Synthesis of few-layer N-doped graphene from expandable graphite with melamine and its application in supercapacitors

In this paper,we introduced a novel method to prepare the few-layer nitrogen-doped graphene(FNG)from expandable graphite with melamine.The super-capacitive properties of FNG were thoroughly characterized by a three-electrode system,and the results showed the FNG electrode achieved a specific capacitance as high as 83.8 mF/cm2 together with excellent cycling stability.This method could be a novel approach to combine the pseudo-capacitors and electric double layer capacitors.     

超级电容器石墨烯-聚苯胺复合材料的研究进展

超级电容器具有功率密度高、充放电速度快、循环寿命长和维护成本低的特点,在电动车动力电池领域具有潜在的应用前景。超级电容器性能主要由其电极材料所决定。聚苯胺易合成、理论比容量高,而且导电性能优异,作为超级电容器电极材料有很高的应用价值。但是,在长期使用过程中,它的体积容易发生膨胀或收缩,循环寿命差。为了解决这个问题,将聚苯胺与石墨烯复合可以扬长避短,充分利用两者之间的协同效应,赋予复合材料优异电化学电容性能。本文综述了超级电容器用石墨烯-聚苯胺复合材料的制备方法,包括原位聚合法、油水界面合成法、电化学合成法、层层自组装法等;提出了三维网状石墨烯和对石墨烯-聚苯胺复合材料进行改性来提高复合材料的电化学电容性能的思路。     

Activated carbon felts with exfoliated graphene nanosheets for flexible all-solid-state supercapacitors

Porous activated carbon felts (ACFs) with exfoliated graphene nanosheets were prepared by a simple thermal treatment strategy. They exhibit high gravimetric and areal specific capacitances as well as long-term cycling stability. Impressively, the all-solid-state supercapacitors based on ACFs electrodes deliver stable electrochemical performance even under different bending states.     

Improving the performance of all-solid-state supercapacitors by modifying ionic liquid gel electrolytes with graphene nanosheets prepared by arc-discharge

Ionic liquid gel polymers have widely been used as the electrolytes in all-solid-state supercapacitors, but they suffer from low ionic conductivity and poor electrochemical performance. Arc discharge is a fast, low-cost and scalable method to prepare multi-layered graphene nanosheets, and as-made graphene nanosheets （denoted as ad-GNSs） with few defects, high electrical conductivity and high thermal stability should be favorable conductive additive materials. Here, a novel ionic liquid gel polymer electrolyte based on an ionic liquid （EM1MNTF2） and an copolymer （P（VDF-HFP）） was modified by the addition of ad-GNSs as an ionic conducting promoter. This modified gel electrolyte shows excellent thermal stability up to 400 ℃ and a wide electrochemical window of 3 V. An all-solid-state supercapacitor based on commercial activated carbon was fabricated using this modified ionic liquid gel polymer electrolyte, which shows obviously improved electrochemical behaviors compared with those of the corresponding all-solid-state supercapacitor using pure ionic liquid gel polymer electrolyte. Specially, smaller internal resistance, higher specific capacitance, better rate performance and cycling stability are achieved. These results indicate that the ionic liquid gel polymers modified by ad-GNSs would be promising and suitable gel electrolytes for high performance all-solid-state electrochemical devices.     

Sulfur-decorated nanomesh graphene for high-performance supercapacitors

Sulfur-decorated nanomesh graphene(S@G) has been synthesized by a 155℃ heat treatment of a mixture of nanomesh graphene and S. The as-obtained S@G materials keep a high specific surface area,and exhibit obviously enhanced conductivity and hydrophilicity as compared to the pristine graphene.X-ray photoelectron spectroscopy and thermogravimetric analysis indicate that most S atoms in the S@G samples are stably combined with nanomesh graphene via covalent bonds rather than exist as free elemental S. As an electrode material for aqueous supercapacitors, the S@G with a S content of 5 wt% delivers a specific capacitance up to 257 F/g at the current density of 0.25 A/g, which is 23.6% higher than that of the undoped graphene. Our results provide a simple approach to scalable synthesis of S-doped porous carbon materials, which have potential applications in the high-performance capacitive energy storage devices.     

Ionic liquid-functionalized graphene as modifier for electrochemical and electrocatalytic improvement: comparison of different carbon electrodes

Electrochemical activities of typically electrochemical targets at three kinds of modified carbon electrodes, i.e. carbon ionic liquid electrode (CILE), graphene/carbon paste electrode (CPE), and ionic liquid-functionalized graphene (IL-graphene)/CPE, were compared in detail. The redox processes of the probes at IL-graphene/CPE were faster than those at CILE and graphene/CPE from cyclic voltammetry. An electrochemical method for the simultaneous determination of guanine and adenine was described with detection limits of 6.5 × 10⁻⁸ mol L⁻¹ (guanine) and 3.2 × 10⁻⁸ mol L⁻¹ (adenine). Single A → G mutation of sequence-specific DNA could be discriminated by the IL-graphene/CPE.     

A facile preparation and electrochemical properties of nickel based compound-graphene sheet composites for supercapacitors

Composites of a nickel based compound incorporated with graphene sheets(NiBC-GS) are prepared by a simple flocculation,using hydrazine hydrate as flocculant and reductant,from a homogeneous intermixture of nickel dichloride and graphene oxide dispersed in N,N-dimethylformamide.Morphology,microstructure and thermal stability of the obtained products were characterized by field-emission scanning electron microscopy,X-ray diffraction and thermal gravimetric analysis.Furthermore,the electrochemical properties of NiBC-GS,as electrode materials for supercapacitors,were studied by cyclic voUammetry and galvanostatic charge/discharge in 2 mol L~(-1) KOH solution.It was determined that for NiBC-GS annealed at 250 ℃.a high specific capacitance of 2394 Fg~(-1) was achieved at a current density of 1 Ag~(-1),with 78%of the value(i.e.,1864 Fg~(-1)) retained after 5000 times of repeated galvanostatic charge/discharge cycling.The high specific capacitance and available charge/discharge stability indicate the synthesized NiBC-GS250 composite is a good candidate as a novel electrode material for supercapacitors.     

Free-standing nitrogen doped graphene/Co(OH)_2 composite films with superior catalytic activity for aprotic lithium-oxygen batteries

The recent boom in large-scale energy storage system promotes the development of lithium-oxygen batteries because of their high theo retical energy density.However,their applications are still limited by the sluggish kinetic,insoluble discharge product deposition and the undesired parasitic reaction.Herein,the free-standing nitrogen doped reduced graphene oxide/Co(OH)_2(NRGO/Co(OH)_2) composite films were prepared by a facile hydrothermal method,The NRGO/Co(OH)_2 composite films display interconnected three-dimensional conductive network,which can not only promote the diffusion of O_2 and the transport of electrolyte ions,but also provide abundant storage space for discharge products.Moreover,the introduction of nitrogen-containing functional groups results in improved conductivity and electron adsorption ability,which can facilitate electron transport and enhance the surface catalytic activity.Combining with excellent catalytic performance,the lithium-oxygen batteries with NRGO/Co(OH)_2 composite film cathodes deliver low charge overpotential and excellent cycling performance.     

Influence of graphene nanoscrolls on the crystallization behavior and nano‐mechanical properties of polylactic acid

Graphene nanoscrolls (GNS), one‐dimensional carbon‐based nanomaterials, have been predicted to possess extraordinary characteristics due to their unique open topology with scrolled graphene monolayers. In this study, the conversion of planar 2‐D graphene nanoplatelets (GNPs) to tubular and scrolled 1‐D GNSs is described. The effects of GNS as a nucleating agent to modulate the morphology, crystallization, and nano‐mechanical properties of polylactic acid (PLA) were studied. The nucleating effect of GNS and its unique topological characteristics proves to influence the crystallization of PLA. Fourier transform infrared (FTIR) spectroscopy indicated nonpreferential interactions of PLA chains around GNS due to the bulky and helical PLA macromolecular chains. Superior interfacial interactions and strain in GNS provide better load transfer between GNS and PLA matrices, resulting in higher modulus and hardness. This study is the first detailed analysis to elucidate the role of unique GNS to favorably modulate the properties of a polymer.     

Phenylenediamine-formaldehyde chemistry derived N-doped hollow carbon spheres for high-energy-density supercapacitors

Porous carbon spheres represent an ideal family of electrode materials forsupercapacitors because of the high surface area,ideal conductivity,negligible aggregation,and ability to achieve space efficient packing.However,the development of new synthetic methods towards porous carbon spheres still remains a great challenge.Herein,N-doped hollow carbon spheres with an ultrahigh surface area of2044 m²/g have been designed based on the phenylenediamine-formaldehyde chemistry.When applied in symmetric supercapacitors with ionic electrolyte(EMIBF_4),the obtained N-doped hollow carbon spheres demonstrate a high capacitance of 234 F/g,affording an ultrahigh energy density of 114.8 Wh/kg.Excellent cycling stability has also been achieved.The impressive capacitive performances make the phenylenediamine-formaldehyde resin derived N-doped carbon a promising candidate electrode material for supercapacitors.     

多孔Fe3O4修饰的Ni(OH)2纳米片的制备及其析氧性能研究

近年来,基于析氧反应(OER)的电化学能量转换体系(如电化学制氢、金属空气电池、氮气电还原和二氧化碳电还原)日益受到人们的关注.各种过渡金属基(Mn,Ni,Co,Fe,Cu等)纳米材料(硫化物、氢氧化物、氧化物、磷化物和氮化物等)被认为是潜在的、可以代替贵金属的碱性OER催化剂.其中,高活性和低成本的Ni(OH)2基电催化剂被广泛关注.由于面积效应、结构效应、电子效应和协同效应等因素,Ni(OH)2基纳米材料的电化学活性与其形貌和化学成分密切相关.引入纳米尺寸的孔,不仅加快了传质,而且增加了边缘活性原子的数量,因而有利于活性的增强.超薄二维(2D)纳米片因具有独特的结构特征,可以为电催化反应提供充足的反应位点和低配位数的表面活性原子.杂原子的引入可以调节纳米材料的电子结构和几何结构以提高它们的电催化活性.本文提出了一种简单的混合氰胶水解策略,成功合成了Fe掺杂的Ni(OH)2纳米片(Ni(OH)2-Fe H-STs).氰胶前驱体骨架结构有助于形成超薄多孔的2D结构,而且,通过调节前驱体的浓度就可以获得一定镍铁原子比的产物.不同Fe含量的Ni(OH)2纳米片的OER活性测试结果表明,Ni/Fe比为3:1的Ni(OH)2-Fe H-STs-Ni3Fe1在碱性环境中具有最佳的OER活性.由于Ni(OH)2-Fe H-STs-Ni3Fe1的超薄2D结构使大多数金属原子暴露在表面,使原子利用率最大化.同时,超薄表面上高活性的低配位数的中心原子,可以作为催化OER的高活性中心.薄片上的孔隙有效地增加了高活性边缘原子的数量并且能够加速反应物和生成物的传质.XPS测试结果表明,Fe的引入显著改变了Ni的电子结构,提高了Ni(OH)2 H-STs的导电性,从而促进了电化学过程中NiIV活性物种的产生,进而改变其OER本征活性.三维镍泡沫(NF)可以防止负载纳米材料的聚集,提高转移反应物/产物的传质速率.因此,本文将Fe掺杂的Ni(OH)2纳米片直接生长在NF基底(简写为Ni(OH)2-Fe H-STs/NF).结果表明,NF基底的引入进一步提升导电性和增加传质.综上所述,由于具有高比表面积、丰富的活性原子、Fe/Ni原子之间的协同效应以及NF基底的高导电性和三维多孔特性,通过氰胶水解法获得的Ni(OH)2-Fe H-STs/NF在KOH溶液中表现出优异的OER活性,在10 mA cm^–2电流密度下过电位仅为200 mV,Tafel斜率为56 mV dec^?1,并且材料具有良好的稳定性.     

Synthesis of Pt/ionic liquid/graphene nanocomposite and its simultaneous determination of ascorbic acid and dopamine

A water-soluble and electroactive composite - Pt nanoparticles/polyelectrolyte-functionalized ionic liquid (PFIL)/graphene sheets (GS) nanocomposite was synthesized in one pot. The structure and composition of the Pt/PFIL/GS nanocomposite were studied by means of ultraviolet-visible (UV-vis) and X-ray photoelectron spectra (XPS). Scanning electron microscopy (SEM) and transmission electron microscope (TEM) images reveal Pt nanoparticles are densely dispersed on the transparent thin PFIL-functionalized graphene sheets. The obtained Pt/PFIL/GS nanocomposite-modified electrode was fabricated to simultaneously determine ascorbic acid (AA) and dopamine (DA) by cyclic voltammetry. It is worthwhile noting that the difference between the two peak potentials of AA and DA oxidation is over 200 mV, which leads to distinguishing AA from DA. The detection of increasing concentrations of AA in the presence of DA and the oxidation of continuous addition of DA in the presence of AA were also studied using differential pulse voltammetry. The proposed sensor in real sample analysis was also examined in human urine samples. Three independent oxidation peaks appear in urine sample containing AA and DA. Therefore, the Pt/PFIL/GS nanocomposite might offer a good possibility for applying it to routine analysis of AA and DA in clinical use.     

Nitrogen-doped carbon nanotube-encapsulated nickel nanoparticles assembled on graphene for efficient CO_2 electroreduction

Exploring 3 D hybrid nanocarbons encapsulated with metal nanoparticles(NPs) are recently considered as emerging catalysts for boosting CO_2 electroreduction reaction(CRR) under practical and economic limits.Herein,we report a one-step pyrolysis strategy for fabricating N-doped carbon nanotube(CNT)-encapsulated Ni NPs assembled on the surface of graphene(N/NiNPs@CNT/G) to efficiently convert CO_2 into CO.In such 3 D hybrid,the particle size of Ni NPs that coated by five graphitic carbon layers is less than 100 nm,and the amount of N dopants introduced into graphene with countable CNTs is determined to 7.27 at%.Thanks to unique CNT-encapsulated Ni NPs structure and N dopants,the achieved N/NiNPs@CNT/G hybrid displays an exceptional CRR activity with a high Faradaic efficiency of 97.7% and large CO partial current density of 7.9 mA/cm~2 at-0.7 V,which outperforms those reported metallic NPs loaded carbon based CRR electrocatalysts.Further,a low Tafel slope of 134 mV/dec,a turnover frequency of 387.3 CO/h at-0.9 V,and tiny performance losses during long-term CRR operation are observed on N/NiNPs@CNT/G.Experimental observations illustrate that the Ni NPs encapsulated by carbon layers along with N dopants are of great importance in the conversion of CO_2 into CO with high current density.     

Mesoporous tubular graphene electrode for high performance supercapacitor

Mesopores tubular graphene, synthesized by template method, have unique bi-directional ions transfer channel in unstack graphene layers and high mesopore ratio, exhibiting excellent capacitance performance in the EDLC using ionic liquid electrolyte at 4 V.     

A comparison of H+-restacked nanosheets and nanoscrolls derived from K4Nb6O17 for visible-light degradation of dyes

H⁺-restacked nanosheets and nanoscrolls peeled from K₄Nb₆O₁₇ display different structures and surface characters. The two restacked samples with increased surface areas have an amazing visible-light response for the photodegradation of dyes, which is superior to commercial TiO₂ (P25) and Mb₂O₅. By comparison, H⁺/nanosheets have a relatively faster photodegradation rate originated from large and smooth basal plane. The work reveals that dye adsorbed on the unfolded nanosheets can effectively harvest sunlight. Due to facile preparation, low-cost and high photocatalytic efficiency, H⁺/nanosheets and H⁺/nanoscrolls might be used for the visible light-driven degradation of organic dyes as a substitute for TiO₂ in industry.     

Layer-by-layer assembled multilayer of graphene/Prussian blue toward simultaneous electrochemical and SPR detection of H2O2

A new type of chemically converted graphene sheets, cationic polyelectrolyte-functionalized ionic liquid decorated graphene sheets (PFIL-GS) composite, was synthesized and characterized by Ultraviolet-visible (UV-vis) absorption, Fourier transform infrared, and Raman spectroscopy. It was found that the presence of PFIL enabled the formation of a very stable aqueous dispersion due to the electrostatic repulsion between PFIL modified graphene sheets. With respect to the excellent dispersibility of this material, we have fabricated a novel PFIL-GS/Prussian blue (PB) nanocomposite multilayer film via classic layer-by-layer (LBL) assembly. The assembly process was confirmed by UV-vis spectroscopy and surface plasmon resonance (SPR) spectroscopy, which showed linear responses to the numbers of the deposited PFIL-GS/PB bilayers. Moreover, the as-prepared composite films were used to detect hydrogen peroxide (H₂O₂) by electrochemical surface plasmon resonance (EC-SPR) spectroscopy. This real time EC-SPR technique can provide simultaneous monitoring of both optical SPR signal and electrochemical current responses upon injecting H₂O₂ into the reaction cell. The experimental results revealed that both the electrochemical and SPR signal exhibited splendid linear relationship to the concentration of the injected H₂O₂, and the detection limit could be up to 1 μM.     

氮掺杂石墨烯的制备及其对氧还原反应的电催化性能

以氧化石墨烯(GO)为原料、丙酮肟(DMKO)为还原剂和氮掺杂剂,采用化学还原法制备了不同氮掺杂含量的石墨烯(NG).利用场发射透射电子显微镜(FETEM)、紫外-可见(UV-Vis)光谱、傅里叶变换红外(FTIR)光谱、X射线光电子能谱(XPS)、zeta电位和纳米粒度分析、循环伏安(CV)和旋转圆盘电极(RDE)等手段对材料的形貌、结构、成分和电化学性质进行表征.结果显示:DMKO能有效地还原GO,且通过调节GO与DMKO的质量比,可以得到不同还原效果的NG,其氮含量范围为4.40%-5.89%(原子分数);GO与DMKO的质量比为1:0.7时制备的氮掺杂石墨烯(NG-1)在O2饱和0.1 mol·L-1KOH溶液中对氧还原反应(ORR)的电催化性能最佳,其ORR峰电流为0.93 mA·cm-2,电子转移数为3.6,这归因于其较高含量的吡啶-N增加了材料的ORR活性位点.此外,石墨化-N由于其较高的电子导电性倾向于产生较高的氧还原峰电流,而吡啶-N较低的超电势倾向于产生较正的氧还原峰电位.与商用Pt/C相比,该材料展现出了优异的抗CH3OH"跨界效应"的特性.     

氮掺杂石墨烯的制备及其对氧还原反应的电催化性能

以氧化石墨烯（GO）为原料、丙酮肟（DMKO）为还原剂和氮掺杂剂,采用化学还原法制备了不同氮掺杂含量的石墨烯（NG）. 利用场发射透射电子显微镜（FETEM）、紫外-可见（UV-Vis）光谱、傅里叶变换红外（FTIR）光谱、X射线光电子能谱（XPS）、zeta 电位和纳米粒度分析、循环伏安（CV）和旋转圆盘电极（RDE）等手段对材料的形貌、结构、成分和电化学性质进行表征. 结果显示：DMKO能有效地还原GO,且通过调节GO与DMKO的质量比,可以得到不同还原效果的NG,其氮含量范围为4.40%-5.89%（原子分数）;GO与DMKO的质量比为1：0.7时制备的氮掺杂石墨烯（NG-1）在O₂饱和0.1 mol·L^-1 KOH溶液中对氧还原反应（ORR）的电催化性能最佳,其ORR峰电流为0.93 mA·cm^-2,电子转移数为3.6,这归因于其较高含量的吡啶-N增加了材料的ORR活性位点. 此外,石墨化-N由于其较高的电子导电性倾向于产生较高的氧还原峰电流,而吡啶-N较低的超电势倾向于产生较正的氧还原峰电位. 与商用Pt/C相比,该材料展现出了优异的抗CH₃OH“跨界效应”的特性.     

Surface modulated hierarchical graphene film via sulfur and phosphorus dual-doping for high performance flexible supercapacitors

The steam-assistant heteroatoms of sulfur and phosphorus dual-doped graphene film fabricated via an ice-template and thermal-activation approach demonstrates an excellent pseudocapacitive behavior in flexible electrochemical capacitors.