Modification of hydrophobic/hydrophilic properties of Vulcan XC72 carbon powder by grafting of trifluoromethylphenyl and phenylsulfonic acid groups

Carbon supports (glassy carbon and Vulcan XC72 powder) were modified by electrochemical and spontaneous grafting of phenylsulfonic acid (PSA) or trifluoromethylphenyl (TFMP) groups via diazonium ion reduction. The effectiveness of the grafting was confirmed electrochemically, by XPS measurements and elemental analyses. The hydrophobic or hydrophilic character of carbon surfaces was evidenced by measuring the contact angles of drops of different liquids (water, ethylene glycol and glycerol) in heptane. The surface energy was calculated and it was found, for example, that spontaneous grafting of a glassy carbon surface by PSA groups led to an increase by a factor 20 of the surface energy compared with an unmodified glassy carbon surface. The study of the grafting of such groups on XC72 carbon powder indicated that a very low grafting ratio (in wt%) led to a significant change in the macroscopic properties of the powder. Thermogravimetric analysis coupled with mass spectroscopy measurements (TGA-MS) showed that these grafted layers were thermally stable even in the presence of dispersed platinum nanoparticles. It was shown by cyclic voltammetry that the carbon substrate modification did not affect the electrochemical behavior of platinum catalyst, since the same active surface area was determined on Pt-XC72, Pt-PSA-XC72 and Pt-TFMP-XC72 catalysts.     

高灵敏度串联薄层溶出电解池研制及在尿铅测定中的应用

将薄层大面积玻碳电解池与小面积玻碳电解池以串联方式连接,在程控状态下使用.铅离子首先在大面积玻碳汞膜电极(LGCE)上预富集,溶出后在小面积玻碳汞膜电极(SGCE)上两次富集,因此提升了SGCE富集效率.测量25 0μg/L铅标准溶液,峰高的相对标准偏差RSD=1.2％.测量铅含量为25.6 μg/L的尿样,测得值27.4μg/L,相对标准偏差RSD=2 3％.富集时间400 s检出限为0.008 8 μg/L;定量检测限为0.029 2 μg/L.与常规的溶出分析比较,检出限降低11 90倍,显著提高检测的灵敏度.流动式电解池在溶出时的底液中不含样品基体.     

Functionalization of glassy carbon spheres by ball milling of aryl diazonium salts

Solvent free derivatization has been achieved by a simple ball mill grinding procedure to functionalize glassy carbon spheres with anthraquinonyl and nitrophenyl groups using aryl diazonium salts. Grinding facilitates the mechanical activation of the carbon substrate material with the creation of active centres and may induce the decomposition of the diazonium salt. The functionalized glassy carbon spheres were characterized electrochemically by studying their cyclic voltammetry. These modified carbon spheres were also characterized by X-ray powder diffraction and Transmission electron microscopy to ascertain particle size reduction or change in surface morphology of the carbon spheres. The covalent attachment of these functional moieties to the surface of glassy carbon spheres were studied by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy.     

Preparation of dendritic bismuth film electrodes and their application for detection of trace Pb(Ⅱ)and Cd(Ⅱ)

In this paper,dendritic Bi film electrodes with porous structure had successfully been prepared on glassy carbon electrode using a constant current electrolysis method based on hydrogen bubble dynamic templates.The electrode prepared using a large applied current density showed an increased internal electroactive area and a significantly improved electrochemical performance.The analytical utility of the prepared dendritic Bi film electrodes for the determination of Pb(Ⅱ)and Cd(Ⅱ)in the range of 5–50 μg·L~(-1)were presented in combination with square wave stripping voltammetry in model solution.Compared with non-porous Bi film electrode,the dendritic Bi film electrode exhibited higher sensitivity and lower detection limit.The prepared Bi film electrode with dendritic structure was also successfully applied to real water sample analysis.     

Electrooxidation of alcohols at a nickel oxide/multi-walled carbon nanotube-modified glassy carbon electrode

Electrocatalytic oxidation of methanol and some other primary alcohols on a glassy carbon electrode modified with multi-walled carbon nanotubes and nano-sized nickel oxide (GCE/MWNT/NiO) was investigated by cyclic voltammetry and chronoamperometry in alkaline medium. The results were compared with those obtained on a nickel oxide-modified glassy carbon electrode (GCE/NiO). Both the electrodes were conditioned by potential cycling in the range of 0.1–0.6 V versus Ag/AgCl in a 0.10 M NaOH solution. The effects of various parameters such as scan rate, alcohol concentration, thickness of NiO film, and real surface area of the modified electrodes were also investigated and compared. It was found that the GCE/MWNT/NiO-modified electrode possesses an improved electrochemical behavior over the GC/NiO-modified electrode for methanol oxidation.     

Anodic behaviour of carbon materials in NaCl saturated NaAlCl4 fused electrolyte at low temperatures: A cyclic voltammetric study

The anodic behaviour of compacted graphite, graphite powder, glassy carbon and reticulated vitreous carbon electrodes in basic sodium chloroaluminate melt in the temperature range 428–573 K was studied using cyclic voltammetry. Chlorine evolution (> + 2.1 V vs Al) alone was the predominant reaction on the compact glassy carbon and fresh RVC electrodes. On compacted graphite, chlorine-assisted chloroaluminate intercalation was found to be a competitive process to the chlorine evolution. At high sweep rates, intercalation/deintercalation near the graphite lattice edges occur faster than chlorine evolution. Subsequent intercalation, however, is a slow process. Chlorine evolution predominates at higher temperatures and at higher anodic potentials. On graphite powders, a more reversible free radical chlorine adsorption/desorption process also occurs in the potential region below chlorine evolution. The process occurs at the grain boundaries, edges and defects of the graphite powder material. Intercalation/deintercalation processes are mainly responsible for the disintegration of graphitic materials in low-temperature chloroaluminate melts. Repeated intercalation/deintercalation cycles result in the irreversible transformation of the electrode surface and electrode characteristics. The surface area of the electrode is increased substantially on cycling. Electrode materials and operating conditions suitable for chlorine generation, intercalation/deintercalation and chlorine adsorption/desorption and power sources based on these processes are identified in this work.     

Adsorption efficiency of poly(malachite green) films towards oxidation of ascorbic acid

Thickness of poly(malachite green) films electropolymerized on a glassy carbon electrode surface, the concentration of ascorbic acid, pH value of the solution, and accumulation time were found to affect the adsorption-controlled anodic peak current of ascorbic acid on this polymer film coated electrode. Adsorption efficiency, defined as the ratio of the active sites in polymer films to the amount of adsorbed ascorbic acid molecules, was then proposed and estimated from the comparison of mathematically simulated cyclic voltammograms with experimental ones. The concentration of ascorbic acid is the greatest parameter affected the adsorption efficiency. Poly(malachite green) film electropolymerized on the glassy carbon electrode was found to be not totally active towards oxidation of ascorbic acid when the concentration of ascorbic acid is too high or when the poly(malachite green) film is too thick. The potential shift of ascorbic acid on the modified electrodes was also discussed.     

Growth of nano-porous Pt-doped cerium oxide thin films on glassy carbon substrate

Glassy carbon (GC) substrates were treated by the oxygen plasma over several periods of time. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atomic force microscopy (AFM) study showed the dramatic influence of oxygen plasma on the morphology of glassy carbon. The treatment leads to the formation of nanostructured surface, which consists of well separated rod-like nanostructures oriented perpendicularly to the substrate surface. The surface roughness was found to increase with increasing treatment time.By using magnetron co-sputtering of platinum and cerium oxide we can prepare oxide layers continuously doped with Pt atoms during the growth. This technique combines etching of the carbon substrate and growth of the deposit. This leads to the formation of high surface area catalyst which makes this method promising for production of thin film catalysts.     

Anodic electrodeposition of cobalt oxides from an alkaline bath containing Co-gluconate complexes on glassy carbon. An electroanalytical investigation

In this study an electrodeposition procedure of cobalt oxides operating under anodic condition and directly from 0.5 M NaOH solutions containing 12 mM gluconate and 12 mM CoCl₂ was defined for the modification of glassy carbon surface electrode. Different experimental approaches based on cyclic voltammetry, steady-state potentiostatic technique, chronoamperometry and scanning electron microscopy were used to characterize the deposited cobalt oxide films and to evaluate the kinetics and mechanism of electrodeposition. Some aliphatic aldehydes were tested as compound model in order to evaluate the electroanalytical properties of the electrodeposited cobalt film as active redox material for amperometric applications in strong alkaline aqueous solutions. Interesting results in terms of surface electrode modification “in situ” of glassy carbon substrate with cobalt oxides were obtained and critically discussed.     

Multilayer graphene grown by precipitation upon cooling of nickel on diamond

Multilayer graphene is grown by precipitation upon cooling of a thin nickel film deposited by e-beam evaporation on single crystal diamond (0 0 1) oriented substrates. Nickel acts as a strong catalyst inducing the dissolution of carbon from diamond into the metal. Carbon segregation produces multilayers of graphene on the top surface. Characterization by Raman spectroscopy reveals that these thin layers display relatively narrow Raman phonon peaks that are typically associated with graphene. Atomic force microscope measurements reveal a multigrain structure that reproduces small domains in the nickel film. The multilayer graphene is transferred onto a optical microscope glass slide for further analysis. The thickness of the layers estimated from optical transmission measurements is 12 nm. The catalytic reaction found for nickel on diamond is not observed when glassy carbon is used as substrate. This method provides a venue for the fabrication of large area graphene films.     

Deposition rate and temperature of carbon films during laser-induced CVD on a moving substrate

The feasibility of using pyrolytic laser-induced chemical vapor deposition (LCVD) to deposit carbon coatings on moving fused quartz substrates is investigated. This LCVD system uses a CO₂ laser to locally heat a substrate in open air to create a hot spot. Pyrolysis of hydrocarbon species occurs and subsequently deposits a layer of carbon film onto the substrate surface. The results of this study indicate that growth kinetics and the geometry of uniform carbon stripes deposited by pyrolytic LCVD strongly related to the laser power, the traverse velocity of the substrate, the type of hydrocarbon species used in deposition, and the diameter of the substrate. The deposition rate of carbon film increases exponentially with the laser power, while an increase in traverse velocity of the substrate will also increase the deposition rate until a maximum deposition rate is reached; further increases in the traverse velocity will decrease the deposition rate. We suspect that this optimal deposition rate is caused by substrate motion, which affects the substrate surface temperature, and consequently the effective surface area available for film deposition. The substrate temperature is observed to behave linearly with the deposition parameters considered in this study.     

Electrocatalysis of metal phthalocyanine thin film prepared by the plasma-assisted deposition on a glassy carbon in the reduction of carbon dioxide

The intermittent plasma-assisted vacuum deposition technique has been found to introduce the effective electrocatalytic activity and stability for CO₂ reduction into metal phthalocyanine thin films formed on a glassy carbon. The film properties are significantly influenced by the chemical state of the film. It is suggested that the electrode process is determined by the surface chemical reaction involving adsorbed H and/or H⁺ and a carbon containing intermediate.     

Structure and electrochemical characterization of carbon films formed by unbalanced magnetron (UBM) sputtering method

We previously reported nanocarbon films formed by the electron cyclotron resonance (ECR) sputtering method. The films contain a nanocrystalline structure consisting of sp³ and sp² bonds with an extremely flat surface (Ra = 0.07 nm). The film also has a wider potential window than glassy carbon and superior electrochemical activity to boron doped diamond for certain species. However, ECR sputtering equipment is much more expensive than that used for conventional sputtering and requires a ring-shaped target. Therefore, it is difficult to use this method to develop new electrode materials such as metal-carbon hybrid film. Here, we describe a nanocarbon film electrode that we developed with a potential window and electrochemical activity equivalent to those of ECR nanocarbon films by using unbalanced magnetron (UBM) sputtering equipment. Our approach uses conventional equipment and has widely controllable sputtering conditions including a high sputtering rate, a large sputtering area and the capacity for co-sputtering multiple materials. The film can contain a maximum of 53% sp³ bonds by increasing the substrate bias voltage between the target and substrate, and also exhibits a potential window equivalent to that of the ECR nanocarbon film. However, the electrode surface is about one order of magnitude rougher than that of the ECR nanocarbon film due to the effect of reflected Ar⁺ ions caused by the fact that the target surface is facing the substrate surface. By employing transmission electron microscopy, we could observe nanocrystalline graphene structures in the UBM nanocarbon film, which are difficult to observe in conventional diamond-like carbon film. The electron transfer rate at the UBM nanocarbon film is similar to those of ECR nanocarbon film for Ru(NH₃)₆^3 + and Fe(CN)₆^4 −, suggesting that the nanocrystalline structure could contribute to a relatively fast electron transfer rate. The UBM nanocarbon films were successfully used for detecting kynurenic acid, which has a high oxidation potential and is difficult to detect with a conventional glassy carbon electrode.     

Influence of activated carbon pore structure on oxygen reduction at catalyst layers supported on rotating disk electrodes

Carbon materials are often used as catalyst supports, and for catalysts in electrodes of a polymer electrolyte fuel cell, carbon black has been used. Recently, it was found, however, that activated carbon could replace carbon black and besides, significantly improve the activity of the electrode catalyst layer for oxygen reduction. In the present study, to optimize the pore structure of activated carbon for further activity improvement, the influence of the pore structure on the activity was investigated using activated carbon of various specific surface areas and mean pore diameters. A catalyst layer was formed from activated carbon loaded with platinum and a polymer electrolyte. The activity of the layer was measured in an oxygen-saturated perchloric acid solution, supporting the layer on a rotating glassy carbon disk electrode. We found that increases in the specific surface area and mean pore diameter increased the activity and that the latter was more effective than the former mainly due to the enhanced mass-transfer in the pores; the catalyst layer formed from activated carbon with the largest mean pore diameter was the most active. Unless pores excessively develop and lose connections between particles, a large pore diameter is therefore desired for the fuel cell electrodes.     

Synthesis of large area carbon nanosheets for energy storage applications

We report the large area growth of highly conductive carbon nanosheets (CNS) composed of few layer graphene on 200 mm diameter Si substrates using conventional radio frequency plasma-enhanced chemical vapour deposition. Raman spectroscopy is used to characterise the evolution of the CNS nucleation and growth with time in conjunction with TEM revealing the nano-sized graphene-like nature of these films and the intimate contact to the substrate. An individual sheet can have edges as thin as 3 graphene layers. The influence of the growth support layer is also discussed as film growth is compared on titanium nitride (TiN) and directly on Si. Electrochemical cyclic voltammogram (CV) measurements reveal these layers to form an excellent electrical contact to the underlying substrate with excellent stability towards oxidation whilst having a large electrochemical surface area. The resistance of a 150 nm film was measured to be as low as 20 μohm cm. The high percentage of narrow few layer graphene edge sites exposed allows for faster electrochemical reaction rates compared to carbon nanotubes (CNTs) and other electrode materials (glassy carbon and Pt).     

The production of porous glassy carbon membranes from swift heavy ion irradiated Kapton

A porous glassy carbon membrane was obtained by first producing ion tracks in a polymeric Kapton film by irradiation with high energy krypton or xenon ions. Pores are formed by selective chemical etching along the ion tracks, and then the film was converted to glassy carbon by heat treatment at 1000 °C under an inert atmosphere. The process yields a self-supported glassy carbon thin membrane. The density of the pores in the membrane depends on the ion irradiation fluence, and the length, diameter and shape of the pores could be controlled by the ion energy and etching procedure.     

漆酶的直接电化学研究

本文研究了漆酶-明胶-离子液体复合膜在玻碳电极表面的直接电化学研究,研究结果表明此复合膜在电极上能进行准可逆的直接电化学反应,并保持对氧气的电催化还原的作用。     

Preparation of carbon material with SiC-concentration gradient by silicon impregnation and its oxidation behaviour

A carbon material with a SiC-concentration gradient was prepared by a silicon impregnation process. In order to prepare the carbon material with a SiC-concentration gradient without any adhesion of metallic silicon, the weight of silicon powder per physical surface area of the carbon substrate was in the range of 3·9-4·1 g cm⁻² and then heating the carbon substrate in silicon powder at 1450°C for 3 h, but the amount of silicon powder beyond this range resulted in the adhesion of metallic silicon. The concentration of SiC along the thickness in the sample obtained decreased rapidly up to 0·5 mm and gradually in a range of 0·5-1·0 mm. A remarkable improvement in the oxidation resistance was observed on the sample with a SiC-concentration gradient at 1400°C, which was due to the formation of a protective film of SiO₂ glass on the surface. In the results of the thermal shock test in the sample, no destructions and no cracking of the samples were observed.     

Controllable electrode activities of nano-carbon films while maintaining surface flatness by electrochemical pretreatment

A carbon film consisting nanocrystallites with mixed sp² and sp³ bonds formed by using the electron cyclotron resonance (ECR) sputtering method was studied with respect to the changes in characteristics caused by electrochemical pretreatment (ECP). Unlike glassy carbon, our sputtered nanocrystalline carbon film deposited at an acceleration voltage of 75 V (ECR-75 nano-carbon film) largely retained its surface flatness after the ECP. This robust surface could be caused by an increase of 42% in the sp³ carbon realized by increasing the acceleration voltage during sputtering. The electrode activity of ECR-75 nano-carbon film was improved for surface sensitive species including Fe^3+/2+ unlike the boron doped diamond (BDD) electrode. This is because a sufficient quantity of surface sp² bonds remained and because the introduction of surface oxygen-containing groups is more efficient than with the BDD electrode. With pretreated ECR-75 nano-carbon film, the peak potential of glutathione was reduced solely due to the increase in the surface hydrophilicity with a sufficient quantity of surface sp² bonds, thus achieving the lowest detection limit (0.4 μM) ever obtained with carbon electrodes. We also achieved the stable measurement of 30 μM of serotonin (20 times) without the electrode surface fouling found with other electrodes.