Glassy Carbon Disk Research Articles

Carbon monoxide and methanol oxidation on potential-modified Pt–Ru/C electrocatalyst for polymer electrolyte fuel cells

In this paper, the effect of the anodic treatment of carbon-supported Pt−Ru nanoparticles using a HP 20% 1:1 Pt−Ru alloy on Vulcan XC-72 carbon black on the CO stripping and methanol oxidation reaction (MOR) has been analyzed. Thin-layer electrodes were prepared by depositing catalyst inks of Pt−Ru/C and Nafion on glassy carbon (GC) disks. Steady-state polarization at potentials >1.00V vs. RHE in 0.5M H2SO4 was used for the electrochemical activation of the specimen. Cyclic voltammetry was applied for electrochemical testing. The morphological analysis was performed by transmission electron microscopy (TEM), energy dispersive X-ray (EDX), selected-area electron diffraction (SAED), and Fast Fourier Transform (FFT). The present results showed that the anodic potential treatment causes Ru segregation with some carbon oxidation and agglomeration of nanoparticles. Activation of CO and methanol oxidation was found, indicating the production of the beneficial hydrous Ru oxide, RuOxHy, the promoting species for both reactions. For the MOR, the optimum potential of anodic treatment was located at 1.40–1.60V. An apparent double Tafel slope behavior with values of 120 and 200mVdec−1 was obtained after this optimum potential treatment, which was tentatively attributed to the existence of two different active sites for the MOR.

Mechanistic study of direct electron transfer in bilirubin oxidase

The mechanism of direct electron transfer in multicopper oxidases is not well understood. In this work, the mechanism of oxygen reduction in Bilirubin oxidase (BOD) is analyzed using a rotating ring-disc electrode (RRDE). The glassy carbon disc potential was swept from 0.8 V to 0 V while the platinum ring potential was held at 0.8 V, resulting currents were measured. Minimal hydrogen peroxide evolution from BOD is detected on the Pt ring, independent of rotation rate. The electron transfer rate constant, k et, is calculated to be 1.14 × 10 −3 cm/s. The number of electrons transferred per molecule of oxygen is calculated to be 3.92 electrons using Koutecky–Levich equation and 3.7 ± 0.2 electrons using mass/charge balance which corresponds to 7.5 ± 5% of oxygen reduction via the 2 electron pathway with a hydrogen peroxide intermediate. The 4 electron transfer mechanism is preferred because it is more efficient than the two electron mechanism.

Performance of Ex Situ Bismuth Film Rotating Disk Electrode in Trace Metal Analysis by Stripping Chronopotentiometry: Definition of the Depletion Regime and Optimization of Experimental Parameters

AbstractThe potentiality of the ex situ deposited bismuth film electrode, allied to the rotation of a glassy carbon disk electrode (BiFE‐RDE), was exploited in trace metal analyses of lead(II) and cadmium(II) by stripping chronopotentiometry (SCP). A single BiFE (6.2 nm film thickness) can be used for a 1‐day term with no significant variation in the analytical signal. The limit of detection (3σ) for a deposition time of 40 s and an oxidation current of 15×10−9 A was 1.5×10−8 M for Pb(II) and 3.0×10−8 M for Cd(II). BiFE‐RDE was successfully applied to the direct SCP determination of lead(II) in a fresh water certified material.

Extraordinary Oxygen Reduction Activity of Pt3Ni7

Nanostructured thin film catalysts (NSTF) with widely varying compositions of PtxMy and PtxMyNz (M, N = Ni, Co, Zr, Hf, Fe, Mn) have been evaluated for 0 ≤ x, y, z < 1. The catalysts’ activity for oxygen reduction (ORR) was measured in 50 cm2 fuel cell membrane electrode assemblies. Pt1-xNix was found to be unique in showing an extraordinarily sharp peak in ORR activity as a function of the as-made composition around x = 0.69 ± 0.02 determined gravimetrically. This composition gave a corresponding fcc lattice parameter of 3.71 Angstroms and a grain size of 7.5 nm. Both surface area and specific activity increases contribute to the increased mass activity of the resultant dealloyed films. The ORR mass activity of the Pt3Ni7 is 60% higher than for the NSTF standard Pt68Co29Mn3 alloy. Rotating disk electrode measurements of a Pt1-xNix series on NSTF coated glassy carbon disks show a similar large and sharp peak in activity. In contrast, PtCo shows a diminished but still sharply peaked mass activity in 50 cm2 tests near x = 0.62 by electron microprobe over the 0 < x < 0.7 range examined.

Oxygen Reduction Activity of Dealloyed Pt1–xNix Catalysts

Pt and intermixed Pt1–xNix (0.65 < x < 0.75) catalysts were sputtered-deposited onto both bare and nanostructured thin film (NSTF)-coated glassy carbon disks. The oxygen reduction reaction (ORR) activities of the disks were determined from Rotating Disk Electrode (RDE) measurements. Experiments on the NTSF-coated disks examined both catalytic activities and the effects of high surface area supports in a single measurement. The RDE measurement protocols were designed to examine changes in catalyst properties and performance during de-alloying and thus did not include the typical “electrochemical cleaning” procedure at the beginning. Instead, a continuous CV-ORR measurement protocol was used to monitor the electrochemical performance indicators such as active surface area (SEF) and ORR kinetic current density of the catalysts over the course of 9 h. As an example, the SEF of Pt25Ni75 on the NSTF-support was initially 20 cm2Pt/cm2planar and the SEF increased rapidly at the beginning of the experiment, then stabilized near ∼50 cm2/cm2 as Ni de-alloyed. This is compared with sputtered Pt on NSTF support that showed SEF ∼15 cm2/cm2. De-alloying is an effective way to create Pt-transition metal catalysts on NSTF with extremely high active surface area.

Reductive-Oxidation Electrogenerated Chemiluminescence (ECL) Generation at a Transparent Silver Nanowire Electrode

We present the fabrication of a conductive, transparent electrode composed of Ag nanowires (NW) for spectroelectrochemical studies. Reductive-oxidation electrogenerated chemiluminescence (ECL) of Ru(bpy)3(2+) is generated at the Ag NW electrode in the presence of hydrogen peroxide and collected through the new transparent electrode. The ECL performance at the new nanostructured electrode is compared with several other electrodes, including bulk silver wire, glassy carbon disk, and thermally reduced transparent graphene oxide (tr-GO) electrodes. The Ag NW electrode is found to be the best electrode for the reductive-oxidation ECL generation because of its catalytic properties with respect to the reduction of hydrogen peroxide and its high surface area.

Effect of Pt-loaded carbon support nanostructure on oxygen reduction catalysis

This work demonstrates the impact of the nanostructure (pore size, wall thickness and wall crystallinity) of several carbon materials on their performance as oxygen reduction reaction (ORR) catalyst supports in PEM fuel cell applications. Two different mesoporous carbons [a surfactant-templated ordered mesoporous carbon (OMC) with 1.6 and 3.3 nm pores, and a silica colloid-imprinted carbon (CIC) with a 15 nm pore size], selected as being the most active in their class, were compared with microporous Vulcan Carbon. After loading with 20 and 40% Pt, both 3D transmission electron microscopy and electron tomography revealed that the Pt nanoparticles reside inside the majority of the pores of the OMC and CIC, but are located only on the outer surface of the VC particles. ORR performance studies on a rotating glassy carbon disc electrode in O 2-saturated 0.5 M H 2SO 4 showed that the Pt-loaded CIC outperforms both Pt-loaded OMC and VC. This is attributed to the higher electronic conductivity (due to the thicker and more crystalline walls, seen by both X-ray diffraction and thermogravimetric analysis) and facilitated mass transport in the larger pores of the CIC support.

Electrocatalysis at Co–poly(difluoropyrrole) electrodeposited on Vulcan carbon supports: demonstration of halogenated polypyrrole as an electrocatalytic material

Halogenated polypyrroles are rendered significantly more stable against oxidative degradation than native polypyrrole and the electron-withdrawing substituents also permit tuning of the electronic state of coordinated catalytic metal ions. Poly(difluoropyrrole), or poly(dfp), was deposited on high-surface-area Vulcan carbon (VC) via bulk electrolytic oxidation of the monomer 3,4-difluoropyrrole at VC slurried in (n-C4H9)4NClO4/acetonitrile; the carbon-supported polymer was subsequently metallated with cobalt(II) ions. As determined by thermal, micrographic, elemental, and chemical state analyses, the Co-poly(dfp)/VC composite is ∼7 wt% poly(dfp) with the polymer inhomogeneously deposited over the Vulcan carbon, and the incorporated Co(II) ions coordinated by nitrogen atoms in the pyrrole moieties. Films of Co-poly(dfp)/VC cast on glassy carbon disk electrodes are electrocatalytically active for the two-electron reduction of oxygen in 0.1 M aqueous perchloric acid as assessed by hydrodynamic voltammetry, thereby demonstrating the viability of halogenated polypyrroles as electrocatalytic materials.

Sensitive Determination of Bismuth in Iron and Steel by Stripping Voltammetry after Extraction of the Matrix

A highly sensitive method is described for the determination of bismuth by differential pulse anodic stripping voltammetry after preliminary separation of iron matrix. Most of the iron in an acidic sample solution was removed by the 4-methyl-2-pentanone (MIBK) extraction method, and MIBK dissolving in the aqueous phase was then removed by extracting three times with cyclohexane. Bismuth(III) remaining in the aqueous phase was electrodeposited on a rotating glassy carbon disk electrode at −0.6 V vs. Ag/AgCl for 600 s with stirring; the deposit was then anodically stripped at a scan rate of 50 mV s−1 to 0.2 V vs. Ag/AgCl. The calibration (peak height vs. Bi(III) concentration) graph was linear over the concentration range of 5 to 75 ng mL−1(correlation coefficient >0.999), with relative standard deviation of ca. 5% for 50 ng mL−1 (n=3). The interference from copper(II) weakened somewhat by adding 1,2-diaminopropane-N,N,N′,N′-tetraacetic acid. The minimum limit of determination of the proposed method was ca. 0.1 μg g−1, and bismuth at the μg g−1 level in iron and steel was determined with good precision and accuracy.

Electrochemical Behaviour of Poly(benzopyrene) Films Doped with Eriochrome Black T as a Pb2+-Sensitive Sensors

Poly(benzopyrene) films were electrosynthesized on glassy carbon disk electrodes from benzo(a)pyrene by cyclic voltammetry in the presence of eriochrome black T, which forms strong complexes with lead ions. In consequence, by conditioning the films in high concentration of lead (0.1 mol dm−3 Pb(NO3)2) potentiometric sensitivity to lead ions down to 10−5 mol dm−3 Pb2+ was induced, and a novel type of lead-sensitive electrode was obtained. The electrode is characterized by high stability of the potential readouts, good reproducibility of the calibration curves as well as a minor hysteresis effects. The performance of our lead-sensitive electrode was favourable compared to PEDOT and PPy-based electrodes doped with eriochrome black T. We conclude that poly(benzopyrene) doped with eriochrome black T is a new electroactive material that may be applied in sensor technology.

Chemical and electrochemical synthesis of crosslinked aniline sulfide resin

A strategy was used to control the crosslinking of polyaniline (PANi) to allow the synthesis of high-molecular-weight, conductive copolymers. Aniline sulfide resin (ASR) was synthesized by the reaction of aniline and sulfide dichloride. Crosslinked ASR (ASC) was prepared in the presence of ammonium peroxydisulfate and aniline in an aqueous solution as the oxidant and monomer, respectively. The graft copolymer was obtained by oxidizing aniline on ASR in the presence of an initiator and an excess amount of aniline, in which the aniline was oxidized to form PANi through a radical cation mechanism. By changing the ratio of ASR to aniline during the polymerization reaction, it was possible to control the number of crosslinked sites, the electrical conductivity, the molecular weight and the solubility. The structure was characterized by spectroscopic data. The method introduced here describes a strategy for controlling the molecular weight of PANi and in turn its physical properties. This approach may be extended to the synthesis and modification of other polymers. Electropolymerization was carried out by coating ASR on the surface of a glassy carbon disk electrode and then growing this on graft copolymer ASC in the presence of fresh aniline and an acidic solution. The electrical conductivity of ASC was studied by a four-point probe method and produced a conductivity of 8.5 × 10−3 S cm–1. Aniline sulfide resin (ASR) is synthesized by the reaction of aniline and sulfide dichloride. Crosslinked ASR (ASC) has been prepared in the presence of ammonium peroxydisulfate and aniline in aqueous solution as oxidant and monomer, respectively. By changing the ratio of ASR to aniline during the polymerization reaction, it is possible to control the number of crosslinked sites, electrical conductivity, molecular weight and solubility. Electropolymerization was carried out by coating ASR on the surface of glassy carbon disk electrode, and then grown on a graft copolymer ASC in the presence of fresh aniline and acidic solution. Electrical conductivity of ASC has been studied by four-point probe method and produced 8.5 × 10−3 S cm–1 conductivity for it.

Bismuth‐Coated Reticulated Vitreous Carbon and Bismuth‐Coated Glassy Carbon Electrodes for On‐Line Coupling of ASV with ICP‐MS

AbstractAnodic stripping voltammetry (ASV) has been combined on‐line with inductively coupled plasma‐mass spectrometry (ICP‐MS) using both Bi‐coated reticulated vitreous carbon (RVC) and Bi‐coated glassy carbon (GC) disk electrodes. Because the same flow cell is used for the RVC and GC disk electrodes, the analytical performances between these two types of Bi‐coated electrodes can be accurately compared for their utilizations in the ASV‐ICP‐MS technique. Comparison of the performances includes signal enhancement, reproducibility, dynamic range, and hydrodynamic stability of the Bi coating. The results indicate that the signal enhancement produced by the Bi‐coated RVC electrode (in the flow‐through configuration) is greater, while the hydrodynamic stability of the Bi‐coated GC disk electrode is better. Both types of electrodes were found to be highly effective in eliminating the matrix effects that are detrimental to ICP‐MS analysis. For the purpose of metal preconcentration, Bi has similar properties to Hg (e.g., high hydrogen overpotential and ability to accumulate a range of analytes). However, the Bi film is more robust than the Hg film in a flow system and, unlike Hg2+, Bi3+ in the solution does not cause the memory effect (i.e., it does not adhere onto glass nebulizer and spray chamber of ICP over a long period of time). The nontoxicity of bismuth also makes it an environmentally friendly alternative to mercury for coupling ASV on‐line with ICP‐based techniques.

Rational Design of Electrocatalytic Interfaces: The Multielectron Reduction of Nitrate in Aqueous Electrolytes

An electrode incorporating two distinct heterogeneous electrocatalysts acting in series was specifically designed to promote the reduction of nitrate beyond the nitrite stage in weakly buffered aqueous solutions (pH = 3) containing Cd2+. This novel interface consists of Au nanoparticles, Au(np), on which underpotentially deposited Cd reduces nitrate predominantly to nitrite, dispersed on a hemin-modified glassy carbon (GC) surface, Hm|GC, where nitrite is further reduced to yield hydroxylamine as the only product detected using a rotating Au(ring)|Hm|Au(np)|GC (disk) electrode. Additional evidence in support of this series mechanism was obtained from numerical simulations in which the bifunctional electrode was regarded as a hexagonal, closed-packed array of coplanar concentric Cd|Au(np) disks and Hm|GC rings (with no insulating gap), using rate constants determined independently from rotating Au and Hm|GC disk electrodes in solutions containing either nitrate or nitrite, respectively.

Evaluation of the Performance of Carbon Supported Pt–Ru–Ni–P as Anode Catalyst for Methanol Electrooxidation

AbstractThis research is aimed to improve the activity and stability of ternary alloy Pt–Ru–Ni/C catalyst. A novel anodic catalyst for direct methanol fuel cell (DMFC), carbon supported Pt–Ru–Ni–P nanoparticles, has been prepared by chemical reduction method by using NaH2PO2 as a reducing agent. One glassy carbon disc working electrode is used to test the catalytic performances of the homemade catalysts by cyclic voltammetric (CV), chronoamperometric (CA) and amperometric i–t measurements in a solution of 0.5 mol L–1 H2SO4 and 0.5 mol L–1 CH3OH. The compositions, particle sizes and morphology of home‐made catalysts are evaluated by means of energy dispersive analysis of X‐ray (EDAX), X‐ray diffraction (XRD) and transmission electron micrographs (TEM), respectively. TEM images show that Pt–Ru–Ni–P nanoparticles have an even size distribution with an average diameter of less than 2 nm. The results of CV, CA and i–t curves indicate that the Pt–Ru–Ni–P/C catalyst shows significantly higher activity and stability for methanol electrooxidation due to the presence of non‐metal phosphorus in comparison to Pt–Ru–Ni/C one. All experimental results indicate that the addition of non‐metallic phosphorus into the Pt–Ru–Ni/C catalyst has definite value of research and practical application for enhancing the performance of DMFC.

Zinc Electrodeposition from a Deep Eutectic System Containing Choline Chloride and Ethylene Glycol

Deep eutectic electrolytes have recently been considered as alternatives to classical room-temperature ionic liquids. This work is an initial study of the zinc deposition process from a basic choline chloride/ethylene glycol deep eutectic solvent containing at . The system was examined by cyclic voltammetry at static and rotating glassy carbon disk electrodes and by potential step techniques. There was little deposition initially on sweeping or stepping the potential to −0.5 to −0.8 V vs Zn/Zn(II), but more rapid deposition was observed when the potential was subsequently raised to −0.4 to −0.2 V. The role of choline chloride was also studied by comparing with a choline-free electrolyte, which exhibited a more conventional voltammetric response. The formation of a dissolved, intermediate species on the cathodic sweep was proposed to account for the observed deposition behavior in the deep eutectic. Furthermore, an observation of the electrodeposition behavior with the addition of sodium ethoxide supports the suggestion that is a complex of and deprotonated components of the solvent.

A Study of Zinc Electrodeposition From Zinc Chloride: Choline Chloride: Ethylene Glycol

This work is an initial study of the zinc deposition process from a Lewis-basic choline chloride/ ethylene glycol deep eutectic solvent containing ZnCl2 at 30{degree sign}C. The system was examined by cyclic voltammetry at static and rotating glassy carbon disc electrodes and by potential step techniques. Although there was little deposition initially on sweeping or stepping the potential to -0.5 to -0.8 V vs. Zn/Zn(II) more rapid deposition was observed when the potential was raised to -0.4 to -0.2 V. The role of choline chloride was also examined by comparison with a choline-free electrolyte, which exhibited a more conventional voltammetric response. A tentative suggestion has been proposed to account for the observed deposition behaviour.

Theoretical Analysis of the Limiting Diffusion Current at a 'Particulate Rotating Disk Electrode'

A model is presented to calculate the current at a 'particulate rotating disk electrode' (prde), that is a rotating disk electrode which active surface is comprised of particles supported on an inactive substrate. The analytical expressions are obtained for the current under diffusion limiting conditions, including two contributions, one from reaction on the front surface of the particles and the other from the edges of the particles. It is shown that this second contribution is the largest under most typical prde parameters. The expressions show a dependence with hydrodynamic parameters (ω, ν, DO) and with parameters describing interaction of electroactive species on non active areas and diffusion towards the edge of the particles. The model predicts for a prde a non linear dependence of i vs. ω0.5, as a difference with the linearity of continuous rde. However, linearity maintains for a Koutecky-Levich plot (1/i vs. 1/ω0.5). This plot type should be used with prde to determine kinetics parameters (n). Experimental results are shown with platinum particles electrodeposited on glassy carbon disk, that validate the main conclusions of the model.

Diffusion regimes at nanoelectrode ensembles in different ionic liquids

The electrochemical and diffusion behaviour of different redox probes in different ionic liquids is studied at gold nanoelectrode ensembles (NEEs) in comparison with millimetre sized gold (Au-macro) and glassy carbon (GC) disk electrodes. The redox probes are neutral ferrocene (Fc), the ferrocenylmethyltrimetylammonium cation (FA +) and the ferrocenylmonocarboxylate anion (FcCOO −). The ILs are the dicyanamide, [N(CN) 2] or bis(trifluoromethylsulfonyl)amide), [N(Tf) 2] salts of the following cations: 1-butyl-3-methylimidazolium, [BMIm], 1-butyl-3-methylpyrrolidonium, [BMPy], or tris(n-hexyl)tetradecylphosphonium [P 14,666]. These ILs are characterized by different viscosities, ranging from 32 to 277 cP. The cyclic voltammetric behaviour of the redox probes is reversible and diffusion controlled at GC electrodes. Diffusion coefficients ( D) calculated by the Randles–Sevcik equation scales inversely with the IL viscosity, ranging from 2 × 10 −8 to 3 × 10 −7 cm 2 s −1. Ionic solutes, namely FA + and FcCOO −, present slightly lower D values than neutral Fc. At the Au-macro the electrochemical behaviour of the redox probes is diffusion controlled in the ILs containing the [N(Tf) 2] anion, while it involves relevant adsorption processes in the [N(CN) 2] containing electrolyte. For this reason the diffusion at gold NEEs is studied only in the former ILs. The CVs of the redox probes at the NEEs are peak shaped at low scan rate ( v ), while they are sigmoidally shaped at high v , but with some shift between forward and backward patterns. This is indicative of the occurrence of a total overlap (TO) diffusion condition when v is low which becomes a mixed diffusion layers (MDL) regime, with only a partial overlapping of individual diffusion layers, at high v values. In the most viscous IL, namely [P 14,666] [N(Tf) 2], at v higher than 0.8 V s −1, a plateau current independent on the scan rate is achieved, indicating the tendency to reach the pure radial regime in this IL. The v values at which the transition between TO and MDL is observed scales directly with D and inversely with the IL viscosity. This behaviour is interpreted on the basis of the dependence of individual diffusion layers at each nanoelectrode on redox probe/IL interaction which fits with existing theoretical models very recently developed for nanoelectrode arrays.

Oxygen Reduction on Supported Iridium Oxide Films in Neutral Phosphate Buffer: Implications for Neural Stimulation

Certain aspects of oxygen reduction on (hydrous) iridium oxide (IrO x ) films deposited galvanostatically on smooth Au and glassy carbon (GC) electrodes have been examined in aqueous O 2 -saturated neutral phosphate buffer (pH 7) solutions. Regardless of the nature of the substrate, the onset potential for O 2 reduction, E O2 onset , as determined by cyclic voltammetry, was ca. ―0.1 V vs saturated calomel electrode, which is very close to the corresponding E O2 onset found for both bare Au and GC electrodes. On this basis, the potential range in which the charge stored in the film is available for functional neural stimulation without generation of potentially harmful oxygen-derived species is on the order of 0.9 V. Studies involving a rotating Pt ring GC disk revealed that the reduction of dioxygen on IrO x |GC yields predominantly hydrogen peroxide. Further measurements performed with a rotating GC disk showed that IrO x | GC can oxidize hydrogen peroxide in the potential region associated with the more positive IrO x redox peak, a factor that might mitigate, at least in part, problems associated with the charge imbalance during the bipolar neural stimulation.

Metal–Air Electrochemical Cells: Silver–Polymer–Carbon Composite Air Electrodes

Reported herein is the study of the preparation, characterization, and electrochemical activity of a silver-polymer-carbon composite electrode in a nonaqueous cell. An enhanced oxygen reduction activity for the composite electrode in a nonaqueous, aprotic solvent is demonstrated, relative to uncoated glassy carbon or silver disk electrodes. The improvement of oxygen reduction activity increases the current capability and power output of the air electrode, facilitating future development of small, lightweight, long-life power sources.