氮掺杂有序介孔碳-Ni纳米复合材料的制备及电化学性能

以F₁₂₇为模板剂,NiCl₂为镍源,尿素为氮源,间苯二酚甲醛原位聚合树脂为碳源,分别采用均相法和两相法制备Ni-N-OMC-1,Ni-N-OMC-2纳米复合材料.X射线衍射(XRD)、激光拉曼以及透射电子显微镜(TEM)等测试结果表明,复合材料具有有序介孔结构,Ni以金属微粒形式嵌于碳骨架中,提高了有序介孔碳的石墨化程度.X射线光电子能谱测试(XPS)表明尿素热解后以4种形式存在:sp³杂化与C结合的N原子,吡啶N原子,sp²杂化与C结合的N原子以及quaternary-N原子.Ni-N的共改性改变了碳载体的理化性质,有利于Pt纳米粒子的负载与分散.均相法制备的Ni-N-OMC-1复合材料微波负载Pt后,氧还原极限电流密度为5.32mA·cm^-2,氢氧化电化学活性面积高达138.53m²·g^-1,电化学催化活性优于商业20%Pt/C材料(4.49mA·cm^-2,96.98m²·g^-1).     

氮掺杂有序介孔碳-Ni纳米复合材料的制备及电化学性能

以F127为模板剂,Ni Cl2为镍源,尿素为氮源,间苯二酚甲醛原位聚合树脂为碳源,分别采用均相法和两相法制备Ni-NOMC-1,Ni-N-OMC-2纳米复合材料。X射线衍射(XRD)、激光拉曼以及透射电子显微镜(TEM)等测试结果表明,复合材料具有有序介孔结构,Ni以金属微粒形式嵌于碳骨架中,提高了有序介孔碳的石墨化程度。X射线光电子能谱测试(XPS)表明尿素热解后以4种形式存在:sp3杂化与C结合的N原子,吡啶N原子,sp2杂化与C结合的N原子以及quaternary-N原子。Ni-N的共改性改变了碳载体的理化性质,有利于Pt纳米粒子的负载与分散。均相法制备的Ni-N-OMC-1复合材料微波负载Pt后,氧还原极限电流密度为5.32 m A·cm-2,氢氧化电化学活性面积高达138.53 m2·g-1,电化学催化活性优于商业20%Pt/C材料(4.49 m A·cm-2,96.98 m2·g-1)。     

Construction of a sp3/sp2 Carbon Interface in 3D N‐Doped Nanocarbons for the Oxygen Reduction Reaction

The development of highly efficient metal‐free carbon electrocatalysts for the oxygen reduction reaction (ORR) is one very promising strategy for the exploitation and commercialization of renewable and clean energy, but this still remains a significant challenge. Herein, we demonstrate a facile approach to prepare three‐dimensional (3D) N‐doped carbon with a sp³/sp² carbon interface derived from ionic liquids via a simple pyrolysis process. The tunable hybrid sp³ and sp² carbon composition and pore structures stem from the transformation of ionic liquids to polymerized organics and introduction of a Co metal salt. Through tuning both composition and pores, the 3D N‐doped nanocarbon with a high sp³/sp² carbon ratio on the surface exhibits a superior electrocatalytic performance for the ORR compared to that of the commercial Pt/C in Zn–air batteries. Density functional theory calculations suggest that the improved ORR performance can be ascribed to the existence of N dopants at the sp³/sp² carbon interface, which can lower the theoretical overpotential of the ORR.     

Separation of Spectroscopically Uniform Nanographenes

Excitation‐dependent photoluminescence (PL) is a well‐known property of graphene quantum dots (GQDs). For the development of carbon‐based photofunctional materials, GQDs possessing uniform PL properties are in high demand. A protocol has been established to separate spectroscopically uniform lipophilic GQD‐ 1 a from a mixture of GQD‐ 1 mainly composed of GQD‐ 1 a and GQD‐ 1 b . The mixture of GQD‐ 1 was synthesized through the reaction of p‐methoxybenzylamine with GQD‐ 2 prepared from graphite by common oxidative exfoliation. Size‐exclusion chromatography gave rise to GQD‐ 1 a and GQD‐ 1 b , with diameters of 19.8 and 4.9 nm, respectively. Large GQD‐ 1 a showed that the PL was fairly independent of the excitation wavelengths, whereas the PL of small GQD‐ 1 b was dependent on excitation. The excitation‐dependent nature is most likely to be associated with the structures of sp² domains on the graphene surfaces. The large sp²‐conjugated surface of GQD‐ 1 a is likely to possess well‐developed and large sp² domains, the band gaps of which do not significantly vary. The small sp²‐conjugated surface of GQD‐ 1 b produces small sp²‐conjugated domains that generate band gaps differing with domain sizes.     

Identification of Semiconductive Patches in Thermally Processed Monolayer Oxo‐Functionalized Graphene

The thermal decomposition of graphene oxide (GO) is a complex process at the atomic level and not fully understood. Here, a subclass of GO, oxo‐functionalized graphene (oxo‐G), was used to study its thermal disproportionation. We present the impact of annealing on the electronic properties of a monolayer oxo‐G flake and correlated the chemical composition and topography corrugation by two‐probe transport measurements, XPS, TEM, FTIR and STM. Surprisingly, we found that oxo‐G, processed at 300 °C, displays C?C sp³‐patches and possibly C?O?C bonds, next to graphene domains and holes. It is striking that those C?O?C/C?C sp³‐separated sp²‐patches a few nanometers in diameter possess semiconducting properties with a band gap of about 0.4 eV. We propose that sp³‐patches confine conjugated sp²‐C atoms, which leads to the local semiconductor properties. Accordingly, graphene with sp³‐C in double layer areas is a potential class of semiconductors and a potential target for future chemical modifications.     

A whisker-like carbon composite for the immobilization of laccase and its bioelectrochemistry

A novel mesoporous carbon/whisker-like carbon (MCWC) composite was used for the immobilization of laccase (Lac) and its bioelectrochemical behaviors were studied. It was confirmed by XPS that Lac was strongly adsorbed on the surface of the MCWC composite. The cyclic voltammetric results showed that the immobilized Lac underwent a direct quasi-reversible electrochemical reaction. The value of the electron transfer rate constant k _s was estimated to be 0.770 s^?1, indicating a reasonably fast electron transfer between the immobilized Lac and the underlying electrode. The surface concentration (Γ) of Lac was estimated to be 2.730 × 10^?12 mol/cm². Further experimental results showed that the immobilized Lac displayed an appreciable electrocatalytic activity to the electrochemical reduction of O₂. These properties could be attributed to the particular structure of loosely packed nanometer-scale carbon whiskers and the existence of a large amount of oxygen-containing groups. The immobilization method and the novel carrier (MCWC) may find new applications in fabricating the biocatalysts for biofuel cells.     

Bridging the Surface Charge and Catalytic Activity of a Defective Carbon Electrocatalyst

Electrocatalysis is dominated by reaction at the solid–liquid–gas interface; surface properties of electrocatalysts determine the electrochemical behavior. The surface charge of active sites on catalysts modulate adsorption and desorption of intermediates. However, there is no direct evidence to bridge surface charge and catalytic activity of active sites. Defects (active sites) were created on a HOPG (highly oriented pyrolytic graphite) surface that broke the intrinsic sp²‐hybridization of graphite by plasma, inducing localization of surface charge onto defective active sites, as shown by scanning ion conductance microscopy (SICM) and Kelvin probe force microscopy (KPFM). An electrochemical test revealed enhanced intrinsic activity by the localized surface charge. DFT calculations confirmed the relationship between surface charge and catalytic activity. This work correlates surface charge and catalytic activity, providing insights into electrocatalytic behavior and guiding the design of advanced electrocatalysts.     

Caffeic acid modified glassy carbon electrode for electrocatalytic oxidation of reduced nicotinamide adenine dinucleotide (NADH)

A new modified electrode was prepared by electrodeposition of caffeic acid (CFA) at the surface of an activated glassy carbon electrode. Cyclic voltammetry was used to investigate the redox properties of this electrode at various solution pH values and at various scan rates. The pH dependence of the electrode response was found to be 58.5 mV/pH, which is very close to the expected Nernstian value. The electrode was also employed to study electrocatalytic oxidation of reduced nicotinamide adenine dinucleotide (NADH), using cyclic voltammetry, chronoamperometry and rotating disk voltammetry as diagnostic techniques. It was found that the modified electrode exhibits potent and persistent electrocatalytic properties toward NADH oxidation in phosphate buffer solution (pH 7.0) with a diminution of the overpotential of about 450 mV compared to the process at an unmodified electrode. The electrocatalytic current increases linearly with NADH concentration in the range tested from 0.05 to 1.0 mM. The apparent charge transfer rate constant and transfer coefficient for electron transfer between the electrode surface and immobilized CFA were calculated as 11.2 s⁻¹ and 0.43, respectively. The heterogeneous rate constant for oxidation of NADH at the CFA-modified electrode surface was also determined and found to be about 3 × 10³ M⁻¹ s⁻¹. Finally, the diffusion coefficient of NADH was calculated as 3.24 × 10⁻⁶ cm² s⁻¹ for the experimental conditions, using chronoamperometric results. Received: 6 January 1999 / Accepted: 11 May 1999     

Electrocatalysis of Water Oxidation by H2O‐Capped Iridium‐Oxide Nanoparticles Electrodeposited on Spectroscopic Graphite

Electrocatalysis of water oxidation by 1.54 nm IrO_x nanoparticles (NPs) immobilized on spectroscopic graphite electrodes was demonstrated to proceed with a higher efficiency than on all other, hitherto reported, electrode supports. IrO_x NPs were electrodeposited on the graphite surface, and their electrocatalytic activity for water oxidation was correlated with the surface concentrations of different redox states of IrO_x as a function of the deposition time and potential. Under optimal conditions, the overpotential of the reaction was reduced to 0.21 V and the electrocatalytic current density was 43 mA cm^?2 at 1 V versus Ag/AgCl (3 M KCl) and pH 7. These results beneficially compete with previously reported electrocatalytic oxidations of water by IrO_x NPs electrodeposited onto glassy carbon and indium tin oxide electrodes and provide the basis for the further development of efficient IrO_x NP‐based electrocatalysts immobilized on high‐surface‐area carbon electrode materials.     

Electrochemical determination of nitrite via covalent immobilization of a single-walled carbon nanotubes and single stranded deoxyribonucleic acid nanocomposite on a glassy carbon electrode

A novel method has been developed for determination of nitrite by modifying the surface of a glassy carbon electrode (GCE) using single-walled carbon nanotubes with covalently immobilized single-strand deoxyribonucleic acid. The modified electrodes were characterized by field emission scanning electron microscopy, X-ray photoelectron spectroscopy, and electrochemical techniques. The results demonstrate that the nanotube-DNA nanocomposite has been successfully immobilized on the surface of the GCE. The new electrode, under optimum conditions at room temperature, exhibits excellent electrocatalytic activity towards the oxidation of nitrite, with a significantly reduction of the overpotential. The linear range for the detection of nitrite is from 0.6 to 540 μM, with a sensitivity of 0.216 μA?μM^?1, and a detection limit as low as 0.15 μM. The electrode showed good reproducibility and high stability and was successfully used to analyze nitrite in water and sausage samples.     

Influence of the methylene group between azadithiolate nitrogen atom and phenyl moiety on the protophilic properties of [FeFe]-hydrogenase model complexes

An [FeFe]-hydrogenase mimic 4 with functional benzyl moiety covalently linked to the azadithiolate ligand was synthesized. The structure, protonation, and electrochemical properties of 4 and a phenyl substituted analogue (coded as 3) were simultaneously studied to explore the influence of the methylene group between the bridgehead nitrogen atom and functional phenyl moiety on the protophilic properties of the model complexes. X-ray single crystal diffraction analysis revealed that the nitrogen atoms of 3 and 4 possessed sp ² and sp ³-hybridization, respectively. Although the light-driven electron transfer was prevented in the molecule of 4, the sp ³-hybridized nitrogen atom of 4 could be protonated in the presence of the proton acid to give the [4(NH)]⁺ cation. The generated positive charge could be reduced at ca. ?1.2 V versus Fc/Fc⁺ with a distinctly electrocatalytic proton reduction activity, whereas the proton reduction catalysed by 3 occurred at ca. ?1.45 V. The catalytic proton reductions of 3 and 4 followed ECCE and CECE mechanisms, respectively. It was noteworthy that the potential of 4 was remarkably anodic shifted and closer to that of the proton reduction catalysed by natural enzymes.     

Electrocatalytical properties presented by Cu/Ni alloy modified electrodes toward the oxidation of glucose

This paper concerns the deposition of metal alloys formed by nickel and copper on electrode surface aiming at the development of electrocatalytic systems. Such alloys were formed on platinum electrodes by direct reduction of Ni²⁺ and Cu²⁺ sulfate salts in different proportions in a simple and straightforward electrochemical treatment. After the deposition, the conversion to the electrocatalytic oxide form was done in alkaline solutions by cyclic voltammograms. The experimental parameters, such as deposition time and the proportion of copper and nickel in the synthetic solution, were investigated toward the catalytic oxidation of glucose. The materials were characterized by electrochemical experiments, infrared and Raman spectroscopies, and X-ray diffraction, showing that the material is not a simple mixture of nickel and copper oxides. The modified electrodes showed remarkable electrocatalytic properties, indicating an interesting application in the sensor and fuel cell development.     

Surface oxidation process of a diamond‐like carbon film analyzed by difference X‐ray photoelectron spectroscopy

Difference X‐ray photoelectron spectroscopy (D‐XPS) revealed the surface oxidation process of a diamond‐like carbon (DLC) film. Evaluation of surface functional groups on DLC solely by the C 1s spectrum is difficult because the spectrum is broad and has a secondary asymmetric lineshape. D‐XPS clarified the subtle but critical changes at the DLC surface caused by wet oxidation. The hydroxyl (C―OH) group was dominant at the oxidized surface. Further oxidized carbonyl (C?O) and carboxyl (including carboxylate) (COO) groups were also obtained; however, the oxidation of C?O to COO was suppressed to some extent because the reaction required C―C bond cleavage. Wet oxidation cleaved the aliphatic hydrogenated and non‐hydrogenated sp² carbon bonds (C―H sp² and C―C sp²) to create a pair of C―OH and hydrogenated sp³ carbon (C―H sp³) bonds. The reaction yield for C―H sp² was superior at the surface, suggesting that the DLC film was hydrogen rich at the surface. Oxidation of aromatic sp² rings or polycyclic aromatic hydrocarbons such as nanographite to phenols did not occur because of their resonance stabilization with electron delocalization. Non‐hydrogenated sp³ carbon (C―C sp³) bonds were not affected by oxidation, suggesting that these bonds are chemically inert. Copyright © 2014 John Wiley & Sons, Ltd.     

Surface and bulk properties of severely fluorinated carbon fibres

The development of ultra-inert composites using fluorinated carbon fibres as the reinforcement requires fluorinated carbon fibres with a durable surface composition. Here we report the effect of direct fluorination using an F₂/N₂ mixture at 653 K on the surface and bulk properties of two types of high strength carbon fibres. These were treated up to a surface fluorine content of ∼64 at.% and a bulk fluorine content of ∼15 mass%. A colour change was observed after fluorination caused by the changes in the graphitic band structure of the carbon fibres by the introduction of carbon sp³ hybridisation. The tensile strength and Young's modulus decrease after fluorination by up to 33 and 22%, respectively. XRD shows marginal changes in the interlayer distance but the crystallite size increases. Changes in the electrical conductivity of the fluorinated carbon fibres indicate that the modification is confined to the near surface volume. Predominantly covalent C-F bonds are formed as shown by X-ray photoelectron spectroscopy (XPS) and measured zeta (ζ)-potentials. Hence the fluorinated fibres are hydrophobic and have low surface tensions. This and the large increase in fibre surface area, as determined by nitrogen adsorption, is expected to facilitate interfacial interaction between fluorinated carbon fibres and fluoropolymers.     

Solid-state and surface chemistry of Sn-doped In2O3 ceramics

Tin-doped indium oxide (ITO) ceramics prepared by a high-temperature solid-state synthetic procedure have been studied over the composition range 1–6 at.% Sn by X-ray and ultraviolet photoelectron spectroscopy (XPS and UPS) and high-resolution electron energy loss spectroscopy (HREELS). Surface tin enrichment is evident from XPS with a heat of segregation of around −40 kJ mole⁻¹. However, the surface free-carrier concentration probed via the conduction-to-valence band intensity ratio in UPS or the surface plasmon frequency in HREELS is lower than the nominal tin concentration. It is concluded that electrons associated with segregated Sn ions in the topmost surface plane occupy a lone-pair-likesp hybrid surface state, while the region immediately below the surface is depleted in free carriers as a result of donor trapping effects and evaporation of tin during preparation.     

Niobium oxide dispersed on a carbon-ceramic matrix, SiO2/C/Nb2O5, used as an electrochemical ascorbic acid sensor

A film of niobium oxide was immobilized on a SiO₂/C carbon-ceramic matrix (specific surface area 270 m² g⁻¹) and characterized by N₂ adsorption-desorption isotherms, scanning electron microscopy, X-ray photoelectron spectroscopy and atomic force microscopy. This new carbon-ceramic material, SiO₂/C/Nb₂O₅, was used for construction of electrodes, and it shows ability to improve the electron-transfer between the electrode surface and ascorbic acid. The electrocatalytic oxidation of ascorbic acid was made by differential pulse and cyclic voltammetry techniques, making it potentially useful for developing a new ascorbic acid sensor.     

Electron transfer kinetics on composite diamond (sp3)–graphite (sp2) electrodes

The concept of non-diamond sp² impurity states as charge transfer mediators on boron-doped diamond (BDD) surface was suggested as an explanation for the electrochemical behavior of synthetic diamond based electrodes. In order to verify this concept, graphite particles (sp²) were deposited on diamond electrodes (sp³) by mechanical abrasion. The behavior of the so prepared diamond–graphite composite electrodes were compared with those of as-grown (BDD_ag) and those after mild anodic polarization (BDD_mild).Outer-sphere electron transfer processes such as ferri/ferrocyanide (Fe(CN)₆III/II) and inner-sphere charge transfer reactions such as 1,4-benzoquinone/hydroquinone (Q/H₂Q) were chosen in order to investigate the electrochemical properties of these composite electrodes. Both redox systems became more reversible as the graphite (sp²) loading increased. A strong analogy existed between as-grown diamond electrodes and diamond–graphite composite electrodes.Finally a model is proposed which describes the BDD electrode surface as a diamond matrix in which non-diamond (sp²) impurity states are dispersed. These non-diamond sp² states on BDD surface acts as charge mediators for both inner-sphere and outer-sphere reactions.     

木质纤维类生活垃圾热解过程矿物质和碳结构的演化规律

使用水平管式炉,在不同热解温度(500~1 000 ℃)条件下对废纸屑和樟树叶两种木质纤维类生活垃圾进行了热解实验,分别采用X射线衍射(XRD)和拉曼光谱研究了样品所含矿物质和碳结构随热解温度的变化。结果表明,废纸屑和樟树叶含有的主要矿物分别为方解石和草酸钙,在500 ℃之前草酸钙全部转化为方解石,焦样中的方解石在800 ℃以后逐渐分解并形成生石灰。拉曼光谱对生活垃圾焦的碳结构变化非常敏感,低温热解时生活垃圾的大分子结构发生缩合和解聚,产生了孤立sp²碳原子,导致峰参数D1峰半高宽和峰面积比值I_D1/I_G逐渐增大;高温热解时晶体sp²碳原子增多,导致D1峰半高宽和I_D1/I_G逐渐减小。焦样的碳结构有序度随热解温度升高先降低后提高。     

Bonding structure analysis of carbon nitride films by Raman spectroscopy and X-ray photoelectron spectroscopy (XPS)

Carbon nitride films were prepared by an opposed-target DC reactive sputtering system and the bonding behaviors were investigated according to the nitrogen content and annealing temperature. Annealing leads to a loss of nitrogen from the films and the CN is totally removed at 600 °C. Due to annealing at 600 °C, the C---C out-of-plane vibrational band intensity at 700 cm⁻¹ becomes very low and also the CN band at 2200 cm⁻¹ disappears completely. The sp² bonding in a CN compound is the most stable phase. Due to carbon's atypical nature in having its p orbital more compact and tightly bound compared to s states, the C=N sp² phase is more stable than the C---C sp³ phase. As the C=N sp² phase dominates the structure, the film is mainly graphite-like with some proportion of C---C, CN and N=N bonds.     

Electrochemical Detection of Tryptophan Metabolites via Kynurenine Pathway by Using Nanocarbon Films

We studied nanocarbon film electrodes with the aim of detecting tryptophan metabolites via the kynurenine pathway. The nanocarbon films were formed by using unbalanced magnetron sputtering, and they exhibited superior electrode properties including a wide potential window and a low background current as a result of the sp³-containing structure and ultraflat surface. These properties allowed us to detect certain tryptophan metabolites such as kynurenic acid (KYNA), which has a relatively high oxidation potential. We also investigated the effect of the sp²/sp³ ratio of the nanocarbon film as regards the electrode activity in relation to target molecules. We found that the sp²/sp³ ratio played important roles in both widening the potential window and obtaining superior electrode performance for the metabolites. The nanocarbon film with a high sp³ content was beneficial as regards the electrode performance with respect to the detection limit and sensitivity. Compared with conventional carbon-based electrodes, the nanocarbon film electrode with a high sp³ content exhibited higher electrode activity against KYNA while maintaining a low background current. Computational experiments revealed that the theoretical oxidation potential (E_ox) value for some targets coincided with that obtained in electrochemical experiments using our nanocarbon film electrode.