Preparation of carbon aerogels and its application in electrochemical supercapacitors

本文通过优化碳气凝胶前驱体的配比以及采用3种活化工艺,包括CO2物理活化、KOH化学湿法活化以及CO2、KOH两步活化工艺,研究了制备高比表面积碳气凝胶的工艺参数,并对碳气凝胶的微观结构和相应的电化学特性进行了表征和分析。结果表明,间苯二酚与碳酸钠的摩尔比（R/C）为1500时,获得的碳气凝胶比表面积达到820 m2/g,比电容量为151 F/g;经物理活化、化学湿法活化以及两步活化工艺后获得的活化碳气凝胶的比表面积分别为1589 m2/g、1480 m2/g、2119 m2/g,比电容量分别为181 F/g、229 F/g、259 F/g。相比之下两步活化法不但提升了碳气凝胶的比表面积,而且制备的碳气凝胶材料表现出更良好的电化学性能。     

Electrospun NiO/C nanofibers as electrode materials for hybrid supercapacitors with superior electrochemical performance

In this work, the porous NiO/C nanofibers (NFs) were rationally designed and prepared by a convenient electrospinning method, and followed with a calcination conversion of the precursor in air. The NiO/C composite exhibited a net-like structure that was composed of many intertwined NFs with an average diameter of about 200 nm. The electrochemical measurements demonstrated that the porous NiO/C NFs exhibited an electrochemical feature of battery-type electrode material, and delivered a specific capacity as high as 461.26 C g^?1 under 1 A g^?1 and an excellent rate capability with 82.7% capacity retention at 10 A g^?1. A hybrid supercapacitor (NiO/C NFs//AC HSC) was assembled with NiO/C NFs as positive electrode and activated carbon (AC) as negative electrode, which delivered an energy density of 31.82 W h kg^?1 under a power density of 816.36 W kg^?1 along with an outstanding cyclic stability of 90.9% capacity retention over 5000 cycles at 5 A g^?1. This simple synthetic method can be extended to the fabrication of other transition metal oxides (TMOs)-based NFs for their further applications in high-performance electrochemical energy storage devices such as hybrid supercapacitors, batteries, and so on.     

Preparation of activated graphene/activated carbon dry composite electrode and its application in supercapacitors

采用干法电极制备工艺成功制备了活性石墨烯/活性炭复合电极片,分别用扣式电容器和软包电容器考察活性石墨烯/活性炭复合电极的电化学性能。综合结果表明,复合电极中活性石墨烯的含量为10%（质量分数）较为合适,相较于纯活性炭电极,比容量提高了10.8%。本工作验证了活性石墨烯材料在商用超级电容器中的适用性,证实了活性石墨烯是一种非常具有实际应用价值的电极材料。但目前,活性石墨烯并未真正产业化,其成本远高于商用活性炭。在未来,如何解决活性石墨烯工程制备技术难题和降低成本是材料产业界亟待解决的难题。     

Fabrication and electrochemical performances of porous carbon nanotubes/polyaniline-modified carbon nanotube fiber

通过低电压电泳沉积的方法在碳纳米管纤维（CNF）表面沉积多孔碳纳米管（CNTs）,然后在其表面电化学沉积一层聚苯胺（PANI）,得到CNTs@PANI三维多孔网络结构修饰的核-鞘型纤维电极材料。通过扫描电镜、透射电镜和拉曼光谱表征电极材料表面形貌和微观结构,并利用电化学工作站测试电化学性能,研究结果表明,沉积的多孔CNTs结构可以为PANI提供更多的氧化还原反应活性位点,而PANI也具有固定CNTs的作用,在电流密度为1 mA/cm²时,CNTs和PANI修饰的电极面积比电容达77.28 mF/cm²。以聚二甲基硅氧烷薄膜为基底、PVA-H₃PO₄为电解质制备的对称型固态柔性超级电容器在电流密度为0.25 mA/cm²时,面积比电容为61.25 mF/cm²,恒流充放电4000次后,电容值仍维持在80%,并且串联两个电容器可以点亮电压为1.8 V的LED灯泡。     

Study on preparation and electrochemical properties of biomass-derived spherical activated carbon

以生物质风化煤系腐殖酸（LHA）为炭质前驱体,通过溶剂蒸发和KOH活化方法制备了球形活性炭。使用扫描电子显微镜（SEM）、N2物理吸脱附仪等手段对球形活性炭形貌和孔道结构进行了表征;还将活性炭组装成扣式电容器,进行了充放电容量、循环伏安特性和交流阻抗行为等电化学性能测试。结果表明：所制备的球形活性炭具有良好的球形度,通过少量碱活化后球形活性炭BET表面积为2034 m2/g、总孔容为1.24 cm3/g、平均孔径为2.38 nm。同时,以球形活性炭作为电极材料应用于水系超级电容器后显示了优异的电化学性能,比电容可达到319 F/g,在进行10000次充放电后,比电容保持率为98.9%。此外,球形活性炭相比于颗粒活性炭具有更好的导电性,也展现了更加优异的倍率性能和循环性能。因此说明LHA基球形活性炭是一种有潜在优势的超级电容器材料。     

High performance hybrid supercapacitors with LiNi1/3Mn1/3Co1/3O2/activated carbon cathode and activated carbon anode

Hybrid supercapacitors have been studied as a next generation energy storage device that combines the advantages of supercapacitors and batteries. One important challenge of hybrid supercapacitors is to improve energy density (8.9–42 Wh/kg) with maintaining excellent power density (800–7989 W/kg) and cyclability (98.9% after 9000 cycles). Herein, we demonstrate an approach to design hybrid supercapacitors based on LiNi_1/3Mn_1/3Co_1/3O₂ (NMC)/activated carbon (AC) cathode and AC anode (NMC/AC//AC). The NMC/AC//AC hybrid supercapacitors shows outstanding electrochemical performances due to the enhanced energy and power densities. These findings suggest that the NMC/AC cathode is an effective method for high performance hybrid supercapacitors.     

Synthesis and electrochemical performance of lithium iron phosphate/carbon composites based on controlling the secondary morphology of precursors

In this study, dihydrate iron phosphates with primary and secondary morphology were first prepared with ferric sulfate and phosphoric acid as the major raw materials, which were then taken as the precursor to prepare carbon-coated lithium iron phosphate composite material. Results show that structures of synthesized lithium iron phosphate/Carbon materials are the same, however, the morphologies are significantly different, especially the one synthesized with the secondary morphology iron phosphate precursor. Thus, the particle size, specific surface area and carbon coating effect of the material are changed accordingly, which can affect the electrochemical performance of the composite. The lithium iron phosphate/Carbon synthesized with spherical aggregation morphology (secondary morphology) iron phosphate precursor showed the best electrochemical property. At 0.5C and 10C rates, the first specific discharge capacity is 155.6 and 103.8 mA h/g respectively, which is better than that prepared with cabbage shape aggregation morphology (secondary morphology) and near-spherical simplex (primary morphology), increasing 1.38%, 1.37% and 3.58%, 9.05%, respectively. This research result provided new thoughts to further improve the electrochemical property of lithium iron phosphate/Carbon composites.     

Preparation of Cu atom doped LaFeO3/activated porous carbon composites and their electrocatalytic nitrogen reduction performance

The electrocatalytic N₂ reduction reaction (NRR) under ambient conditions is a green and sustainable method for ammonia (NH₃) synthesis, and the development of efficient electrocatalysts for NRR is a top priority. In recent years, LaFeO₃ has been widely used in the field of catalysis because of its high stability, low cost, and green advantages. Through strategies such as heteroatom doping and carbon loading, we can effectively increase the content of oxygen vacancies and improve the electrical conductivity of the material to produce composites with unique electronic structures and excellent catalytic properties. In the present work, we prepared single-atom doped LaFeO₃/activated porous carbon composites (LFC/AC) for electrocatalytic NRR. The NH₃ yield and Faraday efficiency of LFC/AC were the highest at 23.876 μg h⁻¹ mg⁻¹ and 6.53% in 0.1 M Na₂SO₄ electrolyte solution, both of which were higher than those of LFC. A series of characterizations and tests have shown that LFC/AC has excellent stability, electrical conductivity, and electrocatalytic properties. The density flooding theory (DFT) simulations were performed to explore the main mechanisms to improve the NRR performance of the materials.     

Morphology‐dependent electrochemical performance of nitrogen‐doped carbon dots@polyaniline hybrids for supercapacitors

In this work, the binary N‐CDs@PANI hybrids were fabricated by introducing zero‐dimensional nitrogen‐doped carbon dots (N‐CDs) into reticulated PANI. Firstly, N‐CDs were prepared by one‐pot microwave method, and then, the N‐CDs were introduced into in situ oxidative polymerization of aniline (ANI) monomer. The N‐CDs with abundant functional groups and high electronic cloud density played a significant role in guiding the polyaniline‐ordered growth into intriguing morphologies. Moreover, morphology‐dependent electrochemical performances of N‐CDs@PANI hybrids were investigated and N‐CDs improve static interaction and enhance the special capacitances in the N‐CDs@PANI hybrids. Especially, the specific capacitance of PC4 hybrid can reach 785 F g^?1, which exceed that of pure PANI (274 F g^?1) at current density of 0.5 A g^?1 according to three‐electrode measurement. And the capacitance retention of the PC4 hybrid still keeps 70% after 2000 cycles of charge and discharge. The N‐CDs@PANI hybrids can have potential applications in electrode materials, supercapacitors, nonlinear optics, and microwave absorption.     

Preparation and electrochemical characteristics of LiNi1/3Mn1/3Co1/3O2 coated with metal oxides coating

LiNi_1/3Mn_1/3Co_1/3O₂ prepared by a spray drying method exhibited poor cyclic performance when it was operated at rates of 0.5C and 2C in 3–4.6 V. A metal oxide (ZrO₂, TiO₂, and Al₂O₃) coating (3 wt%) could effectively improve its cyclic performance at both 0.5C and 2C. Electrochemical impedance spectroscopy (EIS) studies suggested that both the surface resistance and the charge transfer resistance of the bare LiNi_1/3Mn_1/3Co_1/3O₂ significantly increase after 100 cycles, whose origin is mainly related to the change in both the particle surface and electrode morphologies. The presence of a thin metal oxide layer could remarkably suppress the increase in the total resistance (sum of the surface resistance and the charge transfer resistance), which was attributed to the improvement in good cyclic performances.     

Comparative study of EC/DMC LiTFSI and LiPF6 electrolytes for electrochemical storage

Lithium bis(trifluoromethane sulfonyl) imide (LiTFSI) salt are potentially a good alternative to LiPF₆ since it could both improve the chemical and thermal stability as salt for electrolyte. This work presents a systematic comparative study between LiPF₆ and LiTFSI in a mixture of EC/DMC on the basis of some of their physicochemical properties. Transport properties (viscosity and conductivity) are compared at various temperatures from −20 to 80 °C. Using Walden rule, we have demonstrated that LiTFSI 1 M in EC/DMC is more ionic than LiPF₆ 1 M in the same binary solvent. Moreover, the electrochemical storage properties of an activated carbon electrode were investigated in EC/DMC mixture containing LiTFSI or LiPF₆. The specific capacitance C_s of activated carbon was determined from the Galvanostatic charge-discharge curve between 2 and 3.7 V, at low current densities. The capacitance values were found to be 100 and 90 F g⁻¹ respectively for LiTFSI and LiPF₆ electrolytes at 2 mA g⁻¹. On the basis of the physicochemical and electrochemical measurements, we have correlated the improvement of the specific capacitance with activated carbon to the increase of the ionicity of the LiTFSI salt in EC/DMC binary system. The drawback concerning the corrosion of aluminium collectors was resolved by adding a few percentage of LiPF₆ (1%) in the binary electrolyte. Finally, we have studied the electrochemical behavior of intercalation-deintercalation of lithium in the graphite electrode with EC/DMC + LiTFSI as electrolyte. Results of this study indicate that the realization of asymmetric graphite/activated carbon supercapacitors with LiFTSI based electrolyte is possible.     

Ni-doped hierarchical porous carbon with a p/n-junction promotes electrochemical water splitting

The p/n-junction in heteroatoms-doped carbon might be engineered to adjust the population of the charge carriers to perform the oxygen evolution reaction (OER) with holes in a p-type region and hydrogen evolution reaction (HER) with electrons in a n-type region. The carbons (AC) with introduced Fe, Ni and Co species of hierarchical porous structures were derived by pyrolysis of melted poly (styrenesulfonic acid-co-maleic acid) salts. The obtained materials were used as HER, OER and water splitting catalysts. Although all samples were catalytically active, their activity differed depending on the kind of metal. The most promising results were obtained on Ni-AC. An overpotential of Ni-AC to reach 10 mA cm⁻² was 259, 382 and 640 mV for HER, OER and water splitting, respectively. Mott-Schottky tests indicated that Ni-AC has p/n-type semiconductor features. While its n-type region was responsible for HER, the p-type region governed OER. A high dispersion of the nickel-based catalytic centers in the hierarchical pore system resulted in an efficient utilization of the active sites for the electron transfer processes. Besides the satisfactory performance, the advantage of the derived catalyst is in its simple synthesis from a commodity polymer.     

Preparation methods and progress of manganese dioxide/graphene based composites in supercapacitors

综述了基于MnO₂/石墨烯的二元、三元复合材料在超级电容器方面的最新研究进展。由于范德华力造成的堆叠,石墨烯实际比电容并不高。MnO₂理论比电容高达1370 F/g,但因其赝电容受MnO₂片层厚度的限制,实际比电容远小于理论值。将石墨烯和MnO₂复合,MnO₂纳米结构锚定在石墨烯纳米片之间充当间隔物,可以有效抑制石墨烯的堆叠,增强界面电荷转移,借助二者的协同效应有望实现高比电容、高电导率和良好的循环稳定性。介绍了MnO₂/石墨烯复合材料的制备方法及电化学性能。对比分析了MnO₂/石墨烯三元复合材料的电化学性能,由于金属氧化物或导电聚合物的引入,电化学性能进一步提升。最后总结指出基于MnO₂/石墨烯的多元复合材料和器件还面临着安全可靠、规模化生产以及降成本等一系列问题。随着技术的不断成熟和突破,有望在工业、交通以及日常电子器件中获得应用。     

Preparation of hierarchical porous carbon and its rate performance as anode of lithium ion battery

A hierarchical porous carbon with low oxygen content has been prepared by using polystyrene (PS) spheres as template and its structure, composition and performances as anode of lithium ion battery are characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, element analysis (EA), electrochemical impedance spectroscopy (EIS), and galvanostatic charge/discharge test. The results obtained from SEM, TEM, XRD, FTIR, and EA indicate that the prepared sample has a well-interconnected pore structure with a pore size of 170 nm and has an oxygen content of 3.3 ± 0.2 wt.%. The low oxygen content of the prepared sample can be ascribed to the low decomposition temperature of the template that was determined by thermal analysis. EIS shows that the prepared sample has lower electrochemical impedance for the lithium insertion/de-insertion than commercial natural graphite and charge/discharge tests show that the battery using the prepared sample as anode exhibits better rate performance than that using the graphite.     

Controlled synthesis of MnO2/CNT nanocomposites for supercapacitor applications

Abstract

In this work, manganese oxide (MnO₂)/carbon nanotube (CNT) nanocomposites have been prepared as electrode materials for supercapacitor applications. The materials were synthesised using a traditional and facile chemical deposition method. Effects from CNT amounts, synthesis time, pH value and CNT treatment using nitric acid have been thoroughly investigated. It was found that the sample synthesised for 3 h at pH 5 had achieved the best performance with a specific capacitance of 115 F g^?1 at a discharge rate of 0·5 A g^?1. A capacitance retention of 95% after 1000 cycles has been observed for the sample synthesised in the neutral environment. We believe that findings from this work will pave a road for nanostructured MnO₂/CNT composites with better performance in energy storage applications.     

Preparation of nickel modified activated carbon/AB5 alloy composite and its electrochemical hydrogen absorbing properties

Due to the good catalysis of metal nickel for the electrochemical reduction/oxidation reactions between H₂O and H in alkaline electrolyte, it is separately introduced into activated carbon (AC) by ball milling (named AC-1), liquid phase reduction (AC-2) and hydrothermal (AC-3) methods. The results of scanning electron microscopy (SEM) show that different to the aggregation of metal nickel in AC-1 and the coating of metal nickel on the surface of AC-2, metal nickel introduced by the hydrothermal method is uniformly dispersed among the AC-3 particles. The AC-3/AB₅ alloy (90 wt%) composite shows the best electrochemical hydrogen absorbing activity. Its capacity at a 0.2 C rate reaches to 318 mA h/g. Compared to the AB₅ alloy electrode, its discharge capacity separately increases 16% at a 1 C rate and 59% at a 3 C rate, which is particularly suitable for the high-power nickel metal-hydride (Ni–MH) battery.     

Energy storage in symmetric and asymmetric supercapacitors based in carbon cloth/polyaniline–carbon black nanocomposites

In this work, the construction of electrochemical capacitors using polyaniline–carbon black nanocomposites as electrode material is described. Symmetric and asymmetric cells were assembled. The active material was supported on carbon cloth acting as current collector as well. The electrolyte was H₂SO₄ 0.5 M, and the selected potential range was 1 V. The electrochemical behavior of the arrayed supercapacitors was studied by cyclic voltammetry and galvanostatic charge/discharge runs. At a constant current density of 0.3 A/g, a specific capacitance value of 1039 F/g was obtained for a symmetric assembly using both electrodes prepared with polyaniline and carbon black nanocomposites. When the set is asymmetric, being the positive electrode made of polyaniline and carbon black nanocomposites, the specific capacitance value is 1534 F/g. For the latter array, the specific power and energy density values are 300 W/kg and 426 Wh/kg at 0.3 A/g, and 13 700 W/kg and 28 Wh/kg at 13.7 A/g. These results suggest a good capacity of fast energy transfer. Moreover, this asymmetric supercapacitor demonstrated a high stability over 1000 cycles being the loss of only 5%. Copyright © 2015 John Wiley & Sons, Ltd.     

High electrochemical performance of metal azolate framework-derived ZnO/Co3O4 for supercapacitors

Metal azolate frameworks MAF-6 (Zn, Zn Co, and Co) were fabricated with a facile solution mixture method. Flower-like ZnO/Co₃O₄ was synthesized with MAF-6 as the template in a solvothermal condition of 90°C for 2 hours. The produced materials were characterized by XRD, EDS, SEM, and XPS. MAF-6 and the derived metal oxides acted as the electrode materials of supercapacitors. This study reported that ZnO/Co₃O₄ exhibited the maximal specific capacitance of 830.20 F/g at 1A/g, resulting from the synergy of Zn and Co and the enhanced conductivity. Furthermore, ZnO/Co₃O₄ electrode exhibited prominent rate capacitance, high electrochemical reversibility, and long life (89% capacitance was kept after 1000 cycles at 1 A/g). Given the results of this study, the prepared ZnO/Co₃O₄ electrode can be demonstrated as a potential candidate in the field of renewable energy storage.     

In situ self‐template synthesis of cobalt/nitrogen‐doped nanocarbons with controllable shapes for oxygen reduction reaction and supercapacitors

Shape‐controlled Co/N‐doped nanocarbons derived from polyacrylonitrile (PAN) were synthesized by a one‐step in situ self‐template method followed by a pyrolysis procedure. This is the first study to tune the nanostructure of Co/N‐doped carbon materials by providing a metal salt as the template and additive. The moderate surface area (699.47 m² g^?1), highly developed pore structure, homogenous Co and N doping and designed “egg‐box” structure impart Co/N‐doped cross‐linked porous carbon (Co/N‐CLPC) with excellent electrocatalytic activity and capacitive performance. This material displayed an onset potential of 0.805 V (vs RHE), a current density of ?5.102 mA cm^?2, excellent long‐term durability, and good resistance to methanol crossover, which are comparable with the characteristics of a commercial 20‐wt% Pt/C catalyst. In addition, Co/N‐CLPC demonstrated a high specific capacitance of 313 F g^?1 at 0.5 A g^?1, notable rate performance of 63% at 50 A g^?1, and good cycling stability of 104.8% retention after 5000 cycles when used as a supercapacitor electrode. This method enables new routes to obtaining Co/N‐doped nanocarbons with shape‐controlled structures for energy conversion and storage applications.     

Jute sticks derived novel graphitic porous carbon nanosheets as Li-ion battery anode material with superior electrochemical properties

Graphitic porous carbon sheets (GPCS), which were synthesized at a low temperature of 900°C by KOH chemical activation technique, possess a specific surface area of 1246 m² g^-1 with high pore volume. The size of the pores varied in micro-mesopore regions and exhibited three-dimensional sheet-like morphology composed of multilayered graphene sheets with an inter planar distance of 0.360 nm. The GPCS material was tested as anode for Li-ion battery (LIB) application in half cell mode (vs Li⁺/Li). The fabricated GPCS electrode shows excellent electrochemical properties in comparison with commercial graphite such as a high discharge specific capacity of 1022 mA h g^-1 after 10 cycles at 100 mA g^-1 and excellent specific capacity retention of 170 mA h g^-1 at a very high current rate of 8000 mA g^-1 and also retains a high capacity of 541 mA h g^-1 after 250 cycles at 500 mA g^-1, which suggests that GPCS material can be a promising electrode for LIB application. A brief comparison with commercial graphite and various carbonaceous materials from literature demonstrated that the GPCS electrode was potential material for high rate LIBs.