Hierarchical TiO2/SnO2 Hollow Spheres Coated with Graphitized Carbon for High‐Performance Electrochemical Li‐Ion Storage

A self‐templated strategy is developed to fabricate hierarchical TiO₂/SnO₂ hollow spheres coated with graphitized carbon (HTSO/GC‐HSs) by combined sol–gel processes with hydrothermal treatment and calcination. The as‐prepared mesoporous HTSO/GC‐HSs present an approximate yolk‐double–shell structure, with high specific area and small nanocrystals of TiO₂ and SnO₂, and thus exhibit superior electrochemical reactivity and stability when used as anode materials for Li‐ion batteries. A high reversible specific capacity of about 310 mAh g^?1 at a high current density of 5 A g^?1 can be achieved over 500 cycles indicating very good cycle stability and rate performance.     

Synthesis of SnO2 nanoparticles inside mesoporous carbon via a sonochemical method for highly reversible lithium batteries

A sonochemical method was introduced to synthesize SnO₂ nanoparticles in the pores of mesoporous carbon without any other agents. The nitrogen adsorption measurement and transmission electron microscopy results revealed that the SnO₂ nanoparticles with the average particle size of around 10 nm were homogeneous distribution in the matrix. The aggregation of SnO₂ was hindered by the three-dimensioned porous frameworks, resulting in a relatively large surface area of 362 m² g^? 1, which is beneficial for lithium-ion storage in batteries. The resultant composites with 43% SnO₂ exhibited a high reversible capacity of 200 mAh g^? 1 even after 300 cycles, which is 186% higher than that of the initial mesoporous carbon matrix. This strategy is expected to incorporate other functional nanoparticles inside mesoporous carbon for many applications.     

Novel Carbon‐Encapsulated Porous SnO2 Anode for Lithium‐Ion Batteries with Much Improved Cyclic Stability

Porous SnO₂ submicrocubes (SMCs) are synthesized by annealing and HNO₃ etching of CoSn(OH)₆ SMCs. Bare SnO₂ SMCs, as well as bare commercial SnO₂ nanoparticles (NPs), show very high initial discharge capacity when used as anode material for lithium‐ion batteries. However, during the following cycles most of the Li ions previously inserted cannot be extracted, resulting in considerable irreversibility. Porous SnO₂ cubes have been proven to possess better electrochemical performance than the dense nanoparticles. After being encapsulated by carbon shell, the obtained yolk–shell SnO₂ SMCs@C exhibits significantly enhanced reversibility for lithium‐ions storage. The reversibility of the conversion between SnO₂ and Sn, which is largely responsible for the enhanced capacity, has been discussed. The porous SnO₂ SMCs@C shows much increased capacity and cycling stability, demonstrating that the porous SnO₂ core is essential for better lithium‐ion storage performance. The strategy introduced in this paper can be used as a versatile way to fabrication of various metal‐oxide‐based composites.     

Aerosol‐Assisted Heteroassembly of Oxide Nanocrystals and Carbon Nanotubes into 3D Mesoporous Composites for High‐Rate Electrochemical Energy Storage

Nanostructured composites built from ordinary building units have attracted much attention because of their collective properties for critical applications. Herein, we have demonstrated the heteroassembly of carbon nanotubes and oxide nanocrystals using an aerosol spray method to prepare nanostructured mesoporous composites for electrochemical energy storage. The designed composite architectures show high conductivity and hierarchically structured mesopores, which achieve rapid electron and ion transport in electrodes. Therefore, as‐synthesized carbon nanotube/TiO₂ electrodes exhibit high rate performance through rapid Li⁺ intercalation, making them suitable for ultrafast energy storage devices. Moreover, the synthesis process provides a broadly applicable method to achieve the heteroassembly of vast low‐dimensional building blocks for many important applications.     

Enhanced visible light photocatalytic activity for g-C<Subscript>3</Subscript>N<Subscript>4</Subscript>/SnO<Subscript>2</Subscript>:Sb composites induced by Sb doping

In this paper, g-C₃N₄/SnO₂:Sb composite photocatalysts were fabricated by in situ loading Sb-doped SnO₂ (SnO₂:Sb) nanoparticles on graphitic carbon nitride (g-C₃N₄) nanosheets via a facile hydrothermal method. The synthesized g-C₃N₄/SnO₂:Sb composites delivered enhanced visible light photocatalytic performance for degradation of rhodamine B in comparison with g-C₃N₄/SnO₂ composites without doping Sb. Various techniques including XRD, SEM, TEM, FTIR, XPS, PL and electrochemical method were employed to demonstrate the successful fabrication of g-C₃N₄/SnO₂:Sb composite and to investigate the enhanced mechanism of photocatalytic activity. The improvement of visible light absorption and the promotion of separation efficiency and interfacial transfer of photogenerated carriers induced by Sb doping were responsible for the enhancement of photocatalytic activity. This study provides a simple and convenient method to synthesize a visible light responsive catalyst with promising performance for the potential application in environmental protection.     

A facile synthesis of mesoporous graphene-tin composites as high-performance anodes for lithium-ion batteries

Graphene-based metals and their oxides usually exhibit enhanced electrochemical behavior in lithium-ion batteries due to the outstanding properties of graphene. Moreover, the structure and morphology of electrodes can also take an important role in their electrochemical properties. Herein we describe a facile synthesis of graphene–Sn composites containing ca. 3–6 nm diameter mesopores formed by aggregation of Sn nanoparticles on the graphene surface. These mesoporous composites with large surface area deliver higher capacity and better cycle performance in comparison with pristine Sn particles. Furthermore, the mesoporous composites treated under hydrothermal treatment exhibit higher rechargeable capacities and cycle performances.     

The effect of SnO2 on the improvement of mechanical properties of MgO–MgAl2O4 composites

Incorporation of SnO₂ into MgO–spinel (M–S) increased mechanical properties significantly. Relationships between the parameters improving mechanical properties and microstructural variables were examined. Basic parameters improving the mechanical properties of M–S–SnO₂ composites were identified as follows: (a) when microcracks come across with either Mg₂SnO₄ particles or pores; crack branching and deviation of interlinked microcracks or crack arresting occurred more effectively than those of spinel particles, (b) fracture type was converted to intergranular fracture with incorporation of spinel into MgO, and transgranular fracture with addition of SnO₂ to M–S; additionally with the incorporation of additives, (c) critical defect size, (d) work of fracture values increased, and (e) MgO grain size decreased. R_st thermal shock parameter values of M–S–SnO₂ composites were markedly higher than those of M–S materials, associated with low strength loss, high thermal shock damage resistance and thus longer service life of M–S–SnO₂ composites for high-temperature industrial applications.     

Microwave synthesis and electrochemical characterization of mesoporous carbon@Bi2O3 composites

An efficient and quick microwave method has been employed to prepare worm-like mesoporous carbon@Bi₂O₃ composites for the first time. As-prepared products have been characterized by X-ray diffraction, N₂ adsorption-desorption, scanning electron microscopy, transmission electron microscopy and inductive coupled plasma atomic emission spectroscopy. The electrochemical measurement shows the worm-like mesoporous carbon@Bi₂O₃ composites exhibits excellent capacitance performance and the maximum specific capacitance reaches 386 F g⁻¹, three times more than the pure worm-like mesoporous carbon.     

Ternary Sn–Ti–O Based Nanostructures as Anodes for Lithium Ion Batteries

SnO_x (x = 0, 1, 2) and TiO₂ are widely considered to be potential anode candidates for next generation lithium ion batteries. In terms of the lithium storage mechanisms, TiO₂ anodes operate on the base of the Li ion intercalation–deintercalation, and they typically display long cycling life and high rate capability, arising from the negligible cell volume change during the discharge–charge process, while their performance is limited by low specific capacity and low electronic conductivity. SnO_x anodes rely on the alloying–dealloying reaction with Li ions, and typically exhibit large specific capacity but poor cycling performance, originating from the extremely large volume change and thus the resultant pulverization problems. Making use of their advantages and minimizing the disadvantages, numerous strategies have been developed in the recent years to design composite nanostructured Sn–Ti–O ternary systems. This Review aims to provide rational understanding on their design and the improvement of electrochemical properties of such systems, including SnO_x–TiO₂ nanocomposites mixing at nanoscale and nanostructured Sn_xTi_1‐xO₂ solid solutions doped at the atomic level, as well as their combinations with carbon‐based nanomaterials.     

Patterning Graphene Surfaces with Iron‐Oxide‐Embedded Mesoporous Polypyrrole and Derived N‐Doped Carbon of Tunable Pore Size

This study develops a novel strategy, based on block copolymer self‐assembly in solution, for preparing two‐dimensional (2D) graphene‐based mesoporous nanohybrids with well‐defined large pores of tunable sizes, by employing polystyrene‐block‐poly(ethylene oxide) (PS‐b‐PEO) spherical micelles as the pore‐creating template. The resultant 2D nanohybrids possess a sandwich‐like structure with Fe₂O₃ nanoparticle‐embedded mesoporous polypyrrole (PPy) monolayers grown on both sides of reduced graphene oxide (rGO) nanosheets (denoted as mPPy‐Fe₂O₃@rGO). Serving as supercapacitor electrode materials, the 2D ternary nanohybrids exhibit controllable capacitive performance depending on the pore size, with high capacitance (up to 1006 F/g at 1 A/g), good rate performance (750 F/g at 20 A/g) and excellent cycling stability. Furthermore, the pyrolysis of mPPy‐Fe₂O₃@rGO at 800 °C yields 2D sandwich‐like mesoporous nitrogen‐doped carbon/Fe₃O₄/rGO (mNC‐Fe₃O₄@rGO). The mNC‐Fe₃O₄@rGO nanohybrids with a mean pore size of 12 nm show excellent electrocatalytic activity as an oxygen reduction reaction (ORR) catalyst with a four‐electron transfer nature, a high half‐wave‐potential of +0.84 V and a limiting current density of 5.7 mA/cm², which are well comparable with those of the best commercial Pt/C catalyst. This study takes advantage of block copolymer self‐assembly for the synthesis of 2D multifunctional mesoporous nanohybrids, and helps to understand the control of their structures and electrochemical performance.     

表面活性剂对纳米SnO2负极材料形貌结构及电化学性能的影响

为了提高SnO_2负极材料的电化学性能,本文以锡酸钠为原料、聚乙烯吡咯烷酮(PVP)、尿素、十二烷基硫酸钠(SDS)分别作为表面活性剂,采用水热法制备了具有纳米结构的SnO_2负极材料.利用扫描电子显微镜(SEM)、X射线衍射(XRD)、电化学测试仪测试了材料的形貌、结构和电化学性质.结果表明,使用不同表面活性剂,可获得不同形貌的纳米结构,并且对材料的电化学性能有较大的影响.当尿素作表面活性剂时,获得了分散较好的球形材料,在0.01~3.0 V,以200 mA/g进行充放电测试,首次放电容量2 256.6 mAh/g,经过50次循环后,放电容量保持在440 mAh/g,表现了较好的循环性能.     

Preliminary studies in the processing and characterization of Al2O3/SnO2 laminated composites

All oxide composites (reinforcement and matrix both being oxides) exhibit high temperature oxidation resistance in addition to high strength and hardness. A major drawback of these materials is that the oxide fiber and oxide matrix tend to react, which strengthens the interface and therefore drastically reduces the damage tolerance. To overcome this problem, a mechanically weak interphase material, which also serves as a diffusion barrier, is generally used. One such materials system is tin dioxide (SnO₂) in alumina-based composites. Previous attempts to fabricate such alumina matrix composites have been unsuccessful due to the higher temperatures needed to densify Al₂O₃ coupled with the fact that SnO₂ decomposes to SnO in reducing environments. SnO has a relatively low melting point (1125 °C). In this paper we report the successful fabrication of Al₂O₃/SnO₂, laminated composites and some observations on microstructural and mechanical characterization of the laminates. As expected from the phase diagram, no chemical compound formation was observed between Al₂O₃ and SnO₂ which means that no primary chemical bonding developed between individual laminae. TEM observations showed, however, a strong mechanical interlocking at the SnO₂/Al₂O₃ interfaces. In spite of the relatively strong interfacial bond, cracks did deflect. Our microstructural studies showed that SnO₂ served as a weak interphase material.     

Constructing Biomass-Based Ultrahigh-Rate Performance SnOy@C/SiOx Anode for LIBs via Disproportionation Effect

To break the stereotype that silica can only be reduced via a magnesiothermic and aluminothermic method at low-temperature condition, the novel strategy for converting silica to SiO_x using disproportionation effect of SnO generated via low-temperature pyrolysis coreduction reaction between SnO₂ and rice husk is proposed, without any raw materials waste and environmental hazards. After the low-temperature pyrolysis reaction, SnO_y@C/SiO_x composites with unique structure (Sn/SnO₂ dispersed on the surface and within pores of biochar as well as SiO_x residing in the interior) are obtained due to the exclusive biological properties of rice husk. Such unique structural features render SnO_y@C/SiO_x composites with an excellent talent for repairing the damaged structure and the highly electrochemical storage ability (530.8 mAh g⁻¹ at 10 A g⁻¹ after 7500 cycles). Furthermore, assembled LiFePO₄||SnO_y-50@C/SiO_x full cell displays a high discharge capacity of 463.7 mAh g⁻¹ after 100 cycles at 0.2 A g⁻¹. The Li⁺ transport mechanism is revealed by density functional theory calculations. This work provides references and ideas for green, efficient, and high-value to reduce SiO₂, especially in biomass, which also avoids the waste of raw materials in the production process, and becomes an essential step in sustainable development.     

Oxalate-Assisted Synthesis of Hollow Carbon Nanocage With Fe Single Atoms for Electrochemical CO2 Reduction

Metal single-atom catalysts are promising in electrochemical CO₂ reduction reaction (CO₂RR). The pores and cavities of the supports can promote the exposure of active sites and mass transfer of reactants, hence improve their performance. Here, iron oxalate is added to ZIF-8 and subsequently form hollow carbon nanocages during calcination. The formation mechanism of the hollow structure is studied in depth by controlling variables during synthesis. Kirkendall effect is the main reason for the formation of hollow porous carbon nanocages. The hollow porous carbon nanocages with Fe single atoms exhibit better CO₂RR activity and CO selectivity. The diffusion of CO₂ facilitated by the mesoporous structure of carbon nanocage results in their superior activity and selectivity. This work has raised an effective strategy for the synthesis of hollow carbon nanomaterials, and provides a feasible pathway for the rational design of electrocatalysts for small molecule activation.     

In situ synthesis of SnO2/graphene nanocomposite and their application as anode material for lithium ion battery

SnO₂/graphene nanocomposite was prepared via an in situ chemical synthesis method. The nanocomposite was characterized by X-ray diffraction, filed emission scanning electron microscope and transmission electron microscope, which revealed that tiny SnO₂ nanoparticles could be homogeneously distributed on the graphene matrix. The electrochemical performance of the SnO₂/graphene nanocomposite as anode material was measured by galvanostatic charge/discharge cycling. The SnO₂/graphene nanocomposite showed a reversible capacity of 665 mAh/g after 50 cycles and an excellent cycling performance for lithium ion battery, which was ascribed to the three-dimensional architecture of SnO₂/graphene nanocomposite. These results suggest that SnO₂/graphene nanocomposite would be a promising anode material for lithium ion battery.     

Carbon nanotubes anchored with SnO2 nanosheets as anode for enhanced Li-ion storage

The carbon nanotubes (CNTs) anchored with SnO₂ nanosheets were prepared using a hydrothermal method. The as-prepared products were characterized by X-ray diffraction, fourier transform infrared spectroscopy, thermogravimetric analyses, field emission scanning electron microscope and transmission electron microscope. The electrochemical performances of SnO₂ nanosheets/CNTs composite were measured by galvanostatic charge/discharge cycling, cyclic voltammetry and electrochemical impedance spectroscopy. The results show that the SnO₂ nanosheets/CNTs composite maintains high lithium storage capacity and good cycling stability. The designed structure plays key role in improving electrochemical performance. The CNTs anchored with SnO₂ nanosheets will be an ideal candidate of anode material for lithium ion batteries.     

Synthesis and characterisation of SnO2 nano-single crystals as anode materials for lithium-ion batteries

Rutile structure SnO₂ nano-single crystals have been synthesized using tin (IV) chloride as precursor by the modified hydrothermal method. Controllable morphology and size of SnO₂ could be obtained by adjusting the concentration of the hydrochloric acid. The SnO₂ nanoparticles were characterised by transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and electrochemical methods. The SnO₂ nanoparticles as anode materials in lithium-ion batteries exhibit high lithium storage capacities. The reversible capacities are more than 630 mA h g^− 1.     

Effect of addition of Ag on the microstructures and electrical properties of sol-gel derived SnO2 glass composites

The effect of addition of Ag on the microstructure and electrical properties of sol-gel derived SnO₂-glass composites was examined. Comparisons of the microstructures and electrical properties were carried out between glass composites prepared by a sol-gel method and a conventional one using glass frit. The glass composite gels and the SnO₂-glass powder mixtures containing AgNO₃ were calcined at 500 °C in order to decompose AgNO₃ into Ag and then fired at 900 °C. In the sol-gel derived glass composites, the grain growth of Ag was suppressed and Ag particles connected mutually at the boundaries of aggregated gel particles to form three-dimensional networks. Thus, the glass composite derived by the sol-gel method showed a high electrical conductivity and a positive temperature coefficient of resistance (TCR). The highly electrical conductive paths of Ag in the glass composite were effectively formed when powder compacts were formed at a higher pressure. On the other hand, in the glass composites prepared using SnO₂-glass powder mixtures, coarse-grained Ag particles were isolated in closed pores regardless of the forming pressure, and therefore did not contribute to electrical conduction in the glass composite.     

Preparation of periodically organized mesoporous bicomponent TiO2 and SnO2-based thin films by controlling the hydrolytic kinetics of inorganic precursors during EISA process

Highly organized cubic mesoporous TiO₂ and SnO₂ nanocrystalline thin films were reproducibly synthesized via an evaporation-induced self-assembly (EISA) process with a triblock copolymer (Pluronic F127) as the template, by precisely controlling the water content and chelating agent in the initial sol solution as well as by controlling the external relative humidity during the aging step. It has been found that the mesoscopic regularity of the fabricated mesoporous films critically depends on the hydrolytic reactions of inorganic precursors. That is, suppressing the hydrolysis reaction in the initial sol and providing the long-term stability for the sol in the coated film during the aging step are key factors in the formation of highly organized structure. The synthetic strategy was also extended to obtain various TiO₂- and SnO₂-based mixed oxide thin films with tunable composition, including WO₃/TiO₂, SiO₂/TiO₂, Nb₂O₅/SnO₂, by selectively controlling the kinetics of hydrolytic reaction for the additional inorganic precursors. The prepared composite films were crack-free, ultra-highly transparent, and thermally stable.     

Lithium insertion into the composites of acid-oxidized carbon nanotubes and tin oxide

Lithium intercalation into the composites of acid-oxidized carbon nanotubes and tin oxide was studied in an electrolyte system, 1 M solution of LiPF₆ dissolved in a 50:50 mixture by volume of ethylene carbonate (EC) and dimethyl carbonate (DMC). The electrochemical method that is constant current charge–discharge test was used for electrochemical properties of the acid-oxidized carbon nanotubes and tin oxide. The nanocomposites show higher specific capacities than the acid-oxidized carbon nanotubes and better cyclability than SnO₂, and the improvement is believed to be due to the improved maintainability of high dispersion of SnO₂ in the carbon nanotubes. The second cycle de-lithiation capacity of 255 mAh/g from the nanocomposites was nevertheless reduced to 250 mAh/g after 50 deep charge and discharge cycles, and the nanocomposites of acid-oxidized carbon nanotubes and SnO₂ may be considered as a candidate anode material for Li-ion batteries.