Matrix graphite (MG) was purified by high temperature purification (HTP), and their properties and microstructures were measured and analyzed to investigate the effect of HTP temperature on the property improvement of A3-3 MG as a pebble fuel element, and to optimize the purification temperature. Results showed that all the properties of MG specimens purified at temperatures from 1600 to 1900 ℃ met the technical requirements. X-ray diffraction analysis results showed that the microstructures of MG after HTP were significantly improved. With increasing the purification temperature from 1600 to 1900 ℃, MG gradually became ordered, the microstructures became better gradually for improving the comprehensive performance. The ash content decreased abruptly after HTP at 1600 ℃, but changed little when the purification temperature rose from 1600 to 1900 ℃. The microstructure improvement at high temperatures played a decisive role in increasing the oxidative corrosion resistance of MG. Therefore, HTP is very important and necessary, and cannot be canceled in the production of pebble fuel elements. This study provides an important reference to determine an optimal HTP temperature of pebble fuel elements for improving the production efficiency and reducing production cost in the commercial production of pebble fuel elements in the future.
Graphene, owing to its outstanding thermal and electrical conductivity, has been regarded as one of the promising substitutes for heat dissipation or electromagnetic shielding and attracted widespread attention recently. Here, we attempt to summarize the current state of reduced graphene oxide films, graphene films and graphene-based composite films for thermal management, including the preparation and the applications. Additionally, the key factors that determine the thermal conductive performance of graphene films are also discussed to figure out the main challenges, especially in the scalable manufacturing of graphene-based films in the near future.
The development of modern technology has put forward higher and more urgent needs for thermal management materials. Due to their low thermal expansion coefficient, excellent thermal conduction and high-temperature resistance, vertically aligned carbon nanotube arrays and carbon/carbon composites have aroused extensive interests as ideal lightweight and stable thermal management materials. Here, we firstly introduce the thermal conducting mechanism of carbon materials. Then, we present the general fabrication methods, the main factors affecting thermal conductivity of vertically aligned carbon nanotube arrays and carbon/carbon composites as well as their applications in thermal management. The preparation-structure-performance relationships are outlined and the strategies for achieving high thermal conductivity are summarized. Finally, critical consideration on the challenges and prospects in thermal management applications of vertically aligned carbon nanotube arrays and carbon/carbon composites are presented.
As the power consumption and heat generation of electronic devices continue to increase, higher demands are therefore placed on thermal management materials for heat dissipation. Graphene has been widely used as the thermal conductive filler to improve the thermal conductivity of polymers. However, the poor dispersibility of graphene nanoplates in polymers dramatically limits their practical applications in thermal management. A promising strategy to increase the thermal conductivity of polymer composites is to construct the interconnected three-dimensional graphene networks. This review summarizes the recent advancements in the construction and applications of three-dimensional graphene-based polymer composites (3D GPCs). The approaches to enhance the thermal conductivity of 3D GPCs are presented. The current challenges and our perspectives in the preparation and applications of 3D GPCs are proposed.
Aromatic polyimide (PI)-based graphite nanofibers are obtained from the graphitization of graphene oxide (GO)-doped electrospun PI nanofibers. GO improves the PI molecular orientation, crystalline structure and thermal conductivity of PI graphite nanofibers. The degree of PI molecular orientation of the nanofibers is enhanced during fiber preparation by GO. The improvement of molecular orientation facilitates the increase in the thermal conductivity of the graphite nanofibers. As the addition of only 0.1% GO can lead to an apparent increase in the thermal conductivity of PI-based graphite nanofibers. The effect of GO on the thermal conductivity is not by itself, but by the improvement in PI molecular orientation and its role as nucleation centers in graphitization. This approach and the resulting high thermal conductivity materials show great potential for practical applications.
The three-dimensional (3D) graphene network structure has aroused great interest because it can effectively solve the agglomeration problem of graphene powder and improve its utilization efficiency. Simultaneously, such a structure possesses many advantages of a porous structure, lightweight, high thermal conductivity and superior electrical conductivity, which is widely used in thermal management and electromagnetic protection fields. To fully understand the 3D graphene networks, herein, we summarize different preparation strategies and properties of the isotropic and anisotropic 3D graphene networks. Then, the latest research progress of the applications of the 3D graphene networks, including thermal interface materials, phase change materials, electromagnetic interference shielding materials and microwave absorbing materials, is reviewed. Finally, the development and outlook of the 3D graphene networks have prospected. This review can provide new perspectives and research directions for the future development of the 3D graphene networks in heat dissipation and electromagnetic protection for 5G electronic devices.
The microstructural characteristics of the high thermal conductive (500−1127 W·m−1·K−1) mesophase pitch-based carbon fibers were investigated based on the characterization of XRD, Raman spectroscopy, SEM and TEM. The relationship between microstructural characteristics and thermal conductivity was discussed. The results show that the radial structure is always accompanied by a split structure and high thermal conductivity. La has more significant impact on the thermal conductivity than Lc, and ID/IG value on the cross section obtained from Raman spectra can be used as an essential index to evaluate the thermal conductivity of the carbon fibers. The microstructural characteristics including large graphite crystallite size, high preferred orientation degree along the axis direction, and few crystallite defects contribute to the high thermal conductivity of the carbon fibers.
将环氧树脂（EP）分别涂敷于聚酰亚胺石墨带（GPTs）和聚酰亚胺石墨膜（GPFs），通过真空热压成型与分别采用堆叠和叠层方法制备得到GPTs/EP复合材料和GPFs/EP复合材料。借助 XRD、SEM和PLM等手段对GPF及其环氧树脂基复合材料的晶体结构、形貌和光学织构进行表征，并研究GPF的体积分数和尺寸对其复合材料导热性能的影响。结果表明，相比于GPFs/EP复合材料，GPTs/EP复合材料的导热性能在不同方向显示出较大波动，其热导率和热扩散系数总体上随GPF体积分数的增加而增大，GPF体积分数为80%时热导率为453~615 W (m·K)−1。而对应的 80 % GPFs/EP复合材料热导率稳定可达894 W (m·K)−1，并具有高取向的“三明治”结构。但在平行于热压方向上两类复合材料热导率都很低，GPF体积分数为80%时，GPTs/EP复合材料和GPFs/EP复合材料的热导率分别为1.82 W (m·K)−1和1.15 W (m·K)−1。
Thermal management has been attracted much more attention due to the rapid development of 5G communication techniques. In this work, we propose an integrated “grafting-welding” method to deliver graphene/polyimide (g-A-mGO/PI) composite films. The modification is firstly conducted by using 1,3-Bis(4-aminophenoxy) benzene (APB-134) to anchor terminal amino groups on GO sheets. Hence, the in-situ polymerization of polyamic acid can directly occur with adding of pyromellitic dianhydride (PMDA) at these reactive sites to connect the micron-sized GO platelets through the chain propagation of polyimide (PI). The optimized g-A-mGO/PI-7% film exhibits a considerable enhancement of in-plane thermal conductivity (κ) by 48.92%. Moreover, it also displays superior anti-bending performance and survives from a 2000-cycle bending with small radius test, delivering an electrical resistance change less than 10%. Such a novel approach enables effective pathway for phonon transportation between graphene sheets to reduce the phonon scattering, and thereby offers a prospective application of the functionalized graphene derivatives for heat dissipation or thermal interface materials.
Multi-walled carbon nanotubes (CNTs) were modified by nano-TiC using a pressureless spark plasma sintering technology. TiC-modified carbon nanotubes (T-CNTs) were added into mesocarbon microbeads (MCMBs) to prepare high performance isostatically pressed graphite materials. The structures of T-CNTs and as prepared isotropic graphite materials were characterized by XRD, SEM, TEM, etc. The mechanical properties and thermal properties of isotropic graphite reinforced by T-CNTs were measured by a micro-controlled electronic universal testing machine, laser thermal conductivity meter and thermal expansion coefficient meter. Results show that nano-TiC is successfully grown on the surface of CNTs. Compared with the isotropic graphite prepared from MCMBs without T-CNTs, the isotropic graphite with T-CNTs has a significant improvement in physical properties (density, open porosity and volume shrinkage). The flexural strength and the degree of graphitization of isotropic graphite with T-CNTs is increased by 70% and 10%, respectively, the thermal properties are also improved to some degree.
Based on the "egg-box" structure of calcium alginate in enteromorpha prolifera (EP), the carbonized products of EP are treated by HCl pickling to remove Ca2+ ions from calcium alginate and form the "egg-box" model initial pore structure. Then EP-based activated carbon is prepared by KOH activation method with the treated carbonized products as precursors. The pore characteristics and electrochemical properties of EP-based activated carbon are studied. The existence of hierarchical porous structures in EP-based activated carbon leads to a high specific surface area (SBET) up to 3283 m2 g−1, with more than 66% surface area provided by mesopores. This hierarchical porous carbon shows excellent electrochemical property when used as electrode materials for a supercapacitor, even at high current densities. The gravimetric capacitance value of the EP-based activated carbon reaches up to 361 F g−1 at the current density of 0.1 A g−1, the capacitance even remains at 323 F g−1 at the current density of 10 A g−1, demonstrating excellent high-rate capacitive performance.
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.
在炭基电极材料中引入氧化还原赝电容是提升其比电容的有效手段，有望解决炭基超级电容器低能量密度的瓶颈问题。本文通过原位电化学氧化，在B、N掺杂二维纳米炭片电极上引入电化学活性含氧官能团，以显著提升炭基电极的赝电容，并研究了B、N掺杂炭在不同氧化工艺下的表面组成和电容性能变化。结果表明，B、N掺杂可以提升氧化电极的电子传输和电荷转移，有效促进电化学氧化效果，提高电极的赝电容。此外，相比于恒压氧化工艺，循环伏安氧化方法可以有效提升炭电极的氧化深度和总氧含量，并且也有利于选择性地生成以电化学活性的醌基为主的含氧官能团。制备的氧化电极在1 A·g−1电流密度下显示出601.5 F·g−1的高比电容，并在20 A·g−1下仍保持74.8%，显示出良好的倍率性能。此外，氧化电极还表现出优异的循环稳定性，在5 A·g−1下8000次循环后保持了初始电容的92.6%。
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.
Because of high-energy density and popular price, lithium-sulfur batteries had been applied extensively for future energy storage. However, it faced with lots of challenges, especially in the sulfur loading and the shuttle effect of the soluble polysulfide. To solve these problems, a three-dimensional multistage porous carbon(3D-MPC) material as the sulfur host of lithium-sulfur battery had been designed. The three-dimensional porous structure was prepared by a template method which removed the polymethyl methacrylate and the zinc oxide. Electron microscopy and BET tests showed that interconnected macroporous channels and abundant large-sized mesoporous materials synergistically constituted a three-dimensional conductive carbon network. The three-dimensional network structure was conductive for electron/ion transfer and the relief area of the cathode volume expansion by the physical limiting effect. The multistage holes alleviated the shuttle effect by the capillary condensation. The electrochemical test result showed that the 3D-MPC-S cathode had an excellent electrochemical property. The first discharge specific capacity of the 3D-MPC-S was 1314.6 mAhg−1 at 0.2 C with the sulfur loading of 70% in the practical environment. After 100 cycles, the high capacity retention rate was 69.13%. At 0.5 C, the capacity retention rate of 200 cycles in the practical environment was 59.02% and the average coulombic efficiency was 98.16%. The 3D-MPC-S cathode will further promote the commercial development of lithium-sulfur batteries.
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.
Micro/mesopore carbon spheres as electrode materials of supercapacitors were prepared by hydrothermal carbonization followed by KOH/NaOH activation using sucrose as the carbon precursor. The effects of KOH and NaOH activation parameters on the specific surface area, pore size distribution and electrochemical performance of the carbon spheres were investigated. Results indicate that the use of NaOH leads to the development of mesopores while the use of KOH is favorable to increase specific surface area and micropore volume. The pore size distribution of carbon spheres could be adjusted by varying the fraction of NaOH in the activation agent. A balanced capacitance and rate performance of the supercapacitor electrode in both 6 mol L−1 KOH aqueous electrolyte and 1 mol L−1 MeEt3NBF4/PC electrolyte is achieved when the carbonized product is activated at a mass ratio of NaOH+KOH/ carbonized product of 3∶1 with a NaOH/KOH mass ratio of 2∶1. As-prepared porous carbon delivers a capacitance of 235 F g-1 at 0.1 A g-1 and capacitance retention rate of 81.5% at 20 A g-1 in the 6 mol L−1 KOH aqueous electrolyte. In 1 mol L−1 MeEt3NBF4/PC, the cell based on the porous carbon delivers the highest energy and power output of 30.4 Wh kg−1 and 18.5 kW kg−1, respectively.
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.
A N, S, P-codoped and oxidized porous carbon (CS-COOH) was prepared by carbonization of poly(cyclotriphosphazene-co-4,4’-sulfonyldiphenol), followed by KOH activation and oxidation with HNO3. The CS-COOH was used as an adsorbent for U(VI) in aqueous solutions. TEM, SEM, XPS and FTIR were used to characterize the microstructures of CS-COOH before and after adsorption. Results indicate that there is an optimal pH value of 6 for U(VI) adsorption. The adsorption kinetics and isotherm are fitted well by the pseudo-second-order model and the Langmuir model, respectively. The maximum adsorption capacity determined by the Langmuir model at 298 K and a pH value of 6 is 402.9 mg g-1. The CS-COOH has an excellent reusability with a 70% capacity retention of the original value after five adsorption-desorption cycles. The high U(VI) adsorption capacity is mainly attributed to the carboxyl, and P ans S groups by the formation of the UO22+(COO−)2 complex, U-O-P and U-O-S bonds.
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.
Transforming waste resources into energy storage materials is a new way to turn waste into treasure and solve the problem of energy shortage and environmental pollution in current society. In this paper, nitrogen/phosphorus co-doped activated carbon material was synthesized from the waste cotton fabric by one-step carbonization and activation in molten salt system combined with ammonium polyphosphate co-doping technology. The morphology, structure and composition of the materials were characterized by scanning electron microscopy (SEM), nitrogen adsorption desorption (BET), Raman spectroscopy (Raman) and X-ray photoelectron spectroscopy (XPS). The cyclic voltammetry (CV) and galvanostatic charge/discharge (GCD) were used to test the supercapacitor performance of the prepared materials. The results show that the waste cotton fabric, which is mixed with ammonium polyphosphate in the ZnCl2/KCl molten salt medium, then treated by carbonization and activation under high temperature, generates the nitrogen/phosphorus co-doped activated carbon with the specific surface area of 751 m2·g−1. In the three-electrode system, the specific capacitance is as high as 423 F·g−1 (at a current density of 0.25 A·g−1), and its capacitance retention is as high as 88.9% of the initial capacitance after 5000 cycles at a current density of 5 A·g−1. Meanwhile, when the material was assembled into a symmetrical supercapacitor, the achieved energy density can be up to 28.67 Wh·kg−1 at a power density of 200 W·kg−1. According to these results, converting waste cotton fabric resources into energy storage materials has succeeded in achieving high value-added reuse of waste textiles.
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.
Hydroxyl- and amino- functionalized carbon fibers (CF-OH and CF-NH2) were prepared by surface oxidation with mixed acid and grafting with ethylenediamine, respectively. The functionalized CFs were sized with a sulfonated poly (ether ether ketone) (SPEEK) sizing agent to prepare CF-OH-SPEEK and CF-NH2-SPEEK. The effect of surface functionalization on the surface properties of CFs and the interfacial properties in PEEK maxtrix composites were investigated. Results show that the contents of polar functional groups and wettability of CFs increase significantly after surface functionalization. There are chemical reactions between CFs and the sizing agent, which improve the interfacial adhesion between CFs and the sizing agent. The interfacial shear strengths of CF-OH-SPEEK and CF-NH2-SPEEK reinforced PEEK matrix composites are increased by 6.2% and 14.0%, respectively, as compared with that of desized-SPEEK CFs. The surface functionalization is beneficial to improve the interfacial adhesion of thermoplastic-coated CF/PEEK composites.
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.
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.