铜族金属与完整及氮掺杂石墨烯的相互作用

基于广义梯度密度泛函理论和周期平板模型,研究了铜族金属单原子和双原子簇与完整及氮掺杂石墨烯的结合情况.结果表明,氮掺杂后石墨烯的电子结构特性由半金属性变为金属性;铜族金属在完整及石墨型氮掺杂石墨烯上的吸附较弱,结合能约为0.5eV,而在吡啶型氮掺杂和吡咯型氮掺杂石墨烯上有较强的化学吸附,结合能一般大于1eV;吡咯型氮掺杂后的构型不稳定,金属原子及簇与包含该结构的石墨烯衬底作用时会使其向吡啶型氮掺杂转变,并最终得到基于吡啶型氮掺杂的稳定吸附构型.Mulliken电荷布居分析显示,吸附在吡啶型氮掺杂石墨烯上的金属单原子与金属双原子簇带电性质相反.态密度及轨道分析表明,Cu与吡啶型氮掺杂石墨烯空位处留有悬挂键的三个原子成键,而Au与其中两个C原子成键.     

First-principles studies on doped graphene as anode materials in lithium-ion batteries

Using density functional theory computations, we investigated Li adsorption, diffusion, and desorption in pristine, B- or N-doped graphene. Compared with pristine graphene, B-doping significantly enhances Li adsorption, whereas Li adsorption is slightly weakened on N-doped graphene, which should be attributed to the different electronic structures due to doping. Li diffusion on various graphene systems was also computed through nudged elastic band method, and the results revealed that Li diffusion on N-doped graphene is faster than on pristine and B-doped graphene. Moreover, for Li desorption from the graphene substrate, N-doped graphene showed the lowest desorption barrier. Our results are in agreement with recent experimental reports and also demonstrate that N-doped graphene is a promising anode material with high-rate charge/discharge ability for Li-ion batteries.     

Low temperature growth of highly nitrogen-doped single crystal graphene arrays by chemical vapor deposition

The ability to dope graphene is highly important for modulating electrical properties of graphene. However, the current route for the synthesis of N-doped graphene by chemical vapor deposition (CVD) method mainly involves high growth temperature using ammonia gas or solid reagent melamine as nitrogen sources, leading to graphene with low doping level, polycrystalline nature, high defect density and low carrier mobility. Here, we demonstrate a self-assembly approach that allows the synthesis of single-layer, single crystal and highly nitrogen-doped graphene domain arrays by self-organization of pyridine molecules on Cu surface at temperature as low as 300 °C. These N-doped graphene domains have a dominated geometric structure of tetragonal-shape, reflecting the single crystal nature confirmed by electron-diffraction measurements. The electrical measurements of these graphene domains showed their high carrier mobility, high doping level, and reliable N-doped behavior in both air and vacuum.     

Electrochemically exfoliating graphite into N-doped graphene and its use as a high efficient electrocatalyst for oxygen reduction reaction

N-doped graphene has been extensively explored because of their intriguing properties. However, most of the conventional heat-processed N-doped graphene (HNG) suffer from the poor hydrophilic property and low electric conductivity when using electrode materials. Herein, we present a facile solution-processed strategy to fabricate N-doped graphene through electrochemical exfoliation of graphite in inorganic electrolyte solution. The resulting electrochemically exfoliated N-doped graphene (ENG) has high level of nitrogen (7.9 at.%) and oxygen (16.5 at.%), moreover, excellent electric conductivity (19 s cm^?1). As a binder-free electrode material for oxygen reduction reaction (ORR), ENG exhibits much better electroactivity than HNG and electrochemically exfoliated graphene (EG), moreover, much better methanol tolerance and long-term durability than that commercial Pt/C catalyst. The results provide new sights into scalable production of noble metal-free catalyst towards ORR.     

High performance supercapacitors based on highly conductive nitrogen-doped graphene sheets

Thermal nitridation of reduced graphene oxide sheets yields highly conductive (～1000-3000 S m(-1)) N-doped graphene sheets, as a result of the restoration of the graphene network by the formation of C-N bonded groups and N-doping. Even without carbon additives, supercapacitors made of the N-doped graphene electrodes can deliver remarkable energy and power when operated at higher voltages, in the range of 0-4 V.     

氮掺杂六角石墨烯纳米结构的近红外等离激元研究

基于含时密度泛函理论研究了氮掺杂六角石墨烯纳米结构的近红外等离激元.沿一定的激发方向,边长为1 nm的氮掺杂六角石墨烯纳米结构在整个近红外光谱区都有强度较大的等离激元共振.参与这种近红外等离激元模式共振的电子在六角纳米结构的中心和边缘区域之间来回振荡.近红外等离激元共振模式的形成依赖于氮掺杂的位置和纳米结构的尺度大小.只有当氮掺杂在靠近边界区域时体系才会在近红外光谱区形成等离激元共振模式.对于边长小于1 nm的六角石墨烯纳米结构,氮掺杂后体系不能在近红外光谱区形成等离激元共振模式.     

The electric field as a novel switch for uptake/release of hydrogen for storage in nitrogen doped graphene

Nitrogen-doped graphene was recently synthesized and was reported to be a catalyst for hydrogen dissociative adsorption under a perpendicular applied electric field (F). In this work, the diffusion of H atoms on N-doped graphene, in the presence and absence of an applied perpendicular electric field, is studied using density functional theory. We demonstrate that the applied field can significantly facilitate the binding of hydrogen molecules on N-doped graphene through dissociative adsorption and diffusion on the surface. By removing the applied field the absorbed H atoms can be released efficiently. Our theoretical calculation indicates that N-doped graphene is a promising hydrogen storage material with reversible hydrogen adsorption/desorption where the applied electric field can act as a switch for the uptake/release processes.     

氮掺杂石墨烯的生长机理及其在乙苯选择性氧化中的应用

以热解氧化石墨烯材料为碳基底,分别使用有机氮源和无机氮源对其进行氮掺杂处理,制备了一系列氮掺杂石墨烯材料.采用透射电子显微镜、扫描电子显微镜、拉曼光谱和X射线光电子能谱等表征方法考察了氮掺杂石墨烯的生长机理.结果表明,随着制备过程中退火温度的改变,氮掺杂石墨烯中不同氮物种的含量有显著差别.这种差异是由不同氮物种化学环境的差异所导致的.所制备的含氮石墨烯材料对乙苯选择性氧化制苯乙酮反应均表现出优良的催化活性.其中,石墨氮的含量对于提高苯乙酮收率起到至关重要的作用.此外,通过氧化剂控制活化的方法可以消除过多的结构缺陷和过量氮掺杂对催化反应的不利影响,有效提升氮掺杂石墨烯的催化活性.     

Theoretical investigation of formation mechanism of bipyridyl molecule on Ni(111) surface: implication for synthesis of N-doped graphene from pyridine

The formation mechanism of bipyridyl molecule catalyzed by nickel catalyst with pyridine precursor has been studied using density functional theory calculations. The formation of bipyridyl on Ni(111) surface from two pyridine molecules is considered as the initial process of N-doped graphene growth, and the minimum energy pathway for the formation has been investigated in detail. The whole formation processes mainly includes three steps, i.e., the dehydrogenation of the first pyridine, adsorption and dehydrogenation of the second pyridine, and formation of the bipyridyl molecule. It is found that the C-H bond of pyridine could be selectively dissociated while the C-C and C-N bond connections are retained during the catalytic processes. The N-doped graphene formed by pyridine only contains pyridine-like nitrogen atoms, suggesting a possible way to produce N-doped graphene with pure pyridine-like nitrogen atoms. The comparison of formation mechanisms between bipyridyl and biphenyl molecules was carried out, and the results imply a lower temperature process for synthesis of N-doped graphene from pyridine than that for graphene from benzene.     

氮掺杂碳层包覆金属钴颗粒与氮掺杂石墨烯纳米复合材料作为高容量锂离子电池负极材料

合成了一种石墨烯基纳米复合材料即：由氮掺杂碳层包覆的金属钴纳米颗粒,充分分散于氮掺杂的石墨烯表面。这种纳米复合材料进一步提高了石墨烯的导电性,增加了石墨烯的储锂容量。该材料被用作锂离子电池负极材料,在性能测试中展现了良好的循环性能,在以100 mA·g^-1的电流密度循环200圈后,放电容量高达950.1 mAh·g^-1,库伦效率约为98%。     

氮掺杂碳层包覆金属钴颗粒与氮掺杂石墨烯纳米复合材料作为高容量锂离子电池负极材料

合成了一种石墨烯基纳米复合材料即：由氮掺杂碳层包覆的金属钴纳米颗粒,充分分散于氮掺杂的石墨烯表面。这种纳米复合材料进一步提高了石墨烯的导电性,增加了石墨烯的储锂容量。该材料被用作锂离子电池负极材料,在性能测试中展现了良好的循环性能,在以100 mA·g^-1的电流密度循环200圈后,放电容量高达950.1 mAh·g^-1,库伦效率约为98%。     

Facilely synthesized N-doped graphene sheets and its ferromagnetic origin

Inducing ferromagnetism into graphene is vital today because it has a wide range of applications such as spintronics devices and magnetic memory devices. In this paper, we will report a new method to synthesize ferromagnetic graphene by nitrogen doping. X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy were utilized to testify the N-doped material and further discuss the N-doped process. The superconducting quantum interference device (SQUID) was put in and used to analyze the magnetic properties of the N-doped graphene sheets. It shows that the material exhibits ferromagnetism at both 3 K and 300 K and the ferromagnetic saturation moment is 0.412 emu/g and 0.051 emu/g, respectively. The mechanism of the origin of the ferromagnetism in N-doped graphene sheets will also be discussed in this paper. It shows that, when the amount graphitic N reached the threshold, the origin of the ferromagnetism will change from defects induced by nitrogen atoms to the transition in energy band caused by graphitic N.     

Nitrogen-doped graphene as an excellent candidate for selective gas sensing

The toxic gases,such as CO and NO,are highly dangerous to human health and even cause the death of person and animals in a tiny amount.Therefore,it is very necessary to develop the toxic gas sensors that can instantly monitor these gases.In this work,we have used the first-principles calculations to investigate adsorption of gases on defective graphene nanosheets to seek a suitable material for CO sensing.Result indicates that the vancancy graphene can not selectivly sense CO from air,because O2 in air would disturb the sensing signals of graphene for CO,while the nitrogen-doped graphene is an excellent candidate for selectivly sensing CO from air,because only CO can be chemisorbed on the pyridinic-like N-doped graphene accompanying with a large charge transfer,which can serve as a useful electronic signal for CO sensing.Even in the environment with NO,the N-doped graphene can also detect CO selectively.Therefore,the N-doped graphene is an excellent material for selectively sensing CO,which provides useful information for the design and fabrication of the CO sensors.     

Graphene aerogel supported Pt-Ni alloy as efficient electrocatalysts for alcohol fuel oxidation

Alcohol fuels oxidation plays a significant role in carbon sustainable cycling and high-performance catalyst with a strong anti-poisoning effect is desired. Herein, Pt-Ni alloy supported on the N-doped graphene aerogel synthesized by simple freeze-drying and annealing was demonstrated to have such catalytic ability for alcohol fuel oxidation. Pt-Ni alloy particles were found uniformly dispersed over the surface of 3D N-doped graphene aerogel. High anti-poisoning ability for CO-like intermediates...     

Effect of the Method of Production of Reduced Graphene Oxide on its Catalytic Activity in the Hydrogenation of Ethylene

Theoretical and Experimental Chemistry - The catalytic properties of N-doped hydrazine-reduced graphene oxide (N-RGO) and thermally reduced graphene oxide (TRGO) in the hydrogenation of ethylene by...     

Enhanced electrocatalytic performance of Fe-TiO2/N-doped graphene cathodes for rechargeable Li-O2 batteries

Journal of Solid State Electrochemistry - The Fe3+-doped TiO2 on nitrogen-doped graphene (Fe-TiO2/N-doped graphene) electrocatalyst is synthesized and employed as cathode material for Li-O2...     

Heterogeneous liquid phase oxidation of ethylbenzene to acetophenone with graphene carbon-based catalyst

The series of graphene materials and N-doped graphene materials were successfully synthesized and improved by high-temperature treatment with trace iron oxide. XRD, Raman, FT-IR, TEM and XPS were employed for these catalysts. The catalytic performance of these catalysts was investigated in the selective oxidation of ethylbenzene with tert-butyl hydroperoxide as oxidant. The impacts of temperature, mass of catalysts, reaction time and oxidants on the selective oxidation of ethylbenzene were also investigated. The N-doped graphene materials exhibit greatly remarkable catalytic performance than others. The conversion of ethylbenzene is more than 90% and the selectivity of acetophenone is more than 95% at 353 K. Graphene can be used as catalyst owing to its unique structures and chemical properties. The characterization tests show that the doping of N atoms can create more defects and more active sites in the N-doped graphene materials which could greatly improve the catalytic performance. Furthermore, such cost-effective graphene-based catalysts possess good stability and could be reused at least five times without remarkable loss of the catalytic activity.     

3D nitrogen-doped graphene aerogel-supported Fe3O4 nanoparticles as efficient electrocatalysts for the oxygen reduction reaction

Three-dimensional (3D) N-doped graphene aerogel (N-GA)-supported Fe(3)O(4) nanoparticles (Fe(3)O(4)/N-GAs) as efficient cathode catalysts for the oxygen reduction reaction (ORR) are reported. The graphene hybrids exhibit an interconnected macroporous framework of graphene sheets with uniform dispersion of Fe(3)O(4) nanoparticles (NPs). In studying the effects of the carbon support on the Fe(3)O(4) NPs for the ORR, we found that Fe(3)O(4)/N-GAs show a more positive onset potential, higher cathodic density, lower H(2)O(2) yield, and higher electron transfer number for the ORR in alkaline media than Fe(3)O(4) NPs supported on N-doped carbon black or N-doped graphene sheets, highlighting the importance of the 3D macropores and high specific surface area of the GA support for improving the ORR performance. Furthermore, Fe(3)O(4)/N-GAs show better durability than the commercial Pt/C catalyst.     

Lithiophilic Sites in Doped Graphene Guide Uniform Lithium Nucleation for Dendrite-Free Lithium Metal Anodes

Lithium (Li) metal is the most promising electrode for next-generation rechargeable batteries. However, the challenges induced by Li dendrites on a working Li metal anode hinder the practical applications of Li metal batteries. Herein, nitrogen (N) doped graphene was adopted as the Li plating matrix to regulate Li metal nucleation and suppress dendrite growth. The N-containing functional groups, such as pyridinic and pyrrolic nitrogen in the N-doped graphene, are lithiophilic, which guide the metallic Li nucleation causing the metal to distribute uniformly on the anode surface. As a result, the N-doped graphene modified Li metal anode exhibits a dendrite-free morphology during repeated Li plating and demonstrates a high Coulombic efficiency of 98 % for near 200 cycles.     

不同氮掺杂石墨烯氧还原反应活性的密度泛函理论研究

N掺杂石墨烯作为一种具有较高活性和稳定性的氧还原反应(ORR)催化剂,受到人们的广泛关注。然而不同的N掺杂类型对氧还原活性的影响一直存在争议。本文通过密度泛函理论分别对石墨型和吡啶型两种N掺杂石墨烯的ORR活性进行比较研究。能带结构分析表明,石墨氮掺杂石墨烯(GNG)的导电性随掺N量的增加而降低;吡啶氮掺杂石墨烯(PNG)的导电性则随掺N量的增加先提高后降低。当N掺杂浓度达到4.2%(原子分数)时,PNG具有最优导电性。且当N掺杂浓度大于1.4%时,PNG的导电率总是高于GNG。氧还原自由能阶梯曲线发现O₂的质子化是整个氧还原过程的潜在控制步骤。在同等氮掺杂浓度下,O₂的质子化自由能能变在GNG上低于在PNG上,意味着若在同等电子传输能力的情况下,GNG具有比PNG更优异的催化活性。进一步分析发现：当N掺杂浓度在低于2.8%时,GNG和PNG导电性差异小,其催化ORR活性由O₂质子化反应难易程度决定,GNG的催化活性优于PNG;当N掺杂浓度高于2.8%时,氮掺杂石墨烯的电子传输性能(导电性)成为决定催化剂ORR活性的主要因素,因此PNG表现出较GNG更高的活性。