Sulphur-doped ordered mesoporous carbon with enhanced electrocatalytic activity for the oxygen reduction reaction

Metal-free,heteroatom functionalized carbon-based catalysts have made remarkable progress in recent years in a wide range of applications related to energy storage and energy generation.In this study,high surface area mesoporous ordered sulphur doped carbon materials are obtained via one-pot hydrothermal synthesis of carbon/SBA-15 composite after removal of in-situ synthesized hard template Si O₂.2-thiophenecarboxy acid as sulphur source gives rise to sulphur doping level of 5.5 wt%.Comparing with pristine carbon,the sulphur doped mesoporous ordered carbon demonstrates improved electro-catalytic activity in the oxygen reduction reaction in alkaline solution.     

含氮前驱体对氮杂有序介孔炭材料及其氧还原电催化性能的影响

燃料电池中贵金属铂的大量使用是阻碍其发展的关键因素,亟需探索高效廉价的替代型电催化剂.在目前的替代型非贵金属催化剂研究中,氮杂炭材料是一类氧还原反应催化活性最好、成本最低廉的催化剂,被认为是最有可能取代Pt催化剂而获得实际应用的催化剂.氮杂有序介孔炭材料因具有极高的比表面积和规整的孔道结构,可实现活性位点的密集组装与反应物料的快速传输,受到研究者的广泛关注.本文分别以苯胺、吡咯和邻菲罗啉为含氮前驱体,介孔分子筛SBA-15为硬模板,采用纳米浇铸法成功制备了具有高比表面积的氮杂有序介孔炭材料,系统研究了不同含氮前驱体对氮杂有序介孔炭材料的影响.采用氮气吸附-脱附等温线、透射电子显微镜(TEM)、X射线衍射(XRD)和X射线光电子能谱(XPS)等方法研究了氮杂有序介孔炭的组成与结构,采用循环伏安法(CV)以及线性扫描伏安法(LSV)等手段考察了其电化学行为与氧还原反应极化性能.氮气吸附-脱附等温线结果表明,采用三种不同含氮前驱体制备的氮杂炭材料都对应Ⅳ型吸脱附等温线以及H4型滞后环,表明所制备的氮杂炭材料具有介孔结构.由TEM可以清楚地观察到氮杂炭材料已经成功地反转了SBA-15模板的孔道结构.同时发现,含氮前驱体对氮杂炭材料的比表面积和孔结构产生较大影响:以吡咯和邻菲罗啉为前驱体制备的炭材料C-PY-900和C-Phen-900的比表面积较高,分别为765和746 m2/g,而以苯胺为前驱体制备的炭材料C-PA-900比表面积较小(569 m2/g);三种炭材料平均孔径大小顺序为C-Phen-900 (3.7 nm)＜ C-PY-900 (5.0 nm)＜ C-PA-900 (5.9 nm),这是由于不同含氮前驱体在高温焙烧过程中热分解行为不同所致.XRD结果发现,含氮前驱体对氮杂炭材料的晶型基本没有影响,均为无定形碳.XPS结果表明,采用苯胺、吡咯以及林菲啰啉为前驱体制备的氮杂炭材料中氮含量基本相同,分别为3.13 at％,3.32 at％和3.33 at％,说明在相同热解条件下材料中的氮含量基本不受前驱体的影响,但不同配位环境的氮含量以及氮活化碳原子的含量却有较大差异,其氮活化碳原子的相对含量分别为15.60％,19.87％和23.04％.电化学测试结果表明,三种氮杂介孔炭材料的氧还原反应电催化活性顺序为C-PA-900＜C-PY-900＜C-Phen-900,其H2O2产率低于30％,说明氧还原反应经历4电子转移路径.在碱性条件下,所制氮杂有序介孔炭材料C-PY-900和C-Phen-900表现出较商品Pt/C催化剂更加优异的氧还原反应电催化性能.综上可见,通过改变含氮前驱体的类型可以有效调变氮杂炭材料的比表面积、孔道结构以及N 1s与C 1s化学态,从而调控氧还原反应活性,本文不仅制备出高活性的非贵金属氧还原电催化剂,同时也为高活性炭基电催化剂的可控制备提供了思路.     

Fluorinated carbon with ordered mesoporous structure

Fluorination and structural change of highly ordered mesoporous carbons were studied. Mesoporous and fluorinated carbons with ordered cubic structure were synthesized and characterized with TEM, FTIR, adsorption, and EDX.     

Oxygen reduction on carbon nanomaterial-modified glassy carbon electrodes in alkaline solution

Electroreduction of oxygen in alkaline solution on glassy carbon (GC) electrodes modified with different carbon nanomaterials has been studied. Electrochemical experiments were carried out in 0.1 M KOH employing the rotating disk electrode and rotating ring-disk electrode methods. The GC disk electrodes were modified with carbon nanomaterials using polytetrafluoroethylene as a binder. Four different carbon nanomaterials were used: multiwalled carbon nanotubes, carbon black powder, and two carbide-derived carbons (CDC). For the first time, the electrocatalytic behavior of CDC materials toward oxygen reduction is explored. Electrochemical characterization of the materials showed that all the carbon nanomaterial-modified GC electrodes are highly active for the reduction of oxygen in alkaline solutions.     

Effect of surface hydrophobicity/hydrophilicity of mesoporous supports on the activity of immobilized lipase

Taking advantage of the virtue of hydrophilic surface, lipase was firstly immobilized on SBA-15 as a support. Then the surface of the SBA-15 with enzyme entrapped inside the channels was modified by grafting with organic moieties. It has been found that the silylation with n-decyltrimethoxysilane (DE) and 3-(trimethoxysilyl)propyl methacrylate (MA) following the lipase immobilization increases the surface hydrophobicity. But the surface modified by MA shows more hydrophilicity than that modified by DE. The activity assay indicates that the hydrolytic activity for the hydrolysis of insoluble or partly soluble substrates increases with enhanced surface hydrophobicity.     

硅胶表面替米考星分子印迹聚合物的制备

表面印迹接枝技术即在硅胶表面或有机聚合物载体表面[1]、毛细管表面[2]进行接枝聚合并引进分子印迹的技术[3-6]。替米考星(Tilm icosin)是一种由泰乐菌素半合成的大环内脂类畜禽专用抗生素。本文以替米考星为模板分子,以甲苯为溶剂,以甲基丙烯酸为功能单体,乙二醇二甲基丙烯酸     

Oxygen reduction on rotating porous cylinder of modified reticulated vitreous carbon

A rotating cylinder porous electrode (RCPE) of reticulated vitreous carbon (RVC) matrix was used for oxygen reduction reaction (ORR) in H₂SO₄ solutions. Cyclic voltammetry and hydrodynamic voltammetric techniques were used for electrochemical characterization of the ORR. Cyclic voltammograms in stationary solutions showed better performance of the anodically oxidized RVC (for periods of 1 and 5 min) for the ORR than the untreated RVC in which the first scan (ORR) after the surface treatment was of no utility, and the second scan was presented here. The hydrodynamic voltammograms obtained at the treated RCPE gave well-defined limiting current plateau with positively shifted onset potential as compared with the untreated (plain) RVC electrode. The analysis of the limiting current data on RCPE and the determination of a limiting current enhancement factor α enabled us to quantify the enhancement extent exerted by the anodic oxidation treatment. An enhancement factor of up to ∼3 was obtained at the RCPE electrode anodically oxidized for 5 min. It was found that the α slightly decreased with the rotation speed depending on the extent of anodic oxidation of RVC. This was attributed to the different mode of mass transfer (diffusion) to the interior of the micropores with different microstructure resulting from different extent of anodic oxidation. X-ray photoelectron spectroscopic and scanning electron microscopic measurements helped us to characterize the anodically oxidized RVC surface.     

Grafting of chain-end-functionalized perfluorocyclobutyl (PFCB) aryl ether ionomers onto mesoporous carbon supports

Water-soluble perfluorocyclobutyl (PFCB) aryl ether ionomers bearing sulfonic acid groups in the main chain and phosphonic acid end groups were prepared and used to modify the surfaces of mesoporous carbon materials containing dispersed zirconia nanoparticles. Ionomer surface grafting occurred via phosphonate bonding onto the zirconia particle surfaces.     

Temperature dependence of oxygen reduction activity at Nafion-coated bulk Pt and Pt/carbon black catalysts

Oxygen reduction reaction (ORR) activity and H(2)O(2) formation at Nafion-coated film electrodes of bulk-Pt and Pt nanoparticles dispersed on carbon black (Pt/CB) were investigated in 0.1 M HClO(4) solution at 30 to 110 degrees C by using a channel flow double electrode method. We have found that the apparent rate constants k(app) (per real Pt active surface area) for the ORR at bulk-Pt (with and without Nafion-coating) and Nafion-coated Pt/CB (19.3 and 46.7 wt % Pt, d(Pt) = 2.6 to 2.7 nm) thin-film electrodes were in beautiful agreement with each other in the operation conditions of polymer electrolyte fuel cells (PEFCs), i.e., 30-110 degrees C and ca. 0.7 to 0.8 V vs RHE. The H(2)O(2) yield was 0.6-1.0% at 0.7-0.8 V on all Nafion-coated Pt/CB and bulk-Pt and irrespective of Pt-loading level and temperature. Nafion coating was pointed out to be a major factor for the H(2)O(2) formation on Pt catalysts modifying the surface property, because H(2)O(2) production was not detected at the bulk-Pt electrode without Nafion coating.     

Effect of the nature of carbonaceous supports on the bioelectrocatalytic activity of peroxidase, immobilized on the supports, in the hydrogen peroxide reduction reaction

Electrochemical properties of such disperse carbonaceous materials as acetylene black AD-100, finely divided colloidal graphite (FCG), ultradisperse diamond (UDD), and carbon nanotubes (CNT) are examined. Effect of the nature of disperse carbonaceous supports on bioelectrocatalytic activity of adsorbed peroxidase (POD) in the hydrogen peroxide reduction reaction is investigated. It is shown that the hydrogen peroxide reduction on the biocatalysts studied proceeds in conditions of direct bioelectrocatalysis independently of the disperse-support type. It is also demonstrated that the biocatalysts’ activity depends on the structure and properties of the surface of the supports defining the magnitude of the POD adsorption in an orientation favorable for direct bioelectrocatalysis. Maximum activity is inherent in the catalysts manufactured on the basis of materials with moderate hydrophobic and hydrophilic properties. By the magnitude of the activity in the hydrogen peroxide reduction reaction, depending on the nature of the carbonaceous support, the fabricated catalysts (carbonaceous material with adsorbed POD) form the series AD-100, CNT > FCG > UDD.     

Electrochemical reduction of oxygen to hydrogen peroxide in a gas-diffusion electrode based on mesoporous carbon

Mesoporous carbon prepared by template synthesis using SBA-15 mesostructured silicate material was tested as an electrocatalyst for electrochemical synthesis of Н₂О₂ from О₂ in a two-layer gas-diffusion electrode. Preparative syntheses of Н₂О₂ in 0.06 to 2.0 M aqueous solutions of various electrolytes (pH 2–8) were performed at current densities in the interval 0.05–0.19 A cm^–2. Solutions with an Н₂О₂ concentration of 1–2.8 M were prepared with 46–70% current efficiency. Thus, the material tested shows promise as an electrocatalyst of two-electron reduction of oxygen to Н₂О₂.     

Size and structure dependence of carbon monoxide chemisorption on cobalt clusters

We have carried out a series of ab initio calculations to investigate changes in the structural and magnetic properties of pristine cobalt clusters upon CO chemisorption. Our results show that binding energies of CO to 13-55 atom (0.5-1.5 nm) cobalt nanoparticles and preferred chemisorption sites depend on the cluster structure (whether fcc or icosahedral), size, and surface coverage. In addition, we find a strong influence of CO on the magnetism of the cluster, leading to magnetic moments smaller than in the bulk, at variance with pristine clusters which have magnetic moments larger than the bulk. Our findings suggest important changes in catalytic properties of cobalt at the nanoscale. Our theory suggests that at the nanoscale cluster size and surface coverage might control catalysis.     

Oxygen reduction reaction activity of monodispersed Pt nanoparticles-loaded carbon black catalyst prepared with a Pt carbonyl cluster anion

Pt nanoparticles-loaded carbon black (CB) was prepared from Pt carbonyl cluster complexes, and had much narrower size distribution than commercial Pt nanoparticles/CB. In the former the monodispersed Pt nanoparticles were highly dispersed on CB without aggregation even at high Pt loading of 80 wt.%. Hydrodynamic voltammograms in O₂-saturated 0.05 M H₂SO₄ solution at 30 °C showed that the onset potential of oxygen reduction reaction (ORR) current for the monodispersed Pt nanoparticles/CB electrode was more positive than that for a polycrystalline Pt electrode and similar to that for the commercial Pt nanoparticles/CB electrode. Moreover, the mass activity for ORR for the monodispersed Pt nanoparticles/CB electrode was ca. 4.9 times higher than that for the commercial Pt nanoparticles/CB electrode, clearly indicating that the control of size distribution of Pt nanoparticles is meaningful for reducing the Pt consumption.     

Palladium catalysts on carbon supports. 3. Correlation of substructural and adsorptive properties of the carbon supports

Adsorption of H₂PdCl₄, on various carbon supports is studied. Correlations between the adsorptive properties (concentration of adsorptive centers, adsorptive equilibrium constants) and substructural characteristics of the supports are found.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1478–1483, July, 1990.     

Pressure dependence of local structure in liquid carbon disulfide

High pressure x-ray diffraction measurements on liquid carbon disulfide up to 1.2 GPa are performed by using an energy dispersion method. The results are compared with a molecular dynamics calculation with usual Lennard-Jones potential. They give very good agreement for all pressures measured. It becomes clear that the liquid structure changes like hard core liquid up to the pressure just below crystallizing point. The relation between structural change and optical response at high pressure is discussed.     

利用石墨烯-炭黑组成的二元碳载体增强甲酸在钯催化剂上电化学氧化的活性

本文采用"一锅法"将氧化石墨烯(GO)、炭黑(C)和钯离子用NaBH4共还原,制备了石墨烯-炭黑二元载体(Gr-C)负载的钯催化剂(20%Pd/Gr-C),用于催化甲酸的电氧化反应.电化学测试结果表明,前驱体GO和C的质量比为3:7的Pd/Gr0.3C0.7催化剂催化活性最好,它的峰电流密度(102.14 mA mgPd-1)约为Pd/C催化剂(34.40 mA mgPd-1)的3倍,为钯/石墨烯催化剂(Pd/Gr,38.50 mA mgPd-1)的2.6倍.甲酸在Pd/Gr0.3C0.7催化剂电极直接氧化时的峰电位比Pd/C催化剂的峰电位负移约120 mV,比Pd/Gr催化剂的峰电位负移约70 mV.采用透射电子显微镜(TEM)、扫描电子显微镜(SEM)、X射线衍射(XRD)、X射线光电子能谱(XPS)、拉曼光谱、电感耦合等离子发射光谱(ICP-AES)等手段对催化剂进行了表征.从SEM图像可以观察到,球形的炭黑团簇聚集在具有褶皱的石墨烯面上,形成了炭黑团簇/石墨烯三维立体结构,有效地抑制了相邻石墨烯层在范德华力作用下的吸引聚集和堆叠造成的石墨烯表面积减小,减小了单层石墨烯叠合成为多层石墨所造成的导电性损失,避免了相邻石墨烯片叠合形成封闭空间,有助于反应物和产物分子的运动.载体的三维结构使反应物分子更容易到达钯纳米粒子,有利于催化性能的提高.XPS结果也证实了二元Gr-C载体对Pd催化的促进作用.Pd/Gr0.3C0.7催化剂的Pd 3d5/2峰发生了右移,表明Pd 3d电子结合能正移,Pd 3d电子云密度降低.具有较低的3d电子云密度的Pd不易与甲酸氧化过程中吸附的中间体(COOH)ads结合,钯催化剂上(COOH)ads表面覆盖率降低,从而使甲酸更容易直接脱氢氧化生成CO2,有利于甲酸通过直接途径进行电化学氧化.与Pd/C,Pd/Gr相比,Pd/Gr0.3C0.7催化剂对甲酸电氧化有最好的催化活性.Pd/Gr0.3C0.7催化剂优异的催化活性可归因于其内在的三维纳米结构:炭黑团簇有效地抑制了石墨烯纳米片的聚集,保持了其大的比表面积和高导电性,促进了反应物和产物分子的运动.此外,Pd纳米粒子与二元载体之间的强相互作用降低了Pd的3d电子云密度,使甲酸氧化主要经直接途径进行.本文证实了钯金属和石墨烯-炭黑二元载体之间的强相互作用,提供了简单和高性价比的方法以提高钯基催化剂的活性,有利于工业化的应用.     

掺氮介孔炭作为双功能材料用于氧还原与超级电容器

以壳聚糖为含氮碳源,正硅酸乙酯为软模板,硝酸镍为催化剂,通过简单的低温水热法及后续炭化,成功合成出掺氮介孔炭材料（NMC-1）.NMC-1含有多孔结构以及氮氧等杂原子,能提高其电催化性能、双电层电容与赝电容.由于NMC-1在碱液中表现出显著的催化氧还原反应活性和具有较高的超级电容器比电容（在0.2A/g时为252F/g）及好的循环稳定性,因此,它有可能作为一种可再生、环保的双功能材料同时应用于燃料电池与超级电容器领域.     

Oxygen reduction catalysis at anthraquinone centres molecularly wired via carbon nanotubes

Multi-walled carbon nanotubes (MWCNTs) have been chemically derivatised via the reduction of anthraquinone-1-diazonium chloride with hypophosphorous acid to attach 1-anthraquinonyl groups to the MWCNTs, most likely at edge plane like defects. The covalently attached quinone moiety attached to the nanotubes (‘molecular wire’) acts as an effective mediator for the electrocatalytic reduction of oxygen.     

Synthesis of carbon nanotubes on water-soluble supports

Gas-phase pyrolytic synthesis of carbon to give multilayer carbon nanotubes on Ni catalysts supported by NaCl and K₂SO₄ mineral water-soluble substrates was studied. The morphology of the nanotubes synthesized was examined.