Showing papers on "Supporting electrolyte published in 2019"

Bipolar Electrochemistry: A Powerful Tool for Electrifying Functional Material Synthesis

Abstract: Electrosynthesis is a powerful method for the synthesis of organic, inorganic, and polymeric materials based on electron-transfer-driven reactions at the substrate/electrode interface. The use of electricity for synthetic reactions without the need for hazardous chemical oxidants and reductants is recognized as a green and sustainable method. Other advantages include control of the reaction selectivity by tuning the electrode potentials. A different mode for driving electrochemical reactions has recently been proposed, in which bipolar electrodes (BPEs) are available as wireless electrodes that undergo anodic and cathodic reactions simultaneously. Bipolar electrochemistry is an old technology that has recently garnered renewed attention because of the interesting features of BPEs: (i) the wireless nature of a BPE is useful for sensors and material synthesis; (ii) the gradient potential distribution on BPEs is a powerful tool for the preparation of gradient surfaces and materials; and (iii) electrophoresis is available for effective electrolysis. In addition to these unique features, a BPE system only requires a small amount of supporting electrolyte in principle, whereas a large amount of electrolyte is necessary in conventional electrochemistry. Hence, bipolar electrochemistry is an inherently green and sustainable chemical process for the synthesis of materials. In this Account, recent progress in bipolar electrochemistry for the electrosynthesis of functional materials is summarized. The wireless nature of BPEs was utilized for symmetry breaking to produce anisotropic materials based on the site-selective modification of conductive objects by electrodeposition and electropolymerization. Potential gradients on a BPE interface have been successfully used as controllable templates to form molecular or polymeric gradient materials, which are potentially applicable for high throughput analytical equipment or as biomimetic materials. The electric field necessary to drive BPEs is also potentially useful to induce the directed migration of charged species. The synergetic effects of electrophoresis and electrolysis were also successfully demonstrated to obtain various functional materials. These features of bipolar electrochemistry and the various combinations of techniques have the potential to change the methodologies of material synthesis. Furthermore, the fundamental principle of bipolar electrochemistry infers that very small amounts of supporting electrolyte are necessary for an electrode system, which is expected to lead new methods of sustainable organic electrosynthesis.

Electrochemical fluoromethylation triggered lactonizations of alkenes under semi-aqueous conditions

Abstract: An electrochemical difluoromethylation triggered lactonization of alkenes was developed for the first time. This protocol employs readily prepared CF2HSO2Na as the difluoromethylating reagent, affording unprecedented CF2H-containing lactones in moderate yields. Moreover, with CF3SO2Na as the trifluoromethylating reagent, a wide array of CF3-containing lactones were obtained under additional supporting electrolyte- and catalyst-free conditions.

Electrochemical Sensor for Rapid and Sensitive Detection of Tryptophan by a Cu2O Nanoparticles-Coated Reduced Graphene Oxide Nanocomposite.

Abstract: In this paper, a nanocomposite of cuprous oxide and electrochemically reduced graphene oxide (Cu2O‒ERGO) was prepared by a simple and low-cost method; hereby, a new method for the electrochemical determination of tryptophan (Trp) by this composite modified glassy carbon electrode (GCE) is proposed. The prepared materials and modified electrodes were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and cyclic voltammetry (CV). The results showed that Cu2O‒ERGO/GCE had good electrocatalytic activity for Trp. The effects of supporting electrolyte, scanning rate, accumulation potential, and accumulation time on the determination of Trp were studied. Under the optimum experimental conditions, Trp was quantitatively analyzed by square-wave voltammetry (SWV). The oxidation peak current of Trp had a good linear relationship with its concentration in the range of 0.02‒20 μM, and the detection limit was 0.01 μM (S/N = 3). In addition, the modified electrode has high sensitivity, good repeatability, and long-term stability. Finally, the proposed method has been successfully applied in the determination of Trp concentration in practical samples.

Photo-assisted electrochemical degradation of polychlorinated biphenyls with boron-doped diamond electrodes.

Abstract: The capacity of the photo electro-Fenton (PEF) process to degrade a mixture of seven polychlorinated biphenyl (PCB) congeners was studied. Boron-doped diamond (BDD) sheets were used as anode and cathode in the experimental electrolytic cell that contained Na2SO4 0.05 M at pH 3 as supporting electrolyte for the electro generation of H2O2 at the cathode. The effects of UV light intensity (254 and 365 nm), current density (8, 16 and 24 mA cm-2) and ferrous ion dosage (0.1, 0.2 and 0.3 mM) on PCB (C0 = 50 μg L-1) degradation were evaluated. The highest level of PCB degradation (97%) was achieved with 16 mA cm-2 of current density, 0.1 mM of ferrous ion and UV light at 365 nm as irradiation source after 6 h of reaction. PCB28, PCB52 and PCB101 were not detected after 0.5, 1.5 and 3 h of reaction, respectively. The degradation of PCB138, PCB153, PCB180 and PCB209 was also high (>95%). The PEF system outperformed other oxidation processes (electro-Fenton, anodic oxidation, Fenton, photo-Fenton and UV photolysis) in terms of reaction rate and degradation efficiency. These results demonstrate for the first time the degradation of PCB209, the most highly chlorinated PCB congener, by an advanced electrochemical oxidation process.

Electrochromism of Ferrocene- and Viologen-Based Redox-Active Ionic Liquids Composite

Abstract: Redox-active ionic liquids (RAILs) require no other additional reagents such as solvent and supporting electrolyte for electrochemical reactions under undiluted condition. Viologen-based RAILs are one of the electrochromic (EC) ionic liquids with sharp color contrast and high chemical stability. An operation of an EC cell requires two electroactive elements, an EC material and a charge compensating material. In this study, an equimolar composite of a viologen-based RAIL as the EC material and a ferrocene-based RAIL as the charge compensation material, was synthesized and applied to an EC cell. The EC cell with the composite RAIL of as high concentration as 0.92 M each redox species showed good coloration efficiency (91.4 cm2 C–1 at 540 nm on 1.0 V). The coloration process of the EC cell was diffusion-limited process. The current and absorbance of the EC cell reached constant values at large enough bias voltage because of the charge recombination between reduced viologens and oxidized ferrocenes. The recom...

Electrolyte-Dependent Oxygen Evolution Reactions in Alkaline Media: Electrical Double Layer and Interfacial Interactions

Abstract: Traditional understanding of electrocatalytic reactions generally focuses on either covalent interactions between adsorbates and the reaction interface (i.e., electrical double layer, EDL) or electrostatic interactions between electrolyte ions. Here, our work provides valuable insights into interfacial structure and ionic interactions during alkaline oxygen evolution reaction (OER). The importance of inner-sphere OH- adsorption is demonstrated as the IrOx activity in 4.0 M KOH is 6.5 times higher than that in 0.1 M KOH. Adding NaNO3 as a supporting electrolyte, which is found to be inert for long-term stability, complicates the electrocatalytic reaction in a half cell. The nonspecially adsorbed Na+ in the outer compact interfacial layer is suggested to form a stronger noncovalent interaction with OH- through hydrogen bond than adsorbed K+, leading to the decrease of interfacial OH- mobility. This hypothesis highlights the importance of outer-sphere adsorption for the OER, which is generally recognized as a pure inner-sphere process. Meanwhile, based on our experimental observations, the pseudocapacitive behavior of solid-state redox might be more reliable in quantifying active sites for OER than that measured from the conventional EDL charging capacitive process. The interfacial oxygen transport is observed to improve with increasing electrolyte conductivity, ascribing to the increased accessible active sites. The durability results in a liquid alkaline electrolyzer which shows that adding NaNO3 into KOH solution leads to additional degradation of OER activity and long-term stability. These findings provide an improved understanding of the mechanistic details and structural motifs required for efficient and robust electrocatalysis.

Sensitive voltammetric determination of bromate by using ion-exchange property of a Sn(II)-clinoptilolite-modified carbon paste electrode

Abstract: A modified carbon paste electrode with Sn(II)-exchanged clinoptilolite nanoparticles (CNP-Sn(II)-CPE) showed voltammetric current (in cyclic voltammetry (CV)) for Sn(II)/Sn(IV) in sulfuric acid electrolyte (pH 2). The peak current was decreased when bromate was added to the solution. Hence, this decrease was used for indirect voltammetric determination of bromate. In designed experiments using response surface methodology (RSM) approach in square-wave voltammetry (SqW), strong acidic pH values (pH 1.8–2.5) caused an increased SqW voltammetric response, because such pH values bring sufficient Sn(II) as the electroactive species at the electrode surface via ion-exchange process. The optimal variables obtained are sulfuric acid as supporting electrolyte at pH 1.80, modifier% at 25, amplitude at 498.4 mV, step potential at 5.4 mV, and frequency at 25 Hz. The peak current of Sn(II)/Sn(IV) redox pair was inversely proportionate to the concentration of bromate. Hence, ΔI (difference in peak current in the absence and presence of bromate) was proportionally increased with increasing the concentration of bromate in the range of 5.00 to 100.00 μmol L−1 with a detection limit of 0.06 μmol L−1 bromate. The effect of some strong oxidizing agents was studied, and the results showed that when such agents are present at levels of 2.5 to 5 times greater than the bromate in the solution, they can cause a maximum error of 3% in the determination of bromate in sulfuric acid electrolyte at pH 2.5.

Electrochemical detection of Cr(VI) with carbon nanotubes decorated with gold nanoparticles

Abstract: A nanocomposite consisting of gold nanoparticles deposited on the side walls of functionalised multi-walled carbon nanotubes, Ox-MWCNT-Aunano, was prepared using a simple chemical reduction. The nanoparticles were well dispersed with a mean diameter of 7.5 nm and had a face-centred cubic structure and a gold loading between 2.0% and 2.6% by weight. These gold decorated nanotubes were cast onto a gold electrode to form a uniform and homogeneous sensor. Using cyclic voltammetry, the reduction of Cr(VI) was observed at a peak potential of 0.52 V versus SCE in an acidified H2SO4 solution, pH 2.0. A linear calibration curve with a sensitivity of 0.28 mA mM− 1 and a LOD of 7.2 × 10− 7 M was obtained using constant potential amperometry coupled with rotating disc voltammetry. The electrochemical detection of Cr(VI) was also observed at a MWCNT-modified gold substrate but with a higher LOD, illustrating the advantage of combining the gold nanoparticles with MWCNTs. The sensor showed good selectivity for the detection of Cr(VI) in the presence of Cu(II), chloride and nitrates and in a real water sample. This was attributed to the electropositive reduction potentials of Cr(VI), the acidic H2SO4 supporting electrolyte that provides a well-known cleaning effect at gold, and the size and good dispersion of the gold nanoparticles that minimise particle agglomeration.

Carbon quantum dots co-catalyzed with multiwalled carbon nanotubes and silver nanoparticles modified nanosensor for the electrochemical assay of anti-HIV drug Rilpivirine

Abstract: In this study, a novel and sensitive voltammetric nanosensor has been developed for the first time, for the detection of Rilpivirine based on amine-functionalized multiwalled carbon nanotubes (NH2-fMWCNT) with Ag nanoparticles onto carbon quantum dots modified glassy carbon electrode. Scanning electron microscopy, cyclic voltammetry and electrochemical impedance spectroscopy (EIS) were employed for characterization of the modified electrode. The Rilpivirine showed two irreversible oxidation peaks at 1.20 V and 1.42 V, at all the investigated pH values. The cyclic voltammetry results demonstrated excellent electrocatalytic activity of the modified electrode toward the oxidation of Rilpivirine as endorsed by the enhanced current responses compared to bare electrode. The electrochemical catalytic activity was further utilized as a sensitive detection method for the investigation of the redox mechanism of Rilpivirine using differential pulse voltammetry (DPV). For experimental conditions optimization the influence of supporting electrolyte and pH was examined and 0.5 M H2SO4 was selected as the best electrolyte for getting intense current signals of the target analyte. The relationship of anodic peaks potentials for peak 1 and peak 2 (EP1 and EP2) with pH values and scan rate was also studied. Scan rate results showed that the oxidation of Rilpivirine at the nanosensor surface occurs under adsorption controlled manner. Therefore, differential pulse adsorptive stripping voltammetric technique was employed for the determination of Rilpivirine. Optimum accumulation potential and time were found as 0 V and 60 s, respectively. Under these optimum conditions, response of Rilpivirine demonstrated a linear behavior in the concentration range from 1.00 × 10−9 to 7.00 × 10-9 M, with a limit of detection value of 3.00 × 10-11 M and 6.40 × 10-11 M for peak 1 and peak 2 in aqueous medium containing 0.5 M H2SO4 as supporting electrolyte, respectively. Interferences studies were achieved in the presence of 500 fold higher concentration of interfering agents to check the selectivity of the developed method. The designed method was successfully applied for the determination of Rilpivirine in biological fluids, urine and synthetic human serum as a real sample. The value of limit of detection were found to be 1.79 × 10-10 M, 4.47 × 10-10 M in serum samples, 5.26 × 10-10 M and 8.27 × 10-10 M in urine samples for peak 1 and peak 2, respectively. Recovery experiments were carried out to check the accuracy and precision of the designed method. Moreover, the repeatability, reproducibility and stability of the modified electrode in supporting electrolyte, serum and urine samples were investigated.

Rational Design of a Redox-Active Nonaqueous Electrolyte for a High-Energy-Density Supercapacitor Based on Carbon Nanotubes

Abstract: A redox-active electrolyte supercapacitor (RAES) is a promising system that increases the energy density of a supercapacitor by providing additional pseudocapacitance, which arises from an inserted redox couple in an electrolyte. However, the energy density of RAESs is still considerably low for practical applications, and enhancing the operating voltage window as well as the capacitance of RAESs is very necessary. In this study, we rationally designed a nonaqueous redox-active electrolyte mainly on the basis of the relative position of the electrochemical stability window of a supporting electrolyte and the redox potential of a redox couple. Therefore, the judicious combination of a redox pair, decamethylcobaltocene/decamethylcobaltocenium, and a supporting electrolyte, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide dissolved in adiponitrile, not only provides additional capacitance from a faradaic redox reaction (21.3 → 57.1 F g–1) but also extends the operating voltage window to almost t...

Application of TiO2-nanotubes/PbO2 as an anode for the electrochemical elimination of Acid Red 1 dye

Abstract: In this study, galvanostatic electrolysis, through the use of the platinum supported on Ti (Ti/Pt) and Ti/TiO2-nanotubes/PbO2 anodes, was conducted in an electrochemical cell with 0.2 L of solution containing 100 mg dm−3 of the textile dye Acid Red 1 (AR1) using Na2SO4 as supporting electrolyte, applying 7.5 and 60 mA cm−2. From the voltammetric curves, it was possible to understand that Ti/TiO2-nanotubes/PbO2 electrode has high oxygen evolution overpotential than Ti/Pt anode. A direct electron transfer reaction is attained between the dye molecules and Ti/Pt surface, at lower currents. Conversely, the AR1 oxidation involves water decomposition intermediates, mainly ·OH radicals at Ti/TiO2-nanotubes/PbO2 anode. The electrolytic process was monitored by the UV–visible spectrometry and the chemical oxygen demand (COD). Results clearly show that Ti/TiO2-nanotubes/PbO2 anode performs better than Ti/TiO2 in removing ARI due to the electrosynthesis of strong oxidants on its surface (·OH and persulfates), achieving a higher oxidation rate, higher current efficiency, and less energy consumption than Ti/Pt electrode.

Unlocking Simultaneously the Temperature and Electrochemical Windows of Aqueous Phthalocyanine Electrolytes

Abstract: The change from organic solvents to aqueous solvents for safe and robust battery electrolytes is desirable for electrochemical energy storage. Thermodynamically, water has an electrochemical stability window of 1.23 V, and pure water freezes at 0 °C. Such properties clearly restrict the high-voltage applications and temperature adaptability of aqueous electrolytes. Herein, we report an aqueous supporting electrolyte containing imidazolium chloride, showing unprecedented large temperature and electrochemical windows. Thermal analysis over −80 to 80 °C shows such an aqueous electrolyte to be free of transition events of icing and phase changes. X-ray scattering results of these aqueous solutions in the presence of active materials reveal the pivotal role of imidazolium chloride to preserve the liquid phase at rather low temperatures. Metal phthalocyanines with electroactive organic ligand rings and multi-electron-transfer reactions at low negative potentials (−0.2 to −1.6 V vs Ag) are demonstrated in water-...

Supporting-Electrolyte-Free Electrochemical Methoxymethylation of Alcohols Using a 3D-Printed Electrosynthesis Continuous Flow Cell System

Abstract: We describe the development of a novel low‐cost small‐footprint 3D‐printed electrosynthesis continuous flow cell system that was designed and adapted to fit a commercially available Electrasyn 2.0. The utility and effectiveness of the combined flow/electrochemistry system over the batch process was demonstrated in the development of an improved and supporting‐electrolyte‐free version of our anodic methoxymethylation of alcohols.

Influence of Electrolyte Composition on the Electrochemical Reaction Mechanism of Bismuth Fluoride Electrode in Fluoride Shuttle Battery

Abstract: Fluoride shuttle battery (FSB) is a promising next-generation battery candidate. In the FSB, metal fluoride and organic solvent containing supporting electrolyte salt and anion acceptor were used a...

A new sensor consisting of Ag-MWCNT nanocomposite as the sensing element for electrochemical determination of Epirubicin

Abstract: Here, we introduce a new electrode comprising silver decorated multiwall carbon nanotube (Ag-MWCNT) as the sensing element for voltammetric investigation of anticancer drug Epirubicin (EP) in human whole blood, urine and injection. Field emission scanning electron microscopy (FE-SEM), TEM, EDX and XRD methods were used to study the surface structure and topography of the modified electrode. We used electrochemical impedance spectroscopy (EIS) as a powerful tool to analyze the electrochemical properties of the new electrode. This modified electrode was applied for investigation of EP by cyclic voltammetry (CV) and square wave voltammetry (SWV) in an acetate buffer solution as a suitable supporting electrolyte (pH 1.5 - 6.8). The CV of EP in the potential range of -1.0 to 1.0 V showed reversible redox peaks that were dependent on pH. We optimized the conditions needed for practical application of the new electrochemical sensor, for which the redox peak current at pH 4.7 was linearly proportional to the concentration of EP in the range of 0.003 - 0.25 μM with a detection limit of 1.0 × 10-3 μM (RSD

Preparation of a novel electrochemical sensor for phosphate detection based on a molybdenum blue modified poly(vinyl chloride) coated pencil graphite electrode

Abstract: Molybdenum blue was electrodeposited on a pencil graphite electrode (PGE) by cyclic voltammetry and it was used in the detection of phosphate ions for the first time in the literature. Polyvinyl chloride was used as a coating agent for the modified electrodes to improve their stability. The characterization of the electrodes was done by using microscopic and electrochemical methods. Parameters affecting the analytical response of the electrode in differential pulse voltammetry such as concentration of supporting electrolyte, immersion time, operation temperature and thickness of film were optimized before the analysis of a soil sample containing phosphate. The prepared electrode exhibited high sensitivity for phosphate. The limit of detection (LOD) and limit of quantification (LOQ) were determined as 2.19 × 10−8 M (S/N = 3) and 7.30 × 10−8 M (S/N = 10), respectively. Quantification of phosphate in soil samples was confirmed by spectroscopic analysis.

Effect of electrolytes on the simultaneous electrochemical oxidation of sulfamethoxazole, propranolol and carbamazepine: behaviors, by-products and acute toxicity

Abstract: In this work, the effect of supporting electrolytes on the simultaneous electrochemical oxidation of the pharmaceuticals sulfamethoxazole (SMX), propranolol (PRO), and carbamazepine (CBZ) in aqueous solutions has been studied. Based on the identified by-products, the degradation mechanisms were proposed and the acute toxicity was evaluated for each electrolyte. Assays were carried out in batch mode in a 2 L undivided reactor using a niobium coated with boron-doped diamond (Nb/BDD) mesh anode and Ti cathode at 2.5 A in presence of different supporting electrolytes (Na2SO4, NaCl, or NaBr) at the same concentration of 7 mM. The degradation rates were higher in the assays with NaCl and NaBr. Reaction by-products were identified by gas chromatography–mass spectrometry. Indirect oxidation by electrogenerated reactive halogen species (RHS) was the main mechanism when halide ions were used as electrolytes. Ten by-products were detected using Na2SO4 as electrolyte, while 19 (12 non-halogenated and 7 halogenated) and 20 (10 non-halogenated and 10 halogenated) using NaCl and NaBr respectively. The proposed degradation pathways involve transformation (hydroxylation, deamination, desulfonation, and halogenation) and bond rupture to produce less molecular weight compounds and their further transformation until total degradation. Chlorinated and brominated by-products confirm halogenation reactions. The electrogenerated RHS presented a significant inhibition effect on Vibrio fischeri; nevertheless, acute toxicity was not presented using Na2SO4 as electrolyte and a pharmaceutical concentration of 5 μg/L. In this view, the role of the supporting electrolyte in electrochemical oxidation process is crucial since it strongly influence degradation rate, by-products, and acute toxicity.