Showing papers on "Supporting electrolyte published in 2018"

Ultrathin Hierarchical Porous Carbon Nanosheets for High-Performance Supercapacitors and Redox Electrolyte Energy Storage

Abstract: The design of advanced high‐energy‐density supercapacitors requires the design of unique materials that combine hierarchical nanoporous structures with high surface area to facilitate ion transport and excellent electrolyte permeability. Here, shape‐controlled 2D nanoporous carbon sheets (NPSs) with graphitic wall structure through the pyrolysis of metal–organic frameworks (MOFs) are developed. As a proof‐of‐concept application, the obtained NPSs are used as the electrode material for a supercapacitor. The carbon‐sheet‐based symmetric cell shows an ultrahigh Brunauer–Emmett–Teller (BET)‐area‐normalized capacitance of 21.4 µF cm−2 (233 F g−1), exceeding other carbon‐based supercapacitors. The addition of potassium iodide as redox‐active species in a sulfuric acid (supporting electrolyte) leads to the ground‐breaking enhancement in the energy density up to 90 Wh kg−1, which is higher than commercial aqueous rechargeable batteries, maintaining its superior power density. Thus, the new material provides a double profits strategy such as battery‐level energy and capacitor‐level power density.

MoP Nanoparticles Supported on Indium-Doped Porous Carbon: Outstanding Catalysts for Highly Efficient CO2 Electroreduction

Abstract: Electrochemical reduction of CO2 into value-added product is an interesting area. MoP nanoparticles supported on porous carbon were synthesized using metal-organic frameworks as the carbon precursor, and initial work on CO2 electroreduction using the MoP-based catalyst were carried out. It was discovered that MoP nanoparticles supported on In-doped porous carbon had outstanding performance for CO2 reduction to formic acid. The Faradaic efficiency and current density could reach 96.5 % and 43.8 mA cm-2 , respectively, when using ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate as the supporting electrolyte. The current density is higher than those reported up to date with very high Faradaic efficiency. The MoP nanoparticles and the doped In2 O3 cooperated very well in catalyzing the CO2 electroreduction.

Catalyst- and Supporting Electrolyte-Free Electrosynthesis of Benzothiazoles and Thiazolopyridines in Continuous Flow

Abstract: A catalyst- and supporting electrolyte-free method for electrochemical dehydrogenative C–S bond formation in continuous flow has been developed. A broad range of N‑ arylthioamides have been converted to the corresponding benzothiazoles in good to excellent yields and with high current efficiencies. This transformation is achieved using only electricity and laboratory grade solvent, avoiding degassing or the use of inert atmosphere. This work highlights three advantages of electrochemistry in flow, which is (i) a supporting electrolyte-free reaction, (ii) an easy scale‑ up of the reaction without the need for a larger reactor and, (iii) the important and effective impact of having a good mixing of the reaction mixture, which can be achieved effectively with the use of flow systems. This clearly improves the reported methods for the synthesis of benzothiazoles.

Ion transport mechanisms in bipolar membranes for (photo)electrochemical water splitting

Abstract: Bipolar membranes (BPMs) have attracted growing interest in electrochemical and photoelectrochemical systems, as they allow the unique ability to pair two different electrolytes which can be optimized for their respective oxidation and reduction reactions. Understanding the membrane voltage at a non-extreme pH gradient (ΔpH < 14) is an important step towards practical applications for electrochemical conversions, as many (photo-)electrodes and catalysts can only operate efficiently in a limited pH range. To obtain a better understanding of the individual effects that determine the BPM voltage, a complete series of experiments measuring the actual BPM voltage as a function of the pH, salt type/concentration, flow rate and current density is needed. In this paper, we present experimental results of voltage–current relations for a BPM using 16 different pH differences, 4 concentrations, 7 flow rates and permeation of 6 different ionic species. The results show that both ion cross-over and local diffusion boundary layers play important roles in the BPM voltage. We also show that the supporting electrolyte composition plays an important role, even more important than the pH itself, which is an important parameter to realize practical application of BPMs in electrochemical cells.

Electrochemical decolorization of Rhodamine B dye: Influence of anode material, chloride concentration and current density

Abstract: Surface water contamination by dyes released from a variety of industries is an environmental problem of great concern. However, electrochemical oxidation is a promising alternative for water treatment. In this paper, we studied the electrochemical oxidation of Rhodamine B (RhB) dye on the Ti/RuO2–IrO2 (DSA®) and SnO2 anodes comparing their efficiencies. The effect of some parameters, such as current density, initial pH (pH0), nature, concentration of electrolyte and temperature at the electrochemical oxidation was investigated evaluating the decolorization and the chemical oxygen demand (COD) removal at optimal conditions. Complete decolorization of RhB was achieved in the presence of chloride ions at different times using both electrodes. An optimum efficiency was obtained at pH 6.5, T = 25 °C. Also, the current density of 40 mA cm−2 using the DSA electrode in NaCl 0.05 mol L−1+ Na2SO4 0.1 mol L−1 mixture solution as a supporting electrolyte, 100% color removal and 61.7% chemical oxygen demand removal after 90 min of electrolysis were achieved. DSA showed better performance than SnO2 in wide operating conditions and was proved to be more cost-effective and more efficient. The effectiveness of the degradation is explained by indirect electrochemical oxidation, where in the presence of chlorides electrolyte leads to the electro-generation of strong oxidant species, such as Cl2 and ClO− ions, improving the efficiency of treatment at both electrodes.

Electrochemical oxidation of paracetamol in water by graphite anode: Effect of pH, electrolyte concentration and current density

Abstract: Paracetamol is one of the micropollutant in water and most frequently used drugs as moderate pain reliever. These micropollutants are serious threat to human and environment. In the present investigation, we made attempt to degrade the electrochemical oxidation of paracetamol in water by graphite as anode. Electrooxidation behavior of paracetamol at graphite anode was tested by cyclic voltammetry technique performed in the potential range of -1.0 to +1.0 V versus Ag/AgCl. The optimized conditions were obtained by varying different factors, such as electrolyte concentration (0.02-0.1 M), current density (3.1–7.1 mA/cm2), initial pH (4–8) and paracetamol concentration (20 mg L−1). The results showed that the maximum removal of paracetamol concentration, chemical oxygen demand (COD) and total organic carbon (TOC) reached >90%, >82% and >65% after 240 min electrolysis at an initial pH 4, having paracetamol concentration of 20 mg L−1 at a constant current density of 5.1 mA/cm2 with 0.1 M Na2SO4 supporting electrolyte. Different SO42- concentrations in water promoted the electro generation of strong mediator oxidant species, such as OH, SO4 - and S2O82- increasing the removal efficiency of paracetamol. The degradation of paracetamol and its mineralization trend were monitored by UV–vis spectrophotometric method and total organic carbon (TOC) analyzer, respectively. FT-IR spectra confirmed that the functional group changes after electrolysis of paracetamol. HPLC studies revealed the byproduct (hydroquinone, benzoquinone and carboxylic acid) formation during the electrolysis process. On the other hand, researchers are actively involved in ozonation, photocatalysis, activated charcoal and biological treatments etc., to remove/degrade micropollutant, which are major drawbacks for the implications.

Surface Reconstruction of Polycrystalline Cu Electrodes in Aqueous KHCO_3 Electrolyte at Potentials in the Early Stages of CO_2 Reduction

Abstract: The reconstruction of the Cu(pc) polycrystalline surface at potentials that correspond to the early stages of CO_2 reduction in 0.1 M KHCO_3 was investigated by electrochemical scanning tunneling microscopy (ECSTM) at −0.90 V (SHE). A kinetically hindered surface reconstruction of the topmost layers of Cu(pc) into the (100) face was observed, reminiscent of the transformation previously reported at the same electrode potential in 0.1 M KOH. Evidently, the same reconstructed surface, Cu(pc)-[Cu(100)], can be generated in either 0.1 M KHCO_3 (pH 8) or 0.1 M KOH (pH 13). In addition, only minimal structural disruption was observed when the reconstructed surface was transferred from KHCO_3 to KOH electrolyte, and vice versa, provided the solution exchange was executed potentiostatically at −0.90 V. The structural convergence toward the same (100) facet regardless of pH or supporting electrolyte strongly suggests that the Cu(pc) → Cu(pc)-[Cu(100)] surface reorganization is a general phenomenon driven primarily by the rather negative potential applied on the electrode.

Solution Properties and Practical Limits of Concentrated Electrolytes for Nonaqueous Redox Flow Batteries

Abstract: Nonaqueous redox flow batteries (NRFBs) use energized organic fluids that contain redox active organic molecules (ROMs) and supporting electrolyte. Such all-organic electrolytes have wider electrochemical stability windows than the more familiar aqueous electrolytes, potentially allowing a higher energy density in the solutions of charged ROMs. As this energy density increases linearly with the concentration of the charge carriers, physicochemical properties of concentrated ROM solutions in both states of charge present considerable practical interest. For NRFBs to become competitive with other types of flow cells, the current techno-economic analyses favor highly concentrated solutions (>1 M) with high ionic conductivity (>5 mS/cm). It is not presently clear that such solutions can have the required dynamic properties. In this study, we show that ion diffusivities and conductivities of ROM-containing electrolytes reach maxima around 0.5 M and decrease significantly at higher concentrations; realistic lim...

Photoelectrocatalytic performance of nanostructured p-n junction NtTiO2/NsCuO electrode in the selective conversion of CO2 to methanol at low bias potentials

Abstract: Aiming a selective reduction of CO2 to methanol, a p-n junction semiconductor was constructed based on CuO nanospheres (NsCuO) deposited at TiO2 nanotubes (NtTiO2). The NtTiO2/NsCuO material demonstrated smaller charge transfer resistance, smaller flat band potential and wider optical absorption when compared with NtTiO2 and/or Ti/TiO2 nanoparticles coated by higher size particles of CuO (Ti/TiO2/CuO). The selective reduction of dissolved CO2 to methanol was promoted at lower potential of +0.2 V and UV–vis irradiation in 0.1 mol L−1 K2SO4 electrolyte pH 8 with 57% of faradaic efficiency. Even though the performance of the nanostructured material NtTiO2/NsCuO was similar to the non-completely nanostructured material Ti/TiO2/CuO (0.1 mmol L−1 methanol), the conversion to methanol has been significantly increased when hydroxyls (0.62 mmol L−1) and holes scavengers (0.71 mmol L−1), such as p-nitrosodimethylaniline (RNO) or glucose, respectively, were added in the supporting electrolyte. It indicates that photogenerated electron/hole pairs are spatially separated on p-n junction electrodes, which produces effective electrons and long-life holes, influencing the products formed in the reaction. A schematic representation of the heterojunction effect on the photoelectrocatalytic CO2 reduction is proposed under the semiconductor and each supporting electrolyte, which improves the knowledge about the subject.

Photo-electro-Fenton process applied to the degradation of valsartan: Effect of parameters, identification of degradation routes and mineralization in combination with a biological system

Abstract: In this work, the oxidation of the antihypertensive drug valsartan by the Electro-Fenton (EF) and photo-electro-Fenton (PEF) processes was studied using a Ti/IrO2 doped with SnO2 as anode, and a carbon felt air diffusion electrode as cathode. Initially, the influence of variables such as supporting electrolyte type, current density, and pH on EF and/or PEF processes was evaluated. The processes were carried out in batch mode, in an open and undivided cell of 200 cm3. The efficiency of the systems was evaluated in terms of the removal of the initial contaminant and rate of mineralization. When NaCl was used as a supporting electrolyte at pH 3.0 and current density 3.46 mA/cm2 adding 3.6 × 10−5 mol/L of Fe2+, total valsartan (20 mg/L) degradation was observed after 45 min. After 120 min, even if total removal of valsartan was reached, only 25% of mineralization was obtained. Thus, valsartan degradation tests at near neutral pH in presence of oxalic acid (4.6 × 10−5 mol/L) lead to comparable results with those obtained at pH 3.0. Primary aromatic intermediates were identified by high resolution mass spectrometry (HRMS) using hybrid quadrupole- time-of-flight (QTOF) MS, from which an initial degradation pathway was proposed. At the end of the PEF system, several aliphatic acids were accumulated and observed, which were effectively removed in a subsequent aerobic biological system. The results demonstrate the feasibility of PEF and biological coupling process to completely mineralize emerging pharmaceutical pollutants, such as valsartan, at natural pH.

Understanding electroanalytical measurements in authentic human saliva leading to the detection of salivary uric acid

Abstract: The electroanalytical responses of several redox-active species are investigated in authentic human whole saliva. First, we show that ferrocenemethanol (FcCH2OH) and ferrocyanide ([Fe(CN)6]4−) display well-defined voltammetry in undiluted saliva at a carbon microdisc electrode without the addition of supporting electrolyte. Second, we demonstrate that dissolved oxygen is detectable in saliva. The ferrocenemethanol oxidation is shown not to be altered by the medium apart from the steady-state currents which change according to the viscosity of the solvent. In contrast, the voltammetry of ferrocyanide oxidation and oxygen reduction in authentic saliva are significantly different from those in synthetic saliva or aqueous electrolyte. It is demonstrated that the electrode is partially blocked by organic molecules or other electrochemically inert species when placed in authentic saliva samples. The distortion in voltammetry thus reflects the different surface sensitivity of the two processes. Ohmic drop is proved to be minimal at microelectrodes even without added electrolyte. Microelectrodes are thus suitable for use in electrochemical analysis of saliva samples. Finally, we demonstrate that uric acid which is a potential biomarker for gout, oral cavity cancer and other several diseases can be directly detected in authentic saliva at a carbon microelectrode with the interference of ascorbic acid and dopamine of no more than 10%.