Modification of glassy carbon electrodes with a poly-L-lysine/glutaraldehyde film

A film of poly-L-lysine (PLL) adheres better to the surface of a glassy carbon electrode when the PLL is partially cross-linked by means of glutaraldehyde. A film composition of 97.5% PLL/2.5% glutaraldehyde gives good adhesion and retains the anionic exchange capability of the PLL. The performance of the film was tested with hexacyanoferrate(III) using electrochemical and nonelectrochemical accumulation.

Treatment of Reticulated Vitreous Carbon by Dielectric Barrier Discharge Plasma for Electrodes Production

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Multi-walled carbon nanotubes modified screen-printed electrodes for cisplatin detection

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Carbon nanotubes modified with antimony nanoparticles: A novel material for electrochemical sensing

In this study, a novel material for the electrochemical determination of bisphenol A using a nanocomposite based on multi-walled carbon nanotubes modified with antimony nanoparticles has been investigated. The morphology, structure, and electrochemical performance of the nanocomposite electrodes were characterised by field emission gun scanning electron microscopy, energy-dispersive X-ray spectroscopy, and cyclic voltammetry. A scan rate study and electrochemical impedance spectroscopy showed that the bisphenol A oxidation product is adsorbed on nanocomposite electrode surface. Differential pulse voltammetry in phosphate buffer solution at pH 6, allowed the development of a method to determine bisphenol A levels in the range of 0.5-5.0 mu mol L-1, with a detection limit of 5.24 nmol L-1 (1.19 mu g L-1). (C) 2012 Elsevier Ltd. All rights reserved.

Electrochemical surface modification of Single walled carbon nanotubes and graphene-based electrodes for (bio)sensing applications

Sensors are devices that have shown widespread use, from the detection of gas molecules to the tracking of chemical signals in biological cells. Single walled carbon nanotube (SWCNT) and graphene based electrodes have demonstrated to be an excellent material for the development of electrochemical biosensors as they display remarkable electronic properties and the ability to act as individual nanoelectrodes, display an excellent low-dimensional charge carrier transport, and promote surface electrocatalysis. The present work aims at the preparation and investigation of electrochemically modified SWCNT and graphene-based electrodes for applications in the field of biosensors. We initially studied SWCNT films and focused on their topography and surface composition, electrical and optical properties. Parallel to SWCNTs, graphene films were investigated. Higher resistance values were obtained in comparison with nanotubes films. The electrochemical surface modification of both electrodes was investigated following two routes (i) the electrografting of aryl diazonium salts, and (ii) the electrophylic addition of 1, 3-benzodithiolylium tetrafluoroborate (BDYT). Both the qualitative and quantitative characteristics of the modified electrode surfaces were studied such as the degree of functionalization and their surface composition. The combination of Raman, X-ray photoelectron spectroscopy, atomic force microscopy, electrochemistry and other techniques, has demonstrated that selected precursors could be covalently anchored to the nanotubes and graphene-based electrode surfaces through novel carbon-carbon formation.

Polyaniline-coated carbon papers for supercapacitor electrodes

Graphene and carbon nanotubes are promising materials for supercapacitor electrodes because of their high specific surface area and excellent electrical, thermal, and mechanical properties. However, these materials suffer from a high manufacturing cost and some aggregation of graphene layers or the presence of toxic residual metallic impurities of carbon nanotubes.

Electrochemical analysis of the performance of carbon supported Pd nanoparticles for direct formic acid fuel cells: from gold supported electrodes to catalyst-coated membranes

In this work carbon supported Pd nanoparticles were prepared and used as electrocatalysts for formic acid electrooxidation fuel cells. The influence of some relevant parameters such as the nominal Pt loading, the Nafion/total solids ratio as well as the Pd loading towards formic acid electrooxidation was evaluated using gold supported catalytic layer electrodes which were prepared using a similar methodology to that employed in the preparation of conventional catalyst coated membranes (CCM). The results obtained show that, for constant Pd loading, the nominal Pd loading and the Nafion percentage on the catalytic layer do not play an important role on the resulting electrocatalytic properties. The main parameter affecting the electrocatalytic activity of the electrodes seems to be the Pd loading, although the resulting activity is not directly proportional to the increased Pd loading. Thus, whereas the Pd loading is multiplied by a factor of 10, the activity is only twice which evidences an important decrease in the Pd utilization. In fact, the results obtained suggest the active layer is the outer one being clearly independent of the catalytic layer thickness. Finally, catalyst coated membranes with Pd catalyst loadings of 0.1, 0.5 and 1.2 mg cm-2 were also tested in a breathing direct formic acid fuel cell.

Binderless thin films of zeolite-templated carbon electrodes useful for electrochemical microcapacitors with ultrahigh rate performance

Controlled nanozeolite deposits are prepared by electrochemical techniques on a macroporous carbon support and binderless thin film electrodes of zeolite-templated carbon are synthesized using the deposits as templates. The obtained film electrodes exhibit extremely high area capacitance (10–12 mF cm−2) and ultrahigh rate capability in a thin film capacitor.

Electrochemical behaviour of different redox probes on single wall carbon nanotube buckypaper-modified electrodes

In the present work, the electrochemical properties of single-walled carbon nanotube buckypapers (BPs) were examined in terms of carbon nanotubes nature and preparation conditions. The performance of the different free-standing single wall carbon nanotube sheets was evaluated via cyclic voltammetry of several redox probes in aqueous electrolyte. Significant differences are observed in the electron transfer kinetics of the buckypaper-modified electrodes for both the outer- and inner-sphere redox systems. These differences can be ascribed to the nature of the carbon nanotubes (nanotube diameter, chirality and aspect ratio), surface oxidation degree and type of functionalities. In the case of dopamine, ferrocene/ferrocenium, and quinone/hydroquinone redox systems the voltammetric response should be thought as a complex contribution of different tips and sidewall domains which act as mediators for the electron transfer between the adsorbate species and the molecules in solution. In the other redox systems only nanotube ends are active sites for the electron transfer. It is also interesting to point out that a higher electroactive surface area not always lead to an improvement in the electron transfer rate of various redox systems. In addition, the current densities produced by the redox reactions studied here are high enough to ensure a proper electrochemical signal, which enables the use of BPs in sensing devices.

Enhanced electro-oxidation resistance of carbon electrodes induced by phosphorus surface groups

The electro-oxidation of carbon materials enormously degrades their performance and limits their wider utilization in multiple electrochemical applications. In this work, the positive influence of phosphorus functionalities on the overall electrochemical stability of carbon materials has been demonstrated under different conditions. We show that the extent and selectivity of electroxidation in P-containing carbons are completely different to those observed in conventional carbons without P. The electro-oxidation of P-containing carbons involves the active participation of phosphorus surface groups, which are gradually transformed at high potentials from less-to more-oxidized species to slow down the introduction of oxygen groups on the carbon surface (oxidation) and the subsequent generation of (C*OOH)-like unstable promoters of electro-gasification. The highest-oxidized P groups (–C–O–P-like species) seem to distribute the gained oxygen to neighboring carbon sites, which finally suffer oxidation and/or gasification. So it is thought that P-groups could act as mediators of carbon oxidation although including various steps and intermediates compared to electroxidation in P-free materials.

Mercury determination in urine samples by gold nanostructured screen-printed carbon electrodes after vortex-assisted ionic liquid dispersive liquid–liquid microextraction

A novel approach is presented to determine mercury in urine samples, employing vortex-assisted ionic liquid dispersive liquid–liquid microextraction and microvolume back-extraction to prepare samples, and screen-printed electrodes modified with gold nanoparticles for voltammetric analysis. Mercury was extracted directly from non-digested urine samples in a water-immiscible ionic liquid, being back-extracted into an acidic aqueous solution. Subsequently, it was determined using gold nanoparticle-modified screen-printed electrodes. Under optimized microextraction conditions, standard addition calibration was applied to urine samples containing 5, 10 and 15 μg L−1 of mercury. Standard addition calibration curves using standards between 0 and 20 μg L−1 gave a high level of linearity with correlation coefficients ranging from 0.990 to 0.999 (N = 5). The limit of detection was empirical and statistically evaluated, obtaining values that ranged from 0.5 to 1.5 μg L−1, and from 1.1 to 1.3 μg L−1, respectively, which are significantly lower than the threshold level established by the World Health Organization for normal mercury content in urine (i.e., 10–20 μg L−1). A certified reference material (REC-8848/Level II) was analyzed to assess method accuracy finding 87% and 3 μg L−1 as the recovery (trueness) and standard deviation values, respectively. Finally, the method was used to analyze spiked urine samples, obtaining good agreement between spiked and found concentrations (recovery ranged from 97 to 100%).

Preparation and anode property of Pt-CeO2 electrodes supported on carbon black for direct methanol fuel cell applications

A platinum (Pt) on pure ceria (CeO2) supported by carbon black (CB) anode was synthesized using a combined process of precipitation and coimpregnation methods. The electrochemical activity of methanol oxidation reaction on synthesized Pt-CeO2/CB anodes was investigated by cyclic voltammetry and chronoamperometry experimentation. To improve the anode property on Pt-CeO2/CB, the influence of particle morphology and particle size on anode properties was examined. The morphology and particle size of the pure CeO2 particles could be controlled by changing the preparation conditions. The anode properties (i.e., peak current density and onset potential for methanol oxidation) were improved by using nanosize CeO2 particles. This indicates that a larger surface area and higher activity on the surface of CeO2 improve the anode properties. The influence of particle morphology of CeO2 on anode properties was not very large. The onset potential for methanol oxidation reaction on Pt-CeO2/CB, which consisted of CeO2 with a high surface area, was shifted to a lower potential compared with that on the anodes, which consisted of CeO2 with a low surface area. The onset potential on Pt-CeO2/CB at 60 degrees C became similar to that on the commercially available Pt-Ru/carbon anode. We suggest that the rate-determining steps of the methanol oxidation reaction on Pt-CeO2/CB and commercially available Pt-Ru/carbon anodes are different, which accounts for the difference in performance. In the reaction mechanism on Pt-CeO2/CB, we conclude that the released oxygen species from the surface of CeO2 particles contribute to oxidation of adsorbed CO species on the Pt surface. This suggests that the anode performance of the Pt-CeO2/CB anode would lead to improvements in the operation of direct methanol fuel cells at 80 degrees C by the enhancement of diffusion of oxygen species created from the surface of nanosized CeO2 particles. Therefore, we conclude that fabrication of nanosized CeO2 with a high surface area is a key factor for development of a high-quality Pt-CeO2/CB anode in direct methanol fuel cells.

Carbon nanostructure based electrodes for high efficiency dye sensitized solar cell

Synthesis and functionalization of large-area graphene and its structural, electrical and electrochemical properties has been investigated. First, the graphene films, grown by thermal chemical vapor deposition (CVD), contain three to five atomic layers of graphene, as confirmed by Raman spectroscopy and high-resolution transmission electron microscopy. Furthermore, the graphene film is treated with CF4 reactive-ion plasma to dope fluorine ions into graphene lattice as confirmed by X-ray photoelectron spectroscopy (XPS) and UV-photoemission spectroscopy (UPS). Electrochemical characterization reveals that the catalytic activity of graphene for iodine reduction enhanced with increasing plasma treatment time, which is attributed to increase in catalytic sites of graphene for charge transfer. The fluorinated graphene is characterized as a counter-electrode (CE) in a dye-sensitized solar cell (DSSC) which shows ~ 2.56% photon to electron conversion efficiency with ~11 mAcm−2 current density. Second, the large scale graphene film is covalently functionalized with HNO3 for high efficiency electro-catalytic electrode for DSSC. The XPS and UPS confirm the covalent attachment of C-OH, C(O)OH and NO3- moieties with carbon atoms through sp2-sp3 hybridization and Fermi level shift of graphene occurs under different doping concentrations, respectively. Finally, CoS-implanted graphene (G-CoS) film was prepared using CVD followed by SILAR method. The G-CoS electro-catalytic electrodes are characterized in a DSSC CE and is found to be highly electro-catalytic towards iodine reduction with low charge transfer resistance (Rct ~5.05 Ωcm 2) and high exchange current density (J0~2.50 mAcm -2). The improved performance compared to the pristine graphene is attributed to the increased number of active catalytic sites of G-CoS and highly conducting path of graphene. We also studied the synthesis and characterization of graphene-carbon nanotube (CNT) hybrid film consisting of graphene supported by vertical CNTs on a Si substrate. The hybrid film is inverted and transferred to flexible substrates for its application in flexible electronics, demonstrating a distinguishable variation of electrical conductivity for both tension and compression. Furthermore, both turn-on field and total emission current was found to depend strongly on the bending radius of the film and were found to vary in ranges of 0.8 - 3.1 V/μm and 4.2 - 0.4 mA, respectively.

Surface structured platinum electrodes for the electrochemical reduction of carbon dioxide in imidazolium based ionic liquids

The direct CO2 electrochemical reduction on model platinum single crystal electrodes Pt(hkl) is studied in [C2mim+][NTf2−], a suitable room temperature ionic liquid (RTIL) medium due to its moderate viscosity, high CO2 solubility and conductivity. Single crystal electrodes represent the most convenient type of surface structured electrodes for studying the impact of RTIL ion adsorption on relevant electrocatalytic reactions, such as surface sensitive electrochemical CO2 reduction. We propose here based on cyclic voltammetry and in situ electrolysis measurements, for the first time, the formation of a stable adduct [C2mimH–CO2−] by a radical–radical coupling after the simultaneous reduction of CO2 and [C2mim+]. It means between the CO2 radical anion and the radical formed from the reduction of the cation [C2mim+] before forming the corresponding electrogenerated carbene. This is confirmed by the voltammetric study of a model imidazolium-2-carboxylate compound formed following the carbene pathway. The formation of that stable adduct [C2mimH–CO2−] blocks CO2 reduction after a single electron transfer and inhibits CO2 and imidazolium dimerization reactions. However, the electrochemical reduction of CO2 under those conditions provokes the electrochemical cathodic degradation of the imidazolium based RTIL. This important limitation in CO2 recycling by direct electrochemical reduction is overcome by adding a strong acid, [H+][NTf2−], into solution. Then, protons become preferentially adsorbed on the electrode surface by displacing the imidazolium cations and inhibiting their electrochemical reduction. This fact allows the surface sensitive electro-synthesis of HCOOH from CO2 reduction in [C2mim+][NTf2−], with Pt(110) being the most active electrode studied.

Remediation Of 17-α-ethinylestradiol Aqueous Solution By Photocatalysis And Electrochemically-assisted Photocatalysis Using Tio2 And Tio2/wo3 Electrodes Irradiated By A Solar Simulator.

TiO2 and TiO2/WO3 electrodes, irradiated by a solar simulator in configurations for heterogeneous photocatalysis (HP) and electrochemically-assisted HP (EHP), were used to remediate aqueous solutions containing 10 mg L(-1) (34 μmol L(-1)) of 17-α-ethinylestradiol (EE2), active component of most oral contraceptives. The photocatalysts consisted of 4.5 μm thick porous films of TiO2 and TiO2/WO3 (molar ratio W/Ti of 12%) deposited on transparent electrodes from aqueous suspensions of TiO2 particles and WO3 precursors, followed by thermal treatment at 450 (°)C. First, an energy diagram was organized with photoelectrochemical and UV-Vis absorption spectroscopy data and revealed that EE2 could be directly oxidized by the photogenerated holes at the semiconductor surfaces, considering the relative HOMO level for EE2 and the semiconductor valence band edges. Also, for the irradiated hybrid photocatalyst, electrons in TiO2 should be transferred to WO3 conduction band, while holes move toward TiO2 valence band, improving charge separation. The remediated EE2 solutions were analyzed by fluorescence, HPLC and total organic carbon measurements. As expected from the energy diagram, both photocatalysts promoted the EE2 oxidation in HP configuration; after 4 h, the EE2 concentration decayed to 6.2 mg L(-1) (35% of EE2 removal) with irradiated TiO2 while TiO2/WO3 electrode resulted in 45% EE2 removal. A higher performance was achieved in EHP systems, when a Pt wire was introduced as a counter-electrode and the photoelectrodes were biased at +0.7 V; then, the EE2 removal corresponded to 48 and 54% for the TiO2 and TiO2/WO3, respectively. The hybrid TiO2/WO3, when compared to TiO2 electrode, exhibited enhanced sunlight harvesting and improved separation of photogenerated charge carriers, resulting in higher performance for removing this contaminant of emerging concern from aqueous solution.