Ordered and disordered carbons have been commonly used as coating materials for silicon (Si) anodes, however the effect of carbons with different crystallinities and pore structures on their electrochemical performance remains controversial. We used pitch and phenolic resin (PR) as the precursors of ordered and disordered carbon, respectively, to prepare carbon-coated silicon (Si@C) with strictly controlled carbon contents and surface functional groups. Their electrochemical behavior was investigated. An ordered crystalline structure is favorable for electron transport, and mesopores and macropores are conducive to the diffusion of lithium ions. Such a coating with a small pore volume is an excellent buffer for the expansion of Si, and the electrode maintains structural integrity for 50 cycles. A disordered porous structure is less robust and produces a large polarization, which produces continuous volume expansion with cycling and leads to inferior electrochemical performance. As a result, the capacity and capacity retention after 100 cycles at 0.5 A g−1 of Si@C-Pitch are respectively 8 times and 1.9 times those of Si@C-PR. This study provides theoretical guidance for the selection of carbon materials used in Si@C anodes.
Nitrogen-doped carbon materials are promising for electrochemical energy storage and conversion. Dopant control and pore engineering play important roles in improving their performance. This work demonstrates the synthesis of nitrogen-doped ordered mesoporous carbons (N-OMCs) with bimodal mesopores using the facile solvent-free nanocasting method. The simplest amino acid (glycine, Gly) is adopted as the sole precursor and the ordered mesoporous silica SBA-15 as the hard template. The confined pyrolysis of Gly in SBA-15 leads to efficient carbonization and nitrogen doping and interesting structuration. The N-OMCs possess high surface areas (923–1374 m2·g−1), large pore volumes (1.32–2.21 cm3·g−1), bimodal mesopores (4.8 and 6.2–20 nm) and high nitrogen contents (3.66%–12.23%). The effects of Gly/SBA-15 mass ratio (1–3) and temperature (700–1000 °C) on the physicochemical properties of the N-OMCs are studied. The N-OMCs as electrode materials possess high performance in supercapacitor. The typical sample shows a large specific capacitance of 298 F·g−1, a good rate capability (70 % retention at 30 A·g−1) and a high stability. The different capacitance and rate capability of the N-OMCs are discussed by correlating with their physicochemical properties. The balance of surface area, graphitization, and nitrogen doping and open mesoporous structure is essential to achieve the best performance. The O-NMCs also show good performance in electrocatalytic oxygen reduction reaction (ORR). The typical sample shows high onset and half-wave potentials of 0.92 and 0.83 V and a large limiting current density of 5.06 mA·cm−2.
Novel hybrid aerogels, which can be magnetically extracted from water to avoid filtration, were prepared by adding ZnCl2, NiCl2·6H2O, FeCl2·4H2O and FeCl3·6H2O into a suspension of graphene oxide and oxidzed carbon nanotubes followed by co-precipatation under basic condition, crosslinking with polyvinyl alcohol in water and freeze-drying. The hybrid aerogels consist of magnetic Ni0.5Zn0.5Fe2O4 nanoparticles, graphene oxide, carbon nanotubes and polyvinyl alcohol, which have active sites that attract dye molecules and can be extracted from water by applying magnetic field. Under an optimal mass ratio of the components, the optimized hybrid aerogel has a high adsorption capacity (qe=71.03 mg g−1 for methylene blue) and a moderate magnetic strength of MS = 3.519 emu g−1. Its removal efficiencies for methylene blue, methyl orange, crystal violet and their mixture with an equal mass are 70.1%, 4.2%, 8.9% and 11.1%, respectively under the same dye concentration of 0.025 mg. mL−1. It can be reused for 3 regeneration cycles with a regeneration efficiency of over 82%. Also it is not toxic to the living organism, suggesting that it is promising as an adsorbent for treating industrial wastewater.
With environmental degradation and energy crisis, the storage and utilization of sustainable energy, such as solar, wind energy, etc., become urgent. The attention to electrochemical energy storage (EES) devices, as a means of efficiently storing these emerging energy sources, exhibits an increasing trend. Electrode materials are critical to the performance of EES, and carbon-based nanomaterials have become extremely promising due to their unique and outstanding advantages. The structure design and controllable synthesis of electrode materials thus determine the electrochemical performance of EES to a large extent. Focusing on the unique and outstanding advantages of carbon-based nanomaterials, the preparation progress of carbon-based materials with different dimensions are summarized and discussed, and their applications in different energy storage devices in recent years are also presented. This review facilitates in-depth understanding of the relationship between material structures with different dimensions and electrochemical features, and a perspective and reference to the design and synthesis of exceptional-performance carbon-based nanomaterials for the EES devices are provided.
Fenton-like reactions which could overcome the limitations of narrow pH range and excessive sludge production have drawn great attention. Despite the poor catalytic activity toward hydrogen peroxide, the porous carbons could play diverse roles, including catalyst carriers, adsorbents and electrocatalysts for production and activation of hydrogen peroxide, which was an oxidant in Fenton-like reaction. Recent developments in the above fields regarding porous carbons were discussed in this review. Porous carbons possess the advantages of diverse functionality, well-developed synthetic methods, and high chemical and thermal stability, making them favored materials as components of composites in Electro-Fenton and Fenton-like reactions. They effectively promote electron and mass transfer, prevent metal leaching and improve the contaminant degradation efficiency.
Metal–organic frameworks (MOFs) and covalent organic frameworks (COFs) are serials of crystalline porous materials. MOFs, COFs and their derivatives have attracted much attention in energy storage devices due to their highly ordered structures, large surface areas, tunable pore sizes and topologies as well as well-defined redox-active porous skeletons. Furthermore, MOFs, COFs and their derivatives should have structural stability, an abundance of redox-active sites and improved electronic conductivity to fabricate high-performance supercapacitor electrodes. In this study, we review the recent research progress on the design strategy of MOFs and COFs, the hybridization of MOFs or COFs with conductive materials (e.g. conductive polymer, graphene and carbon nanotubes) and MOF- and COF-derived carbon materials, whose chemical and physical properties, capacitive performances and the structure-property relationships are also discussed. Finally, the challenges and prospects of MOFs- and COFs-based electrode materials are presented.
Owing to their large specific surface area, high chemical and thermal stability, and good electronic conductivity, porous carbons have found wide applications in the field of electrochemical energy storage and conversion. Their performance hinges heavily on the structure, making the structure regulation of porous carbons the research frontier in the development of these materials. In addition to the straightforward hard-templating processes, the in-situ templating synthesis has been considered as another appealing strategy for the precise engineering of porous carbons. Herein, the recent progress on synthesizing porous carbon materials via in-situ templating processes for energy storage and conversion is summarized. First, the rising of in-situ templating synthesis of porous carbons is outlined by elaborately comparing with the traditional hard templating methods. Then, the in-situ templating methods are classified based on the template formation processes including top-down, state-change, and bottom-up during the syntheses. After that, the performance of these materials in the application of electrochemical energy storage and conversion is presented, highlighting the advantages of the in-situ templating syntheses. At last, the possible obstacles and future perspectives are provided.
Lithium (Li) metal is regarded as a promising anode material to construct next-generation high-energy-density batteries. However, the plating/stripping process of Li metal is often accompanied by the formation of high-tortuosity dendrites, which induces the short lifespan and even safety hazards of batteries. To date, various approaches have been developed to suppress the dendrite growth and regulate the uniformity of solid electrolyte interphase. Carbon materials with lightweight, highly conductive, hierarchically porous, chemically and physically stable features have been designed and employed for stabilizing Li metal in distinguishable types. Based on different functions, this review summarizes the advances of carbon materials categorized as hosts, electrolyte additives, and coating layers in stabilizing Li metal batteries (LMBs). The advantages and limitations of various carbon materials have been discussed in terms of structural and chemical aspects. Finally, the outlooks on future developments of carbon materials for propelling the applications of LMBs are proposed.
Mesoporous carbon materials exhibit high specific surface area, tunable composition and pore structure, good chemical stability and conductivity. They have attracted intensive attentions due to their multifarious applications in environmental remediation, industrial catalysis, energy conversion and storage. The carbon source is an important parameter for synthesis of mesoporous carbon with different properties. Plant polyphenols are one kind of universal biomass for carbon source with low cost, nontoxicity and sustainability. Most importantly, the good adhesive property and metal chelate ability for plant polyphenol can be used to synthesize mesoporous carbon composites. Despite great progress, there are few reviews on the topic of mesoporous carbon derived from plant polyphenol. In this review, different kinds of mesoporous carbon materials originated from plant polyphenols have been systematically summed up, including porous carbon foam, ordered mesoporous carbon, mesoporous carbon spheres, heteroatom doped carbon, and mesoporous metal/carbon composites. Then, the applications of these mesoporous carbon in environmental and energy are summarized. This review will bring the bridge for the research of polyphenol chemistry and nanoporous carbon. It would inspire more researchers to explore the functional mesoporous carbon employing plant polyphenol as a sustainable carbon source.
The low volumetric capacity and sluggish diffusion at high mass loading hindered the application of supercapacitor in portable electronics and electric automobiles. In this work, crumpled graphene with nitrogen content of 11.38 atm% was obtained by the heat shock of crumpled graphene/urea composite. The volumetric capacitance as high as 384.0 F cm−3 and fast ions transfer were achieved by using the crumpled graphene as electrodes. Even at high current density (10 A g−1) and high loading (21.00 mg per electrode), the specific capacitance retention could still be 76.3% and 83.6%, respectively. It was proposed that N2 (pyrrole, imide, lactam, or other types of pyridine-like nitrogen) and high surface area of the sample were key factors for improving the capacitance, and crumpled structure provided high mass transfer of the ions. Furthermore, as many as thirty-six white light-emitting diodes (assemble as “USST”) were powered by four nitrogen-enriched crumpled graphene-based supercapacitor coins, and the emitting-time of “USST” can sustain as long as 10 minutes with one-charge.
Activated carbon fiber (ACF) possess high adsorption capacities and can be used in the treatment of benzene, while electrospun nanofibers are expected to be used as used as filtration material due to their intercepting capability to particles. In this work, two series hybrids of electrospun nanofibers and activated carbon cloths were prepared through electrospinning the polyvinyl alcohol (PVA) and polyacrylonitrile (PAN) nanofibers onto the phenolic resin based activated carbon fiber (PRACFC). The filtration performance of hybrids was evaluated by a filtration efficiency system. The results indicate a positive correlation between the filtration efficiency and the amounts of electrospun nanofiber. Surprisingly, the filtration efficiencies increase with the increasing of air velocity, which is attributed to the piezoelectric effect introduced by electrospun nanofibers. Moreover, the hybrids have a good adsorption capacity towards benzene as well. It suggests that the hybrid of electrospun nanofibers and activated carbon cloth are promising to be used in air pollution treatment.
To obtain excellent carbonaceous precursors, the oxidation reaction mechanism and kinetics of ethylene tar were investigated. The oxidation process of ethylene tar was divided into three stages (350-550 K, 550-700 K and 700-900 K) according to the thermogravimetric curve. To reveal the oxidation reaction mechanism of ethylene tar, the components of evolved gases at different stages were further analyzed online by mass spectrometry and infrared technology. Then, based on the thermogravimetric curve of ethylene tar at different reaction temperatures, the whole reaction process was divided into four parts to perform kinetics simulation calculation. With the help of the iso-conversional method (Coats-Redfern) to analyze the linear regression rates (R2) between 17 common reaction kinetics models and experimental data, the optimal reaction kinetics model for expressing oxidation process of ethylene tar was determined. The results show that: (1) In the oxidation process, the side chains of aromatic compounds firstly react with oxygen to form alcohols and aldehydes, leaving peroxy-radicals to aromatic rings. After that, the aromatic compounds with peroxy-radicals undergo polymerization/condensation reaction to form larger molecular. (2) The fourth-order of reaction model is adopted to describe the first three parts of the oxidation process, and the activation energies are 47.330 kJ·mol−1, 18.689 kJ·mol−1 and 9.004 kJ·mol−1 respectively. The three-dimensional diffusion model is applied to the fourth part of the oxidation process, and the activation energy is 88.369 kJ·mol−1.
Li-Se Batteries has been considered as promising lithium-ion batteries due to their super volumetric energy density and high electrical conductivity of Se. However, the development of Li-Se batteries application is impeded by the boring volume expansion and polyselenide dissolution of electrodes during cycling, as well as the low selenium loading. A feasible and effective approach to settle these three issues is to keep selenium into a carbon host with sufficient pore volume and simultaneously enhance the interfacial interaction between selenium and carbon. A novel cathode material of Se encapsulated into honeycomb 3D porous carbon (HPC@Se) with Se-C bonds for Li-Se Batteries is synthesized by impregnating Se into the tartrate salt derived honeycomb 3D porous carbon. The pore volume of the obtained honeycomb 3D porous carbon is up to 1.794 cm3 g−1, which allows 65%wt selenium to be uniformly encapsulated. Moreover, the strong chemical bonds between selenium and carbon are beneficial for stabilizing selenium, thus further relieving its huge volume expansion and polyselenide dissolution as well as promote the charge transfer during cycling. As expected, HPC@Se cathode presents fantastic cyclability and rate performance. After 200 cycles, its specific capacity remained at 561 mA h g−1 (83% of the theoretical specific capacity) at 0.2 C. And the capacity recession is just 0.058 percentage each cycle. Besides, HPC@Se cathode can also demonstrate a considerable capacity of 472.8 mA h g−1 under the higher current density of 5 C.
It is a big challenge to synthesize porous carbon nanosheets without acid treatment for high-performance supercapacitors (SCs). Herein, we report a facile and no pickling method to construct N/S co-doped interconnected porous carbon nanosheets (NS-IPCNs) from coal tar pitch (CTP). The as-prepared NS-IPCN800 has interconnected three-dimensional (3D) structure composed of two-dimensional (2D) nanosheets with abundant hierarchical pores. Of which, rich microspores increase active sites for electrolyte ion adsorption and short mesopores provide channels for ion transmission. In addition, interconnected 3D structure provides highways for electrons transportation. Heteroatom doping provides additional pseudocapacitance for NS-IPCNs electrodes. Benefitting from these merits, NS-IPCN800 electrode exhibits an excellent capacitance of 302 F g−1 at 0.05 A g−1 in 6 mol L−1 KOH electrolyte. Besides, the NS-IPCN800 capacitor shows high energy density of 9.71 Wh kg−1 at power density of 25.98 W kg−1. More importantly, NS-IPCN800 capacitor exhibits superior cycle stability with capacitance retention over 94.2% after 10,000 charge-discharge cycles. This work opens a less harmful strategy for constructing NS-IPCNs from CTP as high-performance SC electrode materials.
Photocatalytic H2 evolution reaction is considered as one of the most promising technologies for H2 production. Carbon materials are potential candidates for large-scale and cost-effective photocatalytic water splitting, yet their activity needs to be further enhanced. Here, we report the synthesis of nitrogen-doped porous carbon with peat moss as precursor and urea as nitrogen source and the properties of the as-synthesized carbons as photothermal-assisted visible-light photocatalyst. Due to the photothermal effect, the system temperature rises quickly, up to 55 oC within 15 min under visible light irradiation, which subsequently helps to increase the photocatalytic activity by about 25%. It has been found that the crystallinity and doping content of nitrogen of the peat-derived carbon materials can be tuned by changing the carbonization temperature, which have an impact on the photocatalytic activity of the concerned carbons. Under the photothermal-assisted visible-light conditions, the peat-derived carbon with N content of 4.88 at.% and an appropriate crystallinity exhibits an outstanding photocatalytic activity, evidenced by the high H2 evolution rate of 75.6 μ mol H2 g−1 h−1.
Electroreduction of carbon dioxide (CO2) driven by renewable and intermittent energy is an important route of CO2 conversion and utilization. Formic acid (HCOOH), as an important chemical basic raw material and safe hydrogen storage material, is one of the main and promising products for CO2 electroreduction. In this review, the physical and chemical properties of CO2 and the reaction mechanism for CO2 electroreduction to HCOOH were outlined in detail. Subsequently, recent development of carbon-based catalysts including metal-free carbon catalysts, carbon-supported catalysts for CO2 electroreduction to HCOOH was also reviewed. Moreover, the design and optimization strategy of reactors for HCOOH production was summarized and commented. Specially, the hybrid CO2 electrolysis technology was analyzed by taking CO2 electroreduction coupled with methanol electrooxidation reaction as an example. Lastly, the key challenges and development directions for CO2 electroreduction to HCOOH were presented, which is expected to provide a novel idea and guidance for further progresses of this technique.
In recent years, various types of renewable energy conversion and storage equipment have been researched due to the energy over consumption and environmental pollution. Designing effective electrocatalysts is the key to improve the energy conversion efficiency. Understanding and analyzing the mechanism of action of electrocatalysts, especially metal-free doped carbon-based electrocatalysts, is essential for their applications. However, few reviews have summarized and analyzed in more detail the improvement of OER activity due to heteroatom doping. In this overview, the metal-free heteroatom doped carbon-based electrocatalysts including N, P, S and B are summarized, and the mechanisms for improving the electrocatalysis of them are analyzed. Furthermore, the co-doped carbon materials, such as N/P, N/S, as electrocatalysts and the mechanism are also summarized briefly. Finally, the problems that need to be solved and challenge in the future are proposed, the suitable doping methods for metal-free heteroatoms and the corresponding reasons are also given.
In recent years, metal-free carbon materials have shown great research value and application potential in replacing high-cost Pt-based oxygen reduction electrocatalysts. A myriads of research papers in this field have been dedicated to the preparation and characterization of various metal-free nanocarbon materials, as well as to their practical applications. Non-metal heteroatom doping and introduction of edge defects are typical nanocarbon modification methods, which can significantly reduce the overpotential of ORR in alkaline and acidic electrolytes. In order to perform well in activity in actual devices such as fuel cells, it is necessary to enhance the ORR intrinsic activity of nanocarbon. Despite lots of publications in this field, the intrinsic relationship between nanocarbon composition, structure regulation and carbon catalytic activity remains not very clear up to date, thus still needing to be explored. The basic goal of this review is to present the various nanocarbons as well as their reaction mechanisms for the ORR so as to propose scientific and specific structural modification strategies. Therefore, this article will summarize and prospect the development of carbon-based metal-free electrocatalysts in the field of oxygen reduction catalysis in recent years, aiming to provide relevant knowledge for the design, synthesis and application of carbon-based non-metallic oxygen reduction catalysts in the future.
It is known that the electrochemical determination of phenacetin, a widely used analgesic, is challenging for the interference of these electroactive intermediates acetaminophen (APAP). Phenacetin has been proved being electroactive in 1980s, but the electrochemical determination have not been widely reported. We studied the electrochemical behavior on electrochemical reduced graphene (ERGO) modified electrode, and the comparative experiment was performed on ERGO several nitrogen-doped graphene. ERGO was proved possessing higher current response and lower oxidation potential, A detection limit of 0.91 μM was established. It suggested ERGO modified electrode is a desirable phenacetin sensor. The redox mechanism of phenacetin was interfered via electrochemical experiments, and the reaction under different pH value was proposed. Acetaminophen was considered the main intermediate. The interfering between acetaminophen and phenacetin was studied, the main electroactive intermediate acetaminophen was proved not interfered the determination of phenacetin. But phenacetin was considered interfered with the response of APAP obviously, suggesting that simultaneous detection of phenacetin and APAP via DPV is not reliable. Interference experiment results further illustrated that usual species, such as Cu2+, Al3+, methanol, ethylene glycol, glucose, and ascorbic acid, hardly caused interference.
Lithium–sulfur (Li–S) batteries suffer from fast capacity fading and inferior rate performance due to severe polysulfide (LiPS) shuttle and slow redox kinetics. To solve these issues, three-dimensional (3D) CNTs/Ti3C2Tx aerogel was successfully prepared with Ti3C2Tx as the active matrix and CNTs as the conductive pillars, and utilized as a LiPS immobilizer and promoter to modify the commercial Li–S battery separator. The unique design of highly porous 3D aerogel structure results in the sufficient exposure of Ti3C2Tx active sites by preventing their restacking, which not only offers abundant charge transport pathways, but also strengthens the adsorption and catalytic conversion of LiPSs. Moreover, the introduction of CNTs forms a highly conductive network to connect the adjacent Ti3C2Tx sheets, thereby improving the conductivity and structure robustness of the 3D aerogel. Owing to these merits, Li–S cells using CNTs/Ti3C2Tx aerogel modified separator show a high rate capacity of 1043.2 mAh g–1 up to 2 C and an admirable cycling life over 800 cycles at 0.5 C with a low capacity decay rate of 0.07% per cycle.
Biomorphic hard carbon recently attracted widely interest as anode materials for potassium ion batteries (PIBs) owing to their high reversible capacity, but high preparation cost and poor cycle stability significantly hinder its practical application. In this study, coconut shell-derived hard carbon (CSHC) was prepared from waste biomass coconut shell using a one-step carbonization method, which was further used as anode materials for potassium ion batteries. The effects of carbonization temperature on the microstructure and electrochemical properties of the CSHC materials were investigated by X-ray diffraction, nitrogen adsorption-desorption isotherms, Raman spectroscopy, scanning electron microscope, transmission electron microscope, and cyclic voltammetry, etc. The results suggested that the coconut shell hard carbon carbonized at 1 000 °C (CSHC-10) possessed suitable graphite microcrystallines size, pore structure and surface defect content, which exhibited the best electrochemical performance. Specifically, CSHC-10 presented 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 was 87.5% after 100 cycles and 75.9% after 400 cycles at 100 mA·g−1. The CSHC with high capacity and good cycling stability demonstrates to be an excellent potassium storage material.
In the context of sustainable development, tackling the severe solid wastes pollution has become extremely urgent. Herein, the solid waste gangue was successfully recycled to synthesize the ceramic based composite microwave absorbing materials decorated with Co particles through a novel synthesis method. The magnetic Co particles were uniformly loaded in the ceramic matrix by the pelletizing process with gangue and Co2+ following by the in situ carbothermal reaction, and the Co content in ceramic composites can be precisely controlled by adjusting the Co2+ concentration. Furthermore, compared with gangue, the obtained composites displayed optimized performance, the minimum reflection loss value reached −48.2 dB and the effective absorbing band was measured to be 4.3 GHz with the coating thickness of 1.5 mm, which is mainly attributed to the enhanced magnetic loss and multiple interface polarization. Such innovative design of recycling gangue in this work can effectively realize the resource utilization of gangue, which is also beneficial for the low-cost and light-weight of microwave absorbing materials as well.
Benefiting from their high concentration of in-plane nitrogen element, superior chemical/thermal stability, tunable electronic band structure and environmental friendly feature, graphite-like carbon nitride (g-C3N4) as a new promising metal-free material has drawn numerous attention in photo-/electric-catalysis. Comparing to the regulation of band structure in photocatalysis, the deliberately synthesis of g-C3N4 electrocatalysts is mainly focused on the construction of catalytic sites and the modulation of the charge transfer kinetics. Herein, this work reports a rapid method for synthesizing ultrafine g-C3N4 quantum dots (QDs) via electrochemical exfoliation using Al3+ ions. The uniform g-C3N4 QDs with smaller lateral dimension and thickness are collected due to the higher charge density and stronger electrostatic forces of Al3+ ions in the lattice of host materials as compared to the conventional univalent alkali cations. The as-obtained g-C3N4 QDs exhibit average lateral dimension and thickness of 3.5 nm and 1.0 nm, respectively, as determined by the TEM and AFM measurements. Also, the presence of the rich C/N defects is verified by the UV-vis spectra. Encouragingly, the ultrafine g-C3N4 QDs exhibit superior hydrogen evolution reaction (HER) performance with an ultra-low onset-potential closely approaching to 0 V, and a low overpotential of 208 mV at 10 mA/cm2, as well as a remarkably low Tafel slope (52 mV·dec-1) in acidic electrolyte. Taking the fabrication of the ultrafine g-C3N4 QDs with rich C/N defects as an example, this work provides a simple and feasible way to exfoliate 2D layered materials into low-dimensional nanomaterials towards highly-efficient electrocatalysis, as well as the exploration of their fascinating physic-chemical properties.
A reduced graphene oxide (H-rGO)/TiO2-composite (H-TiO2@rGO) as a catalyst for photocatalytic degradation of rhodamine B (Rh B) and methyl orange (MO) was prepared by hydrothermal treating a dispersant of TiO2 nanoparticles with sizes of 5-10 nm and GO obtained by the Hummers method from coal-based graphite in water. Compared with the M-TiO2@GO and M-TiO2@rGO composites by a wet mixing method, results indicated that the TiO2 nanoparticles in H-TiO2@rGO were uniformly decorated on both sides of rGO sheet, forming a stacked-sheet structure while apparent aggregation of TiO2 nanoparticles was found in both M-TiO2@GO and M-TiO2@rGO. Therefore, H-rGO@TiO2 had the highest catalytic activity towards degradation of Rh B and MO under visible light irradiation among the three, where the incorporation of rGO into TiO2 helps to narrow the band gap of TiO2, inhibit the recombination rate of electron–hole pairs and provide conductive networks for electron transfer.
Developing highly selective, economical and stable catalysts for electrochemical converting CO2 into value-added carbon products to mitigate both CO2 emission and energy crisis is still challenging. Here, we report an efficient and robust electrocatalyst for CO2 reduction reaction (CO2RR) by embedding single-atom CoN4 active sites into graphene matrix. These highly dispersed CoN4 sites show an extraordinary CO2RR activity, with a high CO Faradaic efficiency of nearly 95% at −0.76 V (vs. RHE) and remarkable durability. The corresponding overpotential is 0.65 V. Our finding could pave the way for the design of high-efficiency electrocatalyst for CO2RR at the atomic scale.
Graphite is the most widely used anode material for lithium ion batteries (LIBs), and increasing the sphericity and density of graphite is the main way to further improve energy density of LIBs. Herein, we report a simple preparation of high tap-density graphite granules by the high-shear wet granulation. In this way, we densified two kinds of graphite into granule, namely wet-granulation graphitic onion-like carbon (WG-GOC) and wet-granulation artificial graphite (WG-AG). It is found that, compared with the original graphite before granulation, the tap density of WG-GOC increases by ca.34%, and WG-AG increases by ca.44%. Therefore, when as the anode of LIBs,, the volumetric capacities of WG-GOC and WG-AG have increased by ca.35% and ca.55%, respectively, at the current density of 50 mA g−1. In addition, the rate performance of WG-GOC also has been significantly improved. The volumetric capacity of WG-GOC increased by 169.1% at the current density of 2000 mA g−1. The significant improvement of electrochemical performance benefits from the higher tap density of the prepared graphite granules. Hence, we developed a facile wet-granulation to prepare high tap-density graphite anodes, which conducive to the development of high volumetric capacity.
In this study, cost-effective anthracite and industrial silicon powder were used as precursor and catalyst, respectively, to prepare graphite with various structure, during which the catalytic mechanism was analyzed. The results demonstrate that the as-obtained sample with 5% silicon catalyst (G-2800-5%) exhibits the best overall lithium storage performance. In detail, G-2800-5% display the best graphite structure with graphitization degree of 91.5%. As anode materials, a high reversible capacity of 369.0 mAh g−1 can be achieved at 0.1 A g−1. Meanwhile, the reversible capacity of 209.0 mAh g−1 can be obtained at the current density of 1 A g−1. It also delivers good cyclic stability with a 92.2% retention after 200 cycles at 0.2 A g−1. The highly developed graphite structure, which is favorable to the formation of stable SEI and reduced lithium ion loss should be responsible for the superior electrochemical performance.
In this paper, a liquid-phase sintering method was developed by combining in-situ reaction method with slurry method to prepare HfB2-MoSi2-SiC coatings with controllable composition, content and thickness. The effect of MoSi2 content on the oxidation protection behavior of HfB2-MoSi2-SiC composite coating under dynamic aerobic environment at room temperature ~ 1500 ℃ and static constant temperature air at 1500 ℃ was studied, the relative oxygen permeability was used to characterize the oxidation resistance of the coating. The results of dynamic oxidation test at room temperature ~ 1500 ℃ showed that the initial oxidation weight loss of the samples was delayed from 775 ℃ to 821 ℃, and the maximum weight loss rate decreased from 0.9×10−3 mg·cm−2·s−1 to 0.2×10−3 mg·cm−2·s−1 with the increase of MoSi2 content, the lowest relative oxygen permeability was reduced to 12.2%, resulting in the weight loss of the sample from 1.8% to 0.21%. In this paper, the mechanism of MoSi2 enhancing the ability of oxidation protection of the coating is revealed. With the increase of MoSi2 content, the amount of SiO2 glass phase in the coating is increased, and the dispersion of Hf-oxide on the coating surface is promoted, thus, the Hf-Si-O compound glass layer with higher stability can be formed, and the weight loss rate of the sample reduced from 0.46% to 0.08% after 200 h oxidation at 1500 ℃ in constant temperature air.
Designing electrically conductive electrode material with a hierarchical pore structure from abundant raw material remains a significant challenge in the development of energy storage research. In this work, 3D porous carbons with high surface areas are synthesized via high-temperature carbonization and activation. The synthesized activated carbons deliver a specifical capacitance of 280 F g−1 and area-specific capacitance of 1.3 F cm−2 at a current density of 0.5 A g−1. The assembled symmetric supercapacitor can deliver a high energy output (7.7 Wh kg−1 at 5200 W kg−1). Thus, it is demonstrated the repurposing of lignin waste as electrode material can be a feasible resource that goes beyond the limitations of utilizing lignin in low value-added applications.
The phosphorus-doped carbon materials as one of novel carbon catalysts towards the hydrogen evolution reaction (HER) have attracted considerable attention over the past years. However, the role of C-P species palyed in the HER activity is still not clear up to now. Phosphorus-doped carbon nanotubes (P-CNTs) were prepared by chemical vapor deposition and annealed at 900, 1000 and 1200 ℃ to remove all or parts of phosporus species, resulting in four samples with different proportions of graphite-, pyridine- and pyrrole-like P species. The correlations between their HER activity and the contents of three types of P species were investigated. Results showed that the content of graphite-like P decreased with the annealing temperature and no graphite-like P was retained at 1200℃. The HER activity increased with the annealing temperature and the one annealed at 1200 ℃ had the highest HER activity in an acid medium with an overpotential of 0.266 V at a current density of 10 mA/cm−2. Density functional theory calculations revealed that the pentagon- and nine-membered ring defects formed by the destruction of graphite-P species contributed mainly to the HER activity, which gave a deep insight into the active sites for HER.
Graphite is one of the most promising anode materials for potassium-ion batteries (PIBs) due to its low cost and stable discharge plateau. However, its poor rate performance still needs to be improved. Herein, a novel graphitic anode was designed from commercial mesocarbon microbeads (MCMB) by KOH treatment. Through limited oxidation and slight intercalation, an expanded layer with enlarged interlayer spacing formed on the surface of MCMB, by which the K+ diffusion rate was significantly improved. When served as the PIB anode, this modified MCMB delivered a high plateau capacity below 0.25 V (271 mAh g−1), superior rate capability (160 mAh g−1 at 1.0 A g−1), excellent cycling stability (about 184 mAh g−1 after 100 cycles at 0.1 A g−1), and high initial coulombic efficiency with carboxymethyl cellulose as binder (79.2%). This work provides a facile strategy to prepare graphitic materials with superior potassium storage property.
Highly efficient synthesis of nitrogen-doped carbons with different porous structures is reported using shrimp shell as the carbon and nitrogen source, and its CaCO3 component as the hard template and the activator. The content of CaCO3 in shrimp shell can be tuned easily in the range of 0-100% by leaching with an acetic acid solution for different times. CaO derived from decomposition of CaCO3 acts as the activator and template to tailor the pore sizes of the carbons. CO2 derived from decomposition of CaCO3 also plays an activating role. Their specific surface areas, pore volumes, ratios of micropore volumes to total pore volumes can be adjusted in the range of 117.6-1137 m2 g-1, 0.14-0.64 cm3 g-1, and 0-73.4%, respectively. When used as the electrodes of supercapacitor, the porous carbon obtained with a leaching time of 92 min exhibits the highest capacitances of 328 F g-1 at 0.05 A g-1 in a 6 M KOH electrolyte and 619.2 F g-1 at 0.05 A g-1 in a 1 M H2SO4 electrolyte. Its corresponding energy density at a power density of 1470.9 W kg-1 is 26.0 Wh kg-1. This work provides a low cost method for fabricating porous carbons to fulfill the high-value-added use of biomass.