摘要: Potassium ion batteries (KIBs) and potassium-based dual ion batteries (KDIBs) are newly-emerging energy storage devices that have attracted considerable attention owing to the low-cost of potassium resources and their comparable performance to lithium-ion batteries (LIBs). Graphite materials, as the successful commercialized anode materials of LIBs, can also be used as anodic and cathodic host materials for the intercalation of the large potassium cations and other anions, respectively. However, there are still some challenges hindering the practical application of graphite materials in the anode for KIBs and the cathode for KDIBs. The huge volume changes after intercalation (61% for K and 130% for anions) result in graphite interlayer slipping and structural collapse, causing capacity fade and a short cycle life. Moreover, the intercalation of large K+ and anions have poor kinetics due to the small graphite interlayer spacing, restricting the rate capability. To solve these issues of the use of graphite materials, this review attempts to provide a better understanding of the intercalation mechanisms for K+ and anions, and to correlate the electrochemical performance of KIBs and KDIBs to the microstructure of graphite, and the physicochemical properties of electrolytes and binders. Finally, research prospects are provided to guide the future development of graphite materials for potassium-based energy storage.
摘要: Graphene quantum dots (GQDs), as a unique member of the nanocarbon family, have become important catalysts for overall water splitting and metal-air batteries because of their high specific surface area, abundant surface chemical reaction sites and high electron mobility. Understanding the fundamental catalytic mechanism of GQDs in heterogeneous catalysis is conducive to the rational design of high performance GQD-based catalysts. This article summarizes current research progress in the synthesis, modification and applications of GQD-based heterogeneous catalysts in overall water splitting, metal-air batteries and other fields. The issues related to the use of GQD-based catalysts in these fields are discussed together with their future development.
摘要: In the process of global transition to a sustainable low-carbon economy, the two major low-carbon energy technologies, namely, methane (CH4) storage and methane capture face the same challenge, that is, the lack of efficient adsorbents. Metal-organic framework (MOF) materials have potential value in the field of gas adsorption storage because of their high specific surface area, good porosity, and adjustable pore structure. In this study, the structural design and synthesis methods of MOFs are introduced, and the research progress and problems associated with MOF materials in methane storage and capture are reviewed. The current research status of methane storage at high pressure is introduced in terms of volumetric and gravimetric uptake. For methane capture at atmospheric pressure, emphasis is placed on CH4/N2 and CO2/CH4 separation and methane capture technologies. Finally, the problems and challenges of using MOF materials to achieve efficient methane storage and capture are analyzed and future prospects are presented.
摘要: Although carbon-based materials, such as graphene, metal-organic frameworks (MOFs), polymers and biomolecules, have aroused increasing scientific interest in the fields of physics, chemistry, materials science and molecular biology, their atomic-scale observation is still a challenge due to their structural instability under the electron beam. Ambiguous atomic arrangements have critically limited the fundamental understanding on these materials and their potential applications in electronics, mechanics, thermodynamics, catalysis, bioscience and medicine. Very recently, revolutionary sub-Ångström resolution achievements of transmission electron microscopy (TEM) using a low voltage, a low electron dose, or a cryogenic environment have greatly facilitated the atomic-scale structural and chemical examination of electron beam sensitive materials. In particular, the ability to image light elements atom by atom gives unprecedented insight into the structures and properties of novel carbon-based materials. In this review, the recent developments in advanced TEM combined with various imaging and spectroscopy techniques, and their use in examining graphene-based materials, MOFs, polymers, and biomacromolecules are summarized and discussed. The current challenges in materials research and trends for the future design of TEM equipment are outlined, which is expected to provide a deeper understanding of structure–performance relationships and the discovery of new carbon materials.
摘要: Diamonds with two extreme sizes, large single crystal and nanocrystalline, have completely different properties, and have aroused the continuous attention of researchers. Each has its own merits and can be converted into the other. The synthesis of large single crystal diamond can be described as the aggregation, assembly and combination of nanocrystalline nuclei, i.e., diamond transforming from the nano-scale to the inch scale. A large single crystal diamond can be transformed into nanocrystals by surface nanocrystallization. The preparation methods, properties and applications of single crystal diamonds of different sizes are introduced and the transformations between them are described. Research interest in controlling the crystal size is discussed.
摘要: Carbon dots (CDs) have been regarded as a new star in the family of carbon nanomaterials, and have been widely studied since they were accidentally discovered in 2004. CD-based solid-state luminescent (CD-SSL) materials have the advantages of being environmentally friendly, non-toxic and low cost, which makes them ideal candidates to replace rare earth/semiconductor quantum dot-based luminescent materials. However, because of their quenching caused by aggregation, it is a great challenge to retain their luminescent properties when they are transferred from solution to the solid state. This review gives a brief introduction to the synthesis methods for CDs, followed by a detailed description of the most widely used strategies for the preparation of CD-SSL materials and their typical applications in white light-emitting diodes and optical sensors. Finally, the shortcomings of current research on CD-SSL materials are discussed, and their future in the above-mentioned as well as other fields is briefly considered.
摘要: Electrochemical capacitors, also called supercapacitors (SCs), have been gaining a more significant position as electrochemical energy storage devices in recent years. They are energy storage devices with a considerable power density, a satisfactory energy density and a long-life cycle, suitable for a large number of applications. The further development of these devices relies on providing suitable, low-cost, environmentally friendly, and abundant materials for use as the active materials in the electrodes. Among the current materials used, activated carbons have a superior performance. Their excellent electrochemical performance, high specific surface area, high adsorption, tunable surface chemistry, fast ion/electron transport, abundant functional moieties, low cost, and abundance have made them promising candidates as SC electrodes. These advantages can be enhanced if the activated carbons are prepared from biomass precursors. Recently, scientists have focused on biomass because it is abundant and renewable, low cost, simply processed, and environmentally friendly. The fundamentals of SCs as an electrochemical energy storage device are discussed and biomass from various sources is categorized and introduced. Finally, the activation techniques for these biomass precursors and their use as electrode materials for SCs are discussed.
摘要: Developing an anode material with high-rate Li+ intercalation and stable charge/discharge platform is important for achieving high performance lithium ion capacitors (LICs). Reduced graphene oxide (rGO)-encapsulated MnO microspheres (~2 μm) are obtained by a simple process including solvothermal and calcination techniques. The material contains a large number of mesopores (~2.8 nm diameter). The MnO/rGO has a favorable cycling stability (846 mAh g−1 at 0.1 A g−1 after 110 cycles) and an outstanding rate performance (207 mAh g−1 at 6.4 A g−1). Kinetic analysis reveals that a pseudocapacitive contribution plays a dominant role for the energy storage. The improvement in the pseudocapacitive behavior is ascribed to the fact that the uniform rGO coating on the MnO provides continuous pathways for electron transport, and the mesoporous structure provides numerous migration paths for Li-ions. Furthermore, MnO/rGO//activated carbon (AC) LICs have a high energy density of 98 Wh kg−1 at a relatively high power density of 10350 W kg−1, and have a capacity retention of 71% after 5 000 cycles at 1.6 A g−1. These outstanding results indicate that the enhanced Li+ intercalation of the anode offsets the kinetic imbalance between the two electrodes.
摘要: Carbon dots (CDs) have become an emerging carbon nanomaterial for use in energy-conversion systems because of their large surface area and rapid electron transfer. Carbon dots (BN-CDs) doped with both boron and nitrogen were synthesized by a simple one-step electrochemical etching approach using low-cost petroleum coke as precursor. Compared with CDs doped with only B or N, BN-CDs showed an excellent four-electron oxygen reduction reaction (ORR) activity with a positive onset potential of 0.958 V and a large diffusion-limited current density of −4.32 mA cm−2. Furthermore, the long-term stability and methanol tolerance of BN-CDs were better than those of a commercial Pt/C catalyst. It was found by density functional theory (DFT) calculation that the co-doping of N and B promoted the adsorption of O2 molecules in the ORR process. This work provides new insight into the rational design of carbon nanomaterials and their use in energy conversion.
摘要: Graphitic hollow porous carbon spheres (GHPCSs) have the advantages of a unique cavity structure, high surface area and excellent conductivity, and are promising electrode materials for energy storage. A Fe–tannic acid (TA) framework synthesized using TA as the carbon source and K3 [Fe(C2O4)3] as a complexing agent, was self-assembled onto a melamine foam, which was converted to GHPCSs by carbonization, where the K3 [Fe(C2O4) 3] also acts as an activating-graphitizing agent. The outer shell of the as-prepared GHPCSs has a large specific surface area, a micropore-dominated structure and excellent electrical conductivity, which ensure a large enough active surface area for charge accumulation and fast ion/electron transport in the partially graphitized carbon framework and pores. The optimum GHPCS has a high capacitance of 332.7 F g−1 at 1 A g−1. An assembled symmetric supercapacitor has a high energy density of 23.7 Wh kg−1 at 459.1 W kg−1 in 1 mol L-1 Na2SO4. In addition, the device has long-term cycling stability with a 92.1% retention rate after 10 000 cycles. This study not only provides an economic and time-saving approach for constructing GHPCSs by a self-assembly method, but also optimizes ion/electron transport in the carbon spheres to give them excellent performance in capacitive energy storage.
摘要: A 3D assembly of nitrogen-doped carbon nanofibers (NCFs) derived from polyacrylonitrile was synthesized by a combined electrospinning/carbonization technique and was used as the positive current collector in lithium sulfur (Li-S) batteries containing a Li2S6 catholyte solution. The physical and electrochemical behavior of the NCFs were investigated and it was found that their electrochemical performances depended on the pyrolysis temperature. Of the samples carbonized at 800, 900 and 1 000 °C, those carbonized at 900 °C performed best, and delivered a reversible capacity of 875 mAh•g−1 at a high sulfur loading of 4.19 mg•cm2 and retained at 707 mAh•g−1 after 250 cycles at 0.2 C. The coulombic efficiency of the NCF-900@Li2S6 electrode was almost 98.55% over the entire cycle life. In addition, the capacity retention of the electrode reached 81.53% even at a high current density of 1 C for over 150 cycles. It was found that the NCFs carbonized at 900 °C had the highest electrical conductivity, which might be the dominant factor that determined its performance for use as a positive current collector.
摘要: Nanostructured phenolic resin-based carbon aerogels with an extensive network structure are regarded as ideal energy storage materials for supercapacitors. However, the initial bulk form and low capacitance of previously reported porous carbon aerogels are problematic for practical use. Phenolic resin-based porous carbon spheres were synthesized by a simple hydrothermal process using ammonia, ethylenediamine or hexylenediamine as a catalyst. The porous carbon spheres were investigated by SEM, BET, XPS, etc. It was found that the number of ammonium groups, length of the alkyl chain and processing temperature play vital roles in determining the pore structure, size and uniformity of the carbon spheres. NH4+ is necessary to obtain the carbon spheres and but changing the other parameters has no obvious effect on their crystal structure. The sample prepared at a hydrothermal temperature of 80 °C using ammonia as the catalyst has the highest specific capacitance of 233.8 F g−1 at a current density of 1.0 A g−1. It has an excellent capacitance retention of 98% after 10 000 charge/discharge cycles at 7 A g−1, indicating its good cycling stability and rate capability. This result shows that a higher specific surface area, porosity and defect density are probably the crucial factors in improving the electrochemical capacitance.
摘要: Two kinds of carbon quantum dots, C-dots-160 and C-dots-200 with different fluorescence luminescence behaviors were synthesized by a one-step hydrothermal method at 160 and 200 °C, respectively, using ammonium citrate as the raw material. The relationship between the microstructure of the C-dots and the fluorescence emission behavior was investigated. Results indicate that an increase of synthesis temperature introduces more oxygen and nitrogen atoms into the C-dots, increasing the total number of structural defects and altering their concentation ratio . It is this ratio difference in the two C-dots that causes their different luminescence behaviors. The proportion of several types of defects in the C-dots-200 are relatively balanced, leading to excitation wavelength-dependent fluorescence while the most abundant defects in C-dots-160 are in the form of C＝O, which is the main reason for its excitation independent luminescence behavior. The number of structural defects in C-dots-160 is less than in C-dots-200 and the latter has the stronger fluorescence emission.
摘要: It is very difficult to prepare red/near-infrared emission carbon dots (CDs) for bio-imaging applications which are needed because of their deep tissue penetration, minimal auto-fluorescence, and low emission light damage to bio-tissues. Near-infrared emitting CDs (NIR-CDs) were synthesized from sulfonated tetraphenylporphyrin using a solvothermal method. They have excitation-independent properties with a maximum emission at 692 nm. Studies showed that this unique near-infrared emission mainly originated from the aggregated molecular states of the CDs. The NIR-CDs showed good water solubility, exceptional biocompatibility, low toxicity, and superior cellular labelling ability. This work could significantly advance the structural design and preparation of NIR-CDs and corresponding bio-imaging applications.
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