Yuejiao Chen

Facile synthesis of uniform mesoporous ZnCo2O4 microspheres as a high-performance anode material for Li-ion batteries

In this paper, three dimensional (3D) uniform ZnCo-glycolate precursor microspheres composed of nanosheets were successfully synthesized via a facile ethylene glycol (EG) mediated solvothermal method. Through moderate calcination of the as-synthesized ZnCo-glycolate precursor, they could be converted into uniform mesoporous ZnCo2O4 microspheres with surrounding nanoparticles. The obtained samples were systematically characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and N2 adsorption–desorption. The results demonstrated that tuning of the surface texture and the pore size of the ZnCo2O4 products were very significant in Li-ion batteries (LIBs). The uniform mesoporous ZnCo2O4 microspheres exhibit excellent high specific capacity, superior rate capability, and enhanced cycling performance. At a current density of 100 mA g−1, the uniform mesoporous ZnCo2O4 microspheres exhibited excellent initial specific capacity of 1332 mAh g−1. The capacity maintain at 721 mAh g−1 after 80 discharge–charge cycles. Even as current density reached to 1000 mA g−1, the initial specific capacity still showed 937 mAh g−1 and the discharge capacity of 432 mAh g−1 was retained after 40 cycles.

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.

A green and fast strategy for the scalable synthesis of Fe2O3/graphene with significantly enhanced Li-ion storage properties

In this study, we proposed and demonstrated an environmentally friendly and effective methodology to prepare Fe2O3/graphene composites. The essence of this method was that ferrous ions could serve as both reductant and the iron source for Fe2O3, which is greener and more facile than the preparation methods for other iron oxide/graphene composites. As anode materials for lithium ion batteries, Fe2O3/graphene composites achieved high reversible capacities of about 800 mA h g−1 after 100 cycles at a charge–discharge rate of 0.2 C. Moreover, they delivered rate capacities as high as 420 mA h g−1 at a rate of 5 C. Both the cycling performance and rate capacities of Fe2O3/graphene composites were better than those of commercial Fe2O3 and its graphene composites. The improved performance toward the storage of Li+ was ascribed to graphene sheets, which acted as volume buffers and electron conductors. We believe that the strategy of preparing Fe2O3/graphene composites proposed by us may open a new way for the synthesis of metal oxide/graphene for various potential purposes.

Hierarchical Mo-decorated Co3O4 nanowire arrays on Ni foam substrates for advanced electrochemical capacitors

Herein, we report the synthesis of hierarchical small quantity Mo-decorated Co3O4 nanowire arrays on nickel foam substrates by a powerful two-step solution-based method. The “oriented attachment” and “self-assembly” crystal growth mechanisms are proposed to discuss the growth of the Mo-decorated Co3O4 heterostructures. This heterostructure material with a high specific surface areas provides an extraordinarily high area capacitance of 3.5 F cm−2 at a current density of 17 mA cm−2 (∼2000 F g−1 at a current density of 10 A g−1) in the initial cycles, compared with a bare Co3O4 nanowire array electrode with 2.2 F cm−2 at 17 mA cm−2 (∼1257 F g−1 at 10 A g−1), exhibiting a significant increase in the capacitance of around 60%. When the current density of the hybrid array is increased by 20 times (1.7 to 34 mA cm−2), more than 73% of the specific capacitance can be maintained, which shows a good rate performance. Such a growth approach offers a versatile technique for the design and synthesis of metal oxide hierarchical nanoarrays for electrochemical energy storage applications.

Synthesis of ZnSnO3 mesocrystals from regular cube-like to sheet-like structures and their comparative electrochemical properties in Li-ion batteries

ZnSnO3, as an anode material for lithium ion batteries (LIBs), was investigated for the first time with structures ranging from unique ZnSnO3 nanocubes (ZSCs) to ZnSnO3 nanosheets (ZSSs). These structures were synthesized by a dual-hydrolysis-assisted liquid precipitation reaction and subsequent hydrothermal route. After calcination of the precursors, both formed two types of regular ZnSnO3 mesocrystal. Both mesocrystals showed almost the same capacity at the initial cycle, which agreed with the theoretical value of 1320 mA h g−1. However, they exhibited different cycle abilities and rate performances. The capacity of the ZSSs decayed slowly over the first 12 cycles and no obvious degradation was observed after then. However, the capacity of the ZSCs decayed more quickly. After 50 cycles, the capacity of the ZSSs had only decreased by 38.4%, in contrast to a decrease of 77.5% for the capacity of the ZSCs. The different performances of the same material can be related to the differences in phase and exposed facets.

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.

Gas Sensing of SnO2 Nanocrystals Revisited: Developing Ultra-Sensitive Sensors for Detecting the H2S Leakage of Biogas

As a typical mode of energy from waste, biogas technology is of great interest to researchers. To detect the trace H2S released from biogas, we herein demonstrate a high-performance sensor based on highly H2S-sensitive SnO2 nanocrystals, which have been selectively prepared by solvothermal methods using benzimidazole as a mineralization agent. The sensitivity of as-obtained SnO2 sensor towards 5 ppm H2S can reach up to 357. Such a technique based on SnO2 nanocrystals opens up a promising avenue for future practical applications in real-time monitoring a trace of H2S from the leakage of biogas.

Rational design of Au–NiO hierarchical structures with enhanced rate performance for supercapacitors

Hierarchical structures consisting of highly conductive Au nanoparticles decorated on NiO nanostructures could significantly improve electrical conductivity. Herein, the Au–NiO composite exhibits greatly improved rate performance as pseudo-capacitors, and a high specific capacitance value of 619 F g−1 at a high rate of 20 A g−1, which is much higher than that of pure NiO electrodes (216 F g−1).

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.

Facile construction of graphene-like Ni3S2 nanosheets through the hydrothermally assisted sulfurization of nickel foam and their application as self-supported electrodes for supercapacitors

A facile and low-cost approach has been developed for the fabrication of large-area nickel sulfide nanosheets via the hydrothermally assisted sulfurization of Ni foam. The obtained Ni3S2 nanosheets exhibit perfect supercapacitor performance, retaining almost 93.6% of the maximum capacitance after 3000 cycles. The strategy of self-sulfurization is promising for use in the construction of other nanoarchitectured sulfide (e.g., CuS, FeS and SnS) arrays for electrochemical applications.