Thin solid state reference electrodes for use in solid polymer electrolytes

This paper reports two low-profile (~ 10 μm thick) solid state reference electrodes for use in solid polymer electrolytes. The thin, open geometry of the electrodes enables close positioning between the working and counter electrodes. The first electrode uses the palladium hydride (Pd|PdH_x) couple (PHRE), and the second utilises the hydrous iridium oxide (IrO_x·yH₂O|IrO_a·bH₂O) couple (IORE). To our knowledge this is the first use of the latter as a reference electrode. The PHRE had a stable potential of + 70 mV vs RHE with a 4 mV h^− 1 drift and two hour lifetime, whilst the IORE gave a potential of + 847 mV vs RHE with a drift of 0.3 mV h^− 1 and no deterioration after 24 h of use. The use of these reference electrodes in a three-electrode solid state cell and a fuel cell is demonstrated.     

Determination of hydrogen sulfide in gasoline by Au nanoclusters modified glassy carbon electrode

A promising hydrogen sulfide (H₂S) sensor was prepared by electrodeposition of Au nanoclusters on glassy carbon electrode (GCE) and the surface structure was characterized by SEM and EDAX. These flower-like form Au nanoclusters, which were made up of highly dense clustering Au nanorods with an average diameter of 20 nm and length up to 80 nm, had an average size about 600 nm and uniformly distributed on the GCE surface. The electrocatalytic oxidation of H₂S in gasoline was performed on this modified electrode, which had a satisfactory liner response to H₂S in the range of 1–80 ppm and a detection limit of 0.45 ppm (s/n = 3). This sensor was sensitive, selective and stable.     

Determination of formal potential of NADH/NAD+ redox couple and catalytic oxidation of NADH using poly(phenosafranin)-modified carbon electrodes

The electrochemical regeneration of NADH/NAD⁺ redox couple has been studied using poly(phenosafranin) (PPS)-modified carbon electrodes to evaluate the formal potential and catalytic rate constant for the oxidation of NADH. The PPS-modified electrodes were prepared by electropolymerization of phenosafranin onto different carbon substrates (glassy carbon (GC) and basal-plane pyrolytic graphite (BPPG)) in different electrolytic solutions. The formal potential was estimated to be ? 0.365 ± 0.002 V vs. SHE at pH 7.0. As for the bare carbon electrodes, the oxidation of NADH at the BPPG electrode was found to be enhanced compared with the GC electrode. For the PPS-modified electrodes, it was found that the electrocatalysis of PPS-modified electrodes for the oxidation of NADH largely depends on the carbon substrate and electrolyte solution employed for their preparation, i.e., the PPS-modified BPPG electrode prepared in 0.2 M NaClO₄/acetonitrile solution exhibits an excellent and persistent electrocatalytic property toward NADH oxidation in phosphate buffer solution (pH 7.0) with a diminution of the overpotential of about 740 and 670 mV compared with those at the bare GC electrode and the PPS-modified GC electrode prepared in 0.2 M H₂SO₄ solution, respectively. A quantitative analysis of the electrocatalytic reaction based on rotating disk voltammetry gave the electrocatalytic reaction rate constants of the order of 10³–10⁴ M^?1 s^? 1 depending on the preparation conditions of the PPS-modified electrodes.     

Molybdenum electrodes for hydrogen production by water electrolysis using ionic liquid electrolytes

The hydrogen production by water electrolysis was tested with different electrocatalysts (molybdenum, nickel, iron alloys containing chromium, manganese and nickel) using aqueous solutions of ionic liquid (IL) like 1-butyl-3-methylimidazolium tetrafluoroborate (BMI.BF₄). The hydrogen evolution reaction (HER) was performed at room temperature in a potential of −1.7 V (PtQRE). A Hoffman cell apparatus was used to water electrolysis with current density values, j, between 14.6 mA cm⁻² (for Ni electrode) and 77.5 mA cm⁻² (for Mo electrode). The system efficiency was very high for all electrocatalysts tested, between 97.0% and 99.2%. The energy activation values of HER was determined in an aqueous solution of BMI.BF₄ 10 vol.%, using platinum (23.40 kJ mol⁻¹) and Mo (9.22 kJ mol⁻¹) as electrocatalysts. The results show that the hydrogen production in IL electrolyte can be carried out with cheap material at room temperature, which makes this method economically attractive.     

Electrochemical synthesis of a ferrocenecarboxylic acid–C60 composite and its electrocatalysis to hydrogen peroxide

A new ferrocenecarboxylic acid–C₆₀ composite (Fc–C₆₀) has been synthesized by controlled potential electrolysis. A composite modified glassy carbon electrode has been prepared based on its good electrochemical activity. The modified electrode in 0.1 M NaClO₄ solution shows a reversible oxidation wave at E_1/2 = 0.32 V (vs. SCE) attributed to the oxidation of the ferrocene entity and a quasi-reversible reduction wave of C₆₀ entity at E_1/2 = ?0.54 V (vs. SCE). Electrocatalytic studies show that Fc–C₆₀ at the modified electrode can mediate the reduction of hydrogen peroxide (H₂O₂), and a broad linear range from 1.2 μM to 21.9 mM for H₂O₂ were obtained with a determination limit of 2.5 × 10^?7 M by amperometry.     

Comparison between hydride generation and nebulization for sample introduction in the determination of lead in plants and water samples by inductively coupled plasma mass spectrometry,using external calibration and isotope dilution

Four inductively coupled plasma mass spectrometric methods: nebulization sample introduction with external calibration; hydride generation with external calibration; isotope dilution with nebulization; and isotope dilution with hydride generation, have been tested and compared. Multimode Sample Introduction System (MSIS™) was employed in either nebulization or hydride generation mode. Best limits of detection (below 0.1 μg L^− 1) and accuracy were obtained for isotope dilution techniques in hydride generation and sample nebulization mode. A mixture of HNO₃ and H₂O₂ served both for microwave-assisted digestion as well as a medium for subsequent plumbane generation. Optimal reagent concentrations for hydride generation stage were 0.1 mol L^− 1 HNO₃, 0.28 mol L^− 1 H₂O₂ and 1.5% m/v NaBH₄. Critical effects of acidity, blanks and concomitants have been discussed. Analytical methods were validated by use of plant and water certified reference materials and spiked high-salt solutions (seawater and 20% m/v NaCl) at lead levels in nanograms per gram to micrograms per gram range.     

Promotion of PtIr and Pt catalytic activity towards ammonia electrooxidation through the modification of Zn

Zn is introduced into Pt and PtIr electrodes by applying potential cycles to their corresponding polycrystalline microdisc electrodes in a ZnCl₂-containing ionic liquid bath. Scanning-electron microscopy and energy-dispersive X-ray microanalysis studies show that nanostructured PtIrZn and PtZn layers created on the microdisc electrodes contain approximately 5 wt% Zn. Cyclic voltammetric studies reveal that PtZn and PtIrZn are significantly more active towards electrochemical ammonia oxidation in alkaline media than virgin Pt and PtIr electrodes. The PtIrZn electrode demonstrates a low onset potential of 0.30 V vs RHE and a high exchange current density of 4.3 × 10^− 8 A cm^− 2, which is favorably comparable to state-of-the-art electrocatalyts for the same reaction. The catalytic activity promotion by the Zn modification may be related to the inhibition of the hydrogen electrochemistry. PtIrZn appears therefore to be a very promising anode catalyst for direct ammonia fuel cells and ammonia electrolysis.     

Elucidation of interference mechanisms caused by iron on stibine electrochemical generation by differential pulse anodic stripping voltametry. A case study

The interference effect caused by the presence of iron – both (II) and (III) oxidation states – on the electrochemical generation of SbH₃ has been characterized. Interference from Fe(III) was more severe than for Fe(II). Total signal suppression was obtained for a Fe(III) : Sb(III) concentration ratio of 5 : 1, whereas a 40% suppression was obtained for Fe(II). A mechanism is proposed based on the results obtained by differential pulse anodic stripping voltametry. The standard conditions used for the hydride electrochemical generation were simulated in the differential pulse anodic stripping voltametry measurements in order to achieve valid conclusions. The reduction of Fe(II) onto the cathode surface prevents the formation of stibine avoiding the recombination of Sb⁰ with the hydrogen atoms adsorbed on the surface. The mechanism by which the Fe(III) interferes on the stibine formation is related to the co-deposition of the iron and antimony that also avoid the further recombination of the Sb⁰. The formation of a specie of stoichiometry not determined (probably 1 : 1) on the cathode surface may justify the larger interference effect observed for the Fe(III).     

Photocatalytic reduction of cadmium over CuFeO2 synthesized by sol–gel

The Cd²⁺ photo-electrodeposition was successfully carried out in air-equilibrated aqueous CuFeO₂ suspension. The delafossite CuFeO₂ is p-type semiconductor characterized by a low optical gap, properly matched to the sun spectrum, and a long term chemical stability in neutral solution. It has been elaborated by the sol–gel technique where the specific surface area is increased via the surface/bulk ratio. The TG/DSC plots and IR spectra show that the solid phases are formed only at temperatures exceeding 400 and at 700 °C, the system is mixed phases. When fired at 950 °C under nitrogen flow, the delafossite has been identified (CuO + CuFe₂O₄ → CuFeO₂ + ½O₂). All the XRD lines index in a hexagonal unit cell with the lattice constants a = 284.2 and c = 169.4 pm. The photocurrent onset potential (+0.35 V_SCE) is close to the flat band potential (+0.23 V_SCE) determined from the capacitance measurement. CuFeO₂/Cd²⁺ solution is a self photo-driven system, the absorption of light promotes electrons into CuFeO₂–CB with a potential (?0.93 V_SCE) sufficient to reduce Cd²⁺. This occurs because of the dark Cd²⁺ adsorption on the surface powder. The system was optimized with respect to the following physical parameters: pH 6.8, Cd²⁺ (100 ppm) and a mass concentration C_m (1 mg catalyst/ml solution). The hetero-system CuFeO₂/TiO₂ has been also reported for a comparative purpose. Prolonged irradiation (>50 min) was accompanied by a pronounced decrease in the rate of Cd-deposition owing to the competitive water reduction. Indeed, the generated bi-functional CuFeO₂/Cd particles account for the low over-potential of hydrogen and favour its evolution in aqueous solution.     

Surface poisoning during electrocatalytic monosaccharide oxidation reactions at gold electrodes in alkaline medium

In the present study, the surface poisoning of electrocatalytic monosaccharide oxidation reactions at gold electrodes were investigated. In the cyclic voltammetric studies, the electrocatalytic oxidation of aldohexose and aldopentose type monosaccharides, aminosugars, acetyl-glucosamine and glucronamide were observed at gold plate electrodes in alkaline medium. However, in controlled-potential electrolytic studies ranging −0.3 to −0.2 V in reaction solutions, current flows during electrolyses decreased quickly with time, except when glucosamine was used as a substrate.Results from surface enhanced infrared adsorption (SEIRA) spectroscopic measurements at an evaporated gold electrode for the electrocatalytic oxidation of glucose in 0.1 mol dm⁻³ NaOH at −0.3 V and Gaussian simulated spectra indicated that the gluconic acid as a 2-electron oxidation product and/or its analogs adsorbed onto the gold surface. Electrochemical quartz crystal microbalance (EQCM) measurement results, along with surface adsorption results from surface poisoning at the gold electrode during electrolytic reactions, suggested that gluconic acid and/or its analogs adsorbed vertically onto electrode surfaces in a full monolayer packing-like conformation. In the case of the electro oxidation of glucosamine in 0.1 mol dm⁻³ NaOH at −0.2 V, the obtained SEIRA spectra and EQCM results, clearly indicated that the glucosaminic acid as a 2-oxidation glucosamine product did not strongly bind onto the gold electrode surface.     

Si–AB5 composites as anode materials for lithium ion batteries

The Si–AB₅ (MmNi_3.6Co_0.7Al_0.3Mn_0.4 alloy) composites with a high tap density as anode materials for lithium-ion batteries were synthesized by ball-milling. Si nanoparticles are distributed homogeneously on the surface of the AB₅ matrix. The electrochemical performance of the Si–AB₅ composites as a function of Si content was investigated. It is demonstrated that the Si–AB₅ composite delivers a larger reversible capacity and better cycle ability because the inactive AB₅ alloy can accommodate the large volume changes of Si nanoparticles distributed on the surface of the Si–AB₅ composite during cycling. In particular, the Si–AB₅ composite containing 20 wt% Si with the high tap density of 2.8 g/cm³ obtained after ball-milling for 11 h exhibits an initial and maximum reversible (charge) capacity of 370 and 385 mAh/g. The high capacity retention can be achieved after 50 cycles in the potential range from 0.02 to 1.5 V.     

Controlled-potential electrosynthesis of glucosaminic acid from glucosamine at a gold electrode

The electrocatalytic oxidation of d-glucosamine (2-amino-2-deoxy-d-glucose) in alkaline and neutral solutions was examined using a carbon felt electrode modified with 2 nm core sized gold nanoparticles (Au_2 nm nanoparticles) and a gold plate electrode. The electrocatalytic voltammetric oxidation curves of d-glucosamine were obtained in both solutions. The voltammetric responses for the electrocatalytic oxidation at a Au_2 nm nanoparticle-modified electrode in both alkaline and neutral solutions were almost the same to those at a gold plate electrode. The oxidized product was identified to be d-glucosaminic acid (2-amino-2-deoxy- d-gluconic acid) generated by the 2-electron oxidation product of d-glucosamine by electrospray ionization time-of-flight mass spectra (ESI TOF-MS). The HPLC results also indicated that the oxidation product was d-glucosaminic acid.The controlled-potential electrolysis of d-glucosamine was performed at the Au_2 nm nanoparticle-modified carbon felt electrodes in both alkaline and neutral solutions. In the alkaline solution, at a potential of −0.2 V, d-glucosaminic acid was formed with a current efficiency of 100%. In the neutral solution, electrolysis at 0.4 V on d-glucosaminic acid was obtained with current efficiencies of 70%.     

A sensitivity-controlled hydrogen peroxide sensor based on self-assembled Prussian Blue modified electrode

In this communication, a hydrogen peroxide (H₂O₂) sensor based on self-assembled Prussian Blue (PB) modified electrode was reported. Thin film of PB was deposited on the electrode by self-assembly process including multiple sequential adsorption of ferric ions and hexacyanoferrate ions. The as-prepared PB modified electrode displayed sufficient stability for practical sensing application. At an applied potential of ?0.05 V vs. Ag/AgCl (sat. KCl), PB modified electrode with 30 layers exhibited a linear dependence on H₂O₂ concentration in the range of 1 × 10^?6–4 × 10^?4 M (r = 0.9998) with a sensitivity of 625 mA M^?1 cm^?2. It was found that the sensitivity of H₂O₂ sensors could be well controlled by adjusting the number of deposition cycles for PB preparation. This work demonstrates the feasibility of self-assembled PB modified electrode in sensing application, and provides an effective approach to control the sensitivity of PB-based amperometric biosensors.     

Electrochemically activated MnO as a cathode material for sodium-ion batteries

Besides classical electrode materials pertaining to Li-ion batteries, recent interest has been devoted to pairs of active redox composites having a redox center and an intercalant source. Taking advantage of the NaPF₆ salt decomposition above 4.2 V, we extrapolate this concept to the electrochemical in situ preparation of F-based MnO composite electrodes for Na-ion batteries. Such electrodes exhibit a reversible discharge capacity of 145 mAh g^− 1 at room temperature. The amorphization of pristine MnO electrode after activation is attributed to the electrochemical grinding effect caused by substantial atomic migration and lattice strain build-up upon cycling.     

Electrocatalytic activity and simultaneous determination of catechol and hydroquinone at mesoporous platinum electrode

The electrochemical oxidation of catechol and hydroquinone was investigated using cyclic and differential pulse voltammetries at nanostructured mesoporous platinum film electrochemically deposited from the hexagonal liquid crystalline template of C₁₆EO₈ surfactant. The mesoporous platinum electrode has shown an excellent electrocatalytic activity and reversibility towards the oxidation of catechol and hydroquinone redox isomers in 1.0 M HClO₄. The oxidation and reduction peak separation (ΔE) has been decreased from 485 to 55 mV for hydroquinone and from 430 to 75 mV vs. SCE for catechol at polished polycrystalline and mesoporous platinum electrodes, respectively. The differential pulse voltammograms in a mixture solution of catechol and hydroquinone have shown that the oxidation peaks became well resolved and are separated by about 100 mV, although the bare electrode gave a single broad oxidation peak. Moreover, the oxidation current of hydroquinone and catechol has been enhanced by a factor of two and four times, respectively, at mesoporous platinum electrode. Using differential pulse voltammetry, a highly selective and simultaneous determination of hydroquinone and catechol has been explored at mesoporous platinum electrode.     

A study of the photodeposition over Ti/TiO2 electrode for electrochemical detection of heavy metal ions

Here we reported that UV light irradiation can significantly enhance sensitivity of Ti/TiO₂ electrode for determination of trace heavy metal ions (such as Cu^2 +, Pb^2 + and Cd^2 +) owing to the photodeposition of metal ions on the surface of electrodes. The sensitivity of heavy metal ions can be selectively enhanced over the Ti/TiO₂ electrode, which is attributed to matching between potential of heavy metal ions and the position of the conduction band of TiO₂.     

Amperometric biosensors based on deposition of gold and platinum nanoparticles on polyvinylferrocene modified electrode for xanthine detection

In this study, new xanthine biosensors, XO/Au/PVF/Pt and XO/Pt/PVF/Pt, based on electroless deposition of gold(Au) and platinum(Pt) nanoparticles on polyvinylferrocene(PVF) coated Pt electrode for detection of xanthine were presented. The amperometric responses of the enzyme electrodes were measured at the constant potential, which was due to the electrooxidation of enzymatically produced H₂O₂. Compared with XO/PVF/Pt electrode, XO/Au/PVF/Pt and XO/Pt/PVF/Pt exhibited excellent electrocatalytic activity towards the oxidation of the analyte. Effect of Au and Pt nanoparticles was investigated by monitoring the response currents at the different deposition times and the different concentrations of KAuCl₄ and PtBr₂. Under the optimal conditions, the calibration curves of XO/Au/PVF/Pt and XO/Pt/PVF/Pt were obtained over the range of 2.5 × 10^?3 to 0.56 mM and 2.0 × 10^?3 to 0.66 mM, respectively. The detection limits were 7.5 × 10^?4 mM for XO/Au/PVF/Pt and 6.0 × 10^?4 mM for XO/Pt/PVF/Pt. The effects of interferents, the operational and the storage stabilities of the biosensors and the applicabilities of the proposed biosensors to the drug samples analysis were also evaluated.     

Electrochemical properties of Li symmetric solid-state cell with NASICON-type solid electrolyte and electrodes

All-solid-state phosphate symmetric cells using Li₃V₂(PO₄)₃ for both the positive and negative electrodes with the phosphate Li_1.5Al_0.5Ge_1.5(PO₄)₃ as the solid electrolyte were proposed. Amorphous Li_1.5Al_0.5Ge_1.5(PO₄)₃ was added into the electrode to increase the interface area between the active materials and the electrolyte. Any other phases were not formed at the electrode/electrolyte interface even after hot pressing at 600 °C. The discharge capacity was 92 mAh g^? 1 at 22 µA cm^? 2 at 80 °C, and 38 mAh g^? 1 at 25 °C, respectively. Symmetric cell configuration leads to simplify the fabrication process for all-solid-state batteries and will reduce manufacturing costs.     

Electrodeposition of gold nanoparticles at a solid|ionic liquid|aqueous electrolyte three-phase junction

Gold nanoparticles have been electrodeposited on an electrode through electrogeneration at an ITO|AuCl₄^? solution in an ionic liquid|aqueous electrolyte three-phase junction. The electrodeposition was carried out by inverted double-pulse potential chronoamperometry. The direct reduction of AuCl₄^? ions at the electrode is followed by a counterion transfer through the liquid|liquid interface. Contrary to the electrodeposition from a single ionic liquid phase, scanning electron microscopy reveals that the shape of the resulting nanoparticles is highly angular and well-developed with a diameter of 110 ± 30 nm. Catalytic oxidation of glucose on the modified electrode is demonstrated.     

Electrochemistry of Actinides and Selected Fission Products in the Head End of Spent Nuclear Fuel Reprocessing

The data on the uranium metal corrosion rate in the solutions of nitric acid (0,1 – 4 M) and effect of complex forming agents on uranium corrosion properties are presented. The increase of HNO₃ concentration caused the shift of corrosion potential from 38 mV to 446 mV and the increase of the corrosion rate from 0,02 to 0,62 mg.cm^-2h^-1. Transpassivation potential of U metal was found weakly effected by HNO₃ concentration varying from 448 to 470 mV/Ag/AgCl. The addition of HCOOH to the electrolytes containing less than 3 M HNO₃ found to shift the values of corrosion potentials about 500 mV towards negative direction reducing the passivation of U metal. The data on the kinetics of oxidative dissolution of PuO₂ using Ag(II) and Am(VI,V) as mediators and the effect of the mediator generation techniques are discussed. The electrochemical properties of UC in the solutions 2 – 4 M HNO₃, results of the quantitative determination of “oxidizable carbon” in dissolver solutions are presented. The results of corrosion and dissolution studies of Tc metal and Tc - Ru alloys containing from 19 to 70 at.% Ru in 0.5 0– 6 M HNO3 indicate the formation of passive films of Tc(IV) – Ru(III,IV) hydroxides at the electrode surface in the solutions containing less than 2 M HNO₃ at the potentials less than 650 mV/Ag/AgCl. The increase of HNO3 concentration to values exceeding 3 M and the shift of the electrode potential towards positive direction causes the transition of the Tc and Tc-Ru alloys to transpassive state. The values of transpassivation potentials increase with the increasing with HNO₃ concentration. Quantitative dissolution of Tc metal without application of oxidation potential becomes possible in the electrolytes, containing more than 4 M HNO₃. The rate of Tc – Ru alloys dissolution is noticed to slow down with the increase of Ru content in the alloy.