Showing papers on "Supporting electrolyte published in 2017"

Probing promoting effects of alkali cations on the reduction of CO at the aqueous electrolyte/copper interface.

Abstract: The catalytic selectivity and reactivity of an electrocatalytic interface can profoundly depend on the identity of the supporting electrolyte's cation. In the case of CO2 reduction on copper electrodes, these cation effects have been utilized to suppress undesired hydrogen evolution and to promote the formation of C2 reduction products. However, to more effectively steer the catalytic selectivity of the electrolyte/copper interface by cations, it is crucial to reveal the various physical mechanisms by which cations impact the catalytic properties of this prototypical interface for CO2 reduction. Herein, we employ surface-sensitive infrared spectroscopy to probe how alkali cations (Li+, K+, and Cs+) control the coverage of CO, a key intermediate in CO2 reduction, on a polycrystalline copper electrode. We find that surface-adsorbed CO experiences an increasingly larger interfacial electric field with increasing cation size. The reduction of CO is further promoted by the two larger cations, leading to a significant drop of the CO coverage at high cathodic potential around −1 V vs. RHE. Our results demonstrate for the first time that the coverage of CO on the electrode is very sensitive to the identity of the cation. Since the relative coverage of CO and hydrogen on the copper surface affects the catalytic rates of CO2 reduction and hydrogen evolution, our results represent an essential step towards a better understanding of how cation effects control the product distribution.

Generation of Volatile Cadmium and Zinc Species Based on Solution Anode Glow Discharge Induced Plasma Electrochemical Processes.

Abstract: In this study, a novel high efficiency vapor generation strategy was proposed on the basis of solution anode glow discharge for the determination of Cd and Zn by atomic fluorescence spectrometry. In this approach, a glow discharge microplasma was acted as a gaseous cathode to initiate the plasma electrochemical vapor generation of Cd and Zn. Cadmium/zinc ions could be converted into molecular species efficiently at the plasma-liquid interface from a supporting electrolyte (HCl, pH = 3.2). It was found that the overall efficiency of the plasma electrochemical vapor generation (PEVG) system was much higher than the conventional electrochemical hydride generation (EcHG) and HCl-KBH4 system. With no requirement for other reducing reagents, this new approach enabled us to detect Cd and Zn with detection limits as low as 0.003 μg L-1 for Cd and 0.3 μg L-1 for Zn. Good repeatability (relative standard deviation (RSD), n = 5) was 2.4% for Cd (0.1 μg L-1) and 1.7% for Zn (10 μg L-1) standard. The accuracy of the proposed method was successfully validated through analysis of cadmium in reference material of stream sediment (GBW07311), soil (GBW07401), rice (GBW10045), and zinc in a simulated water sample (GSB 07-1184-2000). Replacing a metal electrode with a plasma offers the advantage of eliminating potential interactions between the species in liquid and the electrode, which solves the issues associated with electrode encountered in conventional EcHG. The ability to initiate electrochemical vapor generation reactions at the plasma-liquid interface opens a new approach for chemical vapor generation based on interactions between plasma gas-phase electrons and solutions.

Multielectron Cycling of a Low-Potential Anolyte in Alkali Metal Electrolytes for Nonaqueous Redox Flow Batteries

Abstract: Recent efforts have led to the design of new anolytes for nonaqueous flow batteries that exhibit reversible redox couples at low potentials. However, these molecules generally cycle through just a single electron-transfer event, which limits the overall energy density of resulting batteries on account of the undesirably high equivalent weight (i.e., ratio of anolyte/supporting electrolyte molecular weight to electrons transferred). In addition, these anolytes generally require expensive alkylammonium salts as supporting electrolytes for stable cycling, which further increases the equivalent weight of the system. The current work describes the multielectron redox cycling of a low-potential anolyte using alkali metal salts as supporting electrolytes. These studies reveal that potassium hexafluorophosphate (KPF6) dramatically lowers the equivalent weight of the anolyte system while supporting flow cell cycling through two redox events at low potentials for 150 cycles with no detectable degradation.

Boosting the energy efficiency and power performance of neutral aqueous organic redox flow batteries

Abstract: Neutral aqueous organic redox flow batteries (AORFBs) have stood out as a promising RFB technology for sustainable and safe energy storage. It is critical to improve their energy efficiency and power density to meet fast charge/discharge responses in the application of large scale electrochemical energy storage. Herein we show a systematic study on the effects of ion exchange membranes and supporting electrolytes on the resistance and electrochemical performance of a neutral AORFB, the FcNCl/MV AORFB, where FcNCl is (ferrocenylmethyl)trimethylammonium chloride and MV is methyl viologen dichloride. Electrochemical impedance spectroscopic studies revealed that the membrane and the supporting electrolyte are the primary and secondary components accountable for the resistance and charge/discharge overpotential of the neutral AORFB. With an optimized combination of the membrane and the supporting electrolyte, unprecedented energy efficiency and power density of 85% at 40 mA cm−2 and 79% at 60 mA cm−2 and 122.7 mW cm−2 were achieved for the neutral AORFB. The present results emphasize the importance of minimizing battery resistance, and also further advance the promise of neutral AORFBs for sustainable and green energy storage of renewable energy.

Indole-based conjugated macromolecules as a redox-mediated electrolyte for an ultrahigh power supercapacitor

Abstract: Balancing energy density and power density has been a critical challenge since the inception of supercapacitors. Introducing redox-active additives in the supporting electrolyte has been shown to increase the energy density, however the power density and cycling stability are severely hampered in the process. Herein, an extensively conjugated indole-based macromolecule consisting of 5,6-dihydroxyindole/5,6-quinoneindole motifs, prepared by electrochemical polymerization of dopamine under acidic conditions, was employed as a redox-active additive. By utilizing the conjugation effect, the HOMO–LUMO gap (HLG) of the extensively conjugated indole-based macromolecule was reduced to ca. 2.08 eV, which enhanced the electronic transfer kinetics, in turn improving the power density and reversibility of redox reactions. When coupled with a porous honeycomb-like carbon (PHC) electrode, the assembled supercapacitor delivered an excellent rate performance with a high specific capacitance of 205 F g−1 at 1000 A g−1. This work reports one of the highest power densities recorded at 153 kW kg−1 for redox-mediated electrolyte systems with a respectable energy density of 8.8 W h kg−1. In addition to an excellent cycling stability of 97.1% capacitance retention after 20 000 charge/discharge cycles, the conjugation degree has to be considered when engineering the redox-active electrolyte so as to improve the power density and stability.

Liquid Spray Dielectric Barrier Discharge Induced Plasma–Chemical Vapor Generation for the Determination of Lead by ICPMS

Abstract: In the present study, a novel and sensitive liquid spray dielectric barrier discharge induced plasma–chemical vapor generation technique (LSDBD–CVG) is developed for the determination of lead concentration by inductively coupled plasma mass spectrometry (ICPMS). The dissolved Pb2+ is readily converted to volatile species by LSDBD plasma induced chemical processes in the presence of 5% (v/v) formic acid in a supporting electrolyte (HCl, 0.01 mol L–1). In this LSDBD approach, the sample solution is converted to aerosol and simultaneously mixed with the DBD plasma generated at the nozzle of a pneumatic nebulizer, which greatly facilitates Pb vapor generation because of the enhanced interaction of sprayed analytes and the plasma. Optimal conditions for LSDBD–CVG were identified, and the interference effects from other metal ions were assessed. Under optimized conditions, the detection limit of Pb was found to be 0.003 μg L–1. The repeatability, expressed as the relative standard deviation (RSD) of the peak he...

Photoelectrochemical mineralization of emerging contaminants at porous WO3 interfaces

Abstract: Nanocrystalline WO3 absorbs visible light up to 470 nm and generates OH radicals via valence band injection. Therefore, it promotes the OH mediated oxidation of organic pollutants, when applied to the near UV–vis photodegradation of environmentally relevant target molecules like atenolol and carbamazepine. They both represent potentially hazardous recalcitrant contaminants of emerging concern (CEC) in waters. In the case of WO3 electrodes, a considerable acceleration of the degradation kinetics (up to 4–5 times) occurs through the application of a 1.5 V potential bias, which is instrumental to optimize the charge separation within the thin films and to maximize holes transfer rate to the electrolyte. Moreover, after sufficiently long irradiation, the complete mineralization of the organics is obtained. Interestingly, the photo-electrochemical degradation process (applied bias condition) maintains its effectiveness and a large efficiency margin over conventional open circuit conditions. Photoelectrocatalysis is observed even in diluted supporting electrolyte conditions, representing the average salinity of natural freshwater samples, demonstrating the advantageous practical feasibility of the photo-electrochemical approach.

Probing the shape-specific electrochemical properties of cobalt oxide nanostructures for their application as selective and sensitive non-enzymatic glucose sensors

Abstract: In this work, a selective and sensitive non-enzymatic electrochemical glucose sensor was developed using cobalt oxide nanoflowers (NF) Herein, for the first time, shape-specific electrochemical properties of cobalt oxide nanostructures were studied by synthesizing the spherical nanoparticle (NP), porous nanorod (NR) and nanoflower (NF) shapes of cobalt oxide by easy and facile wet-chemical processes Cobalt oxide nanoflowers showed high surface-to-volume ratio with superior electrocatalytic behavior, and therefore, are more suited for designing a selective and sensitive non-enzymatic glucose sensor All the as-synthesized samples are characterized using different spectroscopic and microscopic techniques Prior to sensor fabrication, the nanostructures are further analyzed using voltammetric techniques for the determination of electroactive/real surface area and electrode parameters The cobalt oxide nanoflowers exhibit maximum electrocatalytic activity owing to the larger exposure area resulting from its unique 3-D hierarchical architecture with interconnected nanosized petals The influence of supporting electrolyte, electrolyte concentration and applied potential on the electrooxidation of glucose on cobalt oxide nanoflower-modified pencil graphite electrode (NF-PGE) sensor is examined, and the mechanism is explained The developed amperometric glucose sensor exhibits excellent anti-interfering property and two wide linear ranges of 5 to 60 μM and 02 to 30 mM, with high sensitivities of 69302 μA mM−1 cm−2 and 22803 μA mM−1 cm−2 and detection limits (LOD) as low as 004 μM and 014 μM, respectively Furthermore, the practical feasibility of the developed sensor was tested for the quantification of glucose in various commercially available soft drinks, fresh fruit extracts, and human blood samples via standard addition (SA) method

The potential of non-aqueous redox flow batteries as fast-charging capable energy storage solutions: demonstration with an iron–chromium acetylacetonate chemistry

Abstract: Energy-dense non-aqueous redox flow batteries (NARFBs) with the same active species on both sides are usually costly and/or have low cycle efficiency. Herein we report an inexpensive, fast-charging iron–chromium NARFB that combines the fast kinetics of the single iron(III) acetylacetonate redox couple on the positive side with the fastest of the chromium(III) acetylacetonate redox couple on the negative side. In this system, which has an open-circuit voltage of 1.2 V, the charging time was drastically reduced, with fast charging up to 3 V. In a renewable-energy power plant with an intermittent source, this system could be used for rapid storage for later use, when the energy supply is low or unavailable. In this study, we conducted charge–discharge performance tests with a tetraethylammonium ion-conducting composite Nafion/SiO2 membrane in a flow cell containing 0.1 M active species and 0.4 M supporting electrolyte in 84/16 (volume%) acetonitrile/1,3-dioxolane; the system showed nominal coulombic and energy efficiencies of 99% and 53%, respectively, over long cycling, making it more efficient than several previously reported NARFBs using similar cell types and species concentrations. The system demonstrated a good capacity retention that was sustained throughout 50 cycles. The general performance characteristics of the proposed Fe–Cr NARFB, as those of the previously reported NARFBs, are hindered by the high internal resistance; in addition to coupled non-electrochemical reactions suggesting some complications in the anodic reaction. Thus, further attempts to overcome these limitations require continuous research and development.

MgO/ZnO coatings formed on magnesium alloy AZ31 by plasma electrolytic oxidation: Structural, photoluminescence and photocatalytic investigation

Abstract: This paper presents the results of our recent investigation of MgO/ZnO coatings formed on AZ31 magnesium alloy by plasma electrolytic oxidation in phosphate-based alkaline electrolyte with varying concentration of ZnO particles. Surface morphology of obtained coatings is not significantly influenced by the addition of ZnO particles to the supporting electrolyte, while processing time has considerable influence on the morphology of formed coatings. Elemental mapping showed that elements are distributed rather uniformly across the obtained oxide coatings. The content of Zn increases with ZnO particle concentration in the supporting electrolyte as well as with PEO processing time. Incorporation of ZnO particles in obtained coatings was confirmed by X-ray diffraction and Raman spectroscopy. Photoluminescent emission spectra of MgO/ZnO coatings featured sharp band centered at about 380 nm and broad band centered at about 535 nm, with the leading contribution coming from ZnO deposited on the surface. Diffuse reflectance spectra revealed that absorption edge of MgO/ZnO coatings is positioned at about 385 nm. Photoactivity of obtained coatings increases with processing time and ZnO concentration up to 6 g/L.

Magnetic silver(I) ion-imprinted polymeric nanoparticles on a carbon paste electrode for voltammetric determination of silver(I)

Abstract: Magnetic silver ion imprinted polymer nanoparticles (mag-IIP-NPs) were prepared and used as a recognition element in electrochemical detection of silver(I). The procedure involves two steps: (a) the extraction of the Ag(I) by the mag-IIP-NPs, and (b) determination of the preconcentrated Ag(I) ions on the surface of the magneto carbon paste electrode (MCPE) using differential pulse voltammetry. The amount of sorbent, pH value of the sample solution, extraction time, supporting electrolyte, reduction potential and reduction time were optimized. Under optimal conditions and at a working voltage of +0.02 V (vs. Ag/AgCl), the method displays a linear response in the 0.05 to 150 μg⋅L−1 Ag(I) concentration range. Other features include a low detection limit (15 ng⋅L−1), a remarkable selectivity and good reproducibility (with an RSD of 4.7%). The results obtained with this analytical assay when analyzing different water samples were compared with the data obtained by GF-AAS, and the results agreed satisfactorily. In our perception, this approach also may be extended to electrochemical detection for other ions, and this makes it a widely applicable strategy for heavy metal ion analysis.

Electrochemical Reduction of Protic Supercritical CO2 on Copper Electrodes

Abstract: The electrochemical reduction of carbon dioxide is usually studied in aqueous solutions under ambient conditions. However, the main disadvantages of this method are high hydrogen evolution and low faradaic efficiencies of carbon-based products. Supercritical CO2 (scCO(2)) can be used as a solvent itself to suppresses hydrogen evolution and tune the carbon-based product yield; however, it has received little attention for this purpose. Therefore, the focus of this study was on the electrochemical reduction of scCO(2). The conductivity of scCO(2) was increased through the addition of supporting electrolyte and a cosolvent (acetonitrile). Furthermore, the addition of protic solutions of different pH to scCO(2) was investigated. 1m H2SO4, trifluoroethanol, H2O, KOH, and CsHCO3 solutions were used to determine the effect on current density, faradaic efficiency, and selectivity of the scCO(2) reduction. The reduction of scCO(2) to methanol and ethanol are reported for the first time. However, methane and ethylene were not observed. Additionally, corrosion of the Cu electrode was noticed.

Electrochemical oxidation of erythrosine at TiO2 nanoparticles modified gold electrode — An environmental application

Abstract: In the present paper, TiO 2 nanoparticles were utilized to modify the gold electrode surface and to emphasize a useful technique for determination of a food dye, erythrosine. The utilized modifier was characterized by Scanning electronic microscopy (SEM), and X-ray diffraction (XRD) analysis. In the first portion of the work, the oxidation properties of the dye were examined at different pH ranging from 3.0–11.2, varying accumulation time and at different scan rates, by using the cyclic voltammetric technique. The number of electrons and protons involved in the reaction, and heterogeneous rate constant were calculated. The second portion of the work includes the appositeness of the estimated method for the detection of the dye in trace level by utilizing differential pulse voltammetric technique. In optimum conditions (supporting electrolyte pH, accumulation time, modifier amount) the peak current was proportional to the concentration in the range 0.1 μM–10.0 μM with detection limit 2.6 nM. The applicability of the proposed method was achieved for food industries as well as for environmental applications.

Enhanced Potentiometric Detection of Hydrogen Peroxide Using a Platinum Electrode Coated with Nafion

Abstract: The potentiometric response to hydrogen peroxide of a platinum electrode coated with a layer of Nafion is presented. The results show that the Nafion membrane acts as an effective permselective barrier, thus significantly reducing the response to some redox active species, such as ascorbate. Even more interesting, these coated electrodes show a significantly enhanced sensitivity to hydrogen peroxide (H2O2) when the measurements are performed in solutions of high ionic strength. The influence of pH, ionic strength and supporting electrolyte on this enhancement are presented. Under optimized conditions these coated electrodes show a linear dependence with the logarithm of the concentration of H2O2, with sensitivities of −125.1±5.9 mV decade−1 (several times higher than the bare electrodes) and a linear range that spans from 10−5 M to 10−3 M of H2O2. Preliminary studies suggest that the coupling between the redox potential on the Pt electrode and the Donnan potential of the membrane plays a role on this enhancement. Considering this improved sensitivity, selectivity, stability and linear ranges, this system shows promise as a future platform to build enzyme-based potentiometric biosensors.

Voltammetric determination of trace amounts of permanganate at a zeolite modified carbon paste electrode

Abstract: A novel sensitive, simple and fast method is suggested for indirect voltammetric determination of permanganate in aqueous solution. The method is based on the modification of a carbon paste electrode (CPE) by Fe(II)-exchanged clinoptilolite nanoparticles (Fe(II)-NClin). When permanganate was added to H2SO4 supporting electrolyte, the voltammetric peak current of the Fe(II)/Fe(III) redox system was decreased. Hence, this decrease in the peak current was used for indirect determination of permanganate. The results of electrochemical impedance spectroscopy (EIS) confirmed that the modified Fe(II)-NClin/CPE electrode has a remarkable charge transfer ability with respect to the raw CPE and NClin/CPE electrodes. The interaction effects of more influencing variables in square wave voltammetry were studied by an experimental design method using response surface methodology (RSM). The optimal run was obtained as: pH 2.0, amplitude = 0.5 V, modifier% = 16.5 and step potential = 0.023 V. Under the optimum conditions, the square wave voltammetric current of the Fe(II)-NClin/CPE was inversely proportional to permanganate in the concentration range from 35 to 80 nmol L−1 with a detection limit of 0.40 nmol L−1.

Ion selective redox cycling in zero-dimensional nanopore electrode arrays at low ionic strength.

Abstract: Surface charge characteristics and the electrical double layer (EDL) effect govern the transport of ions into and out of nanopores, producing a permselective concentration polarization, which dominates the electrochemical response of nanoelectrodes in solutions of low ionic strength. In this study, highly ordered, zero-dimensional nanopore electrode arrays (NEAs), with each nanopore presenting a pair of recessed electrodes, were fabricated to couple EDL effects with redox cycling, thereby achieving electrochemical detection with improved sensitivity and selectivity. These NEAs exhibit current amplification as high as 55-fold due to the redox cycling effect, which can be further increased by ∼500-fold upon the removal of the supporting electrolyte. The effect of nanopore geometry, which is a key factor determining the magnitude of the EDL effect, is fully characterized, as is the effect of the magnitude and sign of the charge of the redox-active species. The observed changes in limiting current with the concentration of the supporting electrolyte confirm the accumulation of cations and repulsion of anions in NEAs presenting negative surface charge. Exploiting this principle, dopamine was selectively determined in the presence of a 3000-fold excess of ascorbic acid within the NEA.