Supporting Electrolyte Concentration Research Articles

Role of Nanomorphology and Interfacial Structure of Platinum Nanoparticles in Catalyzing the Hydrogen Oxidation Reaction

This work studies the hydrogen oxidation reaction using both single mesoporous platinum nanoparticles (rnp = 23.1 ± 2.1 nm) and low density random arrays of material. The activity of the platinum catalyst, toward the oxidation of hydrogen, is shown to be potential dependent and exhibits two peaks in activity. These peaks in activity are measured at both random arrays of platinum nanoparticles and at the single entity scale. This alteration in the particle activity is directly reflected in the variation of the electrochemical current. These peaks in current do not relate to a mass-transport limitation of the reaction, and at high overpotentials the oxidation reaction becomes fully inhibited. This potential dependency is revealed at high current densities and arises due to the sensitivity of the reaction rate to the platinum interfacial structure; the decrease in activity [at ca. −0.2 V vs Ag/AgCl (1 M KCl) in a nonbuffered condition] directly correlates with the potential at which underpotential deposited hydrogen is removed from the catalytic interface. The contribution of the internal mesoporous nanoparticle structure toward the total particle catalytic activity is further evidenced through comparison of the time-current transients recorded for individual nanoparticles of differing morphology (solid vs mesoporous) and by evidencing the sensitivity of the single particle catalytic activity to the used supporting electrolyte concentration.

No-Carrier-Added Electrochemical Radio-Fluorination of Thioethers

Positron emission tomography (PET) is a powerful molecular imaging method for biomedical research such as cancer research, visualizing enzyme activity and receptor occupancy.1–3 Fluorine-18 is the most frequently used PET-radionuclide in both preclinical research and clinical applications due to its ideal half-life (t1/2 = 109.8 min, 97% β + decay), low positron energy and the possibility to obtain the radioisotope in high activities and in high no-carrier-added specific activities. One drawback is the late stage fluorination of molecules that possess a high electron density, which presents a challenge due to the disadvantaged interaction between a negatively charged fluoride and an electron rich reaction center. Electrochemical 18F-fluorination of organic compounds provides a means to synthesize Positron-Emission-Tomography (PET) tracers difficult to obtain otherwise.4–7 Electrochemical oxidation can create an electron-poor carbon, preparing the organic molecules for nucleophilic fluorination. However, previously reports on electrochemical fluorination of the organic molecules have used a high concentration of fluoride which is not desired for radio-fluorination. A high concentration of fluoride introduces carrier [19F] to the minute concentrations of [18F]-labeled radiotracers, reducing molar activity and their imaging efficacy.4,6,7 In our previous study, where acetonitrile was used as solvent, we showed that decreasing concentration of [19F] resulted in a drastic drop in the fluorination yield, rendering no-carrier-added radio-fluorination impossible with this approach.8 In this study, for the first time, we demonstrate no-carrier-added electrochemical radio-fluorination of organic molecules with a thioether moiety such as (phenylthio)acetonitrile, diethyl phenylthiomethylphosphonate, 2-(phenylthio)acetamide, methyl 2-(ethylsulfanyl)acetate, methyl (methylthio)acetate and methyl (phenylthiol)acetate, using 2,2,2-trifluoroethanol (TFE) as solvent instead of acetonitrile. Figure 1 shows the proposed fluoro-Pummerer type mechanism of no-carrier-added electrochemical radio-fluorination of thioethers where AuxO- is the conjugate base of TFE. A scope study with several thioether compounds was performed and radiochemical fluorination efficiency (RCFE) of up to 95 %, was obtained for methyl 2-(ethylsulfanyl)acetate and methyl (methylthio)acetate. Electrochemical radio-fluorinations were performed using an undivided cell and applying constant potential. Synthesis parameters such as oxidation potential, temperature, type of the solvent, supporting electrolyte concentration and precursor concentration were optimized. It was found that increasing temperature can enhance the RCFE. The products were characterized using gas chromatography–mass spectrometry (GC-MS), nuclear magnetic resonance (NMR), radio-thin-layer chromatography (radio-TLC) and high-performance liquid chromatography (HPLC). Figure 1. Proposed mechanism of the no-carrier-added electrochemical 18F-fluorination of thioethers (AuxOH = auxiliary reagent). References Stenhagen, I. S. R. et al. [18F]fluorination of an arylboronic ester using [18F]selectfluor bis(triflate): application to 6-[18F]fluoro-L-DOPA. Chem. Commun. Camb. Engl. 49, 1386–1388 (2013).Phelps, M. E. Positron emission tomography provides molecular imaging of biological processes. Proc. Natl. Acad. Sci. U. S. A. 97, 9226–9233 (2000). Clinical PET and PET/CT | H. Jadvar | Springer.Waldmann, C. M., Lebedev, A., Allison, N. & Sadeghi, S. An automated synthesizer for electrochemical (18)F-fluorination of organic compounds. Appl. Radiat. Isot. Data Instrum. Methods Use Agric. Ind. Med. 127, 245–252 (2017).Sawamura, T., Takahashi, K., Inagi, S. & Fuchigami, T. Electrochemical Fluorination Using Alkali-Metal Fluorides. Angew. Chem. Int. Ed. 51, 4413–4416 (2012).Yin, B., Inagi, S. & Fuchigami, T. Highly selective electrochemical fluorination of dithioacetal derivatives bearing electron-withdrawing substituents at the position α to the sulfur atom using poly(HF) salts. Beilstein J. Org. Chem. 11, 85–91 (2015).Fuchigami, T. & Inagi, S. Selective electrochemical fluorination of organic molecules and macromolecules in ionic liquids. Chem. Commun. 47, 10211–10223 (2011).Balandeh, M. et al. Electrochemical Fluorination and Radiofluorination of Methyl(phenylthio)acetate Using Tetrabutylammonium Fluoride (TBAF). J. Electrochem. Soc. 164, G99–G103 (2017). Figure 1

Application of the Cation Pool Method for Fluorination and No-Carrier-Added Radio-Fluorination

In 1999 Yoshida and co-workers developed the cation pool method which stabilized carbamate cationic intermediates generated during a two electron oxidation followed by deprotonation that takes place in the anodic compartment of a two compartment cell under low temperatures.1 The method allows for rapid reactions with nucleophiles that may be unstable during electrolysis and can be added to the reaction mixture at the end of electrolysis to form the final product. Here, we report on the extension of the cation pool method for the application of electrochemical fluorination and radio-fluorination of methyl (phenylthio)acetate. Electrochemical fluorination and no-carrier-added radio-fluorination were successfully achieved using the cation pool method . Figure 1 shows the schematic of no-carrier-added electrochemical radio-fluorination of methyl (phenylthio)acetate using cation pool method. The cation pool method has tremendous potential for radiofluorination experiments. The excess concentration of cations may provide an efficient reaction mechanism for late-stage fluorination under low fluoride concentrations encountered in radiochemistry. Furthermore, radiochemical yield, which is reduced by decay of the radioisotope, can benefit from a rapid late-stage fluorination reaction. The cation pool can be prepared prior to cyclotron production of 18F isotope, thereby, providing a rapid late-stage fluorination reaction, maximizing radiochemical yield by minimizing decay through a rapid reaction of the previously prepared cations with 18F-fluoride. Synthesis parameters such as temperature, supporting electrolyte concentration and type, and precursor concentration were studied and optimized. The fluorination and radiofluorination yields of 12% and 6.7% were obtained, respectively, using the optimum conditions. The products were characterized using gas chromatography–mass spectrometry (GC-MS), nuclear magnetic resonance (NMR), radio-thin-layer chromatography (radio-TLC) and high-performance liquid chromatography (HPLC). This method can also be applied for a late-stage no-carrier-added radiofluorination to develop new positron emission tomography (PET) tracers. Figure 1. Schematic of no-carrier-added electrochemical 18F-fluorination of methyl (phenylthio)acetate using cation pool method. References Yoshida, J. et al. Direct Oxidative Carbon−Carbon Bond Formation Using the “Cation Pool” Method. 1. Generation of Iminium Cation Pools and Their Reaction with Carbon Nucleophiles. J. Am. Chem. Soc. 121, 9546–9549 (1999). Figure 1

Electrocatalytic Reduction of Carbon Dioxide on Nanosized Fluorine Doped Tin Oxide in the Solution of Extremely Low Supporting Electrolyte Concentration: Low Reduction Potentials

Fluorine doped tin oxide (FTO) has been prepared via the direct chemical reaction of tin oxide powders and hydrofluoric acid at room temperature. The image of FTO displays a sphere-like structure with an average diameter of 40–100 nm. The spectra of X-ray photoelectron spectroscopy (XPS) demonstrate that fluorine is doped into SnO2. A well-defined reduction peak at −0.50 V (vs SCE) is detected on the cyclic voltammogram (CV) of the nanosized FTO (n-FTO) electrode in CO2-saturated 3.6 × 10–4 μM H2SO4 solution of pH 5.5, which is strong evidence for the electrochemical reduction of CO2. This result indicates that the n-FTO electrode in such an extremely low supporting electrolyte concentration exhibits good electrocatalytic ability toward CO2 reduction under lower potentials. On the basis of reduction peak current as a function of scan rate, the reduction of CO2 is first performed via adsorption of CO2 on the n-FTO electrode surface, and then CO2 is reduced. The product solution obtained under a constant po...

Silver Hexacyanoferrate (III) on a Hybrid Graphene Oxide/PAMAM Dendrimer Surface and Application as an Electrocatalyst in the Detection of Isoniazid

AbstractThe polyamidoamine dendrimer PAMAM was covalently bound to graphene oxide via amide formation between any peripheral amine group dendrimer and the carboxyl groups present in graphene oxide. This material (GOP) was characterized by different spectroscopic techniques, namely Raman Spectroscopy, X‐Ray Photoelectron Spectroscopy (XPS), Fourier Transform Infrared Spectroscopy (FT‐IR) and X‐Ray Diffraction (XRD). The hybrid material was shown to adsorb silver, that in turn complexes with hexacyanoferrate (III) ions (GOPAgH). The complexed hybrid material was electrochemically investigated using cyclic voltammetry. Some electroanalytical parameters, such as different supporting electrolytes, the supporting electrolyte concentrations, hydrogen ion concentration effects and scan rate were evaluated in order to obtain optimum responses. The GOPAgH material was successfully tested in the electrocatalytic detection of Isoniazid using a graphite paste electrode with Limits of Detection and Quantification of 5.0×10−6 mol L−1 and 1.7×10−5 mol L−1, respectively.

Physicochemical characterization of a polymeric conductor: application to defluoridation of industrial effluent by electrodialysis

In many places around the world, the uoride concentration in ground water as raw water is higher than the threshold standard for healthy drinking water. The aim of this work is to study the characteristics of an anionic membrane that will be the subject of an application for de uoridation by electrodialysis. The first objective of this work is to evaluate the physicochemical characteristics of the membrane used in experiments by determination of the exchange capacity, water uptake, ionic conductivity, and transport number (Hittorf method). The second part consists of studying the effect of different parameters such as electrodialysis time, supporting electrolyte concentration, coexisting ions (such as $SO^{2-}_4$, $NO^-_3$ and $Cl^-$) , current density, and the pH of the solution to evaluate the effectiveness of the electrodialysis de uoridation process. The high percentage of de uoridation obtained after treatment of industrial effluent (80.3%) re ects the good efficiency of the electrodialysis process.

An investigation of operating conditions on anodic oxidation of synthetic sulfide-containing wastewaters at the surface of a platinum electrode using cyclic voltammetry

In this paper, cyclic voltammetry (CV) was used to study the effects of operating parameters (i.e., sulfide concentration, sodium chloride concentration as supporting electrolyte, temperature, mixing speed, and potential scan rate) on the anodic oxidation of synthetic sulfide-containing wastewaters at the surface of a platinum electrode. The results revealed that anodic oxidation could be used to eliminate sulfide from wastewaters in a wide concentration range, and the oxidation current was an ascending function of the sulfide concentration. The supporting electrolyte concentration had a negligible effect, as the sulfide dissociated in the aqueous media and brought electrical conductivity to the solution. The optimum concentration of electrolyte was found to be 0.05 mol/L. Increasing temperature improved the kinetics of the oxidation reactions and enhanced the electrical conductivity of the solution, which resulted in increasing the anodic oxidation rate. However, at higher temperatures, undesired side reactions were activated which resulted in lowering the power efficiency of the desired anodic oxidation reactions. The optimum operating temperature was found to be 40 – 60 °C. The mixing speed had a periodic effect on the sulfide oxidation. It decreased the diffusion resistance and also the residence time of sulfide at the electrode surface. These phenomena affected the anodic oxidation oppositely and hence, a middle value around 200 rpm was found to be the optimum. By increasing the potential scan rate, the time of performing the reactions in each cycle increased and the overall oxidation progress improved. It was found that mass transfer resistance was a limiting step in the overall reaction. Based on the findings, anodic oxidation has the potential for treating sulfide-containing wastewaters and in the future may be a competitor for conventional treatment processes.

Single Cylindrical Nanopore Electrodes: Surface Functionalization, Unusual Voltammetry, and Size‐Exclusion Properties

AbstractNanopore electrodes have been proved useful tools for fundamental electrochemical research and real applications. In this work, single cylindrical gold nanopore electrodes (SCAuNEs) were fabricated through a laser‐assisted pulling and electrochemical etching method, and then characterized by scanning electron microscopy, cyclic voltammetry, and finite‐element simulations. Our results showed that the electrochemical response of the nanopore electrode corresponds to the diffusion of redox species passing through the nanopore to the underlying gold electrode: surface functionalization of the interior nanopore led to the conversion of surface charge, which could introduce pH‐dependent ion selectivity by electrostatic interaction between redox species and surface functional groups inside the nanopores. It is interesting to find the unusual voltammetric behavior at low concentrations of supporting electrolyte by using single cylindrical nanopore electrodes: the voltammetric limiting current was increased significantly with decreasing supporting electrolyte concentration, but the shift of E1/2 was dependent on the charge change of the redox species. In addition, the distinct size exclusion of two biomolecules, ferritin (ca. 12 nm) and cytochrome C (ca. 3 nm), passing through nanopores at different diameters could be obtained by monitoring the direct electrochemical signals of two biomolecules. This work is important for fundamental electrochemistry and the real applications for counting or separating biomolecules inside cylindrical nanopores.

Electro-oxidation of cytostatic drugs: Experimental and theoretical identification of by-products and evaluation of ecotoxicological effects

Methotrexate (MTX) and Capecitabine (CPC) as mostly used cytostatic drugs were degraded by electro-oxidation process in this study. Ti/IrO2-RuO2 electrode was used to provide anodic oxidation. The effect of change of current density, initial pH of the solution and supporting electrolyte concentration on electro-oxidation of cytostatic drugs was evaluated. Current density of 30 mA/cm2, neutral pH and supporting electrolyte concentration of 200 mg L−1 were determined as optimum operational parameters. After oxidation process, the transformation by-products of cytostatic drugs were identified by LC–MS-MS analysis. Density functional theory (DFT) modelling was performed and the calculations were given in harmony with analytic results. In addition, toxicity evaluation on the electro-oxidation was assessed due to the possible toxic effect of the metabolites after treatment process. Indeed, the transformation by-products of MTX showed toxic effects after treatment, however; the metabolites CPC did not cause toxicity although lower removal efficiency.

Treatment of industrial estate wastewater by the application of electrocoagulation process using iron electrodes

In this study electrocoagulation (EC) of industrial estate wastewater taken from the inlet of wastewater treatment plant was investigated using sacrificial iron electrodes. Employing a pole changer to homogenous consumption of electrodes, studies on the parameters such as current density, supporting electrolyte concentration and initial pH, which have significant effects on COD removal and hence the energy consumption, were performed. Hydrogen peroxide was used in different concentrations to observe its effects on COD removal efficiency and the energy consumption. Sludge productions were also calculated for all experiments. COD removal efficiency of ∼92% was obtained at the best experimental conditions (i = 30 mA/cm2, SE = 3 mM Na2SO4, pH = original pH (∼6) of the wastewater, 1500 mg/L H2O2) with an energy cost of €3.41/m3 wastewater treated and the sludge production of 5.45 g per g COD removed.

Electro-oxidation of Ofloxacin antibiotic by dimensionally stable Ti/RuO2 anode: Evaluation and mechanistic approach

Present study investigates the potential of Ti/RuO2 electrode for degradation and mineralization of Ofloxacin (OFLX) antibiotic from synthetic wastewater by electro-oxidation (EO) method, not reported earlier. Effects of various EO parameters such as applied current (I), initial pH, initial OFLX concentration (C0) and supporting electrolyte concentration on %OFLX removal efficiency and %TOC removal efficiency were systematically studied and reported. Decay kinetics of OFLX by varying C0 and applied I were also studied. Additionally, mineralization current efficiency and specific energy consumption of OFLX mineralization were evaluated. Moreover, mode of oxidation method involved (direct and/or indirect oxidation) was also explored. Major OFLX transformation products during EO were identified using UPLC-Q-TOF-MS, and possible degradation reaction mechanism was proposed. Furthermore, operating cost analysis was performed to check the economic feasibility of the EO process.The optimum pH and current (I) were found to be ≈6.8 (natural pH of OFLX wastewater) and 1 A, respectively. Mineralization current efficiency decreased from 7.8% to 4.9% with increase in I value from 0.25 to 1 A. ≈80% of OFLX removal in 30 min of electrolysis and 46.3% TOC removal in 240 min of electrolysis at I = 1 A were observed. Pseudo-first-order kinetic model best fitted the experimental data showing R2 value ≈ 0.99 for all the Co and applied I studied.

Double layer effects in voltammetric measurements with scanning electrochemical microscopy (SECM)

Scanning electrochemical microscopy (SECM) operating as a variable gap ultra-thin layer twin-working electrode cell, has long been recognised as a powerful technique for investigating fast kinetics (heterogeneous electron transfer and homogeneous reactions coupled to electron transfer) as a consequence of high mass transport rates between the working electrodes when biased to promote redox shuttling. Recently, SECM has advanced technically and nanogap cells with dimensions on the 10s of nm scale have been reported. In this paper, we consider double layer effects on voltammetric measurements in this configuration, outlining a comprehensive model that solves the Nernst-Planck equation and Poisson equation with charged interfaces. For supporting electrolyte concentrations that have been used for such measurements (50mM and 100mM), it is shown that for typical electrode charges and charge on the glass insulator that encases the ultramicroelectrode (UME) tip used in SECM, there are profound effects on the voltammetric wave-shapes for redox reactions of charged redox couples, in the common modes used to study electron transfer kinetics, namely the tip-voltammetry (feedback) mode and substrate-voltammetry (substrate-generation/tip-collection and competition) modes. Using the reduction and oxidation of a singly charged redox species to a neutral and doubly charged species, respectively, as exemplar systems, it is shown that the charge on the electrodes can greatly distort the voltammetric wave-shape, while charge on the glass that surrounds the UME tip can affect the limiting current. Analysis of SECM voltammograms using methods that do not account for double layer effects will thus result in significant error in the kinetic values derived and tip-substrate distances that have to be estimated from limiting currents in SECM. The model herein provides a framework that could be developed for further studies with nanogap-SECM (e.g. consideration of alternative models for the electrical double layer, other supporting electrolyte concentrations, potential of zero charge on the electrodes and charges on the redox couples). The model results presented are shown to qualitatively match to SECM voltammetric features from experimental data in the literature, and are further supported by experimental data for redox processes of tetrathiafulvalene (TTF), namely the TTF/TTF+ and TTF+/TTF2+ redox couples. This serves to demonstrate the immediate practical application of some of the ideas presented herein. For future applications of SECM, the use of different supporting electrolyte concentrations and a range of tip-substrate separations may allow the determination of both electron transfer kinetics and double layer properties.

An air-breathing microfluidic fuel cell with a carbon felt flow-through anode

Rapid development of portable electronic devices promotes the demand for high performance and durability of micro power sources. As a new kind of portable power sources, microfluidic fuel cells (MFFC) utilize the parallel laminar flow to separate the fuel and the oxidant naturally without a proton exchange membrane (PEM) in traditional PEM fuel cells. As a result, a series of problems related to the PEM such as high cost, complicated water management and degradation of membrane can be eliminated. Therefore, microfluidic fuel cells have been paid more and more attention recently and are gradually becoming one of the promising micro portable power sources. Previous studies on microfluidic fuel cells showed that due to a relatively high oxygen concentration and diffusivity of oxygen in the air, using an air-breathing cathode could alleviate the oxygen transfer limitation in traditional microfluidic fuel cells which used dissolved oxygen as oxidant. As a result, the performance could be improved by the air-breathing cathode. However, the mass transfer at the anode still limits the cell performance. To further enhance the microfluidic fuel cell performance, a porous flow-through anode could be used to achieve the convective transport of the fuel to the electrode, resulting in reduction of the concentration boundary layer thickness at the planar electrode surface. However, in most studies of microfluidic fuel cells with porous flow-through electrodes, the two-dimensional porous carbon paper was used at the anode. As a common electrode material, the three-dimensional porous carbon felt with large porosity and specific surface area is expected to further improve the microfluidic fuel cell performance. In this study, an air-breathing microfluidic fuel cell with a carbon felt flow-through anode was fabricated and compared with the microfluidic fuel cell with a carbon paper anode. The micro morphology of electrode surface was characterized by a scanning electron microscopy (SEM). The electrochemical and cell performances were tested in acidic and alkaline conditions. The mass transport and performance characteristics of the microfluidic fuel cell with the carbon felt flow-through anode were further studied in alkaline condition. The experimental results showed that catalysts were better-distributed on the carbon felt electrode surface than that on the carbon paper electrode surface. The electrochemical performance of carbon felt electrode was superior to carbon paper electrode both in acidic and alkaline conditions because of its inherent three-dimensional porous structure. In acidic condition, the optimal power density and maximum current density of the microfluidic fuel cell with carbon felt anode were 1.8 and 2.8 times than that of the microfluidic fuel cell with carbon paper anode density, respectively. In alkaline condition, the optimal power density and the maximum current density of microfluidic fuel cell with carbon felt anode were 35.1 mW/cm2 and 192.9 mA/cm2, which were 5.2 and 7 times than that of the microfluidic fuel cell with carbon paper anode. Moreover, the cell performance under alkaline condition increased with an increase in the fuel and electrolyte flow rate and then remained almost the same, while it increased at first and then decreased as the fuel concentration, electrolyte and supporting electrolyte concentration increased.

Microelectrode Studies of the Critical Breakdown and Spatial Bifurcation in Additive Derived S-NDR Copper Electrodeposition

Copper electrodeposition is widely used in integrated circuit manufacturing, ranging from damascene plating of sub-100 nanometer features to deposition of micron-scale through-silicon-via (TSV) interconnects used for 3D-chip stacking.1 Electrodeposition of void-free copper structures in high aspect ratio cavities is achieved with various suppressing, accelerating, and leveling organic additives; enabling superconformal, bottom-up filling of these recessed features. Recently, the use of a single suppressing organic additive has been demonstrated and modeled in a variety of different metal systems (Cu, Ni, Co, Au) for TSV-scale feature filling.2-5 In these systems, bottom-up fill is derived from an S-shaped negative-differential-resistance (S-NDR), generating active plating regions at the bottom of the TSVs and passive regions along the walls and surface. This active/passive bifurcation is driven by adsorption/desorption kinetics of the suppressing polymer and chloride complexes, mass-transport of the chemical species, and the TSV geometry. Additional studies of S-NDR systems demonstrate that in the absence of any electrode geometric constraints the bifurcation occurs in random Turing-like patterns.2 In other reaction systems, such bifurcating active-passive reactions are found to be dependent on the electrode size such that for reduced electrode dimensions the ability to bifurcate is frustrated and a homogeneous surface reactions occurs across the electrode.6 In this work, microelectrodes are used to probe the dependence of bath composition on the critical breakdown behavior in single organic additive, acid copper sulfate electrolytes. The well-defined, high mass-transport rates and negligible IR-drop inherent in microelectrodes provides new insight into the chemical behavior of copper S-NDR systems at length scales relevant to industrial applications. Moreover, voltammetry at microelectrodes with dimensions less than the critical dimensions of the spatial instability in an S-NDR system provides more precise kinetic relationships; a result enabled by the homogeneity of the reaction across the electrode surface. However, one challenge of electrodeposition on microelectrodes is significant shape and area change during electrodeposition. Thus, our cyclic voltammetry and galvanodynamic linear sweeps are designed to ensure copper deposition is less than 10% of the microelectrode diameter, maintaining the disk-shaped geometry. Microelectrode experiments that vary chloride concentration demonstrate a clear dependence of the critical breakdown potential (a more negative shift) with increased chloride concentration. This dependence is far more apparent at microelectrodes (12.5 & 25 μm diameter), where an increase in chloride concentration from 10 μM to 100 μM shifts the breakdown potential by 80 mV more negative. At macroscopic electrodes (0.5 cm diameter), the breakdown potential shifts by only 10-20 mV. This observation and its interplay with transport and the polymer-chloride adlayer is currently being further studied in more detail. Similar experiments varying the supporting electrolyte concentration (sulfuric acid in this case) show little dependence on the breakdown potential and overall shape in the cyclic voltammetry hysteresis, validating that microelectrodes indeed have negligible solution IR contributions. In addition to individual microelectrode voltammetry, microelectrode arrays are used to explore the effect of electrode size on the active-passive bifurcation and subsequent pattern formation. References T. P. Moffat, J. E. Bonevich, W. H. Huber, A. Stanishevsky, D. R. Kelly, G. R. Stafford, and D. Josell, “Superconformal Electrodeposition of Copper in 500-90 nm Features”, J. Electrochem. Soc., 147 (2000) 4524.T. P. Moffat and D. Josell, “Extreme Bottom-Up Superfilling of Through-Silicon-Vias by Damascene Processing: Suppressor Disruption, Positive Feedback and Turing Patterns”, J. Electrochem. Soc., 159 (2012) D208.D. Josell and T. P. Moffat, “Bottom-Up Nickel Deposition in High Aspect Ratio Through Silicon Vias”, J. Electrochem. Soc., 163 (2016) D322.D. Josell, M. Silva, and T. P. Moffat, “Superconformal Bottom-Up Cobalt Deposition in High Aspect Ratio Through Silicon Vias”, J. Electrochem. Soc., 163 (2016) D809.D. Josell and T. P. Moffat, “Superconformal Bottom-Up Gold Deposition in High Aspect Ratio Through Silicon Vias”, J. Electrochem. Soc., 164 (2017) D327.S. Bozdech, K. Krischer, D. A. Crespo-Yapur, E. Savinova, and A. Bonnefont, “1/f2 noise in bistable electrocatalytic reactions on mesoscale electrodes”, Faraday Discuss., 193 (2016) 187.

Photo-assisted electrochemical degradation of sulfamethoxazole using a Ti/Ru0.3Ti0.7O2 anode: Mechanistic and kinetic features of the process

This study examined the photo-assisted electrochemical degradation and mineralization of the antibiotic contaminant sulfamethoxazole (SMX). All the experiments were perform using a flow electrolytic cell, in which the influence of the current density (10–60 mA cm−2) and sodium chloride (0.02–0.10 mol L−1) in the supporting electrolyte composition was analyzed. The results showed that the total SMX and 50% TOC removal was achieved in the current density range used. As expected, the degradation kinetics presented a pseudo first order behavior and the rate constant increased from 0.05 min−1 to 0.50 min−1 as the current density raised from 10 to 60 mA cm−1. In addition, the values of the electrical energy per order (EEO) increased from 0.67 to 1.06 kW/hm−3 order−1 as the current density increased from 10 to 60 mAcm−2 and drop from 8.82 to 0.57 kW/hm−3 order−1 at supporting electrolyte concentration of 0.02–0.1 mol L−1. The reaction intermediates identified by liquid chromatography–mass spectrometry allowed proposing a mechanism for the degradation. The use of photo assistance in the electrochemical process involved simultaneous reactions, for example, aromatic ring substitutions and hydroxylation. These reactions led to aromatic rings opening that generated simpler organic molecules, making possible the mineralization of the SMX molecule. Probable degradation pathways were proposed and discussed. Comparison of the efficiencies of the photocatalytic, electrochemical (EC) and photo-assisted electrochemical (PAEC) techniques revealed that the combined process showed a synergism for TOC removal.

Degradation of creatinine using boron-doped diamond electrode: Statistical modeling and degradation mechanism

This study investigated the degradation performance and mechanism of creatinine (a urine metabolite) with boron-doped diamond (BDD) anodes. Experiments were performed using a synthetic creatinine solution containing two supporting electrolytes (NaCl and Na2SO4). A three-level central composite design was adopted to optimize the degradation process, a mathematical model was thus constructed and used to explore the optimum operating conditions. A maximum mineralization percentage of 80% following with full creatinine removal had been achieved within 120 min of electrolysis, confirming the strong oxidation capability of BDD anodes. Moreover, the results obtained suggested that supporting electrolyte concentration should be listed as one of the most important parameters in BDD technology. Lastly, based on the results from quantum chemistry calculations and LC/MS analyses, two different reaction pathways which governed the electrocatalytic oxidation of creatinine irrespective of the supporting electrolytes were identified.

Natural Convection in Redox Electrochemistry: Model, Simulations and Experiments

A natural convection model has been implemented on redox species TMPD with supporting electrolyte TBAP in acetonitrile solvent. The cross section geometry used for the two-dimensional simulations is 20 mm (W) x 10 mm (H). The working electrode is a 2 mm wide strip at the center of the cell floor and the counter electrode is the entire cell ceiling. For the three-dimensional simulations, a 3mm diameter working electrode in the semi-infinite configuration was used. A uniform magnetic field was applied in the direction perpendicular the working electrode surface. The first case we have studied has an initial concentration of 10.3 mM TMPD- and no oxidized form of TMPD. The supporting electrolyte concentration was 0.5 M. The cell was operated in the potential step mode and the applied potential was high enough for operation in the diffusion-limited regime. Simulations were run for two values of the magnetic field intensity. The electrical conductivity of the bulk solution was 0.625 S/m. The density was calculated using the formulation in our natural convection model based on electroneutrality, where non-electroactive ions migrate to the diffusion layer to neutralize the charge buildup due to the redox reaction. Cases with gravity not present, and gravity applied in the +x, -x, +y and -y directions in 2D were investigated. For the 3D simulations, gravity was applied in the direction normal to the electrode, toward and away from the electrode surface. To study the effect of pure natural convection, cases were run without applying the magnetic field. For this electrochemical system, the density changes from the initial bulk density (785 kg/m3) is very small with a maximum value of 0.0231 kg/m3, which gives a difference of 0.00294% between the highest and the lowest density. Even under this small difference, the evolution of the flow field is quite remarkable. With increasing time from the start, the effect of natural convection on the flow field becomes greater. The maximum velocity increased by an order of magnitude in ~30s from the start. At larger times, the maximum velocity tends toward an asymptotic value along with the electrode current also leveling off and reaching an asymptotic value. The behavior of mixed convection characterized by competing forces of buoyancy and Lorentz force was also investigated, where two values of the magnetic field were chosen. The natural convection-only cases show that the effect is stronger when the established flow is away from the electrode than when it is toward the electrode. This can be attributed to the electrode surface acting to provide a stable flow field configuration, confirming published results. The velocity is an order of magnitude higher when the flow is away from the electrode surface. Note that the cell we used is an order of magnitude higher than a typical microfluidic cell. Work is in progress to study the effect of geometry on natural convection where buoyancy is the only body force, and mixed convection where both buoyancy and MHD are present.Experimental results have been obtained on the ferri-ferro-KCL system. Quantitative Micro-schlieren (QMS) is an instrument suitable for measuring density gradients. A lens-based design makes packaging more compact. An LED light source is used to reduce cooling requirements. All the optics are research grade, thereby improving resolution and reducing aberrations. The electrochemical cell was mounted on a three-axis stage that is mounted on the optical rail for easy alignment. This schlieren system differs from conventional schlieren systems in its compact size (~6m X 2m vs. 1.5m x 0.5m, in footprint), its use of a more uniform intensity LED light source, variable density filter, bandpass filter, lenses instead of mirrors, a digital frame camera, and modern image processing techniques to extract quantitative information from the images. While conducting the redox electrochemistry experiments, it’d be important to ensure that the data are not corrupted by natural convection induced by temperature gradients that might be introduced by sources such as LED illumination. While it is not possible to completely eliminate this source of error, it can be minimized by keeping the LED intensity as low as possible and having the LED on only when necessary. The acquired sequence of images during a time period up to ~300s from the start show a column of high density fluid that starts from the surface and grows in length with time. At larger times (>100s) the column develops a transverse instability with a wave length of ~30 mm. Figure 1

Effective degradation of diatrizoate by electro-peroxone process using ferrite/carbon nanotubes based gas diffusion cathode

In this study, ferrite modified carbon nanotubes (MFe2O4/CNTs, M: Fe, Mn) were prepared and employed as cathodic catalysts to assist electro-peroxone (i.e., combined ozonation with electrolysis process using a carbon-polytetrafluoroethylene cathode) treatment of emerging pollutant diatrizoate (DTZ) in aqueous solution. The structural and surface property of synthesized catalysts was studied, and the performance of electro-peroxone process using MFe2O4/CNTs based gas diffusion cathode (GDC) was systematically investigated from the kinetic and mechanistic viewpoints. Results show that the combination of ozonation and electrolysis exhibited synergistic degradation of DTZ. Approximately 71.9% DTZ had been degraded with MFe2O4/CNTs based GDC after 10min, 13.2% higher than with bare CNTs based GDC, implying that the combined treatment efficiency could be enhanced by the presence of MFe2O4. The performance of MFe2O4/CNTs catalytic electro-peroxone process was positively correlated with inlet ozone concentration (10–30mg/L), and an increase in applied current stimulated DTZ degradation at a low cathodic current density (5–40mA/cm2) but inhibited the degradation at a high cathodic current density (40–60mA/cm2). The MFe2O4/CNTs catalytic electro-peroxone treatment also showed a significant dependence on initial pH and reaction temperature, but was little affected by supporting electrolyte concentration. Higher removal efficiency was obtained at a lower initial DTZ concentration. The comparison tests reveal that peroxone reaction was the main pathway of hydroxyl radicals (HO) production in the present system, and the presence of MFe2O4 at the cathode could promote HO generation. These observations suggest that electro-peroxone is efficient for DTZ degradation in aqueous solution, and MFe2O4/CNTs are good and promising cathodic materials and catalysts for this process.

Improving the fabrication of all-polythiophene supercapacitors

The influence of the preparation method in the properties of poly(3,4-ethylenedioxythiophene) (PEDOT) electrodes used to manufacture organic energy storage devices, as for example supercapacitors, have been examined by considering a reduction of both monomer and supporting electrolyte concentrations during the anodic polymerization reaction. Thus, the excellent electrochemical properties of PEDOT films prepared using quiescent solutions have been preserved by applying controlled agitation to the polymerization process, even though the concentration of monomer and supporting electrolyte were reduced 5 and 2 times, respectively. For example, the charge stored for reversible exchange in a redox process, the electrochemical stability and the current productivity of films achieved using quiescent solutions have been preserved using a dynamic reaction medium in which the concentrations of monomer and supporting electrolyte are several times lower. The excellent properties of PEDOT electrodes prepared using optimized dynamic conditions have also been proved by constructing a symmetric supercapacitor. This energy storage device, which has been used as power source for a LED bulb, is rechargeable and exhibits higher charge-discharge capacities than supercapacitors prepared with electrodes derived from quiescent solutions. In addition of bring an efficacious procedure for preparing cost-effective PEDOT films with excellent properties, the proposed dynamic conditions reduce the environmental hazards of depleted reaction media.

Use of a PbO2 electrode of a lead-acid battery for the electrochemical degradation of methylene blue

ABSTRACTIn this work, the electrochemical degradation efficiency of synthetic azo dye, methylene blue, at positive electrode PbO2 of lead-acid battery was investigated. The structure and morphology of the electrode was investigated by X-ray diffraction, scanning electron microscopy, and energy dispersive X-ray spectrometry. The influence of several operating parameters on electro-oxidation of 100 mL of methylene blue solution 100 mg/L was studied. Results indicated that lead-acid battery electrode is effective for removing color and chemical oxygen demand (COD). It is found that current density, the stirring speed, and the supporting electrolyte concentration have a positive effect on decolorization and mineralization, and no significant effect of the distance between the electrodes on methylene blue degradation and COD removal was observed. By contrast, the percentage of color and COD removal decreases with increasing of pH. Kinetic analysis of the results revealed that the COD removal follows a pseudo-first-order kinetics.