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2016, 31(3): .

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Preparation and applications of two dimensional carbon materials

TANG Yan-ping, XU Qing, TANG Rui-zhi, ZHANG Fan

2016, 31(3): 213-231.

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Two dimensional carbon materials have high chemical stabilities, tunable electrical properties, special optical, thermal and mechanical properties owing to their high surface area, two dimensional nature and small size. This paper reviews the fabrication of graphene and its derivatives, porous carbon nanosheets and carbon cloths, as well as their use in adsorption, detection/sensing, lithium ion batteries, supercapacitors, catalysis, et al. The challenges and prospects of these applications are also discussed.

Synthesis of porous carbons from microporous organic polymers

Wang Ke-wei, Tan Bi-en

2016, 31(3): 232-242.

Abstract(793)

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Porous carbons have been a hot research area in chemistry, physics and materials owing to their high specific surface areas, plentiful pores, excellent stability and good conductivity, which have been exploited in various applications such as catalysis, drug delivery and electrochemistry. Microporous organic polymers (MOPs) are currently an important class of porous polymers that have developed rapidly in recent years. MOPs have the advantages of good chemical and physical stability, tunable pore structure, high surface area and easy functionalization compared with traditional porous materials such as zeolite and silica gel. Because of the excellent thermal stability of MOPs,porous carbons with a tunable pore structure can be obtained by their carbonization. In this review, we outline how MOPs were used to make porous carbons and highlight their synthesis and applications.

Applications of porous carbon materials in the electrocatalysis of the oxygen reduction reaction

YANG Hui-cong, LIANG Ji, WANG Zhen-xing, AN Bai-gang, LI Feng

2016, 31(3): 243-263.

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Oxygen reduction reactions (ORRs) are fundamental in various energy storage and conversion devices. Their activity determines the overall performance of these devices. Due to the sluggish kinetics of ORRs, a catalyst is often required, and in this regard, carbon materials are important as supports of noble metals such as Pt and Pd, and various non-noble metals, or even as metal-free catalysts. As a result, the development of porous carbons is playing a very important role in the advancement of ORR catalysts. We review the development of the ORR catalysts based on porous carbons, including their use as noble-/non-noble metal supports and metal-free catalysts, together with their synthesis methods and structural tuning. We also reviewtheir future prospects for ORR catalysis.

Carbon-based cathodes for sodium-air batteries

LIU Shan, LIU Si-si, LUO Jia-yan

2016, 31(3): 264-270.

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Sodium-air batteries are considered promising electrochemical devices for energy storage owing to their high theoretical energy density, high discharge voltage and the abundanceof sodium in nature. The recent progress, current challenges and developing trendsfor Na-air batteries are summarized. The use of carbon materials as their cathode is highlighted.

Surface modification of a hierarchical porous carbon aerogel and its effect on the adsorption of acid fuchsin

CAI Li-feng, FU Ming-lian, CHEN Lu-yi, FU Ruo-wen, WU Ding-cai

2016, 31(3): 271-276.

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The surface of a hierarchical porous carbon aerogel (HPCA-1) was modified with nitric acid to obtain mHPCA-1. Acid fuchsin (AF) adsorption on these carbon aerogels in water was studied. Results indicate that the acid modification has trivial effects on the morphology and pore structure, but obviously increases the number of surface oxygen-containing groups. The isothermal adsorption of AF on these modified carbon aerogels is monomolecular layer adsorption, and can be well described by the Langmuir equation. The maximum adsorption capacity on mHPCA-1 reaches 191.57 mg·g^-1, which is much higher than that on HPCA-1 (120.92 mg·g^-1). The adsorption kinetics can be well described by a first-order kinetic equation and the kinetic constant can be increased by the acid modification.

Preparation of porous carbon nanofibers with controllable pore structures for low-concentration NO removal at room temperature

WANG Ming-xi, GUO Ze-yu, HUANG Zheng-hong, KANG Fei-yu

2016, 31(3): 277-286.

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Porous carbon nanofibers (PCNFs) with controllable pore structures for removing low-concentrations of NO at room temperature were prepared from electrospun polyacrylonitrile nanofibersby oxidative stabilization, carbonization and steam activation. The PCNFs had high surface areas and abundant micropores, which were favorable for the adsorption and catalytic oxidation of NO at ambient temperature. The diameter of the fibers and their pore structure were tailored by adjusting the concentrations of polyacrylonitrile, and the spinning and activation parameters. Their performance in the removal of low-concentration NO was strongly dependent on their pore structure and fiber diameter. The highest NO removal ratio for PCNFs activated at 900℃, which had an average diameter of 175 nm, reached 29.7% when the inlet NO concentration was 20 ppm.

Preparation of Pt-loaded nitrogen-doped activated carbons and their catalytic activities for the oxygen reduction reaction

LI Li-xiang, ZHANG Yan-qiu, SUN Pan-song, AN Bai-gang, XING Tian-yu, SONG Ren-feng

2016, 31(3): 287-292.

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Two nitrogen-doped activated carbons (NACs) were prepared by the in-situ polymerization of pyrrole in activated carbon (AC), followed by carbonization at 700 or 900℃. Platinum was loaded onto the AC and NACs by impregnation with a H₂PtCl₆ solution followed by chemical reduction with excess NaBH₄. The oxygen reduction reaction (ORR) performance of the Pt-loaded AC and NACs were investigated. Results indicate that the nitrogen doping decreases the specific surface area, but improves water dispersibility and surface activity, which makes the platinum loading more uniform on the NACs than on the AC. Of the three sample the material with the highest density of platinum particles with sizes less than 5 nm uniformly distributed on the surface was NAC900, and the platinum loading was higher than that on AC and NAC700. The ORR catalytic performance of the Pt-loaded activated carbons was enhanced by the nitrogen doping. Pt-NAC900 exhibits the most positive ORR peak and the highest ORR peak current, and its ORR peak current decay is the slowest of the three samples.

Effect of the pH of the preparation medium on the microstructure and electrocatalytic activity of carbon nanotubes decorated with PtSn nanoparticles for use in methanol oxidation

LI Hai-chao, CHEN Shui-xia, LI Qi-han, LIU Feng-lei

2016, 31(3): 293-300.

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Carbon nanotubes (CNTs) decorated with PtSn nanoparticles (PtSn/CNT) were prepared by the microwave-assisted ethylene glycol reduction method and characterized by atomic adsorption spectroscopy, X-ray diffraction and transmission electron microscopy. Results indicated that the loading efficiency of the metal catalyst, and the degree of alloying and morphology of the PtSn nanoparticles were significantly affected by the solution pH value of the metallic ions in the ethylene glycol. The required composition of the PtSn/CNT catalysts could be obtained by adjusting the pH value to about 5, which is almost the isoelectric point of the acid-treated CNTs. The size of the PtSn nanoparticles decreased with the pH value in the range 2 to 7, but they became large and agglomerated when the pH value was greater than 7. Electrocatalytic activity tests indicated that the PtSn-CNTs prepared at pH 5 had the best catalytic performance towards methanol oxidation. The improvement in catalytic activity was mainly attributed to a high loading efficiency and control of particle shape and size distribution.

Mechanical and dielectric properties of mesoporous carbon microsphere/phenolic resin composites

ZHOU Jian-guo, ZHU Xiao-lei, ZHANG Li, QIAO Wen-ming, LONG Dong-hui, LING Li-cheng

2016, 31(3): 301-306.

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Mesoporous carbon microspheres (MCMs) were prepared by a scalable spray-drying method using resorcinol-formaldehyde resin as the carbon precursor. The MCMs were used as low density fillers of phenolic resin matrix composites for microwave absorption. They were coated with polyvinyl alcohol (PVA) before being added to the phenolic resin and the composites were prepared by the hot-pressing method. Results showed that the MCMs had a narrow particle size distribution of 1-10 μm and developed mesopores with a total pore volume of 3.0 cm³/g. The PVA coating densified the surface of the MCMs to form a core-shell structure while retaining the mesopores. The density of the composites decreased from 1.36 to 1.12 g/cm³ by increasingthe MCM content from 0 to 10 wt%. The corresponding dielectric constant in the frequency range of 102-107 Hzincreased from 4.0-3.6 to 10.4-9.1. The compressive strength exhibited a maximum of 168 MPa with a MCM content of 5 wt%.The low density, high mechanical strength and high dielectric constant of the composites suggests that the MCMs are ideal fillers for phenolic resin-based microwave absorption materials.

Influence of the KOH activation of carbon nanotubes on their electrochemical behavior in lithium-air batteries

WANG Hai-fan, WEI Wei, QIN Lei, LEI Yu, YU Wei, LIU Ru-liang, LU Wei, ZHAI Deng-yun, YANG Quan-hong

2016, 31(3): 307-314.

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The Li-air battery has attracted considerable attention owing to its high energy density, which is approximately 10 times larger than that of a conventional Li-ion battery. Carbon is frequently used as the cathode material because of its stable structure and excellent conductivity. The surface properties and microstructure of carbon nanotubes (CNTs) were modified by KOH activation and its effects on the electrochemical behaviorof CNTs as a cathode material for Li-air batterieswere investigated. Results indicate that the graphitic layer of the CNT outer surface is etched and more edge carbon atoms are exposed after the modification, which generates a CNT-graphene hybrid nanostructure. This hybrid structure provides a large number of active sites that are beneficial for the generation/decomposition of discharge products, leading to a decrease of the charging overpotential and an improvement in cycling stability.

Preparation of graphene nanoscroll/polyaniline composites and their use in high performance supercapacitors

ZHENG Bing-na, GAO Chao

2016, 31(3): 315-320.

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The graphene nanoscroll is a kind of tubular graphene with an open end and a helical nanostructure. Different amounts of polyaniline were formed on the surface of the nanoscroll by the in-situ polymerization of aniline. SEM observation shows thatthe polyaniline nanoparticles are evenly distributed on the nanoscrolls and the number of free polyaniline clusters increases with the amount of monomer used. The electrochemical performance of three composites with different polyaniline/graphene nanoscroll ratios was evaluated. The best specific capacitance of the composites reaches 320 F/g at 1 A/g and a 92.1% retention capacitance rate is obtained at 100 A/g, indicating that the composite has a rate performance as good as graphene nanoscrolls and a higher specific capacitance.

A binder-free web-like silicon-carbon nanofiber-graphene hybrid membrane for use as the anode of a lithium-ion battery

WU Jun-xiong, QIN Xian-ying, LIANG Ge-meng, YUN Qin-bai, HE Yan-bing, KANG Fei-yu, LI Bao-hua

2016, 31(3): 321-327.

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A binder-free silicon-carbon nanofiber-graphene (Si-CNF-G) hybrid membrane was prepared by embedding Si particles encapsulated in a porous carbon in a cobweb-like carbon scaffold composed of CNFs and G nanosheetsproduced using the coaxial electrospraying method. The binder-free Si-CNF-G electrode delivered an initial reversible specific capacity of 957 mAh·g^-1 with a retention of 74.4% after 100 cycles at 0.2 A·g^-1, and a rate capability of 539 mAh·g^-1 at 2 A·g^-1, which was much better than that of a Si electrode. This can be attributed to the fact that the porous carbon matrix was able to buffer the large volume expansion and contraction of Si during charging and discharging, and that the interconnected carbon scaffold not only created efficient pathways for electron conduction and ion transfer, but also improved the structural stability of the whole electrode.

Electrochemical performance of rod-type ordered mesoporous carbons with different rod lengths for electric double-layer capacitors

LIU Na, YU Lv-qiang, CHEN Xiao-hong, LIAO Li-fang, ZHOU Ji-sheng, MA Zao-kun, SONG Huai-he

2016, 31(3): 328-335.

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Rod-type ordered mesoporous carbons were synthesized by the direct carbonization of sulfuric-acid-treated silica/triblock copolymer composites, followed by etching the silica with a HF solution. The morphologies, microstructures and pore structures of the mesoporous carbons were investigated by scanning electron microscopy, high resolution transmission electron microscopy, X-ray diffraction and nitrogen sorption. Their electrochemical performance as electrodes for supercapacitors was investigated by impedance spectroscopy and charge/discharge tests. It was found that the rod length of the mesoporous carbons can be changed from one to tens of micrometers by changing the synthesis parameters. The sample with the longest rod length has the highest specific capacitance. The sample with two pore sizes has the highest capacitance retention ratio of 92% at a high current density of 2 A/g.

A hierarchically porous CuCo₂S₄/graphene composite as an electrode material for supercapacitors

LIU Li-le, K. P. Annamalai, TAO You-sheng

2016, 31(3): 336-342.

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A CuCo₂S₄/graphene composite was synthesized using a simple hydrothermal method. The sample was characterized by field emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, nitrogen adsorption and electrochemical tests. The composite had a hierarchical porous structure with micropores of 0.7-1.2 nm, mesopores of 2-10 nm and a total pore volume of 0.1 cm³·g^-1, and the CuCo₂S₄ had a nano-belt structure. As the electrode of a supercapacitor the composite showed a high specific capacitance of 665 F/g at 7.5 mV/s, and excellent rate capability and cycling stability.

2016, 31(3): 336-342.

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Preparation and modification of high performance porous carbons from petroleum coke for use as supercapacitor electrodes

TAN Ming-hui, ZHENG Jing-tang, LI Peng, Tsubaki Noritatsu, WU Ming-bo

2016, 31(3): 343-351.

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As a byproduct of oil refining, petroleum coke with a high carbon content (about 90 wt%) has been shown to be a good raw material for porous carbons (PCs). PCs with high specific surface areas were derived from petroleum coke by KOH activation. The effect of KOH/coke mass ratio on the pore structure of the PCs and their electrochemical performance as electrodes of electric double layer capacitors were investigated. Results showed that the specific surface area and pore size distribution of the PCs could be efficiently controlled by the KOH/coke ratio. The pore sizes of the PCs increase with increasing KOH/coke ratio, and the largest specific surface area was as high as 2 964 m²·g^-1. A PC-5 electrode prepared with a KOH/coke ratio of 5:1 has a high specific surface area of 2 842 m²·g^-1 and mesoporosity of 67.0%, and has the largest specific capacitance at all investigated current densities among the PCs examined. This is ascribed to its high specific surface area and high mesoporosity. Hydrothermal modification of PC-3 (KOH/coke ratio at 3:1) in ammonia at 200℃ increases its specific capacitance, especially at high discharge current densities. This improved electrochemical performance can be attributed to nitrogen-doping that occurs during the process, and this can induce pseudo-capacitance and improve the hydrophilicity of the PC electrode to the electrolyte. KOH activation combined with ammonia hydrothermal modification is a simple yet efficient approach to prepare cost-effective PCs for supercapacitors with excellent electrochemical performance.

Hydrothermal synthesis of porous phosphorus-doped carbon nanotubes and their use in the oxygen reduction reaction and lithium-sulfur batteries

GUO Meng-qing, HUANG Jia-qi, KONG Xiang-yi, PENG Hong-jie, SHUI Han, QIAN Fang-yuan, ZHU Lin, ZHU Wan-cheng, ZHANG Qiang

2016, 31(3): 352-362.

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The many uses of carbon nanotubes (CNTs) depend not only on their intrinsic physical properties, but also on their tunable chemical components. Exploring a low-temperature method for the incorporation of phosphorus atoms in the carbon framework is expected to change the chemical properties of CNTs. Here, phosphorus-functionalized CNTs (PCNTs) were prepared by the direct hydrothermal treatment of a CNT-H₃PO₄ mixture at 170℃. The PCNTs had a high phosphorus content of 1.66 at%, a specific surface area of 132 m²·g^-1, and an improved thermal stability with a weight loss peak at 694℃ during oxidation in pure oxygen. They showed good electrocatalytic activity for the oxygen reduction reaction with an onset potential of 0.20 V vs Hg/Hg₂Cl₂, an electron transfer number of 2.60, and a larger current density as well as improved cyclic stability compared with pristine CNTs. PCNTs were also used as conductive scaffolds for the cathode in lithium-sulfur batteries. The cathode delivered an initial discharge capacity of 1 106 mAh·g^-1, a capacity retention of 80% from 0.1 to 1.0 C, and a low decay rate of 0.25% per cycle during 100 cycles.

2016 Vol. 31, No. 3

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