AbstractOne of the most important research areas related to Li-ion batteries is the replacement of the graphite anode with other carbon materials such as hard carbons, activated carbons, carbon nanotubes, graphene, porous carbons, and carbon fibers. Although such materials have shown better electrochemical performance for lithium storage compared to graphite, there is plenty of room for improvement. One of the most effective approaches is to dope heteroatoms (e. g. nitrogen) in the structure of the carbon materials to improve their electrochemical performance when they are used as anode materials. We first describe how N-doping has a positive effect on lithium storage and then provide numerous selected examples of this approach being applied to various carbon materials. The characterization of N doped in the structure of different carbon materials by X-ray photoelectron spectroscopy and scanning tunneling microscopy is then presented since they are able to characterize the N in these structures with a high (atomic) resolution. Finally, a statistical analysis is performed to show how the amount of doped N affects the specific capacity of the N-doped carbon materials.

AbstractCarbon dots (CDs) have attracted increasing attention due to their high specific surface area, good dispersion, abundant surface functional groups, low biotoxicity and photoluminescence. However, their preparation on a large-scale is still a great challenge because of the high cost and environmental problems, and this seriously limits their practical applications. Carbonized corncobs were used as the starting material for the preparation of the CDs by electrochemical oxidation. Their natural porous structures with well-developed channels allow the electrode to be filled with electrolyte, and the electrochemical oxidation takes place both on the inside and outside surfaces of the corncob, achieving a CD output of 79.8 mg h−1 per gram of electrode material at 1 A. The CDs were combined with graphene oxide (GO) to produce CD/rGO composite aerogels by a hydrothermal method. After heat treatment at 600 °C, the materials obtained were used as the anode in a sodium ion battery, which had a capacity of 263.3 mAh g−1 after 1 000 cycles at 1 A g−1. This work suggests a new way to prepare CDs and possibly expand their range of application.

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.

Because of its high carbon content and easy graphitization, pitch is a promising precursor for carbon materials. To produce carbon materials with the desired performance, it is necessary to overcome the inherent shortcomings of pitch. For example, its complex composition and easy melting make it difficult to control the structure of the resulting carbon materials. Recently, researchers have proposed several methods to control the structure of carbon materials produced from pitch for energy storage. The latest advances in the structural design and preparation of pitch-based carbon materials for use in energy storage devices such as supercapacitors and alkali metal ion batteries are reviewed.

Using CO2 as a renewable carbon source for the production of high-value-added fuels and chemicals has recently received global attention. The photoelectrocatalytic (PEC) CO2 reduction reaction (CO2RR) is one of the most realistic and attractive ways of achieving this, and can be realized effectively under sunlight illumination at a low overpotential. Oxygen-incorporated carbon nitride porous nanosheets (CNs) were synthesized from urea or melamine by annealing in nitrogen or N2/O2 gas mixtures. They were used as the photoanode with Bi2CuO4 as the photocathode to realize PEC CO2 reduction to the formate. The electrical conductivity and the photoelectric response of the CNs were modified by changing the oxygen source. Oxygen in CNs obtained from an oxygen-containing precursor improved the conductivity because of its greater electronegativity, whereas oxygen in CNs obtained from the calcination atmosphere had a lower photoelectric response due to a down shift of the energy band structure. The CN prepared by annealing urea, which served as the source of oxygen and nitrogen, at 550 °C for 2 h in nitrogen is the best. It has a photocurrent density of 587 μA cm−2 and an activity of PEC CO2 reduction to the formate of 273.56 μmol cm−2 h−1, which is nearly 19 times higher than a conventional sample. The CN sample shows excellent stability with the photocurrent remaining constant for 24 h. This work provides a new way to achieve efficient catalysts for PEC CO2 reduction to the formate, which may be expanded to different PEC reactions using different cathode catalysts.

Along with the emergence of wearable electronic devices, green energy devices like Zn-ion hybrid supercapacitors (ZHSCs), which are extremely safe and cheap, and have excellent stability and high power energy densities, have received great attention. Carbonenes, mainly including graphene and carbon nanotubes (CNTs), are promising materials for ZHSCs because of their exceptional electrical conductivity and excellent mechanical stability. A comprehensive overview of strategies for the modification of carbonene-based materials for ZHSCs, and a brief summary of their energy storage mechanisms is given and topics for potential research are suggested.

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.

Carbon fiber-reinforced epoxy resin composites (CFRCs) have been used in the automotive and aerospace fields because of their excellent mechanical properties. The recycling of CFRCs has attracted attention worldwide in recent years. Chemical recycling is a promising method, which can selectively destroy specific resin bonds to achieve controllable degradation. Matrix epoxy resins are degraded into monomers or oligomers, and the high-value carbon fibers can be recycled. First, we summarize progress on chemical recovery methods, mainly oxidation, solvolysis and alcoholysis in super- and subcritical fluids, electrochemical recycling etc. Then, we briefly introduce the synthesis and depolymerization mechanism of recyclable thermosetting resins by the insertion of reversible chemical bonds into the resin to prepare recyclable resins, which is beneficial for the recycling and reuse of components in CFRCs. Finally, possible developments in the chemical recycling of CFRCs and the preparation of high-performance recyclable epoxy resins are proposed.

Capacitive deionization (CDI) has rapidly become a promising approach for water desalination. The technique removes salt from water by applying an electric potential between two porous electrodes to cause adsorption of charged species on the electrode surfaces. The nature of CDI favors the use of nanostructured porous carbon materials with high specific surface areas and appropriate surface functional groups. Electrospun carbon nanofibers (CNFs) are ideal as they have a high specific surface area and surface characteristics for doping/grafting with electroactive agents. Compared with powdered materials, CNF electrodes are free-standing and don't require binders that increase resistivity. CNFs with an appropriate distribution of mesopores and micropores have better desalination performance. Compositing CNFs with faradaic materials improves ion storage by adding pseudocapacitance to the electric double layer capacitance. The use of electrospun CNFs as electrodes for CDI is summarized with emphasis on the major precursor materials used in their preparation and structure modification, and their relations to the performance in salt electrosorption.

Micro-supercapacitors hold great promise for powering the Internet of Things devices owing to their high power density and long cycling life. However, the limited energy density hinders their practical use. Electrode materials play an important role in the performance of micro-supercapacitors. With the advantages of a large specific surface area and a high electrical conductivity, graphene has been considered a good candidate for the electrode material of micro-supercapacitors. The two-dimensional surface of graphene is parallel to the direction of transport of the electrolyte ions for micro-supercapacitors with an in-plane structure, which helps improve the ion accessibility of the electrodes. Therefore, the construction of graphene-based in-plane micro-supercapacitors has aroused great interest among researchers. Here, we summarize the recent advances in graphene and graphene-based materials for in-plane micro-supercapacitors from the perspective of electrode material design. The electrode materials include graphenes produced by chemical vapor deposition, liquid-phase exfoliation, reduction of graphene oxide, laser induction and heteroatom doping, as well as graphene-based composites, such as carbon nanotube/graphene, transition metal oxide/graphene, conducting polymer/graphene and two-dimensional material/graphene composites. Challenges and opportunities in graphene-based in-plane micro-supercapacitors are discussed, and future research directions and development trends are proposed.

MXene is a revolutionary two-dimensional material that has a distinct layer structure and the chemical composition of transition metal carbides. It has special physicochemical characteristics including a large specific surface area, good electrical conductivity, excellent mechanical properties and photothermal behavior, which give it a valuable variety of applications. To endow it a broader range of applications, it is often composited with carbon-based materials. Therefore, MXene and MXene/carbon composites have attracted much attention in applications such as electronics, biosensors and biomedicine over recent years. In this review, the fabrication, modification and biomedical applications of MXene and MXene/carbon composites are introduced, focussing on their biomedical applications, such as biosensors, antibacterial materials, drug delivery, and the diagnosis and treatment of diseases.

AbstractSodium-ion batteries (SIBs) have received extensive research interest as an important alternative to lithium-ion batteries in the electrochemical energy storage field by virtue of the abundant reserves and low-cost of sodium. In the past few years, carbon and its composite materials used as anode materials have shown excellent sodium storage properties through structural design and composition regulation. The increasing popularity of wearable electronics has demanded higher requirements for electrode materials. A free-standing electrode is able to eliminate the massive use of electrochemical inactive binders and conductive additives, thereby increasing the overall energy density of the battery system. Research progress on carbon materials such as carbon nanofibers, carbon nanotubes and graphene and their composites (metallic compounds and alloy-type materials) is summarized. The preparation strategies and electrochemical properties of free-standing carbon-based anodes with and without substrates are categorized and reviewed. Finally, proposals are made for future research and developments for free-standing carbon-based anodes for SIBs.

Because of their low price, excellent safety and energy storage performance, aqueous zinc-ion batteries (ZIBs) have great potential for use in the power grid and in wearable devices. However, the Zn anode of ZIBs is not stable, for example, Zn dendrite can be formed on the Zn anode accompanied by hydrogen evolution and side reactions, leading to its instability, which has been an obstacle to its use. Carbon nanomaterials have recently been used to improve the performance of Zn anodes due to their unique structure, excellent conductivity and good stability. This review summarizes the recent development for stabilizing zinc anodes. The carbon nanomaterials are used as hosts, protective coating layers, electrolyte additives and modifiers in the separators to stabilize the Zn electrodes. The challenges involved in doing this are presented, and some future developments are outlined.

A low-cost, green catalyst for nitrobenzene (NB) hydrogenation is needed for aniline production. We report the preparation of highly-dispersed Co particles supported on N-doped carbons by the hydrothermal treatment of glucose, followed by the pyrolysis of a mixture of urea, glucose hydrochar and cobalt nitrate in one-pot. The effect of the pyrolysis temperature on the microstructure of the catalysts was studied. Results indicated that the activity for NB hydrogenation was highly affected by the surface area, Co-loading level and Co-Nx coordination in the catalysts. Co@NCG-800 pyrolyzed at 800 °C with 10% Co in the precursor had extraordinary activity for NB hydrogenation, achieving full conversion and 99% aniline selectivity in isopropanol at 100 °C and 1 MPa H2 pressure for 2.5 h. NB conversion and aniline selectivity over the catalysts remained almost unchanged after six recycles, due to the strong coordination between the N- and Co-species. The reaction system showed not only a high NB activity but also a green and durable catalytic process, with easy operation, easy separation and catalyst reusability.

A lithium-ion capacitor, a combination of a lithium-ion battery and a supercapacitor, is expected to have the advantages of both a battery and a capacitor and has attracted worldwide attention in recent years. However, its energy storage is limited due to the electric double-layer capacitance mechanism of the positive electrode. Consequently, to fundamentally improve the performance of the positive electrode material, a novel dual-ion hybrid capacitance energy storage mechanism is proposed. Porous graphitic carbon with a partially graphitized structure and hierarchical porous structure was synthesized by a one-step heat treatment method using potassium/magnesium/iron citrate as precursors. When used as the positive electrode material, the porous graphitic carbon has a dual-ion hybrid capacitance mechanism in an electrolyte produced using a mixture of Li-TFSI (bis(trifluoromethylsulfonyl) amine lithium salt) and BMIm-TFSI (1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide), which combines electric double-layer capacitance behavior in a lithium-ion capacitor and anion intercalation/de-intercalation behavior in a dual-ion battery. Two mechanisms were observed in the electrochemical characterization process, and the performance of the porous graphitic carbon was compared to porous carbon and artificial graphite, which indicate that its energy storage performance is significantly better due to the additional plateau capacity contributed by anion intercalation at a high potential and the improved conductivity through the local graphitic regions.

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.

Resin carbons have favorable mechanical, electrical and thermal properties, and are widely used as structural and functional materials in aviation, aerospace and energy storage, etc. The inherent molecular structures of resins make their graphitization difficult, which greatly limits wide applications. Research progress on the graphitization and applications of resin carbons in recent years are reviewed. Their graphitized carbon content can be increased and their graphitization temperature reduced by adding catalysts, carbon nanomaterials and easily graphitized co-carbonization agents. Most studies have been devoted to increasing their graphitized carbon content using catalysts and carbon nanomaterials. The degree of graphitization of resin carbons at temperatures below 1 400 °C can reach 74% by adding a catalyst, and above 2 000 °C by adding carbon nanomaterials. Co-carbonization agents may increase their degree of graphitization and also their carbon yield. The thermal and electrical conductivities of carbon/carbon composites could be improved by increasing the degree of graphitization of resin carbons, and this would improve the conductivity, rate performance and power density of supercapacitors and secondary batteries. Challenges and research prospects for the graphitization of resin carbons and their applications are discussed.

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.

Hard carbons have recently attracted wide interest as anode materials for potassium ion batteries (PIBs) because of their high reversible capacity. But, their high preparation cost and poor cycling stability prevent their practical use. Coconut shell-derived hard carbons (CSHCs) were prepared from waste biomass coconut shell using a one-step carbonization method, and were used as anode materials for potassium ion batteries. The effects of the carbonization temperature on the microstructures and electrochemical properties of the CSHCs were investigated by X-ray diffraction, nitrogen adsorption, Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, and cyclic voltammetry, etc. Results indicate that the CSHC carbonized at 1 000 °C (CSHC-10) has a suitable graphite microcrystal size, pore structure and surface defect content, and has the best electrochemical performance. Specifically, it has a high reversible specific capacity of 254 mAh·g−1 at 30 mA·g−1 with an initial Coulombic efficiency of 75.0%, and the capacity retention rates are 87.5% after 100 cycles and 75.9% after 400 cycles at 100 mA·g−1, demonstrating its excellent potassium storage performance.

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 2 800 °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.