surfaces. This result indicates that semiconductor nanowires could have ultra-large elasticity with tunable band structures for promising “elastic strain engineering” applications.

Highly exothermic and superhydrophobic Mg/fluorocarbon core/shell nanoenergetic arrays.

Mg/fluorocarbon core/shell nanoenergetic arrays are prepared onto silicon substrate, with Mg nanorods as the core and fluorocarbon as the shell. Mg nanorods are deposited by the glancing angle deposition technique, and the fluorocarbon layer is then prepared as a shell to encase the Mg nanorods by the magnetron sputtering deposition process. Scanning electron microscopy and transmission electron microscopy show the core/shell structure of the Mg/fluorocarbon arrays. X-ray energy-dispersive spectroscopy, X-ray diffraction, and Fourier transform infrared spectroscopy are used to characterize the structural composition of the Mg/fluorocarbon. It is found that the as-prepared fluorocarbon layer consists of shorter molecular chains compared to that of bulk polytetrafluoroethylene, which is proven beneficial to the low onset reaction temperature of Mg/fluorocarbon. Water contact angle test demonstrates the superhydrophobicity of the Mg/fluorocarbon arrays, and a static contact angle as high as 162° is achieved. Thermal analysis shows that the Mg/fluorocarbon material exhibits a very low onset reaction temperature of about 270 °C as well as an ultrahigh heat of reaction approaching 9 kJ/g. A preliminary combustion test reveals rapid combustion wave propagation, and a convective mechanism is adopted to explain the combustion behaviors.

In Situ Synthesis of CuO and Cu Nanostructures with Promising Electrochemical and Wettability Properties

A strategy is presented for the in situ synthesis of single crystalline CuO nanorods and 3D CuO nanostructures, ultra-long Cu nanowires and Cu nanoparticles at relatively low temperature onto various substrates (Si, SiO2 , ITO, FTO, porous nickel, carbon cotton, etc.) by one-step thermal heating of copper foam in static air and inert gas, respectively. The density, particle sizes and morphologies of the synthesized nanostructures can be effectively controlled by simply tailoring the experimental parameters. A compressive stress based and subsequent structural rearrangements mechanism is proposed to explain the formation of the nanostructures. The as-prepared CuO nanostructures demonstrate promising electrochemical properties as the anode materials in lithium-ion batteries and also reversible wettability. Moreover, this strategy can be used to conveniently integrate these nanostructures with other nanostructures (ZnO nanorods, Co3 O4 nanowires and nanowalls, TiO2 nanotubes, and Si nanowires) to achieve various hybrid hierarchical (CuO-ZnO, CuO-Co3 O4 , CuO-TiO2 , CuO-Si) nanocomposites with promising properties. This strategy has the potential to provide the nano society with a general way to achieve a variety of nanostructures.