摘要: Covalent organic frameworks (COFs) are highly promising electrode materials for next-generation rechargeable metal-ion batteries owing to their robust framework, abundant electrochemically active sites, well-defined and tunable pores and channels for metal ion transfer, and adjustable molecular structures for improving electrochemical performance. Moreover, COFs do not have the problems caused by expensive or toxic elements in conventional inorganic electrode materials or the cycling stability challenges existing in small organic molecules, and thus have great potential as electrode materials in next-generation rechargeable metal-ion batteries. We summarize the electrochemically active sites of these materials for charge storage, and most importantly, we focus on strategies for improving their electrochemical performance, including energy density, rate performance and cycling life by changing their frameworks, pores, active sites, and electronic structures. To fabricate high performance COF electrodes, much more effort is needed to improve their ionic and electronic conductivities, increase their operating voltage, and reveal their mechanisms of energy storage. This review may shed light on developing high performance COF electrode materials for next-generation rechargeable metal-ion batteries.
摘要: As an emerging CO2 conversion technology, the electrochemical CO2 reduction (ECR) reaction has received widespread attention. For the ECR process, the accurate and rational design of electrocatalysts is essential and significant for improving the catalytic performance. Carbon-based materials are considered one of the promising electrocatalysts for ECR because of their variety of abundant sources, high specific surface area, high porosity, and multilevel dimensionality and tunable active sites. Furthermore, doping by heteroatoms and introducing metal atoms in the frameworks or substrates of the carbon materials are effective strategies for further improving the ECR activity. Particularly, nickel-nitrogen-carbon (Ni-N-C) materials show excellent reactivities for the ECR to CO and have the potential for large-scale applications. We summarize the recent development of Ni-N-C catalysts with a multilevel structure for the ECR to CO and also the key principles and primary parameters of the ECR. Furthermore, the rational and precise design of multilevel Ni-N-C catalysts on different carbon frameworks or substrates is discussed and presented, especially including carbon quantum dots, one dimensional (1D) carbon-based materials, two dimensional (2D) carbon-based materials and nanoporous carbon-based materials. The effects of microstructure on ECR performance are also analyzed. Finally, the challenges and outlook for Ni-N-C catalysts in an ECR system are presented. This review provides some new insights and guidelines for rationally designing and preparing Ni-N-C catalysts with a multilevel structure and high performance.
摘要: Recent progress in the synthesis of carbon materials from biomass and coal/heavy oil waste and their use as the electrode materials of supercapacitors and Li-ion batteries is reviewed. The carbon precursors include seafood and agricultural waste, and coal and heavy oil by-products. The carbon materials include 0D carbon quantum dots, 1D carbon nanofibers, 2D carbon nanosheets, and 3D carbon frameworks. Techniques to tailor the carbon porosity/surface include KOH activation with and without self-templating, self-activation and/or in-situ templating, and heteroatom doping with N, O, P and their co-doping. The effects of porosity and heteroatom doping on the electrochemical performance are summarized. The challenges for the synthesis, microstructural tailoring of these materials and their potential use in supercapacitors and Li-ion batteries are analyzed.
摘要: Porous carbon-based electrode materials have been widely used in supercapacitors (SCs) because of their good physicochemical stability, high specific surface area, adjustable pore structure, and excellent electrical conductivity. The factors influencing their SC performance are analyzed, which include specific surface area, pore structure, surface heteroatoms, structural defects and electrode structure. The high surface area accessible to ions provides abundant active sites for their storage, while a suitable pore structure is important for the accommodation and diffusion of ions, thereby influencing the specific capacitance and rate performance of the electrodes. An appropriate pore size with a narrow distribution is required to increase the volumetric energy density while mesopores are favorable for ion transport, so a good balance between micro and mesopore volumes is important to improve both the energy and power densities of the SCs. Structural defects, surface heteroatoms and a rational electrode structural design all play significant roles in the capacitance performance.
摘要: Porous carbons are widely used in the energy storage and conversion field because of their excellent electrical conductivity, high specific surface area and superb electrochemical stability. The template method is one of the most advanced approaches to prepare porous carbons with well-defined pore structures and suitable pore size distributions. The pore formation mechanism and structure-property relationships of porous carbons obtained by template methods for supercapacitor electrodes are summarized. They include hard templates (magnesium-based, silica-based, zinc-based, calcium-based templates), soft templates (conventional soft template, ionic liquids, deep eutectic solvent) and self-templates (biomass, MOFs). Furthermore, the problems in tailoring the pore texture of porous carbons are clarified, and proposals are made for future research.
摘要: Redox flow batteries (RFBs), regarded as the most effective grid-scale electrochemical energy storage technology, are attracting wide attention because of the problems of the energy crisis and environmental pollution. Charge transport properties are critical factors related to the electrochemical performance of energy storage devices. Nanocarbons, which have special morphologies and many physicochemical properties, such as high ionic conductivity, high thermal conductivity and excellent mechanical properties, can play an indispensable role in electrochemical energy storage. Adjusting the microstructure of carbon materials is an effective strategy to improve their electron and ion transport behavior. In this work, the functions of nanocarbons in RFBs are reviewed, especially focusing on the modification and design of nanocarbons used in the electrodes, suspended electrodes in semi-solid RFBs, and bipolar plates (collectors) used to improve the energy efficiency, power density and the stability of high-performance RFBs. A more systematic and comprehensive understanding of the role that nanocarbons play in RFBs could provide a new perspective for the design of high-performance RFB electrodes.
摘要: Raman spectroscopy is a fast, non-destructive and high-resolution characterization tool based on laser physics that can be applied to a wide range of materials science problems. It has proven to be an effective tool in studying phase transitions induced by variables such as temperature, pressure or electrochemical reactions. In-situ Raman spectroscopy can be used to track any microstructural changes of the electrode materials and interface reactions in alkali metal-ion batteries during charging and discharging. Carbon materials have become the most widely used anode materials for lithium-ion batteries because of their good electrochemical reversibility, excellent stability, low electrochemical charge/discharge potential platform, and low cost. The use of in-situ Raman spectroscopy in understanding the reactions occurring in alkali metal-ion batteries using carbon anode materials is summarized with a focus on the energy storage mechanism in Li+/Na+/K+ ion batteries using carbon materials such as graphite and hard carbon as the anode materials. The effects of size, stress, doping, and the solvation-assisted co-intercalation of Li+/Na+/K+ ions on the energy storage behavior in alkali metal-ion batteries are analyzed. Based on the strength and weakness of in-situ Raman spectroscopy, its combination with AFM, in situ XRD and other high-resolution in situ technologies is used to reveal the energy storage mechanisms.
摘要: Secondary-ion batteries, such as lithium-ion (LIBs) and sodium-ion batteries (SIBs), have become a hot research topic owing to their high safety and long cycling life. The electrode materials for LIB/SIBs need to be further developed to achieve high energy and power densities. Anode/cathode active materials based on their alloying/dealloying with lithium, such as the anode materials of silicon, phosphorus, germanium and tin, and the cathode material of sulfur, have a high specific capacity. However, their large volume changes during charging/discharging, the insulating nature of phosphorus and sulfur, as well as the shuttling of polysulfides in a battery with a sulfur cathode decrease their specific capacity and cycling performance. The formation of dendrites in anodes during the deposition/dissolution of Li and Na leads to severe safety issue and hinders their practical use. Carbon materials produced from abundant natural resources have a variety of structures and excellent conductivity making them suitable host frameworks for loading high specific capacity anode/cathode materials. Recent progress in this area is reviewed with a focus on the factors affecting their electrochemical performance as the hosts of active materials. It is found that the mass loading of the active materials and the energy density of the batteries can be enhanced by increasing the specific surface area and pore volume of the carbon frameworks. Large volume changes can be efficiently accommodated using high pore volume carbon frameworks and a moderate loading of the active material. Suppression of the shuttling of polysulfides and therefore a long cycling life can be achieved by increasing the number of binding sites and their binding affinity with polysulfides by surface modification of the carbon frameworks. Dendrite growth can be inhibited by a combination of a high specific surface area and appropriate interface modification. Rate performance can be improved by designing the pore structure to shorten Li+/Na+ diffusion paths and increasing the electrical conductivity of the carbon frameworks. DFT calculations and simulations can be used to design the structures of carbon frameworks and predict their electrochemical performance.
摘要: Capacitive deionization (CDI), in which electrode materials play an important role, is considered a novel desalination technology because of its advantages of low energy consumption, low cost and low pollution. Porous electrode materials with a high accessible surface area, hydrophilic surfaces and excellent electrochemical performance have proved to be ideal. Carbons derived from metal-organic frameworks (MOFs) are most suitable for this purpose because of their controllable morphology and microstructure, suitable pore size distribution, and excellent electrical conductivity. The preparation and of MOF-derived carbon materials and their performance for the use as CDI electrode materials are reviewed. These include MOF-derived carbons, modified MOF-derived carbons, doped MOF-derived carbons and MOF-derived carbon composites with graphene, carbon nanofibers and carbon nanotubes. The advantages and challenges of these carbon electrode materials for CDI are summarized and future development is proposed.
摘要: As a natural abundant high-carbon resource, the use of coal to develop carbon nanomaterials is an important research topic. In recent years, a variety of carbon materials with different morphologies and nanotextures have been designed and constructed using coal and their derivatives as precursors, and their use in energy storage, catalysis, adsorption and absorption have been explored. State-of-the-art research on carbon nanomaterials derived from coals of different rank and their derivatives are summarized with specific attention to the synthesis strategies and structure control. The use of these coal-derived carbons for energy storage, such as secondary batteries and supercapacitors, is also discussed in terms of their structural features. The review aims to provide valuable insight into the present challenges and inspire new ideas for the development of advanced coal-derived carbon materials.
摘要: Potassium-ion batteries (PIBs) have the potential to be used in future large-scale energy storage devices because of the abundance of potassium resources and their relatively high energy density. However, low reversible capacity and poor cycling stability caused by the large size of the potassium ions limit their practical application. N-doped bacterial cellulose-derived carbons (NBCCs) were prepared by impregnating bacterial cellulose with Mg(NO3)2 solutions (0.03, 0.05 and 0.07 mol L−1) as a pore template and nitrogen source, followed by carbonization and acid washing. The effects of the Mg(NO3)2 concentration on the morphology, porosity, N doping level and electrochemical performance of the NBCCs were investigated. NBCC (0.05) is the best of the three because it has an interconnected pore network structure with a homogeneous distribution of N at a concentration of 3.38 at% and a high specific surface area of 1 355 m2 g−1. It delivers an excellent rate capability of 134 mAh g−1 at 5 A g−1 and a capacity of 307 mAh g−1 after 2 500 cycles at 2 A g−1. A NBCC (0.05)-based anode in a potassium ion hybrid capacitor has a high energy density of 166 W h kg−1 at a power density 493 W kg−1 and excellent cyclability with a capacity retention of nearly 95% after 2 000 cycles. This simple synthesis strategy for fabricating carbon anode materials with an excellent electrochemical performance should promote the development of green and large-scale energy storage devices.
摘要: We report a porous carbon material (NPCM) with a high N content as a high-performance supercapacitor electrode material which was prepared by a simple activation-doping process using Metaplexis Japonica shell as the carbon precursor, ammonium chloride as the nitrogen source and zinc chloride as the activation agent. Its high electrical conductivity, large ion-accessible surface area and fast ion transport ability make it possible to achieve a high mass loading of NPCM per area of the electrode and a high energy and high power density supercapacitor. An electrode with a low NPCM mass loading of 1 mg cm−2 has a gravimetric specific capacitance of 457 F g−1 and an areal specific capacitance of 47.8 μF cm−2. At a much high NPCM loading of 17.7 mg cm−2 it has a high gravimetric capacitance of 161 F g−1. Furthermore, an assembled NPCM//NPCM symmetric supercapacitor with an optimal NPCM loading of 12.3 mg cm−2 delivered a high specific energy of 12.5 Wh kg−1 at an ultrahigh power of 80 kW kg−1 in 1 mol L-1 Na2SO4. The achievement of such high-energy and high-power densities using NPCM will open exciting opportunities for carbon-based supercapacitors in many different applications.
摘要: Three-dimensional (3D) graphene aerogels (GAs) with a tunable pore structure, a highly accessible surface area, and exceptional compressibility, elasticity and wettability have been explored as promising absorbents for efficient oil/water separation. However, the strategies for assembling 3D GAs usually involve a high-temperature process, resulting in high cost. We report the synthesis of a 3D porous polyoxometalate (POM)-hybridized GA (POM-GA) as a highly efficient and recyclable absorbent for oil/water separation. The material was fabricated at room temperature by the self-assembly and reduction of graphene oxide using POM as a functional cross-linker and hydrazine hydrate as a reductant. It had a 3D interconnected macroporous structure, a large specific surface area, and exceptional compressibility, elasticity and wettability, and had excellent absorption capacities of 100－210 g g−1 for the rapid removal of various organic pollutants from water, outperforming most of the previously reported graphene-based macro-assemblies synthesized at high temperatures. Moreover, the absorbed oils can be readily removed by squeezing or first squeezing and then burning the remaining organic from the 3D POM-GA. The oil-absorption capacity retention rates of the 3D POM-GA are 96 and 90% after 10 absorbing-squeezing and absorbing-squeezing-burning cycles, respectively. The material therefore has great potential for efficient oil/water separation with wide applicability and excellent durability.
摘要: Gelatin-derived N-doped porous carbons (GPCs) with a large pore volume were synthesized by a method combining templating, freeze-drying and carbonization, using amino acid rich gelatin as the carbon and nitrogen sources, and silica sol and ice as the templates. The pore volume of the GPCs was regulated by adjusting the mass ratio of the silica sol to ice. Lithium polysulfide (LiPS) adsorption experiments show that the materials have a strong chemisorption for LiPSs. Electrochemical measurements show that N-doping accelerates the sulfur reduction kinetics and inhibits the shuttling of LiPSs. In addition, the larger the pore volume of the GPC, the better the cycling stability of the sulfur cathode. A highly N-doped (7.00%) GPC with a pore volume of 2.98 cm3 g−1 could adsorb a high sulfur content of 78.4% and had a high sulfur utilization rate. Its composite with sulfur as a cathode material gave a high initial specific capacity of 1 384 mAh g−1 at 0.1 C, which dropped to 608 mAh g−1 after 100 cycles.
摘要: Although the Co and N co-doped carbon catalyst (Co-NC) has attracted much attention because of its low cost and the natural abundance of the dopants, it has a low oxygen reduction reaction (ORR) activity and a high selectivity for the two-electron (2e-) reduction of oxygen to H2O2, which affects its use in fuel cells. Co-NC catalysts were prepared by the pyrolysis of a mixture of cobalt chloride and chitosan pretreated with zinc chloride at 650, 750 and 850 oC, followed by washing with nitric acid and annealing at 900 oC. The results indicate that zinc chloride helps the complexing of chitosan with Co2+, which is also a chemical activator that generates pores, and annealing caused the evaporation of the spherical Zn metal nanoparticles formed by the carbothermal reduction of Zn ions, leading to a unique porous structure of the catalysts with spherical pores filled with spherical carbon nanoparticles formed by the growth of nitrogen-doped carbon as a result of the Co catalyst. The degree of graphitization is also improved by the Co catalyst. The Co-NC catalyst obtained at a pyrolysis temperature of 750 oC shows the same four-electron (4e-) reduction of oxygen as a commercial Pt/C catalyst, and a significantly higher ORR catalytic activity, longer-term stability and better methanol tolerance than a commercial Pt/C catalyst. These are due to its large specific surface area, high contents of pyridinic nitrogen and graphitic nitrogen that disperse the Co species and its excellent electrical conductivity.
摘要: Intrinsic polysulfide shuttling is the most fatal problem with Li-S batteries but it can be suppressed by functionalizing the separators with strong lithium polysulfide absorbents. Carbon nanotube (CNT)-supported MoSe2 nanoflakes with a large interlayer spacing were coated on a commercial polypropylene separator to build an efficient barrier (M/C-PP) to polysulfide shuttling for Li-S batteries. The battery with the separator had initial specific capacities of 1 485 and 880 mAh g−1 at 0.1 and 2 C, respectively, and an excellent long-term cycling stability with a low decay rate of 0.093% per cycle at 0.5 C after 300 cycles. This excellent performance was attributed to the strong adsorption of polysulfides by MoSe2 and the fast charge transport channels provided by the CNTs.
摘要: 通过在聚丙烯腈（PAN）溶液中添加沥青，经静电纺丝、不熔化和炭化处理后，制备出沥青/聚丙烯腈复合纳米炭纤维无纺布。结果表明，沥青的加入，不仅减小了所制纳米炭纤维的直径、提高了其导电性，而且还增大了纳米炭纤维的比表面积、扩大了孔径分布，有效地改善了纳米炭纤维的容量和倍率性能。当沥青与PAN的质量比为1∶1.5时，所得纳米炭纤维在低电流密度（0.1 A g–1）时的比容量为219 F g–1，其比容量是纯PAN基纳米炭纤维的1.38倍。当电流密度提高到50 A g–1时，样品的容量保持率可达到69.4%（纯PAN基纳米炭纤维的容量保持率仅为42.8%）。将样品组装为对称超级电容器后，其功率密度和能量密度分别可达14.8 kW kg–1和4.8 Wh kg–1，容量保持率在20 000次循环后可达94.1%。