摘要: Fibrous graphite materials are highly attractive due to their unique morphologies, high degree of orientation of their graphite microcrystallites, extremely good mechanical and conductive properties, fascinating growth mechanisms, diverse preparation methods and potential applications. This review summarizes the preparation methods, Raman spectra and the growth mechanisms of graphite whiskers, columnar carbons with cone-shaped top cones, and needle- and rod-like polyhedral crystals, and their optical, electrical and magnetic properties and applications are outlined.
摘要: Sodium-ion batteries (SIBs) have attracted tremendous attention for large-scale stationary grid energy storage. With the upcoming commercialization of SIBs in the foreseeable future, developing high-performance carbon anodes from sustainable biomass is becoming increasingly important in the preparation of cost-effective SIBs. This review summarizes advanced carbon anodes for SIBs derived from various lignocellulose biomass waste. The history of our understanding of sodium storage mechanisms in carbon anodes is first discussed to clarify their structure-performance relationships. Conventional preparation strategies including pore structure design, heteroatom doping, control of the graphitic structure, and morphology control and their effects on the sodium storage capability of biomass-derived carbon anodes are then discussed. Finally, the practical applications, future research directions and challenges for the use of biomass-derived carbon anodes for SIBs are discussed from the aspects of synthesis methods, microstructure control and production costs.
摘要: Natural graphite has many excellent properties such as high thermal and electrical conductivities, high temperature resistance, corrosion resistance, and radiation tolerance. It is widely used in many fields such as thermal management, battery electrodes, and the nuclear industry. The carbon content is an important factor that limits the applications of natural graphite minerals, but the impurities are difficult to remove from high-grade graphite minerals. This review discusses the types of natural graphite and mineral resources, followed by a discussion of traditional graphite purification processes and new methods to obtain high-purity graphite. Recent research on the development of natural graphite for use in thermal management, battery electrodes and the nuclear industry are summarized and the future applications of natural graphite are discussed.
摘要: High-performance electromagnetic wave absorbing materials (EWAMs) are expected to solve electromagnetic wave radiation problems in both the military and civil fields. The desired features of EWAMs include strong absorption over a broad bandwidth, low density, thinness, oxidation resistance, wear resistance, ability to withstand high-temperatures and high strength. Carbon-based materials, including nanostructures and composites, are attractive alternatives to EWAMs because of their unique structures and properties. We summarize recent achievements in carbon-based EWAMs, including different dimensional (0D, 1D, 2D and 3D) carbon nanostructures and various types of carbon composites (dielectric/carbon, magnetic/carbon) and hybrids. The factors affecting the absorption of electromagnetic microwaves include electrical conductivity (σ), permittivity (ε) and permeability (μ) are discussed based on the electromagnetic microwave absorption mechanisms. Representative carbon-based EWAMs and the corresponding mechanisms of improving their electromagnetic microwave absorption are highlighted and analyzed. Strategies for the modification of carbon-based EWAMs are summarized and research trends are proposed.
摘要: Hollow porous carbon fibers for Li-S battery electrodes were prepared by the KOH activation of carbon prepared from hollow polyacrylonitrile fibers. The fibers had a high specific surface area of 2 491 m2·g−1, a large pore volume of 1.22 cm3·g−1 and an initial specific capacity of 330 mAh·g−1 at a current density of 1 C. To improve their electrochemical performance, the fibers were modified by treatment with hydrazine hydrate to prepare nitrogen-doped hollow porous carbon fibers with a specific surface area of 1 690 m2·g−1, a pore volume of 0.84 cm3·g−1 and a high nitrogen content of 8.81 at%. Because of the increased polarity and adsorption capacity produced by the nitrogen doping, the initial specific capacity of the fibers was increased to 420 mAh·g−1 at a current density of 1 C.
摘要: Metal-nitrogen carbon catalysts have received great attention in the field of gas-evolving electrocatalysis due to their high activity, large specific surface area and efficient gas diffusion paths. A solution of porphyrin iron, g-C3N4 and polyacrylonitrile in N,N-dimethylformamide was sonicated and electrospun into doped polyacrylonitrile nanofibers (NFs), and the NFs were then stabilized and carbonized at 900 °C to prepare Fe-N/CNF catalyst for oxygen reduction reaction (ORR). It was found that the addition of g-C3N4 to the electrospinning precursor led to the formation of abundant Fe-N species in Fe3+ and Fe2+ valence states, while Fe3C nanoparticles were formed without adding g-C3N4. Compared to Fe3C/CNF prepared without g-C3N4, the Fe-N/CNF catalyst presents an 4e− improved oxygen reduction reaction activity in both alkaline and acidic media. Furthermore, as a cathode in Zn-air batteries, the Fe-N/CNF catalyst exhibits high performance with an open-circuit voltage of 1.49 V, a power density of 146 mW cm−2 and a specific capacity of 703 mAh g−1. This work suggests a way to prepare metal-nitrogen-carbon catalysts for energy-related electrocatalytic applications.
摘要: 基于低温溶剂法从大宗农林废弃物玉米芯中提取的纤维素，耦合具有优异吸光性能的碳纳米管(CNTs)，构筑复合纤维素水凝胶(CNTs-CH)，利用纤维素凝胶的高保水性、可降解性，以及碳纳米管的高效光热转换能力、优良的力学性能和生物相容性，将其用于太阳能驱动界面水蒸发净化领域。考察了吸光材料CNTs的不同添加量对CNTs-CH复合水凝胶的太阳能吸收率、机械性能及界面光热水蒸发效率的影响。最优条件下，CNTs添加质量百分数仅需0.2%，此CNTs-CH复合纤维素水凝胶的平均蒸发速率可达到~1.52 kg m−2 h−1，太阳能-蒸汽转换效率约为92%；在海水中连续蒸发8 h，蒸发速率可保持在1.37 kg m−2 h−1左右，且无积盐现象，净化水质远高于世界卫生组织和美国环境保护署对饮用水的标准，说明CNTs-CH抗盐性能较强。此外，CNTs-CH水凝胶在强酸/碱性水溶液体系、染料废水和重金属离子污染水体中的蒸发速率可维持为1.30~1.40 kg m−2 h−1，太阳能-蒸汽效率可达到80%~86%，对污染物及盐分截留率高达99.9%，蒸发效果稳定，说明CNTs-CH光热蒸发器在海水淡化和工业废水净化回用领域有广阔的应用前景。
摘要: An innovative and efficient method for preparation of mesocarbon microbeads (MCMBs) was developed based on the dripping behavior and rheological properties of molten pitch during melt-spinning, where a string of beads was formed after the pitch was extruded from spinnerets and dropped into a receiving solvent (tetrohydrofuran or water). The pitch droplets were first carbonized, then activated by KOH or graphitized at 2800 °C to prepare A-MCMBs or G-MCMBs, respectively, and these were respectively used as the electrode materials for electric double layer capacitors (EDLCs) and lithium-ion batteries (LIBs). Results showed that both MCMB-W prepared using water as the receiving solvent and MCMB-T prepared using tetrohydrofuran as the receiving solvent had a spherical shape with sizes of 1-2 μm. A-MCMB-T had a high specific surface area (1 391 m2 g−1), micropore volume (0.55 cm3 g−1) and mesopore volume (0.24 cm3 g−1), with a 30% higher specific capacitance than an activated mesophase carbon prepared under the same conditions, and its capacitance retention was significantly improved when it was used as an electrode material for EDLCs. G-MCMB-T had a high degree of graphitization (0.895) and when it was used as an electrode material for LIBs it had a high specific capacity of 353.5 mAh g−1 after 100 cycles at 100 mA g−1. This work reports a new preparation method for MCMBs, which could be used to prepare energy storage materials.
摘要: Li-Se batteries have risen to prominence as promising lithium-ion batteries thanks to their ultrahigh volumetric energy density and the high electrical conductivity of Se. However, the use of Li-Se batteries is limited not only by the large volume expansion and dissolution of polyselenides in the cathodes during cycling, but also the low selenium loading. A highly effective and currently feasible approach to simultaneously tackle these problems is to position the selenium in a carbon matrix with a sufficient pore volume to accommodate the expansion while increasing the interfacial interaction between the selenium and carbon. We have synthesized a novel cathode material (Se@HPC) for Li-Se batteries of a honeycomb 3D porous carbon derived from a tartrate salt, that was impregnated with Se to produce Se-C bonds. The pore volume of the honeycomb 3D porous carbon was as high as 1.794 cm3 g−1, which allowed 65 wt% selenium to be uniformly encapsulated. Moreover, the strong chemical bonds between selenium and carbon stabilize the selenium, thus inhibiting its huge volume expansion and the dissolution of polyselenides, and promoting charge transfer during cycling. As expected, a Se@HCP cathode has excellent cyclability and a good rate performance. After 200 cycles at 0.2 C, its specific capacity remains at 561 mA h g−1, 83% of the theoretical value, and decays by only 0.058% per cycle. It also has a large capacity of 472.8 mA h g−1 under a high current density of 5 C.
摘要: Carbon-based catalysts for the oxygen reduction reaction (ORR) are considered potential substitutes for the expensive platinum-based catalysts. Recently, transition metal and nitrogen co-doped carbon materials (M-N-C) have attracted much attention from researchers due to their low cost and excellent activity. A cobalt- and nitrogen-co-doped porous carbon material (Co-N@CNT-C800) was prepared by the simple one-step pyrolysis of a star fruit-like MOF hybrid (ZIF-8@ZIF-67) at 800 °C. It consisted of CNTs with substantial Co and N co-doping and had a large surface area (428 m2·g−1). It had an excellent half-wave potential and good current density in alkaline media in the ORR with values of 0.841 V and 5.07 mA·cm−2, respectively. Compared with commercial Pt/C materials it also had excellent electrochemical stability and methanol tolerance. This research provides an effective way to fabricate low cost, high activity electrocatalysts for use in energy conversion.
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