A method for the fabrication of low-noise carbon fiber nanoelectrodes

A new and facile method has been developed for the fabrication of low-noise carbon fiber microelectrodes (CFMEs) and carbon fiber nanoelectrodes (CFNEs). The carbon fiber was flame-fuse sealed in the tip of the glass capillary. The CFMEs were made by cutting the protruding carbon fiber to the desired length, and the CFNEs were achieved by etching the protruding carbon on the flame to form a nanometer-scale tip. The tip of CFNEs can be controlled within the range from 100 to 300 nm. Thus, no epoxy wax was involved in the CFMEs and CFNEs. The experimental results of inspecting CFMEs and CFNEs by scanning electron microscopy demonstrated that the surface of the electrodes and the glass/fiber interface are very smooth. Therefore, the noise caused by the glass/fiber of these electrodes is much lower than that of the electrodes fabricated conventionlly. The electrodes were characterized by ferricyanide, catecholamine (dopamine,DA), norepinephrine (NE), and epinephrine (E)) and 5-hydroxytryptamine (5-HT) neurotransmitters using CV, LSV, DPV, and FSCV. The results showed that the CFMEs and CFNEs have very excellent electrochemical behavior and high sensitivity. The CV and DPV detection limits of DA, NE, and E are 7.6 x 10(-8), 7.0 x 10(-8), and 5.0 x 10(-8) mol/L, and the DPV detection limits of DA, NE, and E are 4.0 x 10(-8), 1.0 x 10(-7), and 2.2 x 10(-7) mol/L, respectively. This experiment offers a new and facile method for the fabrication of CFMEs and CFNEs of very high sensitivity and low noise.     

Carbon nanotube fiber microelectrodes: design, characterization, and optimization

We report on the preparation and interesting electrochemical behavior of carbon nanotube fiber microelectrodes (CNTFM). By combining the advantages of carbon nanotubes (CNT) with those of fiber electrodes, this type of microelectrode differs from CNT modified or CNT containing composite electrodes, because it's made of only CNT without any other components like additives or binders. The active CNT surface is easily regenerated. The performance of CNTFMs has been characterized, among others, by surface modification with phosphomolybdic acid. It is shown that adsorption behavior of these catalyst molecules is highly improved with a controlled orientation of CNT. A better CNT alignment inside the fiber can be achieved by a hot stretching procedure.     

Morphological and electrochemical properties of boron-doped diamond films on carbon cloths with enhanced surface area

The electrochemical properties of doped diamond electrodes (10¹⁷–10¹⁹ B cm^− 3) grown on carbon fiber cloths in H₂SO₄ 0.1 mol L^− 1 electrolyte were investigated. Cyclic voltammograms of B-doped diamond/carbon fiber cloth and carbon fiber cloth electrodes showed that both kinds of electrodes possess similar working potential windows of about 2.0 V. The electrode capacitance was determined by impedance spectroscopy and chronopotentiometry measurements and very close values were obtained. The capacitance values of the diamond film on carbon fiber cloths were 180 times higher than the ones of diamond films on Si. In this paper we have also discussed the capacitance frequency dependence of diamond/carbon cloth electrodes.     

Simultaneous determination of serotonin and dopamine at the PEDOP/MWCNTs-Pd nanoparticle modified glassy carbon electrode

Electrochemical determination of dopamine (DA) and serotonin (5-HT) have been studied at a modified glassy carbon electrode (GCE) in 0.1 M phosphate buffer solution (PBS) using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) at pH 7.4, all over the interfering biomolecule ascorbic acid (AA). The GCE was modified by palladium-functionalized, multi-walled carbon nanotubes (MWCNTs-Pd) with electrochemical deposition of poly 3,4-ethylenedioxy pyrrole (PEDOP), denoted as PEDOP/MWCNTs-Pd/GCE, and investigated by SEM and EIS experiments. The highly electrocatalytic activity of the modified electrode toward 5-HT and DA was demonstrated from the sensitive and well-separated voltammetric experiment. The oxidation peaks found were 0.165 and 0.355 mV for DA and 5-HT, respectively. The composite film shows a significant accumulation effects on two species, as well as the mutual interference among the analytes. This biosensor was best in response compared to other modified electrodes made in the same lab. The lowest detection limits were found to be 5.0 x 10(-9) and 1.0 x 10(-8) for 5-HT and DA, respectively. The respective linear ranges were determined as 1.0 x 10(-7) to 2.0 x 10(-4) and 1.0 x 10(-7) to 2.0 x 10(-4) for 5-HT and DA.     

Nanoscale surface morphology and monomer concentration dependence on impedance of electrocoated 2,2-dimethyl-3,4-propylene-dioxythiophene on carbon fiber microelectrode

Poly(2,2-Dimethyl-3,4-propylenedioxythiophene) (PProDOT-Me2) thin films have been cyclovoltametrically coated onto carbon fiber microelectrode (CFME) as an active functionalized microelectrode. An electrochemical impedance spectroscopic study on the prepared electrodes is reported in this paper which electropolymerization performed under different initial monomer concentrations. The electrochemical impedance data fitted to equivalent circuit model, used to find out numerical values of the proposed components. Effect of the parameters on the capacitive behavior of the (PProDOT-Me2) coated carbon fiber microelectrode and morphology of films obtained by AFM and SEM was discussed. Highly porous coating was obtained at 100 mV/s scan rate and 10 cycles. EDX and ATR-FTIR results indicated the doping of anion of electrolyte due to formation of polaronic and bipolaronic sites. The presence of surface functional groups were determined by ATR-FTIR. Nanoscale conjugated polymer modified carbon fiber microelectrodes exhibited high capacitance of approximately 90 degrees phase angle, and vertical line in Nyquist plot. The capacitive behavior of CFME was increased by this very thin film coating of PProDOT-Me2. The electroactivity of Poly 2,2-Dimethyl-3,4-propylenedioxythiophene on the carbon fiber microelectrode open the possibility of using these coated electrodes for electrochemical microsupercapacitors and biosensor electrodes.     

Fabrication, characterization, and potential application of carbon fiber cone nanometer-size electrodes

A novel method has been developed for the fabrication of carbon fiber cone nanometer-size ultramicroelectrodes (nanoelectrodes) with overall tip dimensions as small as 50 nm in diameter. In this method, carbon fibers were initially etched by an argon ion beam thinner. Afterward, a single etched carbon fiber was inserted into a glass capillary, which was then sealed by heating the glass/fiber interface in a vacuum; thus, no epoxy resin is involved. The success rate of our fabrication route for the electrodes with overall tip diameters of up to 500 nm was about 80%; for those with tip diameters of up to 100 nm, it was about 50%. The fabricated carbon fiber cone nanoelectrodes (CFCNEs) were inspected by optical and scanning electron microscopy. Their electrochemical behavior was examined by cyclic and linear sweep voltammetric measurements of ferricyanide and ferrocene ions in aqueous and nonaqueous media. The potential analytical applicability of the CFCNEs was tested by differential pulse voltammetric measurements of two well-known neurotransmitters, dopamine (DA) and 5-hydroxytryptamine (5-HT), and the results achieved were highly satisfactory. The calibration plots obtained were linear over the ranges from 5.0 × 10(-7) to 1.0 × 10(-4) and from 2.0 × 10(-6) to 1.0 × 10(-4) mol/L, with limits of detection of 1.0 × 10(-7) and 5.0 × 10(-7) mol/L for DA and 5-HT, respectively. Some advantages and improvements of the proposed CFCNE fabrication method, especially with respect to smoothness of the fiber (electrode) surface, strength, and control over the fiber tip dimensions, are also discussed.     

Application of diamond microelectrodes for end-column electrochemical detection in capillary electrophoresis

Highly boron-doped diamond microelectrodes were employed in an end-column electrochemical detector for capillary electrophoresis (CE). The diamond microline electrodes were fabricated from conducting diamond thin films (exposed surface area, 300 x 50 microm), and their analytical performance as CE detectors was evaluated in a laboratory-made CE installation. The CE-ED system exhibited high separation efficiency for the detection of several catecholamines, including dopamine (DA), norepinephrine (NE), and epinephrine (E), with excellent analytical performance, for example, 155,000 theoretical plates for DA. The diamond-based electrochemical detection system also displayed low detection limits (approximately 20 nM for E at S/N = 3) and a highly reproducible current response with 10 repetitive injections of mixed analytes containing DA, NE, and E (each 50 microM), with relative standard deviations (RSD) of approximately 5%. The performance of the diamond detector in CE was also evaluated in the detection of chlorinated phenols (CP). When compared to the carbon fiber microelectrode, the diamond electrode exhibited lower detection limits in an end-column CE detection resulting from very low noise levels and highly reproducible analyses without electrode polishing due to analyte fouling, which makes it possible to perform easier and more stable CE analysis.     

Influence of raw carbon nanotubes diameter for the optimization of the load composition ratio in epoxy amperometric composite sensors

In this work, it is reported the necessity to characterize the raw carbon materials before their application in composite electrodes based on multiwall carbon nanotubes (MWCNTs) dispersed in epoxy resin for the development of improved amperometric sensors. These sensors must contain an optimum MWCNT/epoxy ratio for their best electroanalytical response. The main drawback in MWCNTs composite materials resides in the lack of homogeneity of the different commercial nanotubes largely due to different impurities content, as well as dispersion in their diameter/length ratio and state of aggregation. The optimal composite electrode composition takes into account the high electrode sensitivity, low limit of detection, fast response, and electroanalytical reproducibility. These features depend on carbon nanotube physical properties as the diameter. Three different commercial carbon nanotubes with different diameters were characterized by transmission electron microscopy and the results were significantly different from the ones provided by the manufacturers. Then, the three MWCNTs were used for the MWCNT/epoxy sensors construction. After an accurate electrochemical characterization by cyclic voltammetry and electrochemical impedance spectroscopy, they were employed as working electrodes using ascorbic acid as a reference analyte. Percolation theory was applied in order to verify the electrochemical results. It is demonstrated that the optimum interval load of raw carbon material in the optimized-composite electrodes closely depends on the MWCNTs diameter, needing 5 % in carbon content for the narrowest MWCNTs containing composite electrodes versus 12 % for the widest MWCNTs.     

制备温度对热解炭包覆磷酸铁锂/气相生长炭纤维复合正极材料的影响

采用微波化学气相沉积法一步合成了热解炭包覆磷酸铁锂/气相生长炭纤维复合正极材料. 借助X射线衍射仪、场发射扫描电子显微镜、高分辨透射电镜和电化学测试仪等测试手段研究了不同制备温度对材料晶体结构、显微形貌和电化学性能的影响. 结果表明, 当制备温度由500℃升至600℃时, 磷酸铁锂主晶相的颗粒尺寸没有发生明显变化, 而原位VGCF的网络程度却明显增加, 材料的放电比容量随之提高; 当制备温度进一步升高到700℃时, 磷酸铁锂颗粒异常生长现象加剧, VGCF直径较大且粗细不均, 材料的电化学性能变差. 研究发现, 当温度为600℃时, 材料表现出较优的电化学性能, 25℃在0.2C、0.5C、1C和3C倍率下的放电比容量分别可达163、159、153和143mAh/g.     

纳米纤维素/碳纤维-聚苯胺/碳纳米管电极的制备

目的以纳米纤维素/碳纤维复合膜为导电基底,制备纳米纤维素/碳纤维-聚苯胺/碳纳米管超级电容器电极。方法利用超声处理和真空抽滤制备纳米纤维素/碳纤维复合膜;利用原位聚合法制备聚苯胺和聚苯胺/碳纳米管复合材料;通过真空抽滤法制备纳米纤维素/碳纤维-聚苯胺电极和纳米纤维素/碳纤维-聚苯胺/碳纳米管电极。结果在纳米纤维素/碳纤维复合膜中,碳纤维形成了互穿导电网络结构,是良好的超级电容器电极导电基体;纳米纤维素/碳纤维-聚苯胺/碳纳米管电极具有良好的电化学性能,在扫描速率为5 mV/s的条件下,质量比电容为380.74 F/g,且在1000次循环测试后,电容保留率为88.05%。结论以纳米纤维素/碳纤维导电复合膜作为基体制备的纳米纤维素/碳纤维-聚苯胺/碳纳米管电极具有良好的电化学性能,可以作为超级电容器电极。     

Carbon fiber nanoelectrodes modified by single-walled carbon nanotubes

Microelectrode voltammetry has been considered to be a powerful technique for single biological cell analysis and brain research. In this paper, we have developed a simple method to get highly sensitive carbon fiber nanoelectrodes (CFNE) modified by single-walled carbon nanotubes (SWNTs) on the basis of our previous work. The electrochemical behavior of SWNTs/CFNE was characterized by potassium ferricyanide, dopamine (DA), epinephrine (E), and norepinephrine (NE) using cyclic voltammetry (CV). Compared with CFNE, SWNTs/CFNE has a much larger available internal surface area per external geometric area, which is supported by SEM images. The modified electrodes show very high sensitivity and favorable electrochemical behavior toward these neurotransmitters. The peak current increases linearly with the concentration of DA, E, and NE in the range of 1.0 x 10(-)(7)-1.0 x 10(-)(4), 3.0 x 10(-)(7)-1.0 x 10(-)(4), and 5.0 x 10(-)(7)-1.0 x 10(-)(4) M, respectively. The CV detection limit (S/N = 3) of DA, E, and NE is 7.7 x 10(-)(9), 3.8 x 10(-)(8), and 4.2 x 10(-)(8) M, respectively. The modified electrode exhibited almost the same electrochemical behavior after 15 days, indicating that SWNTs/CFNE is pretty stable and has good reproducibility.     

氯化铜/活性炭复合电极的制备及性能的研究

以酚醛树脂为活性炭基体,采用化学掺杂法掺杂氯化铜,制备氯化铜／活性炭复合电极材料。通过物理吸附考察了金属氯化铜的存在下不同活化时间对金属复合活性炭孔径分布的影响,实验表明活化时间越长,比表面积越大,中孔含量越高。通过透射电镜和X射线衍射对复合电极的微观结构进行了研究,表明金属铜以纳米级均匀分散在活性炭中。通过比较活性炭电极和复合电极的电化学性能,说明掺杂金属铜可以有效提高比电容,并对充放电机理进行了探讨。     

金属Cu的负载方法对活性炭电极电化学性能的影响

采用浸渍法和掺杂法分别在活性炭中负载金属Cu,初步电化学性能测试表明,活性炭负载金属Cu可以提高活性炭电极的放电容量,但不同负载方法对其循环性能造成较大的影响.通过电镜照片和XRD等手段对金属在活性炭上的负载状态进行分析比较,结合电极的充放电性能,发现在活性炭中均匀掺杂金属Cu,可以提高电容器的放电容量,且电化学性能稳定.     

SiC-C fiber electrode for biological sensing

Microelectrodes implanted in the brain can act as transducers for the neuronal impulses. In this work a composite fiber (SiC-C) electrode was studied for neuronal activity sensing and for biochemical detection of electroactive neurotransmitters. An electrolytic etching technique was also developed for fabricating electrode tips from SiC-C composite fiber. SEM was used to study different tip geometries and shapes. Cyclic voltammetry and electrochemical impedance spectroscopy were used for the electrochemical characterization and modeling. Almost square voltammograms showed that the current generated was due to the charging and discharging of the capacitive double layer without any significant redox reaction. The electrodes showed capacitive interaction with the surrounding electrolyte solution which is highly desirable for safe charge transfer. Biochemical sensing of neurotransmitters including dopamine hydrochloride and vitamin C was done with the SiC-C composite electrodes and oxidation currents were found to vary linearly with concentration. In vivo action potential recordings from anesthetized rat's brain with very high signal to noise ratio were obtained.     

Enhanced oxidation of estrone at multi-wall carbon nanotubes film electrode: direct evidence for the advantage of carbon nanotubes over other carbonaceous materials

The electrochemical behaviors of estrone at various carbonaceous nanomaterials-dihexadecyl hydrogen phosphate (DHP) composite films coated glassy carbon electrodes were investigated by cyclic voltammetry (CV), linear sweep voltammetry (LSV), chronocoulometry (CC) and electrochemical impedance spectroscopy (EIS). Comparing with the composite films of acetylene black (AB) and carbon nanofiber (CNF), multi-wall carbon nanotubes (MWCNTs)-DHP film showed the best electrochemical performance towards the oxidation of estrone, reflected by the significantly enhanced oxidation current in the voltammograms as well as the apparently reduced charge transfer resistance in EIS. Studies on the active surface area, the surface coverage and EIS suggested that the apparently improved electrochemical responses of estrone at MWCNTs should arise from their large surface area, good conductivity and the ability to facilitate the charge transfer process. The reaction mechanisms of estrone oxidation at the three composite films were also discussed, which were expected to follow a process involved the total loss of two electrons and two protons.     

聚丙烯腈基碳纤维电化学改性研究现状与展望

综合论述了聚丙烯腈基(PAN)碳纤维电化学表面改性处理研究的发展现状,对比分析了碳纤维电化学改性处理法的研究内容及表征手段,指出了存在的问题,并展望了碳纤维表面电化学改性处理的研究前景.在碳纤维改性工艺参数的研究工作中,为了使实验结果有可比性,迫切需要一套标准来规范实验条件及性能表征方法,而为了更好地体现碳纤维复合材料的性能优势,仍需不断探索和研究碳纤维的电化学改性机理.为使复合材料的性能更好地达到应用要求,有必要提出碳纤维表面改性模型及界面理论.     

碳纤维形貌结构对其电化学氧化行为及其复合材料界面性能的影响

通过调控原丝工艺,制备得到形貌结构不同、力学性能相近的PAN基碳纤维(CF),用以模拟碳纤维表面光滑与沟槽结构对其电化学氧化行为的影响。研究表明:原始形貌光滑碳纤维在电化学过程中保持形貌能力较强,相同的电化学氧化强度下,其表面氧碳比高于原始表面粗糙的碳纤维,表明其氧化程度高。X射线光电子能谱(XPS)分峰结果表明,二者表面氧含量差别来自于表面羰基含量的差异。力学性能测试结果表明具有沟槽形貌的碳纤维拉伸强度及拉伸模量提高的幅度较大,其中拉伸强度提高最大值为17.3%。将氧化前后的碳纤维制备成碳纤维增强树脂基复合材料,探讨碳纤维形貌结构对其复合材料界面性能的影响。结果表明:由具有沟槽形貌的碳纤维制备得到的复合材料层间剪切强度(ILSS)较高,表明碳纤维表面物理形貌也是影响复合材料界面的重要因素。     

Strategies to Optimize the Capacitive Behavior of Polypyrrole Electrodes

Polypyrrole (PPR) and composite PPR-multi-walled carbon nanotube (MCNT) electrodes for electrochemical supercapacitors were manufactured using new anionic additives for PPR polymerization. The analysis of the microstructure of PPR and PPR-MCNTs and electrochemical testing data provided information on the influence of the dopants on the mechanism of chemical polymerization and properties of nanostructured PPR and PPR-MCNT materials. The increase of the size and charge of the aromatic dopants resulted in decreasing PPR particle size, reducing agglomeration, and promoted the formation of PPR coatings on MCNTs. New additives allowed for the manufacturing of advanced electrodes with high active mass loading, excellent capacitance at high charging–discharging rates, and cyclic stability. A capacitance of 2.67 F cm^?2 at a potential variation rate of 100 mV s^?1 was achieved using composite PPR-MCNT electrodes. The electrodes were applied for the manufacturing of supercapacitor cells, which showed good electrochemical performance.     

Effect of processable polyindole and nanostructured domain on the selective sensing of dopamine

The effect of carboxylic acid functionality present in polymer backbone is reported on electrochemical sensing of dopamine (DA). The electropolymerized conducting polymers made from carboxylic acid substituted indole at positions − 5 and − 6 are found processable in aqueous medium and are compatible with suitable additives/precursors for fabricating polymer modified electrodes (PMEs). The modified electrodes are fabricated following two methods, i.e.: (1) the processable polymers are cast over glassy carbon electrode (GCE) using Nafion® followed by chemical modification using hydrophobic organic redox mediators and (2) the processable polymers are encapsulated within organically modified silicate (Ormosil) matrix along with the hydrophilic redox mediator followed by incorporation of silver and gold nanoparticles. The electrochemical performances of these modified electrodes show selective sensing of DA with major findings: (i) both polymers introduced selectivity in electrochemical sensing of DA with analogous sensitivity, (ii) sensitivity is enhanced when hydrophobic organic redox mediators are coupled with modified electrode matrix involving Nafion®, (iii) the polymers are suitable for encapsulation within ormosil matrix thus introducing nanostructured network for further improvement in sensitivity of DA analysis, (iv) the presence of gold and silver nanoparticles within ormosil matrix along with polymers caused > 100 fold increase in sensitivity of DA sensing with lowest detection limit to the order of 100 nM.     

Fast-scan voltammetry of cyclic nitroxide free radicals

Fast-scan cyclic voltammetry at carbon fiber microelectrodes is used to detect the cyclic nitroxide 2,2,6,6-tetramethylpiperidinyl-1-oxy free radical (TEMPO) and three analogs. The electrochemical behavior of the TEMPO analogs at unmodified carbon fiber electrodes is found to differ greatly from their behavior at glassy carbon electrodes. After the electrode is coated with the polymer Nafion, the electrodes exhibit increased sensitivity to TEMPO and 4-amino-TEMPO. Voltammograms of the nitroxides at Nafion-coated electrodes indicate that the oxidized form (oxoammonium ion) and the free radical form have greatly different mobilities through the polymeric coating. Response times to changes in nitroxide concentration vary from subsecond at bare electrodes (all four analogs) and 4-hydroxy-TEMPO at modified electrodes to 1-3 s for TEMPO and 4-amino-TEMPO at modified electrodes. The detection limit for 4-amino-TEMPO is 50 μM at an unmodified electrode and 5 μM at a Nafion-coated carbon fiber electrode. The sensitivity of the Nafion-modified electrode to TEMPO, 4-hydroxy-TEMPO, and 4-amino-TEMPO can be improved by choosing a resting potential at which the oxoammonium ion form of the nitroxide is preconcentrated into the Nafion film. Using fast-scan cyclic voltammetry and the modified carbon fiber electrodes, the reaction of two nitroxide free radicals with ascorbate can be monitored. This work shows that fast-scan voltammetry at microelectrodes is a sensitive method that can be used to follow reactions of cyclic nitroxide free radicals in solution.