Guijuan Wei

Synthesis of few-layer 1T′-MoTe2 ultrathin nanosheets for high-performance pseudocapacitors

The synthesis of layered transition metal dichalcogenide nanocrystals with excellent properties in energy conversion and storage has been well documented in the past several years. However, due to the metallic character of Te, the realization of the chemical synthesis of uniform well-defined MoTe2 nanostructures still remains a challenge, especially to achieve metastable 1T′-MoTe2. In this work, we have developed a colloidal chemical strategy for the synthesis of ultrathin 1T′-MoTe2 nanosheets. The as-achieved sample was characterized by a layered-expanded feature with an interlayer distance of 0.723 nm and rich defects. The shapes of 1T′-MoTe2 can be controlled by varying Mo precursors and the reaction atmosphere, where CO plays an essential role in determining the nanosheet feature. Interestingly, the optimized few-layer 1T′-MoTe2 nanosheets can be used as an efficient supercapacitor electrode with specific capacitances of 1393 F g−1 and 714 F g−1 at current densities of 1 A g−1 and 100 A g−1, respectively. An asymmetric 1T′-MoTe2//activated carbon supercapacitor exhibits a maximum specific capacitance of 158.9 F g−1 with an energy density up to 56.4 W h kg−1. To the best of our knowledge, it is the first time that ultrathin MoTe2 nanosheets have been used as ideal electrode materials for supercapacitors. The present work highlights a facile synthetic strategy to realize uniform transition metal telluride nanostructures for enhancing their electrochemical performances.

Carbon quantum dot-induced self-assembly of ultrathin Ni(OH) 2 nanosheets: A facile method for fabricating three-dimensional porous hierarchical composite micro-nanostructures with excellent supercapacitor performance

Significant efforts have been directed towards the preparation and application of porous hierarchically structured materials owing to their large surface area, rich active sites, and enhanced mass transport and diffusion. In this study, a simple and cost-effective method for the carbon quantum dot (CQD)-induced assembly of two-dimensional ultrathin Ni(OH)2 nanosheets into a three-dimensional (3D) porous hierarchical structure was developed. The electrostatic forces between the CQDs and cations drove the self-assembly of the 3D CQDs/Ni(OH)2 hierarchical structures. As a new type of structure-directing agent, the CQDs played dual roles in tuning the morphology of the products and improving the supercapacitor performance. The multilevel CQDs/Ni(OH)2 micro-nanostructures had a large specific surface area and rich porosity. Owing to their unique structures and the conductivity of the CQDs, an optimized asymmetric supercapacitor using the CQDs/Ni(OH)2 exhibited a maximum specific capacity of 161.3 F·g–1 and a high energy density of 57.4 Wh·kg–1. This study introduces a potential method for the fabrication of many other 3D hierarchical structures with great potential for applications in various fields.

The synthesis of hollow MoS2 nanospheres assembled by ultrathin nanosheets for an enhanced energy storage performance

ZnS@MoS2 core–shell nanospheres were first prepared via a nanotemplate-assisted hydrothermal method. After the removal of ZnS with dilute hydrochloric acid, hollow MoS2 nanospheres (HNS) were successfully obtained. The as-synthesized HNS display a unique hollow structure assembled by ultrathin nanosheets with rich defects. Furthermore, the HNS exhibit an enhanced performance in the electrochemical energy storage devices, for example, in a Li-ion battery, they exhibit a discharge capacity of 750 mA h g−1 at a current density of 100 mA g−1 even after 50 cycles, and in a supercapacitor, they exhibit a specific capacitance of 142.0 F g−1 at a current density of 1 A g−1. These values are much higher than those obtained for their solid counterparts. The present study provides an easily available method for the design and fabrication of other hollow nanomaterials with high energy storage performances.

Urchin-like FeOOH hollow microspheres decorated with MnO 2 for enhanced supercapacitor performance

Ultrathin MnO2 decorated hierarchical urchin-like FeOOH hollow micro-nanospheres have been designed and synthesized through a facile hydrothermal route. The microspheres are made of FeOOH nanofibers with a diameter of 10 nm. Due to the synergetic effect between the unique FeOOH hollow micro/nanostructures and ultrathin MnO2 layer, the as-fabricated FeOOH@MnO2 hybrid electrode exhibits a high specific capacitance of 1192 F g−1 at a current density of 1 A g−1. It also reveals high rate capabilities and superior stability. Moreover, the asymmetric supercapacitor (ASC) assembled from the FeOOH@MnO2 and the active carbon (AC) delivers a high energy density of 40.2 W h kg−1 at a power density of 0.78 kW kg−1, and the energy density could remain 10.4 W h kg−1 under a condition of high power density of 11.7 kW kg−1.摘要本文通过简便的水热技术合成了超薄MnO2修饰的海胆状FeOOH空心微纳米球. 该微米球由直径10 nm的纳米纤维组成. 由于FeOOH独特的微纳米结构和MnO2的协同效应, 所制备的FeOOH@MnO2电极在电流密度1 A g−1下表现出1192 F g−1的比电容, 同时显示出较高的倍率性能和优异的稳定性. 而且由FeOOH@MnO2电极和活性炭组装的非对称电容器在0.78 kW kg−1的功率密度下具有40.2 W h kg−1的能量密度; 在较高的11.7 kW kg−1功率密度下, 功率密度仍能保持在10.4 W h kg−1.

NiS nanoparticle decorated MoS2 nanosheets as efficient promoters for enhanced solar H2 evolution over ZnxCd1−xS nanorods

Facilitating charge separation as well as surface redox reactions is central to improve semiconductor catalyzed solar hydrogen generation. Photocatalysts comprising intimately interfaced photoabsorbers and co-promoters for the enhanced photocatalytic efficiency have gained much attention. In this paper, efficient promoters of NiS decorated MoS2 nanosheets (MoS2/NiS) coupled with ZnxCd1−xS nanorods have been prepared through a convenient hydrothermal method. The as-achieved Zn0.2Cd0.8S/MoS2/NiS nanohybrids exhibited a high solar H2 evolution activity with a rate of 41.29 mmol gcat−1 h−1 and the apparent quantum efficiency of 19% at a wavelength of 435 nm. The result represents one of the most active photocatalysts with noble-metal-free cocatalysts. The synergetic effects of MoS2 and NiS are responsible for the enhanced photocatalytic activity, and the presence of NiS further promotes the photo-induced electron-transfer from Zn0.2Cd0.8S to MoS2. This work opens an avenue for the design of efficient cocatalysts towards the enhancement of photocatalytic performance.

Solar-driven Pt modified hollow structured CdS photocatalyst for efficient hydrogen evolution

Hollow CdS nanostructures have been synthesized by a two-step ionic exchange route, which consists of a first synthesis of Ag2S intermediated hollow frames derived from the reaction of S2− ions with AgCl cube-tetrapods, and a subsequent ion-exchange conversion of the obtained Ag2S to CdS hollow nanoframes. The investigation of the corresponding transformation process with scanning electronic microscopy (SEM) revealed that the obtained CdS particles preserved the framework of the original template. The solar-driven hollow structured CdS modified with 5% (w/w) of promoter of Pt nanoparticles/nanoclusters manifested a high hydrogen evolution rate of 10.07 mmol h−1 g−1, corresponding to the apparent quantum yield of 9.6% measured at a single length of 435 nm, which is due to efficient charge separation, fast transport of the photogenerated carriers, and fast photochemical reaction at the CdS/Pt/electrolyte interfaces. The present work can benefit the development of other hollow structured nano-photocatalysts with high efficiency towards new energy applications.

A facile approach to fabricate superhydrophobic and corrosion resistant surface

In the present study, we have fabricated superhydrophobic CuO nanostructured surfaces by a simple solution-immersion process and a subsequent chemical modification with various thiol groups. The morphology of the CuO nanostructures on the copper foil could be easily controlled by simply changing the reaction time. The influences of reaction time and the thiol groups on hydrophobic properties have been discussed in detail. It is shown that the chemically modified CuO nanostructured surfaces present remarkable superhydrophobic performance and non-sticking behaviour. Furthermore, a lower corrosion current density (icorr) and a higher corrosion potential (Ecorr) of the prepared superhydrophobic surface was observed in comparison with the bare Cu foil by immersing in a 3.5 wt% NaCl solution, indicating a good corrosion resistance capability. Our work provides a general, facile and low-cost route towards the preparation of superhydrophobic surface, which has potential applications in the fields of self-cleaning, anti-corrosion, and oil–water separation.

Ultrathin Metal–Organic Framework Nanosheet-Derived Ultrathin Co3O4 Nanomeshes with Robust Oxygen-Evolving Performance and Asymmetric Supercapacitors

Ultrathin metal-organic framework (MOF) nanosheets possessing inherent advantages of both two-dimensional (2D) features and MOFs are attracting intensive research interest. The direct manufacture of MOF nanosheets is still a challenge up to now. Here, we have developed a novel bottom-up approach to synthesize zeolitic imidazolate framework-67 (ZIF-67) nanosheets, which can be in situ converted into Co3O4 ultrathin nanomeshes after thermal treatment. Interestingly, the obtained Co3O4 nanomeshes are rich in oxygen defects, providing fruitful active sites for the faradaic reaction. The modified electrode exhibits a large specific capacitance (1216.4 F g-1 at 1 A g-1), as well as a high rate capability (925.5 F g-1 at 20 A g-1). Moreover, an asymmetric supercapacitor made of Co3O4//activated carbon shows an energy density of 46.5 Wh kg-1 at 790.7 W kg-1. Furthermore, the 2D Co3O4 ultrathin nanomeshes show an outstanding performance for the oxygen evolution reaction with an overpotential of 230 mV at the onset potential and a small Tafel slope of 74.0 mV dec-1. The present method presents a facile avenue to the preparation of other 2D ultrathin metal oxide nanostructures with various applications in energy catalysis and conversion.

Rational Design of Co(II) Dominant and Oxygen Vacancy Defective CuCo2O4@CQDs Hollow Spheres for Enhanced Overall Water Splitting and Supercapacitor Performance

The hierarchical CuCo2O4@carbon quantum dots (CQDs) hollow microspheres constructed by 1D porous nanowires have been successfully prepared through a simple CQDs-induced hydrothermal self-assembly technique. XPS analysis shows the CuCo2O4@CQDs possesses the Co(II)-rich surface associated with the oxygen vacancies, which can effectively boost the Faradaic reactions and oxygen evolution reaction (OER) activity. For example, the as-synthesized 3D porous CuCo2O4@CQDs electrode exhibits high activity toward overall electrochemical water splitting, for example, an overpotential of 290 mV for OER and 331 mV for hydrogen evolution reaction (HER) in alkaline media have been achieved at 10 mA cm-2, respectively. Furthermore, an asymmetric supercapacitor (ASC) (CuCo2O4@CQDs//CNTs) delivers a high energy density of 45.9 Wh kg-1 at 763.4 W kg-1, as well as good cycling ability. The synergy of Co(II)-rich surface, oxygen vacancies, and well-defined 3D hollow structures facilitates the subsequent surface electrochemical reactions. This work presents a facile method to fabricate energetic nanocomposites with highly reactive, durable, and universal functionalities.