Strong anion receptor-assisted boron-based Mg electrolyte with wide electrochemical window and non-nucleophilic characteristic

Herein we present a strong anion receptor-assisted Mg-ion electrolyte, which is synthesized from tris(2H-hexafluoroisopropyl) borate (THFPB) and MgO in 1,2-dimethoxyethane (DME). The as-prepared borate magnesium oxide complex (BMOC) electrolyte delivers exceptional electrochemical performances, including extremely high anodic stability (up to 4.2 V vs. Mg), non-corrosivity to stainless steel and aluminium foils, and reasonable ionic conductivity of 1.74 × 10^− 4 S cm^− 1. In addition, by virtue of the non-nucleophilic characteristic of the BMOC electrolyte, S ||BMOC ||Mg cells have been assembled, which show a high stable discharge capacity of 1030 mAh g^− 1 for 15 cycles and one well-defined voltage plateau of ≈ 1.1 V vs. Mg, yielding a desirable energy density beyond 1100 Wh kg^− 1 based on the weight of sulfur in cathodes.     

Electrolytic in situ STM investigation of h-BN-Nanomesh

Single sheet boron nitride layers on thin rhodium (1 1 1) films were formed upon thermal decomposition of borazine under ultra-high vacuum (UHV) conditions. They were transferred and investigated in an electrolytic environment. In 0.1 M HClO₄, the presence and stability of the so-called nanomesh super structure with a lattice constant of 3.2 nm is established with electrochemical impedance spectroscopy, cyclic voltammetry and subsequent imaging with in situ scanning tunneling microscopy (STM) under potential control. In the electrolyte, the BN nanomesh acts as a dielectric layer with an unusual behaviour of the impedance, where the capacitive component is larger than on a Rh(1 1 1) reference sample. It exhibits reversible hydrogen adsorption and desorption at a potential of −600 mV vs. a saturated mercury sulphate reference electrode (MSE). The unit cell of the nanomesh is imaged by STM and shows hexagonally arranged two-dimensional pores with a diameter of 2 nm. At a fixed potential, the nanomesh was stable for long time, but after repeated potential sweeps between +260 and −540 mV vs. MSE, STM indicates roughening, though a 12 × 12 superstructure was recovered after annealing in UHV.     

Amperometric biosensing of glutamate using carbon nanotube based electrode

Amperometric biosensing of glutamate using nanobiocomposite derived from multiwall carbon nanotube (CNT), biopolymer chitosan (CHIT), redox mediator meldola’s blue (MDB) and glutamate dehydrogenase (GlDH) is described. The CNT composite electrode shows a reversible voltammetric response for the redox reaction of MDB at −0.15 V; the composite electrode efficiently mediates the oxidation of NADH at −0.07 V, which is 630 mV less positive than that on an unmodified glassy carbon (GC) electrode. The CNTs in the composite electrode facilitates the mediated electron transfer for the oxidation of NADH. The CNT composite electrode is highly sensitive (5.9 ± 1.52 nA/μM) towards NADH and it could detect as low as 0.5 μM of NADH in neutral pH. The CNT composite electrode is highly stable and does not undergo deactivation by the oxidation products. The electrode does not suffer from the interference due to other anionic electroactive compounds such as ascorbate (AA) and urate (UA). Separate voltammetric peaks have been observed for NADH, AA and UA, allowing the individual or simultaneous determination of these bioanalytes. The glutamate biosensor was developed by combining the electrocatalytic activity of the composite film and GlDH. The enzymatically generated NADH was electrocatalytically detected using the biocomposite electrode. Glutamate has been successfully detected at −0.1 V without any interference. The biosensor is highly sensitive, stable and shows linear response. The sensitivity and the limit of detection of the biosensor was 0.71 ± 0.08 nA/μM and 2 μM, respectively.     

Electrochemical cycling of Mg in Mg[TFSI]2/tetraglyme electrolytes

The electrochemical reversibility of magnesium was observed in an electrolyte consisting of 0.5 M Mg[TFSI]₂ in tetraglyme in the presence of a small amount of Mg[BH₄]₂. The cyclic efficiency of the cathodic/anodic process was found to increase initially with [BH₄]⁻ then plateau at about 75% beyond 6 mM in these experiments. This concentration is in the region of that indicated by Karl Fischer analysis of the electrolyte as required of [BH₄]⁻ as a dehydrating agent. Cyclic voltammetry showed the reduction onset potential at approximately − 0.35 V vs. Mg and subsequent oxidation around 0 V vs. Mg. Stable cyclic efficiency of approximately 75% over 500 cycles is demonstrated on a platinum substrate. Mg cycling on magnesium, copper and aluminium substrates all show stable cycling over 500 cycles with cyclic efficiency > 73%.     

Size and stability modulation of ionic liquid functionalized gold nanoparticles synthesized using Elaeis guineensis (oil palm) kernel extract

Bio-synthesis approach for gold nanoparticles (AuNPs) has received tremendous attention as an efficient and eco-friendly process. However, kinetic growth and colloidal stability of AuNPs synthesized by this process remained challenging. In this study, Elaeis guineensis (oil palm) kernel (OPK) extract prepared in an ionic liquid (IL)[EMIM][OAc] (1-ethyl-3-methylimidazolium acetate) was employed to control and tune the size and morphology of AuNPs. Synthesized AuNPs were characterized using UV-vis spectrophotometer, dynamic light scattering (DLS) and transmission electron microscopy (TEM) to observe any changes in absorbance, surface charge and particle size, respectively. IL mediated AuNPs were examined for 120 days and found well dispersed and stable at room temperature. UV-vis analysis demonstrated that volume of extract played an important role to control the stability of AuNPs. After 120 days, only 8.86% reduction from maximum absorbance was observed using 2 mL of volume of extract, which was elevated to 47.64% in case of 0.3 mL. TEM analysis was performed periodically after day 1, day 30, day 60, day 90 and day 120 and minor increase in the size was observed. Insignificant change in zeta potential value after 120 days supported enhanced stability of IL mediated AuNPs. Crystalline nature of AuNPs was confirmed by X-ray diffraction (XRD) pattern. The particles size and zeta potential of AuNPs was measured as 8.72 nm and −18.7 mV, respectively. However, the absence of [EMIM][OAc] from OPK extract resulted into larger particles size (9.64 nm), low zeta potential value (−13.9 mV) and enhanced aggregation of particles. Finally, experimental data were used to predict the theoretical and the experimental settling time for AuNPs to evaluate colloidal stability.     

Influence of surface oxygen groups on V(II) oxidation reaction kinetics

The role of surface oxygen groups on the kinetics of the V(II) oxidation reaction was studied on modified glassy carbon (GC) electrodes by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The reaction was found to be sensitive to the presence of oxygen groups on the electrode surface. Higher O/C ratios determined by X-ray photoelectron spectroscopy (XPS) corresponded to higher reactivities and lower charge transfer resistances measured in a 1 M V(II) electrolyte. The stability of an oxidised GC surface was also investigated in a 1 M V(II) electrolyte by potential holding and cycling experiments. It was found that after holding and cycling to successively more negative potentials up to − 0.8 V/RHE, the electrode surface lost its initial reactivity.     

Cationic nanoemulsions as non-viral vectors for plasmid DNA delivery

Non-viral gene carriers have been extensively investigated as alternatives to viral vectors for therapeutic gene delivery. Many cationic lipid carriers including liposomes, emulsions, and solid lipid nanoparticles are used to transfer plasmid DNA. Stable nanoemulsions were prepared and modified by conjugating fatty acids with cationic amino acids including lysine, arginine, and histidine with the help of carbodiimide. Concentrations of crosslinker and amino acids were optimized to obtain the maximal surface potential. The zeta potential and size distribution of the cationic nanoemulsions were measured using photon correlation spectroscopy. The morphology of nanoemulsion-DNA complexes was examined by transmission electron microscopy. The transfection efficiencies and cytotoxicity of three cationic nanoemulsions were evaluated using 3T3 fibroblast cells. The maximal zeta potentials of lysine-, arginine-, and histidine-modified nanoemulsions were 50, 43, and 7 mV, respectively. The transfection efficiencies of amino acid-modified nanoemulsions were in the order of lysine > arginine > histidine. Low cytotoxicities of these three amino acid-modified nanoemulsions were observed. A facile and inexpensive in situ modification for producing cationic nanoemulsions was developed. The results show the potential of amino acid-modified cationic nanoemulsions as non-viral vectors for gene delivery.     

The effect of temperature oscillation on the passive corrosion properties of Alloy 22

A temperature-oscillating heated electrode technique (TOHET) was developed for investigating the temperature effect on the passive corrosion properties of Alloy 22 (UNS N06022, Ni–22Cr–13Mo–3W–3Fe), which has been selected as the corrosion-resistant material (CRM) of the waste package outer barrier for the high level nuclear waste (HLNW) repository at Yucca Mountain, NV, USA. Cyclic and potentiostatic polarization tests were conducted on a temperature-controlled hot surface of Alloy 22, which was immersed in simulated Yucca Mountain ground waters. The current recorded during cyclic polarization tests was sensitive to temperature changes when the temperature amplitude was greater than 2 °C. Corrosion potential increased from −293 mV to −256 mV (Ag/AgCl) when temperature was decreased from 102 °C to 72 °C. Current variation was also observed during a potentiostatic test at −150 mV over which temperature oscillated between 65 °C and 95 °C. The log–linear plot of passive current density vs. temperature exhibited a linear relationship. In summary, the TOHET method is a valuable technique for studying the effects of temperature on the corrosion rate of passive alloys.     

The electrochemical properties of thermophilic cytochrome P450 CYP119A2 at extremely high temperatures in poly(ethylene oxide)

The electrochemical measurements were carried out by using thermophilic cytochrome P450 CYP119A2 (P450st) modified with poly(ethylene oxide) (PEO) in PEO₂₀₀ as an electrochemical solvent. The PEO modified P450st gave clear reduction–oxidation peaks by cyclic voltammetry in oxygen-free PEO₂₀₀ up to 120 °C. The midpoint potential measured for the P450st was −120 mV vs. [Fe(CN)₆]⁴⁻/[Fe(CN)₆]³⁻ at 120 °C. The peak separation, ΔE, was 16 mV at 100 mV/s. The estimated electron transfer rate of PEO-P450st at 120 °C was 35.1 s⁻¹. The faster electron transfer reaction was achieved at higher temperatures. The electrochemical reduction of dioxygen was observed at 115 °C with the PEO-modified P450st system.     

Bioelectrocatalytic oxidation of glucose by hexose oxidase directly wired to graphite

Glucose-oxidizing enzymes are widely used in electrochemical biosensors and biofuel cells; in most applications glucose oxidase, an enzyme with non-covalently bound FAD and low capability of direct electronic communications with electrodes, is used. Here, we show that another glucose-oxidizing enzyme with a covalently bound FAD center, hexose oxidase (HOX), adsorbed on graphite, exhibits a pronounced non-catalytic voltammetric response from its FAD, at − 307 mV vs. Ag/AgCl, pH 7, characterized by the heterogeneous electron transfer (ET) rate constant of 29.2 ± 4.5 s^− 1. Direct bioelectrocatalytic oxidation of glucose by HOX proceeded, although, with a 350 mV overpotential relative to FAD signals, which may be connected with a limiting step in biocatalysis under conditions of the replacement of the natural redox partner, O₂, by the electrode; mediated bioelectrocatalysis was consistent with the potentials of a soluble redox mediator used. The results allow development of HOX-based electrochemical biosensors for sugar monitoring and biofuel cells exploiting direct ET of HOX, and, not the least, fundamental studies of ET non-complicated by the loss of FAD from the protein matrix.     

Polysulphides reversible faradaic reactions in supercapacitor application

The electrochemical performance of polysulphide compounds as an electrolyte in supercapacitor was studied. Numerous reversible faradaic reactions during which oxidation state of sulphur changes from − 2 to − 0.4 work as an efficient source of faradaic reactions. Polysulphides were synthesized by a simple, inexpensive method. This innovative system offers quite high values of specific capacitance, more than twice as high as electrolyte without polysulphides. In addition, cyclability (5000 cycles) does not influence the capacitance of the electrochemical capacitor when polysulphide compounds are used as the electrolyte.     

Direct electrochemical response of Myoglobin using a room temperature ionic liquid, 1-(2-hydroxyethyl)-3-methyl imidazolium tetrafluoroborate,as supporting electrolyte

Direct electrochemical response of Myoglobin (Myb) at the basal plane graphite (BPG) electrode was observed when a room temperature ionic liquid (RTIL), 1-(2-hydroxyethyl)-3-methyl imidazolium tetrafluoroborate ([HEMIm][BF₄]), was used as the supporting electrolyte. In a 0.17 M [HEMIm]BF₄ aqueous solution, a couple of well-defined redox peaks of Myb could be obtained, whose anodic and cathodic peak potentials were at −0.158 and −0.224 V (vs. Ag/AgCl), respectively. Both anodic and cathodic peak currents increased linearly with the potential scan rate. Compared with the supporting electrolyte of phosphate buffer, [HEMIm][BF₄] played an obvious promotion for the direct electron transfer between Myb and the BPG electrode. Further investigation suggested that Myb was adsorbed tightly on the surface of the BPG electrode in the presence of [HEMIm][BF₄] to form a stable, approximate monolayer Myb film. Myb adsorbed on the BPG electrode surface showed a remarkable electrocatalytic activity for the reduction of oxygen in a [HEMIm][BF₄] aqueous solution. Based on these, a third-generation biosensor could be constructed to directly detect the concentration of oxygen in aqueous solution with a limit of detection of 2.3 × 10⁻⁸ M.     

In situ AFM studies of SEI formation at a Sn electrode

Early stages of the solid electrolyte interphase (SEI) formation at a tin foil electrode in an ethylene carbonate (EC) based electrolyte were investigated by in situ AFM and cyclic voltammetry (CV) at potentials >0.7 V, i.e., above the potential of Sn–Li alloying. We detected and observed initial steps of the surface film formation at ～2.8 V vs. Li/Li⁺ followed by gradual film morphology changes at potentials 0.7 < U < 2.5 V. The SEI layer undergoes continuous reformation during the following CV cycles between 0.7 and 2.5 V. The surface film on Sn does not effectively prevent the electrolyte reduction and a large fraction of the reaction products dissolve in the electrolyte. The unstable SEI layer on Sn in EC-based electrolytes may compromise the use of tin-based anodes in Li-ion battery systems unless the interfacial chemistry of the electrode and/or electrolyte is modified.     

Direct electrochemistry of hemoglobin and its electrocatalytic effect based on its direct immobilization on carbon ionic liquid electrode

Direct electrochemistry of hemoglobin (Hb) has been achieved by its direct immobilization on carbon ionic liquid electrode (CILE). CILE was immersed in a solution containing Hb and ionic liquid, octylpyridinium chloride ([OcPy][Cl]), to directly immobilize Hb on CILE. Cyclic voltammetry of modified electrode exhibited quasi-reversible peaks corresponding to Hb. The oxidation and reduction peak potentials of immobilized Hb in acetate buffer solution, pH 5.0 and at a scan rate of 0.1 V s⁻¹ were obtained at about –150 mV and –290 mV, respectively. The average surface coverage of the electroactive Hb adsorbed on the electrode surface was calculated as 8.4 × 10⁻¹¹ mol cm⁻². Hb retained its bioactivity on modified electrode and showed excellent electrocatalytic activity towards oxygen, hydrogen peroxide and nitrite. Hydrogen peroxide can be determined in the range of 1.0 × 10⁻⁴–5.0 × 10⁻³ M.     

Adsorption of 4-aminopyridine on Co and Ag electrodes probed by SERS

The adsorption of 4-aminopyridine (4-AP) on Co and Ag electrodes in acid or alkaline solutions of KCl and KI electrolyte salts were monitored by the Surface-enhanced Raman Spectroscopy (SERS) technique. The SERS intensity for the Ag electrode was in 2 orders of magnitude higher than for the Co electrode, due to the enhancement of the Raman cross-section on Ag by the surface-plasmon excitation. In acidic chloride medium (pH 4), the SERS results for Ag electrodes indicate that the protonated form of 4-AP (4-APH⁺) adsorbs in the potential range of −0.1 to −0.6 V (Ag|AgCl|KCl sat) through hydrogen-bonding between 4-APH⁺ and Cl⁻ adsorbed on the electrode surface; at more negative potentials the neutral form 4-AP is the predominant adsorbed species. For Co electrode in the same medium, only bands due to neutral 4-AP were observed in the spectra at −0.8 and −0.9 V. For more negative potentials bands assigned to both 4-AP and 4-AP surface complex are observed, with the lasts being enhanced, as the potentials are turned more negative. In alkaline chloride medium (pH 13), for less negative potentials the bands assigned to free 4-AP were observed in the spectra of both Ag and Co surfaces. For more negative potentials, only bands assigned to the 4-AP surface complex were observed. For 0.1 mol L⁻¹ KI acidic or alkaline solutions, bands assigned to 4-AP and 4-APH⁺ were observed in a wider potential range than in chloride solutions. An adsorption scheme of 4-AP on Ag and Co is proposed for acidic and alkaline solutions.     

Efficient passivation of SnO2 nano crystallites by Indoline D-149 via dual chelation

For the first time in SnO₂ based dye solar cells, here we report, efficiency exceeding 3% of the cells consisting with Indoline D-149 dye with unmodified SnO₂ nano-crystallites. The cells sensitized with metal free D-149 dye together with liquid electrolyte comprising with 0.5 M tetrapropyl ammonium iodide and 0.05 M iodine in a mixture of acetonitrile and ethylene carbonate (1:4 by volume) delivered a short circuit current density of 10.4 mA cm^?2 with an open circuit voltage of 530 mV under the illumination of 100 mW cm^?2 (AM1.5) having an efficiency of 3.1%. As evident from the FTIR measurement, strong surface passivation of recombination centers of SnO₂ crystallites due to the dual mode of attachment of dye molecules to the surface of SnO₂ via both COOH and S–O direct bond might be the possible reason for this enhancement in these SnO₂ based cells.     

The qualitative electrochemical determination of clarithromycin and spectroscopic detection of its structural changes at gold electrode

The aim of the present study was the qualitative determination of the pure clarithromycin using a gold electrode in neutral electrolyte by cyclic linear sweep voltammetry. It was shown that in the range of −1.2 V to 1.0 V vs. SCE in 0.05 M NaHCO₃, a gold electrode is successfully employed for the qualitative determination of clarithromycin by detection of the reproductive four anodic and one cathodic peaks. After the potentiostatic measurements at the potential values corresponded to current peaks, the bulk electrolyte was analyzed by FTIR spectroscopy to show the changes in molecular structure of clarithromycin. FTIR analysis of the bulk electrolyte after 4 h of holding the potential at −0.61 V vs. SCE (cathodic peak) showed the apparent changes in clarithromycin molecule structure: in the ester bond of the lactone and in ethers and acetal bonds.     

Sensing characteristics of aged zirconia-based hydrogen sensor utilizing Zn–Ta-based oxide sensing-electrode

We report here the enhanced sensing characteristics to H₂ for a potentiometric sensor using an yttria-stabilized zirconia (YSZ) solid electrolyte and a ZnO(+ 84 wt.% Ta₂O₅) sensing electrode (SE) after aging at 500 °C. The emf response toward 400 ppm H₂ was found to gradually increase up to − 800 mV after 40 days operation (aging) and was stabilized at this value until the 90th day. The aged and stabilized sensor exhibited highly sensitive response to H₂, with minor responses toward other examined gases such as NOx and HCs. The 90% response time toward 100 ppm H₂ was approximately 70 s. The H₂ sensitivity of the stabilized sensor was hardly affected by changes in water vapor as well as O₂ concentration, with repeatable and reproducible responses to H₂.     

Visible light photocatalysis by a Titania–Rhodium(III) complex

Titania hybrid photocatalysts containing 0.5, 1.0, 2.0, and 5.0 wt% of rhodium(III) were prepared by chemisorption of RhCl₃ × 3H₂O onto anatase hydrate powder (TH). Analytical data suggest that a titania–trichlororhodate complex is produced containing a [TiO₂]–O–Rh bond.Similar results are found in the case of modification by RhBr₃ × 3H₂O. Diffuse reflectance spectra exhibit an absorption shoulder throughout the visible region down to 700 nm. Photoelectrochemical measurements indicate that the quasi-Fermi level of electrons is gradually shifted to more anodic potentials with increasing rhodium loading reaching a value of ?0.34 V at pH 7 (vs. NHE) in the case of 5.0%RhCl₃/TH. This is more anodic by 210 mV as compared to unmodified TH. Upon visible light irradiation this photocatalyst induces a fast mineralization of 4-chlorophenol whereas cyanuric acid, which is known to be mineralized in the presence of the analogous Pt(IV) modified titania, is not degraded.     

Dealing with interference challenge in the electrochemical detection of As(III) —A complexometric masking approach

Copper ion has been reported to be a major interference in the electrochemical detection of arsenic (III) ion in water. Therefore the development of a simple approach to alleviate this interference challenge is important. We present the use of ammonia solution as a masking agent for Cu(II) interference in the square wave anodic stripping voltammetry of As(III) on a gold nanoparticle modified glassy carbon electrode (GCE). AuNPs were electrochemically deposited by cyclic voltammetry on a GCE from a potential range of − 400 mV to 1100 mV for 10 cycles. Square wave anodic stripping voltammetry (SWASV) was used to detect As(III) in water with and without Cu(II) based on the following optimised conditions: pH = 3, deposition potential = − 600 mV, and deposition time = 60 s. Ammonia solution was added to the analyte solution and the effect on mitigating copper interference was studied. The presence of ammonia complexed the Cu(II) ion thereby excluding Cu(II) from interfering with the As(III) signal.