Smooth Glassy Carbon Research Articles

Effect of Electrolyte Contaminants and Surface Roughness on the Constant Phase Element

The origin of constant phase element (CPE) to explain electrode/electrolyte interface is subject of debate in the literature. CPE behavior is generally attributed to the presence of reactivity, surface inhomogeneity, various crystal planes and atomic scale defects in the crystal; all these may lead to dispersion of local capacitance at the electrode/electrolyte interface. Therefore, electrode/electrolyte interface of polycrystalline Pt (Pt-PC) and smooth glassy carbon disk electrode (GCE) are investigated in ultra-pure H2SO4 (0.5 M) electrolyte[1]. The surface of GCE is roughened mechanically to test the effect of roughness. The effect of intentional and unintentional contaminants are investigated using halide (Cl˗, Br-, I-) ions[2]. It is found that the CPE is affected by the concentration and nature of anion in the electrolyte. Unintentional impurities and cations do not affect the CPE behavior.[1] Singh, R. K., Devivaraprasad, R., Kar, T., Chakraborty, A., & Neergat, M. (2015). Electrochemical impedance spectroscopy of oxygen reduction reaction (ORR) in a rotating disk electrode configuration: effect of ionomer content and carbon-support. Journal of The Electrochemical Society, 162(6), F489.[2] Devivaraprasad, R., Ramesh, R., Naresh, N., Kar, T., Singh, R. K., & Neergat, M. (2014). Oxygen reduction reaction and peroxide generation on shape-controlled and polycrystalline platinum nanoparticles in acidic and alkaline electrolytes. Langmuir, 30(29), 8995-9006. Figure 1

Comparison of Pt and IrO2-Ta2O5/Ti as a counter electrode in acidic media

Platinum has been widely employed as a counter electrode (CE) for various electrochemical measurements; however, the potential dissolution of Pt from the CE during electrochemical processes may skew the results of electrochemical studies, particularly for cathodic reactions (e.g., hydrogen evolution, oxygen reduction, and CO2 reduction). For this study, we compared the electrochemical behaviors of Pt and IrO2-Ta2O5/Ti electrodes as CEs in 0.5 M H2SO4. To study the effects of various surface areas, a smooth glassy carbon electrode with a small geometric surface area (GSA) of 0.07 cm2 (GCE-s), a smooth medium GCE with a GSA of 0.38 cm2 (GCE-m), and carbon cloth (CC) with a large GSA of 2.00 cm2 were employed as working electrodes (WEs). When Pt was used as the CE, the current of the GCE-s was slowly enhanced after 1000 cycles, while a notable current increase at the GCE-m was seen after 800 cycles. For the CC electrode, a prominent increase in the current was observed after 400 cycles. The increased HER activity was initiated through the deposition of Pt dissolved from the CE during cyclic voltammetric cycles in the potential range between −0.40 and 0.0 V vs. Ag/AgCl. In contrast, no notable current increase was observed for any of the GCE-s, GCE-m, and CC electrodes during 2000 cycles when the IrO2-Ta2O5/Ti electrode was employed as the CE.

Effect of Electrolyte Contaminants and Surface Roughness on the Constant Phase Element

The origin of constant phase element (CPE) to explain electrode/electrolyte interface is subject of debate in the literature. CPE behavior is generally attributed to the presence of reactivity, surface inhomogeneity, various crystal planes and atomic scale defects in the crystal; all these may lead to dispersion of local capacitance at the electrode/electrolyte interface. Therefore, electrode/electrolyte interface of polycrystalline Pt (Pt-PC) and smooth glassy carbon disk electrode (GCE) are investigated in ultra-pure H2SO4 (0.5 M) electrolyte. The surface of GCE is roughened mechanically to test the effect of roughness. The effect of intentional and unintentional contaminants are investigated using halide (Cl˗, Br-, I-) ions. It is found that the CPE is affected by the concentration and nature of anion in the electrolyte. Unintentional impurities and cations do not affect the CPE behavior. Figure 1

Structural and Physical Parameters Controlling the Oxygen Reduction Reaction Selectivity with Carboxylic Acid-Substituted Cobalt Corroles Incorporated in a Porous Carbon Support

Three cobalt(III) complexes of regioisomeric trans-A2B-corroles were designed and efficiently synthesized. The corroles were adsorbed on smooth glassy carbon (GC) and black pearls 2000 (BP2000), hi...

Experimental Validation of the Transmission Line Model Via Impedance Spectroscopy of an Ordered Array on Porous Carbon Electrode

In this paper, the interface of a porous substrate with an arranged and well-defined geometry is investigated for the impedance response with different electrolytes by using the well known electrochemical technique of Electrochemical Impedance Spectroscopy (EIS). Based on De Levie's Transmission Line Model (TLM) for porous electrodes a modification has been done in the model by incorporating the CPE behavior to reflect the non-ideal behaviour for real electrodes at low frequencies. The geometry used to validate the proposed model was fabricated from a smooth Glassy carbon electrode (GCE) surface to correlate the EIS response to that obtained by the model. The desired array was obtained by using laser micromachining tool on a glassy carbon substrate with a goal to study the influence of different electrolytes, varying electrolyte concentrations, the morphological features of pore- depth and radii of pore as well as different pore shapes. The outcomes of the experiments carried out on the in-house setup are compared with the MATLAB simulated results of the impedance. The transition from resistive to capacitive behavior is found to be shifted to lower frequency side and TLM behavior at high frequencies is more apparent as the concentration is increased. For the same concentration, different electrolytes are found to behave differently due to varying conductivity and ion sizes. In all the experiments carried out the impedance response showed CPE (constant phase element) behavior at the low frequency end while for high frequencies the nature/appearance of TLM behavior is found to be dependent on the pore depth to radius ratio. In addition the concept of time constant is also dealt with which exhibits differences for different geometries of the pores on glassy carbon. The results suggest that the GC electrode engaged here could provide a tractable model for studying electrochemical impedance behavior of porous electrodes without using any surface area analysis or pore volume analysis technique. Keywords: Transmission Line Model, Glassy carbon, EIS, MATLAB

Fabrication of a Ga3+ sensor probe based on methoxybenzylidenebenzenesulfonohydrazide (MBBSH) by an electrochemical approach

A thin-layer of (E)-N′-methoxybenzylidenebenzenesulfonohydrazide (MBBSH) was fabricated by the deposition of MBBSH onto a smooth glassy carbon electrode with nafion binder for the sensitive and selective Ga3+ sensor probe.

Doping of cathodically polarized glassy carbon by natural graphite. A simple procedure for overlaying different carbons with electrochemically modifiable graphene layers

The reduction of graphite (at ca. −2V vs. Ag/AgCl, in DMF containing tetraalkylammonium salts) deposited onto smooth glassy carbon leads to intense graphite exfoliation that can be monitored through voltammetric scans or by fixed-potential electrolyses (E<−1.8V). These simple and extremely efficient processes result in very stable modified carbon surfaces exhibiting simple and astonishingly reproducible voltammetric responses (both in nature and intensity). The reduction peaks assigned to the cathodic doping of deposited graphene layers are found to be proportional to the scan rate. The modification of these graphene-like surface structures in two types or reactions: with a series of organic electrophiles (in the reaction with doped graphene that acts as a poly-nucleophile) or with in situ generated benzyl-type radicals was successfully achieved and compared with the results obtained on smooth carbon surfaces. Striking examples with additions of hexylferrocene, benzylic derivatives of anthraquinone, anthracene and perylene, and of para-substituted benzyls (R=NO2, I, Br, F) certainly underline the interest for these new materials.

Electrochemical exfoliation in real time of natural graphite deposited onto glassy carbon. Doping and modifying carbons through ultra-thin graphite layers

Natural graphite, deposited onto smooth glassy carbon, when reduced (around −2V vs. Ag/AgCl) in the presence of tetraalkylammonium salts (TAAX) in aprotic polar solvents, leads to spectacular exfoliation processes followed in real time in the course of voltammetric scans. The method permits to get extraordinary stable modified carbon surfaces, with quite simple voltammetric responses (1 to 4 reversible cathodic steps) that strongly depend on the nature of the cations used. Those cathodic steps exhibit currents quasi perfectly proportional to the scan rate. It is expected the formation of a graphene-like substrate. Surface modifications both by ferrocene and anthraquinone could underline the originality of those new materials.

Electrooxidation of NaBH4 in Alkaline Medium on Well-defined Pt Nanoparticles Deposited onto Flat Glassy Carbon Substrate: Evaluation of the Effects of Pt Nanoparticle Size, Inter-Particle Distance, and Loading

Well-defined Pt nanoparticles deposited at smooth glassy-carbon (GC) surfaces were elaborated and thoroughly characterized. Using such model Pt/GC surfaces enabled demonstrating that the borohydride oxidation reaction (BOR) is subjected to nanoparticle size and ensemble effects: larger particle diameter and shorter inter-particle distance yield faster BOR kinetics and larger faradaic efficiency. As previously noted for smooth Pt (and Au) surfaces, the Pt/GC nanoparticles are self-poisoned in the course of the BOR; surprisingly, such poisoning also proceeds in open-circuit conditions. The adsorbed intermediates formed in the course of the step-wise electrooxidation and heterogeneous hydrolysis processes are most likely yielding the Pt surface blocking below E = 0.6 V vs. Reversible Hydrogen Electrode (RHE). This blocking is, however, reversible, since incursions to potentials E > 0.6 V vs. RHE enable cleaning the Pt surface. Finally, comparing smooth Pt/GC surfaces to volumic active layers composed of Pt/carbon black (CB) demonstrates that the intrinsic activity/faradaic efficiency of the Pt nanoparticles may strongly be biased by mass-transport effects within the active layer. Larger (apparent) faradaic efficiency and lower BOR onset potential are observed for thick active layers, whereas the specific activity in these is artificially lowered following effectiveness factor well below unity in that case. As a result, the determination of the intrinsic activity of an electrocatalytic material should only be done with tremendous care and with a perfect control of the electrode/surface morphology, texture and structure.

Enolization versus carbonylation at glassy carbon surface through cathodic means

The cathodic reduction of ω-bromomethylarylketones in aprotic organic solvents (such as propylene carbonate) containing tetraalkylammonium iodides achieved at smooth glassy carbon (GC) permits through a selective one-electron reduction, the scission of the CBr bond. Quite unexpectedly, the free radical thus formed is prior attached to the carbon surface in its enolic form (GCO(Ar)CCH2). Successive radical addition processes may lead to a redox polymer based on the one-electron oxidation of enol ethers. The average superficial enol concentration at the carbon surface (found to be about 2.5×10−8molcm−2) was assessed by the halogen index (iodine or bromine) via halogen addition to the double bonds followed by the micro-coulometric reduction of the resulting vicinal di-halo compounds.

An accurate evaluation for the activity of nano-sized electrocatalysts by a thin-film rotating disk electrode: Oxygen reduction on Pt/C

Up to now, it remains to be a challenge to accurately and reproducibly evaluate the oxygen reduction reaction (ORR) activity by a thin-film rotating disk electrode (TF-RDE) and results in literatures often disagree. In this work, we developed an “intermittently microcontact-coating fine-droplets” method of preparing homogeneous thin-film to guarantee the accuracy of electro-catalytic activity evaluation by a TF-RDE, in which the measured electrode current is controlled by both the diffusion of the reactant from the electrolyte bulk to the surface of the electro-catalyst and the kinetic process on the surface of the electro-catalyst. By precisely controlling the distribution and varying the loading of nano-sized Pt/C particles on a smooth glassy carbon substrate with an in-house-developed automated electrode-preparation device, we investigated the effect of the distribution of the particles on the accuracy of compensating for diffusion limitations of ORR in an aqueous acid solution. As a reference, a smooth Pt bulk disk electrode was evaluated under the same environment to clarify the effect of the within-thin-film diffusion, which may occur in the TF-RDE. The results show that, the accuracy of correction for diffusion limitations cannot be guaranteed by only a linear relation of 1/I versus (rotation rate)−1/2 in Koutecky–Levich plot and significantly depends on the distribution of the particles on the substrate. Some criteria for judging the accuracy of the compensation and optimization of the thin-film structure have been systematically discussed.

고품질 유리질 카본 코팅을 위한 페놀 수지의 고압 경화

Successful coating of high quality glassy carbon is introduced by applying high pressure during the curing process of dip-coated phenol resin on graphite. The dependence of the applied pressure on the quality of the glassy carbon layer has not been reported so far. Pressure was changed from 0 to 400 psi during curing at 200℃. After carbonized at 1100℃ in inert atmosphere for the 400 psicured sample, as a promising result, a thick (~ 3 ㎜) and smooth glassy carbon layer could be obtained without any breakage, and the yield of carbonization was remarkably increased. It is believed that the cross-linking of resins results in decreasing volatile contents and, thus, increasing the yield of the glassy carbon. The origin of the improvement is discussed on the basis of several analytical results including FE-SEM, FT-IT and Raman spectrum.

Columnar support structures for oxygen reduction electrocatalysts prepared by glancing angle deposition

Abstract Columnar titanium structures were fabricated on smooth glassy carbon (GC) disks using the glancing angle deposition (GLAD) physical vapour deposition technique. This catalyst support consists of 500 nm long posts with a nominal cross-sectional diameter of 100 nm. They have a number density of about 10 billion per cm2 which increases the effective surface area of the GC disks by a factor of 13. Platinum films ranging from 10 to 90 nm in thickness (planar equivalent) were deposited onto these posts by magnetron sputtering. The oxygen reduction activity and H2O2 release of these electrocatalysts were measured by the rotating ring-disk electrode method in O2-saturated 0.1 M HClO4 at room temperature. The electrochemical surface area of the catalysts, obtained from Hupd cyclic voltammograms, is about 10–15 times higher than smooth Pt films. The supports can be fabricated from most vacuum-compatible materials and should be stable over a wide range of processing, annealing, and operating conditions.

Electrodeposition of copper: the nucleation mechanisms

The nucleation mechanisms of copper during electrodeposition of thin films from sulfate solutions were studied by utilizing the electrochemical techniques (cyclic voltammetry and chronoamperometry) and atomic force microscopy (AFM). Near atomically smooth glassy carbon was used as the deposition substrate (electrode). The copper nucleation mechanisms were examined as a function of solution pH, copper concentration, deposition potential, temperature, and background electrolyte. It was found that with pH and copper concentration increase, the nuclei size increased, while the nuclei population density decreased. An increase of deposition potential produced smaller nuclei and higher nuclei population density. Temperature affected the morphology of deposited copper. The presence of background electrolyte also influenced the morphology and population density of copper nuclei. The nucleation mechanisms were examined by fitting the experimental data (chronoamperometry) into the Scharifker–Hills nucleation models. It was found that at pH 1, in the absence of background electrolyte, copper nucleation was instantaneous. At pH 2 and 3, the mechanism was inconclusive. In the presence of background electrolyte, the mechanism at pH 1 and 2 was mixed, while at pH 3, the mechanism was progressive nucleation.

Long-term in vivo experience of an electrochemical sensor using the potential step technique for measurement of mixed venous oxygen pressure

An implantable amperometric blood oxygen sensor was developed to improve rate adaptation of heart pacemakers. Two different working electrode materials in direct contact with the blood were tested, smooth glassy carbon and gold. Reference electrodes of Ag/AgCl and porous pyrolytic carbon were evaluated. A counter electrode being the titanium housing of the pulse generator was partly coated with carbon. An implantable pacemaker system with chronocoulometric oxygen detection was developed. Heart synchronous potential steps were periodically applied to the 7.5 mm 2 working electrode in the atrium. Both single and double potential step techniques were evaluated. The oxygen diffusion limited current was used to calculate the stimulation rate. Bench tests and studies on 31 animals were performed to evaluate long-term stability and biocompatibility. In five dogs, the AV node was destroyed by RF ablation to create a realistic animal model of a pacemaker patient. Sensor stability and response to exercise was followed up to a maximum implantation time of 4 years. Post-mortem examinations of the electrode surfaces and tissue response were performed. The results show that a gold electrode is more stable than glassy carbon. The Ag/AgCl reference was found not to be biocompatible, but activated carbon was stable enough for use as reference for the potentiostat. Double potential steps stabilize the sensor response in comparison to single steps. Blood protein adsorption on the gold surface decreased the oxygen transport but not the reaction efficacy. No adverse tissue reactions were observed.

Differential Capacitance Measurements in Solvent‐Free Ionic Liquids at Hg and C Interfaces

Series‐stacked, double‐layer carbon capacitors are slated to be used in electric vehicles for power management as well as in consumer electronics for memory backup and burst power. Nonaqueous electrolytes are preferred over aqueous electrolytes, since a wider voltage window can be accessed in the former electrolytes, thereby requiring fewer cells in the series stack. However, it has historically been difficult to assess whether the organic solvent and/or the supporting electrolyte determine the anodic limit. We have eliminated this ambiguity by using solvent‐free ionic liquids where the source of anodic oxidation may be ascribed to the anion alone. Even though the new ionic liquids manifested high oxidation limits, we found that when used in practical capacitors comprising high‐surface‐area carbon cloth electrodes, a much lower capacitance (compared to smooth electrodes) was achieved. To understand whether the observed decrease in capacitance might be due to the microporosity of the carbon cloth electrode or to practical limitation of the device itself, we first measured the differential capacitance (Cdl) at a Hg/1‐ethyl‐3‐methyl imidazolium imide. The integral capacitance at the Hg interface was then calculated and compared with that of a smooth glassy carbon electrode, a carbon yarn, and a cloth electrode. In addition, the effect of , and on Cdl were interpreted based on existing theories of double‐layer structure.

A new principle for an electrochemical oxygen sensor

An electrochemical oxygen sensor using a smooth glassy carbon electrode for continuous monitoring of oxygen has been developed, which can find a wide range of application. Two different potential levels of preset durations are imposed on the sensing electrode in a cyclic manner. The current flow due to O 2 reduction at a negative potential is integrated after a time lag. The charge is proportional to the oxygen concentration. The electrode is then held at a positive potential for a longer period before repeating the cycle. Thus, oxygen is consumed only during the short pulse duration. This sensor principle is unique, since the sensing electrode operates without a covering membrane. This is possible because of the low electrocatalytic activity of glassy carbon. The response is immediate and reproducible even at a low consumption of oxygen. The long-term response is stable over 60 h and sensitive to a change of about 0.5 hPa partial pressure of oxygen in saline solution. Measurements with the sensor in bovine serum demonstrated the negligible influence of other substances on the response to oxygen. The sensor has been tested in animal experiments, and shows a good response in blood as well as in tissue.

Influence of macrocyclic compounds on the electrochemical reduction of thionyl chloride at glassy carbon cathodes

The specific features of electrochemical reduction of thionyl chloride were studied on a smooth glassy carbon electrode in the presence of tetraphenylporphyrins (TPP) or tetra( p-methoxyphenyl)porphyrins (TMPP) of copper, manganese, iron, nickel, cobalt and also of metal-free TPP and TMPP. In the presence of metal-free porphyrin and its metallo complexes the potential of the maximum on voltammograms shifts markedly in the positive direction. Introduction into the solution of FeTPP, CoTPP and NiTPP leads to an increase of the maximum current on cyclic voltammograms. The amount of electricity necessary for electrode passivation also changes thereby. This indicates that the role of porphyrins in the SOCl 2 electroreduction is due both to electrocatalytic action and to changing the electrode passivation conditions. With the use of a combination of spectroscopic methods (electron absorption and ESR spectra) it has been found that thionyl chloride interacts chemically with the porphyrins. These chemical interaction products act as catalysts of SOCl 2 electroreduction.

The electrochemical reduction of manganese dioxide in acidic solutions: Part III. voltammetric peak 3

Linear sweep voltammetry in 0.0125–1.25 M H 2SO 4 on thin MnO 2 films electrodeposited onto a smooth glassy carbon (GC) substarte reveals two cathodic current peaks. The first peak, peak 1, is terminated by loss of electrical conductivity of the deposit which remains essentially as γ-MnO 2. Peak 2 occurs ≈1000 mV negative to peak 1 on a GC substrate. In 3.75–7.5 M H 2SO 4 a further peak, peak 3, previously unreported in acidic solutions is observed on GC between peaks 1 and 2. Peak 3 arises according to the following cyclic scheme: 1/2MnO 2 + 1/2Mn 2++2H +Mn 3++H 2O Mn 3++ eMn 2+ The reaction is instigated by the presence of small amounts of Mn 2+ generated previously during peak 1. The charge-transfer reaction proceeds on the GC substrate and not the MnO 2 deposit as the latter has a very low electrical conductivity after peak 1. Some thermodynamic measurements on H 2SO 4 solutions are appended to supplement the general literature.