Zhi Xu

High-performance supercapacitor and lithium-ion battery based on 3D hierarchical NH4F-induced nickel cobaltate nanosheet–nanowire cluster arrays as self-supported electrodes

A facile hydrothermal method is developed for large-scale production of three-dimensional (3D) hierarchical porous nickel cobaltate nanowire cluster arrays derived from nanosheet arrays with robust adhesion on Ni foam. Based on the morphology evolution upon reaction time, a possible formation process is proposed. The role of NH4F in formation of the structure has also been investigated based on different NH4F amounts. This unique structure significantly enhances the electroactive surface areas of the NiCo2O4 arrays, leading to better interfacial/chemical distributions at the nanoscale, fast ion and electron transfer and good strain accommodation. Thus, when it is used for supercapacitor testing, a specific capacitance of 1069 F g(-1) at a very high current density of 100 A g(-1) was obtained. Even after more than 10,000 cycles at various large current densities, a capacitance of 2000 F g(-1) at 10 A g(-1) with 93.8% retention can be achieved. It also exhibits a high-power density (26.1 kW kg(-1)) at a discharge current density of 80 A g(-1). When used as an anode material for lithium-ion batteries (LIBs), it presents a high reversible capacity of 976 mA h g(-1) at a rate of 200 mA g(-1) with good cycling stability and rate capability. This array material is rarely used as an anode material. Our results show that this unique 3D hierarchical porous nickel cobaltite is promising for electrochemical energy applications.

Porous α-Fe2O3 nanosphere-based H2S sensor with fast response, high selectivity and enhanced sensitivity

Porous α-Fe2O3 nanospheres have been successfully prepared by a microwave-assisted hydrothermal method coupled with an annealing technique. The porous α-Fe2O3 nanosphere-based sensor presented a fast response, enhanced sensitivity and excellent selectivity towards H2S due to its intrinsic characteristics, porous structure and nanoscale size.

Mesoporous SnO2@carbon core?shell nanostructures with superior electrochemical performance for lithium ion batteries

SnO2@carbon nanostructure composites are prepared by a simple hydrothermal method. The composite exhibits unique structure, which consists of a mesoporous SnO2 core assembled of very small nanoparticles and a carbon shell with 10 nm thickness. The mesoporous SnO2@carbon core-shell nanostructures manifest superior electrochemical performance as an anode material for lithium ion batteries. The reversible specific capacity of the composite is about 908 mAh g(-1) for the first cycle and it can retain about 680 mAh g(-1) after 40 charge/discharge cycles at a current density of 0.3 C. Moreover, it shows excellent rate capability even at the high rate of 4.5 C. The enhanced performance was attributed to the mesoporous structure and a suitable carbon coating.

WO3 nanoparticles decorated on both sidewalls of highly porous TiO2 nanotubes to improve UV and visible-light photocatalysis

The hybrid structure of nanoparticle-decorated nanotubes has the advantage of both large specific surface areas of nanoparticles and anisotropic properties of nanotubes, which is desirable for many applications. In this study, WO3 nanoparticles decorated on highly porous TiO2 nanotubes along both internal and external sidewalls (WO3@TiO2@WO3 heterostructures) were synthesized through emulsion electrospinning, thermal evaporation, and thermal annealing. The WO3@TiO2@WO3 heterostructures had large specific surface areas, high porous structure and excellent interface (between WO3 nanoparticles and TiO2 nanotubes). Three other samples, TiO2 nanofibers, TiO2 nanotubes, and TiO2 nanofibers decorated by WO3 nanoparticles, were prepared in order to compare with the WO3@TiO2@WO3 heterostructures for photocatalysis with both UV and visible light irradiation. The new material (WO3@TiO2@WO3 heterostructures) had a wide range of light absorption and demonstrated the best photocatalytic performance. The possible growth mechanism and reasons for high photocatalysis are discussed in detail.

Bacteria Absorption-Based Mn2P2O7-Carbon@Reduced Graphene Oxides for High-Performance Lithium-Ion Battery Anodes.

The development of freestanding flexible electrodes with high capacity and long cycle-life is a central issue for lithium-ion batteries (LIBs). Here, we use bacteria absorption of metallic Mn(2+) ions to in situ synthesize natural micro-yolk-shell-structure Mn2P2O7-carbon, followed by the use of vacuum filtration to obtain Mn2P2O7-carbon@reduced graphene oxides (RGO) papers for LIBs anodes. The Mn2P2O7 particles are completely encapsulated within the carbon film, which was obtained by carbonizing the bacterial wall. The resulting carbon microstructure reduces the electrode-electrolyte contact area, yielding high Coulombic efficiency. In addition, the yolk-shell structure with its internal void spaces is ideal for sustaining volume expansion of Mn2P2O7 during charge/discharge processes, and the carbon shells act as an ideal barrier, limiting most solid-electrolyte interphase formation on the surface of the carbon films (instead of forming on individual particles). Notably, the RGO films have high conductivity and robust mechanical flexibility. As a result of our combined strategies delineated in this article, our binder-free flexible anodes exhibit high capacities, long cycle-life, and excellent rate performance.

Hierarchical SnO2 Nanospheres: Bio-inspired Mineralization, Vulcanization, Oxidation Techniques, and the Application for NO Sensors

Controllable synthesis and surface engineering of nanomaterials are of strategic importance for tailoring their properties. Here, we demonstrate that the synthesis and surface adjustment of highly stable hierarchical of SnO2 nanospheres can be realized by biomineralization, vulcanization and oxidation techniques. Furthermore, we reveal that the highly stable hierarchical SnO2 nanospheres ensure a remarkable sensitivity towards NO gas with fast response and recovery due to their high crystallinity and special structure. Such technique acquiring highly stable hierarchical SnO2 nanospheres offers promising potential for future practical applications in monitoring the emission from waste incinerators and combustion process of fossil fuels.

Potassium‐Based Dual Ion Battery with Dual‐Graphite Electrode

A potassium ion battery has potential applications for large scale electric energy storage systems due to the abundance and low cost of potassium resources. Dual graphite batteries, with graphite as both anode and cathode, eliminate the use of transition metal compounds and greatly lower the overall cost. Herein, combining the merits of the potassium ion battery and dual graphite battery, a potassium-based dual ion battery with dual-graphite electrode is developed. It delivers a reversible capacity of 62 mA h g-1 and medium discharge voltage of ≈3.96 V. The intercalation/deintercalation mechanism of K+ and PF6- into/from graphite is proposed and discussed in detail, with various characterizations to support.

A hyperaccumulation pathway to three-dimensional hierarchical porous nanocomposites for highly robust high-power electrodes

Natural plants consist of a hierarchical architecture featuring an intricate network of highly interconnected struts and channels that not only ensure extraordinary structural stability, but also allow efficient transport of nutrients and electrolytes throughout the entire plants. Here we show that a hyperaccumulation effect can allow efficient enrichment of selected metal ions (for example, Sn2+, Mn2+) in the halophytic plants, which can then be converted into three-dimensional carbon/metal oxide (3DC/MOx) nanocomposites with both the composition and structure hierarchy. The nanocomposites retain the 3D hierarchical porous network structure, with ultrafine MOx nanoparticles uniformly distributed in multi-layers of carbon derived from the cell wall, cytomembrane and tonoplast. It can simultaneously ensure efficient electron and ion transport and help withstand the mechanical stress during the repeated electrochemical cycles, enabling the active material to combine high specific capacities typical of batteries and the cycling stability of supercapacitors.

Highly sensitive humidity sensors based on Sb-doped ZnSnO3 nanoparticles with very small sizes

Highly sensitive and fast responding humidity sensors were fabricated based on Sb-doped ZnSnO3 fine nanoparticles, which were synthesized via a dual-hydrolysis-assisted liquid precipitation reaction and subsequent hydrothermal procedure. The nanoparticles were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and UV-visible spectrophotometry. The results demonstrated that ZnSnO3 nanocubes evolved into Sb-doped ZnSnO3 nanoparticles with doping by Sb. This evolution facilitated their application in humidity sensing. At room temperature, the resistance of the humidity sensors based on Sb-doped ZnSnO3 at 30% relative humidity (RH) was 130 times greater than that in air with 85% RH. The response and recovery times were 7.5 s and 33.6 s, respectively, when the sensors were switched between 30% and 85% RH. These results are much better than those reported so far. The present results may present new opportunities for the practical application of high-performance humidity sensors at room temperature.

Large-scale production of silicon nanoparticles@graphene embedded in nanotubes as ultra-robust battery anodes

The nanosized silicon for lithium-ion batteries (LIBs) is mainly limited by cracking and pulverization caused by the large volume change during deep cycles. Here, we demonstrated a commercial viability (scalable synthesis) of Si nanoparticles@graphene encapsulated in titanium dioxide nanotubes (Si@G@TiO2NTs) or carbon nanotubes (Si@G@CNTs) for the next generation of high-energy battery anodes. The nanotubes can not only provide strong protection and sufficient void space to buffer the huge volume expansion of Si nanoparticles during the charge/discharge process, but also enforce a most solid-electrolyte interphase to form on the outer surface of the nanotube instead of on individual Si nanoparticles, leading to ultrahigh coulombic efficiency and excellent cycling stability. The obtained Si@G@TiO2NT and Si@G@CNT electrodes showed a high reversible capacity of 1919.2 mA h g−1 (1.02 mA h cm−2) after 800 cycles and 2242.2 mA h g−1 (1.19 mA h cm−2) after 1000 cycles (>1 year) at the constant current density of 500 mA g−1, respectively. Furthermore, both Si@G@TiO2NT and Si@G@CNT electrodes presented superior average coulombic efficiency more than 99.9% during the whole cycling process.