An investigation into the influence of zinc precursor on the microstructural,photoluminescence, and gas-sensing properties of ZnO nanoparticles

Carbon/silica-nanostructured microfibers were synthesized via electrospinning method using phenol-formaldehyde resin and tetraethyl orthosilicate as carbon and silica precursor with triblock copolymer Pluronic P123 as soft template. The prepared samples show uniform microfiber structure with ~1 μm in diameter and dozens of microns in length. Additionally, the mesopores in the material is about 2–6 nm. When the silica component was removed by HF, the porous carbon microfibers (PCMFs) were obtained. In addition, after the carbon/silica composites were calcined in air, the porous silica microfibers (PSiMFs) were obtained, revealing the converse porous nanostructure as PCMFs. It is a simple way to prepare PCMFs and PSiMFs with silica and carbon as the template to each other. Additionally, PCMFs possess an ultrahigh specific surface area (2,092 m² g^?1) and large pore volume. The electrochemical performance of the prepared PCMF material was investigated in 6.0 M KOH electrolyte. The PCMF electrode exhibits a high specific capacitance (252 F g^?1 at 0.5 A g^?1). Then, superior cycling stability (97 % retention after 4,000 cycles) mainly is due to its unique nanostructure.     

Honeycomb-like manganese oxide nanospheres for redox supercapacitors

Honeycomb-like MnO₂ nanospheres were synthesized using stainless steel substrates by a facile chemical bath deposition method. The obtained nanospheres were about 200–400 nm in diameter and consisted of porous ultrathin nanosheets. Honeycomb-like MnO₂ nanospheres exhibited a high specific capacitance of 240 F g^?1 and 87.1% capacitance retention after 1000 cycles at a current density of 0.5 A g^?1. These remarkable electrochemical results imply great potential for applications of the honeycomb-like MnO₂ nanospheres in supercapacitors.     

Hollow structured Sn-Co nanospheres by galvanic replacement reaction as high-performance anode for lithium ion batteries

Hollow Sn-Co nanospheres have been fabricated by galvanic replacement reaction. In particular, the hollow resultants with different shell thickness and void space can be obtained using sacrificial templates with different sizes. The structural evolution of Sn-Co hollow microspheres and structure changes during charge/discharge process were studied using XRD, SEM, and TEM. As an anodic material, the hollow resultants with thin shell and relatively large void space exhibited a good reversible capacity of 502 mAh g^?1 at a current density of 100 mA g^?1 and a coulomb efficiency over 99 % after 100 cycles. The contributions of the hollow structure and the inactive Co element to electrochemical performance were verified by galvanostatic charge/discharge cycling, electrochemical impedance spectroscope, and TEM measurements. A possible mechanism for hollow structure with different shell thickness to alleviate the volume change was proposed.     

Porous NiO hollow quasi-nanospheres derived from a new metal-organic framework template as high-performance anode materials for lithium ion batteries

Porous hollow metal oxides derived from nanoscaled metal-organic framework (MOF) have drawn tremendous attention due to their high electrochemical performance in advanced Li-ion batteries (LIBs). In this work, porous NiO hollow quasi-nanospheres were fabricated by an ordinary refluxing reaction combination of a thermal decomposition of new nanostructured Ni-MOF, i.e., {Ni₃(HCOO)₆·DMF}_n. When evaluated as an anode material for lithium ion batteries, the MOF derived NiO electrode exhibits high capacity, good cycling stability and rate performance (760 mAh g^?1 at 200 mA g^?1 after 100 cycles, 392 mAh g^?1 at 3200 mA g^?1). This superior lithium storage performance is mainly attributed to the unique hollow and porous nanostructure of the as-synthesized NiO, which offer enough space to accommodate the dramstic volume change and alleviate the pulverization problem during the repeated lithiation/delithiation processes, and provide more electro-active sites for fast electrochemical reactions as well as promote lithium ions and electrons transfer at the electrolyte/electrode interface.     

Hollow polypyrrole nanosphere embedded in nitrogen-doped graphene layers to obtain a three-dimensional nanostructure as electrode material for electrochemical supercapacitor

A novel approach was developed to prepare hollow polypyrrole (PPy) nanospheres and nitrogen-doped graphene/hollow PPy nanospheres (NG/H-PPy) composites. In this process, uniform poly (methyl methacrylate-butyl methacrylate-methacrylic acid) (PMMA-PBMA-PMAA) latex microspheres as sacrificial templates were synthesized by using an emulsion polymerization method. Then, hollow PPy nanospheres were obtained on the surface of PMMA-PBMA-PMAA microspheres by in situ chemical oxidative polymerization. Finally, H-PPy was embedded in NG layers successfully through a simple approach. The nanobeads have been characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectra, and Fourier transform infrared spectra (FTIR). Different electrochemical methods including cyclic voltammetry (CV), galvanostatic charge–discharge (GCD), and electrochemical impedance spectroscopy (EIS) have been applied to study the electrochemical properties. The specific capacitance of NG/H-PPy composites based on the three-electrode system is as high as 575 F g^?1 at a current density of 1 A g^?1 and enhanced stability about 90.1 % after 500 cycles, indicating that the composite has an impressive capacitance and excellent cycling performance.     

Shape-controlled porous carbon from calcium citrate precursor and their intriguing application in lithium-ion batteries

Porous carbon nanosheets (PCNSs), porous carbon nanofibers (PCNFs), and flowerlike porous carbon microspheres (FPCMs) were successfully synthesized through a carbonization method combined with a simple acid pickling treatment using calcium citrate as the precursor. The as-prepared products show uniform morphologies, in which the FPCMs are self-assembled from PCNSs. As anodes of lithium-ion (Li-ion) batteries, these carbon materials deliver a stable reversible capacity above 515 mAh g^?1 after 50 cycles at 100 mA g^?1. Compared with PCNSs and PCNFs, FPCMs demonstrate preferable rate capability (378 mAh g^?1 at 1 A g^?1) and cyclability (643 mAh g^?1 at 100 mA g^?1). These results suggest that an appropriate select of morphology and structure will significantly improve the lithium storage capacity. The study also indicates that the novel shape-controlled porous carbon materials have potential applications as electrode materials in electronic devices.     

Porous Silicon@Polythiophene Core–Shell Nanospheres for Lithium‐Ion Batteries

Polythiophene‐coated porous silicon core–shell nanospheres (Si@PTh) composite are synthesized by a simple chemical oxidative polymerization approach. The polythiophene acts as a flexible layer to hold silicon grains when they are repeatedly alloying/dealloying with lithium during the discharge/charge process. The long lifespan and high‐current‐density rate ­capability (at a current of 8 A g^?1) of the Si@PTh composite are vastly improved compared with as‐prepared Si spheres. Typically, these Si@PTh composite electrodes achieve a reversible capacity of 1130.5 mA h g^?1 at 1 A g^?1 current density after 500 cycles, and can even possess a discharge capacity up to 451.8 mA h g^?1 at 8 A g^?1. The improved electrochemical performance can be ascribed to the synergy effects of the flexible PTh coating and the distinctive core–shell nanospheres with porous structure, which can largely alleviate the volume expansion of the Si during alloying with lithium.     

Synthesis and electrochemical performance of micro-mesoporous carbon-sulfur composite cathode for Li–S batteries

Even though significant improvement has been made in the Li–S battery technology, the poor cycling and rate performance have always limited the further growth. Thus, the development of cost-effective and high performing electrodes is considered to be an important technology for the practical aspect. It is quite logical that the porous electrode systems can improve the electrochemical performance of a given battery system. Here, this study benchmarks a new class of electrodes based on double (micro and meso)porous carbon spheres (MMPCs) prepared by a facile soft template method followed by wet chemical etching. The particle size analysis, performed by scanning electron microscopy, shows that the templating agents, such as sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide(CTAB), have a distinct effect on the size distribution of carbon particles. Different electrochemical characterizations have been carried out to understand the effect of SDS and CTAB on the electrochemical performance of carbon-sulfur nanocomposite electrode. BET analysis shows that the pore size distribution of the carbon spheres prepared by only the soft template method (MPCs) is mainly in the micropore range, which limits the storage and the dispersive capacity. However, the etched samples (MMPCs) showed better electrochemical performance, such as high initial discharge capacity of 921 mAh g^?1(sulfur loading ～77.2%) with 82.7% capacity retention at the end of 150 cycles at 200 mA g^?1 and an impressive rate capability of 1086 mAh g^?1 at a current density of 100 mA g^?1.This improved performance could be attributed to the double porous structure of MMPCs. Such a feasible and facile architecture provides a good strategy to prepare other different materials that require better material dispersion and electrode/electrolyte interactions.     

Electrochemical synthesis and lithium storage properties of three-dimensional porous Sn–Co alloy/CNT composite

Three-dimensional (3-D) porous copper with stable pore structure is prepared by electroless plating. 3-D porous Sn–Co alloy/carbon nanotube (CNT) composite is synthesized by electrodeposition using 3-D porous copper as the substrate. The scanning electron microscope results indicate that 3-D porous Sn–Co alloy/CNT composite contains a large amount of interconnected pores with the diameter size of ~3 μm. Upon cycling, the pore structure gradually disappears, but no serious exfoliation appears due to porous structure and reinforcement by CNT. The charge/discharge results demonstrate that the 3-D porous Sn–Co alloy/CNT composite electrode delivers high first reversible specific capacity of 490 mAh g^?1, and remains 441 mAh g^?1 after 60 cycles tested at different current densities. Even at the current density of 3,200 mA g^?1, the reversible specific capacity remains 319 mAh g^?1, which is 65 % of the first specific capacity cycled at the current density of 100 mA g^?1.     

Facile synthesis of three-dimensional porous carbon networks for highly stable sodium storage

Novel three-dimensional porous carbon network (3D-PC) anode was developed by a facile in situ NaCl-template method utilizing citric acid as carbon source. The synthesis process involves the dissolution of NaCl and citric acid in deionized water, citric acid coated on NaCl template during freeze-drying process, carbonization of the composites, and removal of the template with water. The resultant 3D-PC presents high electrical conductivity, large specific surface area, sufficient active sites, large interlayer distance, and high mechanical flexibility, which are contributed to the efficient Na-storage. Therefore, the 3D-PC anode displays enhanced rate performance of 101 mAh g^?1 at 1000 mA g^?1 and extremely long cycle life of 138 mAh g^?1 after 2000 cycles at 200 mA g^?1. The unique synthesis strategy coupled with the excellent Na-storage performance ensures 3D-PC a promising anode material for low-cost sodium-ion batteries.     

Synthesis of selenium/EDTA-derived porous carbon composite as a Li–Se battery cathode

The carbon substrate with unique 3D macroporous structure has been prepared through the immediate carbonization of ethylenediaminetetraacetic acid (EDTA) and KOH mixture. The porous carbon composed of micro- and small mesoporous (2–5 nm) structure has a BET specific surface area of 1824.8 m² g^?1. The amorphous and nanosized Se is uniformly encapsulated into the porous structure of porous carbon using melting diffusion route, and the weight content of Se in target Se/C composite can be as high as ~50 %. As an Li–Se battery cathode, the Se/C composite delivers a reversible (2nd) discharge capacity of 597.4 mAh g^?1 at 0.24C and retains a discharge capacity of 538.4 mAh g^?1 at 0.24C after 100 cycles. Furthermore, the composite also has a stable capacity of 291.0 mAh g^?1 at a high current of 4.8C. The high specific area and good porous size of EDTA-derived carbon substrate may a be responsibility for the excellent electrochemical performances of Se/C composite.     

Preparation and comparative structural properties of porous SnO2 microrods and submicrorods

A facile two-step approach has been used for the synthesis of porous SnO₂ rods: the initial room-temperature precipitation of precursor SnC₂O₄ and its subsequent thermal decomposition at 550 °C. Both the as-obtained porous SnO₂ microrods (length ～10.0?±?3.5 μm, diameter ～1.1?±?0.4 μm) and submicrorods (length ～5.8?±?1.9 μm, diameter ～0.4?±?0.1 μm) are the crystalline mixtures of major tetragonal and minor orthorhombic crystal phases, showing a tetragonal fraction of 84.7 and 87.0 %, respectively. When applied as a lithium-ion battery anode, the porous submicrorods (specific surface area ～13.6 m² g^?1) can deliver an initial discharge capacity of 1,730.7 mAh g^?1 with a high coulombic efficiency of 61.6 % and show the 50th discharge capacity of 662.8 mAh g^?1 at 160 mA g^?1 within a narrow potential range of 10.0 mV to 2.0 V. Similarly, even the anode of porous microrods (specific surface area ～11.8 m² g^?1) can still exhibit an initial discharge capacity of 1,661.1 mAh g^?1 at 160 mA g^?1 with a coulombic efficiency of 60.9 %. Regardless of the polymorphic nature, the acquired porosity may only alleviate the huge volume change of anodes for the first cycle; thus, the structural parameters of average size and specific surface area can be feasibly associated with the enhanced lithium storage capability. Anyway, these indicate a facile oxalate precursor method for the controlling synthesis and high performance of rodlike SnO₂ for lithium-ion batteries.     

Cu-supported carbon networks containing SnO<Subscript>2</Subscript> as three-dimensional anodes for lithium-ion batteries

Cu-supported SnO₂@C composite coatings constructed by interconnected carbon-based porous branches were fabricated by annealing Cu foils with films formed by knife coating DMF solution containing SnCl₂, polyacrylonitrile (PAN), and poly(methyl methacrylate) (PMMA) on their surface in vacuum. The carbon-based porous branches consist of amorphous carbon matrices, SnO₂ nanoparticles with a size of 30–100 nm mainly encapsulated inside, and many micropores with a size of 1–5 nm. The three-dimensional (3D) porous network structures of the SnO₂@C composite were achieved by volatilization of PMMA and pyrolysis of SnCl₂. The SnO₂@C composite coatings demonstrate good cyclic performance with a high reversible capacity of 642 mA h g^?1 after 100 cycles at a current density of 50 mA g^?1 without apparent capacity fading during cycling and excellent rate performance with a capacity of 276 mA h g^?1 at a high current density up to 10 A g^?1.     

Red phosphorus encapsulated in porous carbon derived from cigarette filter solid waste as a promising anode material for lithium-ion batteries

Red phosphorus (RP) is considered to be one of the promising anode materials for lithium-ion batteries (LIBs) on account of its high theoretical capacity (2596 mAh g^?1), abundant resources, and environmental friendliness. However, the intrinsic insulating nature and large volume change during lithium insertion/extraction process lead to drastic capacity loss upon cycling. Recently, great attention has been devoted to constructing P-based composites via mixing with carbon materials. Here, a novel P/C composite, in which red P nanoparticles were homogeneously distributed in cigarette filter-derived porous carbon (CPC), was fabricated by vaporization-condensation method. Due to the unique characteristics of porous carbon, including high specific area, good conductivity, and rich internal porous structure, CPC obtained by means of heat treatment that serves as conductive matrix to load red P could be of great benefits, which can not only improve the overall electrical conductivity but also mitigate the volume expansion issues. As a result, the RP/CPC composite as an anode material for LIBs delivers a good cycling stability (500 mAh g^?1 at 100 mA g^?1 with a high Coulombic efficiency above 99% after 50 cycles) and rate capability (355 mAh g^?1 even at 1000 mA g^?1).     

Nanoporous carbon microspheres as anode material for enhanced capacity of lithium ion batteries

Nanoporous carbon microspheres (NCMs) are prepared by a one-step carbonizing and activating resorcinol?formaldehyde polymer spheres (RFs) in inert and CO₂ atmosphere for anode materials of lithium-ion batteries (LIBs). Compared with RFs carbon microspheres (RF-C), after activating with hot CO₂, the NCMs with porous structure and high BET surface area of 2798.8 m² g^?1, which provides abundant lithium-ion storage site as well as stable lithium-ion transport channel. When RF-C and NCM are used to anode material for LIBs, at the same current density of 210 mA g^?1, the initial specific discharge capacity are 482.4 and 2575.992 mA h g^?1, respectively; after 50 cycles, the maintain capacity are 429.379 and 926.654 mA h g^?1, respectively. The porous spherical structure of NCM possesses noticeably lithium-ion storage capability, which exhibits high discharge capacity and excellent cycling stability at different current density. The CO₂ activating carbonaceous materials used in anode materials can tremendously enhance the capacity storage, which provides a promising modification strategy to improve the storage capacity and cyclic stability of carbonaceous anode materials for LIBs.     

Hollow Silica Spheres Embedded in a Porous Carbon Matrix and Its Superior Performance as the Anode for Lithium‐Ion Batteries

Silica (SiO₂) is regarded as one of the most promising anode materials for lithium‐ion batteries due to the high theoretical specific capacity and extremely low cost. However, the low intrinsic electrical conductivity and the big volume change during charge/discharge cycles result in a poor electrochemical performance. Here, hollow silica spheres embedded in porous carbon (HSS–C) composites are synthesized and investigated as an anode material for lithium‐ion batteries. The HSS–C composites demonstrate a high specific capacity of about 910 mA h g^?1 at a rate of 200 mA g^?1 after 150 cycles and exhibit good rate capability. The porous carbon with a large surface area and void space filled both inside and outside of the hollow silica spheres acts as an excellent conductive layer to enhance the overall conductivity of the electrode, shortens the diffusion path length for the transport of lithium ions, and also buffers the volume change accompanied with lithium‐ion insertion/extraction processes.     

Synthesis and characterization of nitrogen-doped graphene hollow spheres as electrode material for supercapacitors

Recently, the rapid development of graphene industry in the world, especially in China, provides more opportunities for the further extension of the application field of graphene-based materials. Graphene has also been considered as a promising candidate for use in supercapacitors. Here, nitrogen-doped graphene hollow spheres (NGHS) have been successfully synthesized by using industrialized and pre-processed graphene oxide (GO) as raw material, SiO₂ spheres as hard templates, and urea as reducing-doping agents. The results demonstrate that the content and pretreatment of GO sheets have important effect on the uniform spherical morphologies of the obtained samples. Industrialized GO and low-cost urea are used to prepare graphene hollow spheres, which can be a promising route to achieve mass production of NGHS. The obtained NGHS have a cavity of about 270 nm, specific surface area of 402.9 m² g^?1, ultrathin porous shells of 2.8 nm, and nitrogen content of 6.9 at.%. As electrode material for supercapacitors, the NGHS exhibit a specific capacitance of 159 F g^?1 at a current density of 1 A g^?1 in 6 M KOH aqueous electrolyte. Moreover, the NGHS exhibit superior cycling stability with 99.24% capacitive retention after 5000 charge/discharge cycles at a current density of 5 A g^?1.     

Distinctive slit-shaped porous carbon encapsulating phosphorus as a promising anode material for lithium batteries

A distinctive structure of carbon materials for Li-ion batteries is proposed for the preparation of red phosphorus-carbon composites. The slit-shaped porous carbon is observed with aggregation of plate-like particles, whose isotherm belongs to the H3 of type IV. The density functional theory (DFT) method reveals the presence of micro-mesopores in the 0.5–5 nm size range. The unique size distribution plays an important role in adsorbing phosphorus and electrochemical performance. The phosphorus-slit-shaped porous carbon composite shows initial capacity of 2588 mAh g^?1, reversible capacity of 1359 mAh g^?1 at a current density of 100 mA g^?1. It shows an excellent coulombic efficiency of ～99 % after 50 cycles.     

Hierarchical porous ZnMn<Subscript>2</Subscript>O<Subscript>4</Subscript> synthesized by the sucrose-assisted combustion method for high-rate supercapacitors

A simple sucrose-assisted combustion and subsequent high-temperature calcination route have been employed to prepare hierarchical porous ZnMn₂O₄ nanostructure. When used as an electrode for supercapacitor, the ZnMn₂O₄ electrode displays a high specific capacitance of 411.75 F g^?1 at a current density of 1 A g^?1, remarkable capacitance retention rate of 64.28 % at current density of 32 A g^?1 compared with 1 A g^?1, as well as excellent cycle stability (reversible capacity retention of 88.32 % after 4000 cycles). The outstanding electrochemical performances are mainly attributed to its hierarchical porous architecture, which provides large reaction surface area, fast ion and electron transfer, and good structure stability. All these impressive results demonstrate that ZnMn₂O₄ shows promise for its application in supercapacitors.     

A novel synthesis of size-controllable mesoporous NiMoO<Subscript>4</Subscript> nanospheres for supercapacitor applications

A novel hydrothermal emulsion method is proposed to synthesize mesoporous NiMoO₄ nanosphere electrode material. The size of sphere-shaped NiMoO₄ nanostructure is controlled by the mass ratio of water and oil phases. Nickel acetate tetrahydrate and ammonium heptamolybdate were used as nickel and molybdate precursors, respectively. The resultant mesoporous NiMoO₄ nanospheres were characterized by X-ray diffraction, N₂ adsorption and desorption, scanning electron microscopy, and transmission electron microscopy. The electrochemical performances were evaluated by cyclic voltammetry (CV), cyclic chronopotentiometry (CP), and electrochemical impedance spectroscopy (EIS) in 6 M KOH solution. The typical mesoporous NiMoO₄ nanospheres exhibit the large specific surface area of 113 m² g^?1 and high specific capacitance of 1443 F g^?1 at 1 A g^?1, an outstanding cyclic stability with a capacitance retention of 90 % after 3000 cycles of charge-discharge at a current density of 10 A g^?1, and a low resistance.