Latest ArticlesIn the past few years, the increasing energy consumption of traditional fossil fuels has posed a huge threat to human health. It is very imperious to develop the sustainable and renewable energy storage and conversion devices with low cost and environment friendly features. Hybrid supercapacitors are emerging as one of the promising energy devices with high power density, fast charge-discharge process and excellent cycle stability. However, morphology and structure of the electrode materials exert serious effect on their electrochemical performances. In this review, we summarized recent progresses in transition metal oxide based electrode materials for supercapacitors. Different synthesis routes and electrochemical performances of electrode materials and storage mechanisms of supercapacitor devices have been presented in details. The future developing trends of supercapacitor based on metal oxide electrode materials are also proposed.
Significance of unstable species leaching was for the first time demonstrated on MOF-derived catalysts by taking PtNi-C as an example, that was instructive for the relevant catalyst fabrication and performance study. PtNi-C catalyst was synthesized by combining Pt nanoparticles with Ni-BTC after annealing in the tube furnace and the unstable Ni species can be easily leached out in nitric acid, and the stable PtNi nanoparticles trapped in the graphite carbon layer were obtained. The greatly improved catalytic ability for alcohol fuels oxidation was verified by comparing the fresh and acid leached catalysts in terms of the high peak current density, specific and mass activity and rapid charge transfer kinetics and high catalytic stability. The current work guides the importance of unstable assistant promoter removal for the MOF derived catalysts.
Supercapacitors with good electrochemical performance and flexibility are in great demand. In this paper, the concept of preparing 3D porous carbon monoliths via direct calcination of melamine sponge is presented. This preparation method is simple and has good control of the structure. Porous carbon composite nickel-manganese oxides can be obtained by hydrothermal method followed with calcination. The electrochemical performances were tested and porous carbon monoliths with NiMn oxides exhibited a specific capacitance of 870 F/g in 1 mol/L KOH at a charge/discharge current density of 0.5 A/g and a capacity retention of 89.9% after 5000 times charge and discharge.
As one of the most promising secondary batteries in large-scale energy storage, sodium ion batteries (SIBs) have attracted wide attention due to the abundant raw materials and low cost. Layered transition metal oxides are one kind of popular cathode material candidates because of its easy synthesis and large theoretical specific capacity. Yet, the most common P2 and O3 phases show distinct structural characteristics respectively. O3 phase can serve as a sodium reservoir, but it usually suffers from serious phase transition and sluggish kinetics. For the P2 phase, it allows the fast sodium ion migration in the bulk and the structure can maintain stable, but it is lack of sodium, showing a great negative effect on Coulombic efficiency in full cell. Thus, single phase structure almost cannot achieve satisfied comprehensive sodium storage performances. Under these circumstances, exploiting novel multiphase cathodes showing synergetic effect may give solution to these problems. In this review, we summarize the recent development of multiphase layered transition metal oxide cathodes of SIBs, analyze the mechanism and prospect the future potential research directions.
The first HFIP-promoted catalyst-free cascade reactions for the synthesis of biologically relevant 3, 3-di (indolyl)indolin-2-ones (27 examples, up to 98% yield) from readily available indoles and isatin derivatives are described. This protocol shows well tolerance of different functional groups and features mild reaction conditions such as short reaction time (~1 h), no usage of catalyst, easy operation and product isolation. Of particular interest is the formation of two C—C bonds and one all-carbon quaternary center. This protocol could serve as an alternative strategy to synthesize biologically important 3, 3-di (indolyl)indolin-2-ones for biological testing.
Constructing heterostructures by combining COFs and TMD is a new strategy to design efficient photocatalysts for CO2 reduction reaction (CO2RR) due to their good stability, tunable band gaps and efficient charge separation. Based on the synthesis of completely novel C4N-COF in our previous reported work, a new C4N/MoS2 heterostructure was constructed and then the related structural, electronic and optical properties were also studied using first principle calculations. The interlayer coupling effect and charge transfer between the C4N and MoS2 layer are systematically illuminated. The reduced band gap of the C4N/MoS2 heterostructure is beneficial to absorb more visible light. For the formation of type-Ⅱ band alignment, a built-in electric field appears which separates the photogenerated electrons and holes into different layers efficiently and produces redox active sites. The band alignment of the heterostructure ensures its photocatalytic activities of the whole CO2 reduction reaction. Furthermore, the charge density difference and charge carrier mobility confirm the existence of the built-in electric field at the interface of the C4N/MoS2 heterostructure directly. Finally, the high optical absorption indicates it is an efficient visible light harvesting photocatalyst. Therefore, this work could provide strong insights into the internal mechanism and high photocatalytic activity of the C4N/MoS2 heterostructure and offer guiding of designing and synthesizing COF/TMD heterostructure photocatalysts.
MXene materials have recently attracted considerable attention in energy storage application owing to their metallic conductivity, 2D structure and tunable surface terminations. However, the restacking of 2D MXene nanosheets hinders the ion transport and accessibility to the surface, resulting in adverse effect on their electrochemical performances. Here, with the assistance of hexamethylenetetramine (C6H12N4), 2D Ti3C2Tx MXene nanosheets were fabricated into a 3D architecture with crumbled and porous structure through an electrostatic self-assembly followed by annealing. The resultant 3D structure can expose massive active sites and facilitates the ion transport, which is beneficial for sufficient utilization of the outstanding superiorities of the MXene. Therefore, as a pseudocapacitive material, the 3D crumpled and porous Ti3C2Tx MXene shows a gravimetric capacitance of 333 F/g at 1 A/g, and maintains 261 F/g and 132 F/g at ultrahigh current densities of 100 A/g and 1000 A/g, respectively, revealing promising potential for application in supercapacitors.
Lithium (Li) metal, possessing an extremely high theoretical specific capacity (3860 mAh/g) and the most negative electrode potential (-3.040 V vs. standard hydrogen electrode), is one the most favorable anode materials for future high-energy-density batteries. However, the poor cyclability and safety issues induced by extremely unstable interfaces of traditional liquid Li metal batteries have limited their practical applications. Herein, a quasi-solid battery is constructed to offer superior interfacial stability as well as excellent interfacial contact by the incorporation of Li@composite solid electrolyte integrated electrode and a limited amount of liquid electrolyte (7.5 μL/cm2). By combining the inorganic garnet Aldoped Li6.75La3Zr1.75Ta0.25O12 (LLZO) with high mechanical strength and ionic conductivity and the organic ethylene-vinyl acetate copolymer (EVA) with good flexibility, the composite solid electrolyte film could provide sufficient ion channels, sustained interfacial contact and good mechanical stability at the anode side, which significantly alleviates the thermodynamic corrosion and safety problems induced by liquid electrolytes. This innovative and facile quasi-solid strategy is aimed to promote the intrinsic safety and stability of working Li metal anode, shedding light on the development of next-generation high-performance Li metal batteries.
Nanobubble is a rising research field, which attracts more and more attentions due to its potential applications in medical science, catalysis, electrochemistry and etc. To better implement these applications, it is urgent to understand one of the most important mechanisms of nanobubbles, the evolution. However, few attentions have been paid in this aspect because of the methodology difficulties. Here we successfully used dark-field microscopy to study the evolution process of single nanobubbles generated from formic acid dehydrogenation on single Pd-Ag nanoplates. We found some of the nanobubbles in this system can exhibit three distinct states representing different sizes, which can transform among each other. These transitions are not direct but through some intermediate states. Further kinetic analysis reveals complicated mechanisms behind the evolution of single nanobubbles. The results acquired from this study can be applicable to nanobubble systems in general and provide insights into the understanding of mechanisms affecting the stability of nanobubbles and their applications.
Understanding the unique characteristics of continuous-flow photochemistry will lead to a paradigm shift in the way we enhance sustainability and wellbeing. In this mini-review, we first provide a succinct overview of working principles of this technique and discuss several recent synthetic protocols. Then, emphasis is given to those representative examples which address environmental issues such as indoor air pollutants and water contamination. Finally, recent progress made using this technique to deal with rising CO2 emission, solar energy utilization and biomedical equipment is described. It is believed that this mini-review could inspire more chemists to utilize this technique in their research, either in the academic or industrial field.
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