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[en] The two-dimensional Saul’yev method of simulating processes at an ultramicrodisk electrode is compared with the fully implicit backward differentiation method started with a few backward implicit steps, and an alternating direction implicit method. 2D Saul’yev is convenient to program and although it is significantly slower in execution than the other two methods, it still executes in reasonable time, and yields equally good results with a suitable choice of discrete intervals, and despite its inherent propagation problem, and a certain restriction in the relationship of the spatial and temporal intervals. Saul’yev was implemented for the diffusion limited potential step experiment, as well as linear sweep voltammetry for a reversible system.
[en] Highlights: • Eco-friendly gelatin based electrolyte containing Iodide/triiodide I−/I3− redox mediator. • Integration in Electrochromic Device based on anchored-nanostructured TiO2-viologen. • White to Blue Switch for ECDs stable for thousand cycles. - Abstract: In the present study, a novel gel electrolyte composition combining lithium iodide LiI in 1-butyl-3-methylimidazolium iodide (BMII) ionic liquid,triiodide I3-/I- redox mediator and biodegradable gelatin is proposed for electrochromic devices (ECDs). More precisely, ECDs are assembled using viologen anchored − nanostructured TiO2 (deposited on FTO glass substrate by doctor blading at low temperature) as electrochromic material, FTO as counter-electrode and the gel electrolyte as redox mediator in between. Fast switching times and high cycling stability, up to 20000 cycles, are recorded. The optical reflectance modulation at 550 nm between white and blue color reaches a contrast value ΔR of about 19% in less than 4 seconds after 100 cycles.
[en] Highlights: • Cathodic reduction becomes a feasible alternative to activate persulfate. • A synergistic effect of electro-PS with heat activation improve the DB3 mineralization. • Complete decolorization within 30 min was achieved at 70 °C in the synergic process. - Abstract: This work assesses the role of the operational conditions upon the electro-activation of persulfate (electro-PS) using Ti/IrO2Ta2O5 electrode for the decolorization of anthraquinone azo dye Disperse Blue 3 (DB3). The studied variables include current density (j) (5–80 mA cm−2), persulfate concentration based on the stoichiometric dose for complete DB3 mineralization (20–100%), temperature (30–90 °C) and pH (3–12) as well as the influence of dissolved oxygen. The persulfate activation from cathodic reduction was confirmed by linear sweep voltammetry (LSV). The increase in j enhanced the PS decomposition and, consequently, decolorization efficiency, because of the greater production of sulfate radicals (SO4• −). Besides, the combination of electro-PS with thermal activation resulted in a synergistic effect upon the DB3 mineralization. In the range 30–70 °C, electro-PS led to a significantly higher TOC conversion (above 60% at 40 mA cm−2) than sole heat-activated PS. This difference steeply decreased as temperature increases, achieving similar TOC conversion at 90 °C after 60 min.
[en] Highlights: • Poly-l-histidine was innovatively applied to functionalize the CMWCNTs array. • A self-assembled monolayer of 4-aminothiophenol was introduced to attach CMWCNTs array on AuE. • Developed a mild wet chemical covalent self-assembly procedure via EDC/NHS. • Sensitive detection of glucose both in PBS and human serum samples. • Developed a promising platform based on the PLH-CMWCNTs array for various biosensors fabrication. - Abstract: Novel approachs to functionalize carboxylated multi-walled carbon nanotubes (CMWCNTs) array with poly-l-histidine (PLH) on a self-assembled monolayer (SAM) of 4-aminothiophenol (4ATP) were developed for the first time. With help of π–π interaction and chelation of the side imidazole groups in poly-l-histidine, the array showed efficient electron transfer and mild biocompatibility. By immobilizing glucose oxidase (GOx) to AuNPs electrodeposited on the array, a high-powered glucose biosensor with excellent electrocatalytic performance was fabricated and applied for glucose determination in human serum samples. The prepared biosensor exhibited highly sensitive response to glucose under the operating voltage of 600 mV with sensitivity of 96.04 μA mM−1 cm−2, linear range of 0.005–6.5 mM, lowest detection limit (LOD) of 0.7 μΜ (S/N = 3) and Michaelis constant (KM) of 3.92 mM. Compared with other glucose sensors previously reported, this work showed higher sensitivity, lower detection limit and wider linear range. Furthermore, the developed array may provide a promising platform for various biosensors fabrication.
[en] Unequal electrode capacitance in a symmetric supercapacitor results in an unequal voltage distribution on the two electrodes and the supercapacitor usually cannot utilize the full electrochemical window of electrolyte. In this study, the voltage distribution on the two electrodes of graphene supercapacitor is optimized by an adjustment of electrode mass ratio from 1 to 1.5 and an enlarged energy density of 118 Wh kg−1 is achieved at operating voltage 4.7 V using an ionic liquid electrolyte 1-methyl-1-propylpiperidinium bis (trifluoromethyl sulfonyl) imide (MPPp-TFSI).
[en] Highlights: • An label free aptasensor for sensitive detection of Interleukin 6 is presented. • The linear domain for IL6 detection was from 1 pg mL−1 to 15 μg mL−1. • The aptasensor was applied for serum samples with a detection limit of 0.33 pgmL−1. - Abstract: A highly sensitive, selective, fast and stable electrochemical aptasensor, based on a screen-printed carbon electrode modified with a nanocomposite architecture consisting of polypyrrole and gold nanoparticles was designed for interleukin6 detection in human serum. The simultaneous presence of the conductive polymer and gold at the electrode surface provided a suitable environment for the interleukin6 specific aptamer immobilization of through sulfur-gold bonding. Cyclic voltammetry and electrochemical impedance spectroscopy were used for the monitoring, characterization and optimization of the biosensor during all the steps involved in the fabrication process. After complete optimization, the aptasensor exhibited a good impedimetric response towards the target analyte. The results showed that interleukin6 could be detected in a wide linear range from 1 pg mL−1 to 15 μg mL−1 with a detection limit of 0.33 pg mL−1. The biosensor was tested in the presence of other proteins in human serum samples with good recoveries.
[en] Highlights: • Diffusion of ferrocene in dialkylimidazolium ionic liquids is well described by the Stokes-Einstein equation with slip boundary conditions. • Diffusion is faster in a symmetric than in a non-symmetric IL with same number of alkyl carbons N, with the difference decreasing with increasing N. • The Fc0/+ redox couple is an ideal reference model for voltammetric studies in ILs. - Abstract: The diffusion of ferrocene (Fc) molecules in ionic liquids (ILs) was studied using cyclic voltammetry. The symmetric ILs 1,3-dialkylimidazolium bis[(trifluoromethane)sulfonyl]amide ([(CN/2)2im][NTf2] with N = 4, 6, 8, and 10) and non-symmetric ILs 1-alkyl-3-methylimidazolium bis[(trifluoromethane)sulfonyl]amide ([CN−1C1im][NTf2] with N = 3, 4, 6, 8, and 10) were used to examine the effect of the symmetry of alkyl substitution on the cation and the role of alkyl chain length on the diffusion of Fc. The diffusion coefficient D of Fc was determined by applying the Randles-Sevcik equation to the peak current in the cyclic voltammograms. The diffusion coefficient was found to be higher in a symmetric IL than in a non-symmetric IL with the same number of alkyl carbon atoms N, with the difference decreasing with increasing N. The diffusion of Fc in these ILs is well described by the Stokes-Einstein equation with slip boundary conditions, but with an effective hydrodynamic radius of 0.23 ± 0.01 nm, which is less than the 0.27 nm crystallographic radius of Fc, in agreement with previous studies of the diffusion of solutes in ILs that show the hydrodynamic radius to be less than the van der Waals radius of the solute.
[en] A model of a non-polarizable interface is developed and considered in terms of the specific adsorption of charged redox species and the nonspecific adsorption of the supporting electrolyte. The adsorption coefficients of charged redox species depend on their charges and the potential at the inner Helmholtz plane. The adsorbed amounts of the redox species and supporting electrolyte are estimated using the Frumkin isotherm and Gouy–Chapman theory, respectively. The potential dependence of the adsorbed amount of either one or both of the oxidized and reduced forms of the redox species is maximized near its standard potential. The electrocapillary equation at a non-polarizable liquid metal–solution interface under an externally controlled potential is revisited. The derived electrocapillary equation facilitates calculating the electrocapillary curve of the non-polarizable interface based on the quantity of adsorbed ions. The electrocapillary curve calculated based on the model may have a concave part, which would indicate that the interface is thermodynamically forbidden, near the standard redox potential of the redox couple.
[en] Highlights: • The SrSc0.175Nb0.025Co0.8O3-δ perovskite was evaluated for proton conducting SOFC. • Polarization resistance of SSNC decreased obviously via introducing H2O in gas phase. • The symmetrical cell showed the lowest Rp of 0.26 Ω cm−2 at 600 °C in 3% H2O-air. • This study suggests that in situ creation of H+ is possible at the SSNC cathode. - Abstract: Proton-conducting solid oxide fuel cells (H+-SOFCs) have attracted considerable interest recently. However, the overall cell performance of H+-SOFCs is still low due to the lack of a promising cathode material. In this study, SrSc0.175Nb0.025Co0.8O3-δ (SSNC) was synthesized for evaluation as a cathode material in H+-SOFCs based on a BaZr0.1Ce0.7Y0.2O3-δ (BZCY) electrolyte. The chemical compatibility and stability of the SSNC cathode with the BZCY electrolyte in humidified air were studied. In addition, the electrochemical behavior of the SSNC cathode on the BZCY electrolyte was investigated using SSNC/BZCY/SSNC symmetrical cells at 600 °C in dry air and humidified air at various H2O partial pressures. Promising electrocatalytic activity was observed for the SSNC cathode in humidified air. The area specific resistance obtained on symmetrical cells at 600 °C in a 10% H2O-air atmosphere was 0.26 Ω cm2. A promising peak power density of 498 mW cm−2 was obtained using an anode-supported cell with a 46 μm-thick BZCY electrolyte layer at 700 °C.
[en] Present investigation deals with electrochemical determination of copper(II), lead(II) and mercury(II) ions, using ethylenediaminetetraacetic acid (EDTA) chelating ligand modified polyaniline (PANI) and singe walled carbon nanotubes (SWCNTs) based nanocomposite (PANI/SWNCTs). Stainless steel (SS) electrode was modified with PANI and SWCNTs based nanocomposite. PANI/SWCNTs nanocomposite was electrochemically synthesized using potential cycling technique. Further it was modified with EDTA in the presence of 1-ethyl-3(3-(dimethylamin propyl)carbodiimide (EDC) as activating agent, using dip coating technique at room temperature. The EDTAPANI/SWCNTs/SS electrode was characterized by cyclic voltammetry in 0.5 M H2SO4, which was complemented with electrochemical impedance spectroscopy (EIS). AFM and SEM analysis was applied for the morphological studies of EDTAPANI/SWCNTs nanocomposite structure. FTIR analysis was applied for the structural and compositional analysis of EDTAPANI/SWCNTs nanocomposite. All the characterizations were performed before and after the modification of PANI/SWCNTs nanocomposite structure with chelating ligand. Differential pulse voltammetry (DPV) was used for the determination of Cu(II), Pb(II) and Hg(II) ion concentrations. Analytical characteristic such as selectivity and sensitivity of here above-mentioned metal ions was studied. The limit of detection the EDTAPANI/SWCNTs/SS toward Cu(II), Pb(II) and Hg(II) was determined as 0.08 μM, 1.65 μM and 0.68 μM respectively.