Search

A new design is proposed for biosensors based on carbon-paste electrodes enriched with ruthenium-containing acyclic compounds. Two biologically sensitive elements, a fragment of the cellular wall of Gluconobacter sp.33 containing a new enzyme PQQ-dependent glycerol dehydrogenase and a commercially available preparation of NAD-dependent glycerol dehydrogenase, are analyzed and compared. The activity of biologically sensitive preparations is studied using artificial electron carriers represented by ruthenium-containing acyclic and coordination compounds. [ABSTRACT FROM AUTHOR]

Redox polymer/protein biophotoelectrochemistry was used to analyse forward electron transfer of isolated PSII complexes with natural PsbA-variants. PsbA1- or PsbA3-PSII was embedded in a redox hydrogel that allows diffusion-free electron transfer to the electrode surface and thus measurement of an immediate photocurrent response. The initial photocurrent density of the electrode is up to ~2-fold higher with PsbA1-PSII under all tested light conditions, the most prominent under high-light [2,300 μmol(photon) m-2 s-1] illumination with 5 μA cm-2 for PsbA3-PSII and 9.5 μA cm-2 for PsbA1-PSII. This indicates more efficient electron transfer in low-light-adapted PsbA1-PSII. In contrast, the photocurrent decays faster in PsbA1-PSII under all tested light conditions, which suggests increased stability of high-light-adapted PsbA3-PSII. These results confirm and extend previous observations that PsbA3-PSII has increased P680+•/QA-• charge recombination and thus less efficient photon-to-charge conversion, whereas PsbA1-PSII is optimised for efficient electron transfer with limited stability. [ABSTRACT FROM AUTHOR]

A combinatorial materials approach is suggested for the development of nanoporous thin film oxides for photoelectrochemical solar water splitting. As a precursor for nanoporous WO 3 films, metallic nanoporous W films were synthesized by dealloying sputtered W 1− x Al x and W 1− x Fe x (0.06 < x < 0.67) thin film materials libraries in aqueous HNO 3 solutions with different concentrations for 24 h under open circuit conditions. The variation of the etchant concentration provided different film nanostructures. The films were then transformed into nanoporous WO 3 by controlled thermal oxidation at 500 °C in air. Screening of the photoelectrochemical properties of nanoporous WO 3 films shows a strong porosity- and thickness-dependence of the photocurrent. At the same time the photocurrent density does not depend on precursor composition, because dealloying in acid solutions of certain concentration leads to formation of identical nanostructures in a broad range of precursor compositions. [ABSTRACT FROM AUTHOR]

Abstract: A combinatorial materials approach is suggested for the development of nanoporous thin film oxides for photoelectrochemical solar water splitting. As a precursor for nanoporous WO3 films, metallic nanoporous W films were synthesized by dealloying sputtered W1−x Al x and W1−x Fe x (0.06 < x < 0.67) thin film materials libraries in aqueous HNO3 solutions with different concentrations for 24 h under open circuit conditions. The variation of the etchant concentration provided different film nanostructures. The films were then transformed into nanoporous WO3 by controlled thermal oxidation at 500 °C in air. Screening of the photoelectrochemical properties of nanoporous WO3 films shows a strong porosity- and thickness-dependence of the photocurrent. At the same time the photocurrent density does not depend on precursor composition, because dealloying in acid solutions of certain concentration leads to formation of identical nanostructures in a broad range of precursor compositions. [Copyright &y& Elsevier]

The redox competition mode of scanning electrochemical microscopy (SECM) was used to visualize differences in local electrocatalytic activity of Fe and Ni hexacyanoferrates (HCFs) in hydrogen peroxide reduction. The uniform round-shaped spots of electrocatalysts for the SECM measurements were electrochemically deposited using a scanning droplet cell. A negligible activity of NiHCF towards HO reduction compared to Prussian Blue (PB) was observed. The dependence of local Prussian Blue activity on the applied potential was investigated. The proposed strategy explores the potential application of SECM as a rapid screening tool for HCF film activity within a single experiment. [ABSTRACT FROM AUTHOR]

The feasibility of using iron oxides as negative electrode materials for safe high-power Li-ion batteries is demonstrated by the carbon-coated FeOx/CNT composite synthesized by controlled pyrolysis of ferrocene, which delivered a specific capacity retention of 84% (445 mA h g−1) after 2000 cycles at 2000 mA g−1 (4C). [ABSTRACT FROM AUTHOR]

In operando SECM is employed to monitor the evolution of the electrically insulating character of a Si electrode surface during (de-)lithiation. The solid–electrolyte interface (SEI) formed on Si electrodes is shown to be intrinsically electrically insulating. However, volume changes upon (de-)lithiation lead to the loss of the protecting character of the initially formed SEI. [ABSTRACT FROM AUTHOR]

The formation of the alkyl carbonate-derived solid electrolyte interphase (SEI) enables the use of active materials operating at very cathodic potentials in Li-ion batteries. However, the SEI in semi-solid flow batteries results in a hindered electron transfer between a fluid electrode and the current collector restricting the operating potentials to ca. 0.8 V vs. Li/Li+ for EC-based electrolytes. [ABSTRACT FROM AUTHOR]

Abstract: Thin-film batteries based on zinc/manganese dioxide chemistry with gel ZnCl2 electrolyte were manufactured as single (1.5 V) and double (3.0 V) cells from electrodes printed on paper substrates covered with different polymeric insulating coatings. Their properties were evaluated by means of electrochemical impedance spectroscopy and chronopotentiometry. Best performing cells achieved capacities in the range of 3 mAh cm−2 during discharge with 100 μA current, corresponding approximately to C/100 discharge rate. The influence of the cell elements on the overvoltage was examined and suggestions for the optimization of their performance were postulated. In particular, it was observed that limitations in the delivered power were governed by the poor conductivity of the carbon current collector. An optimized cell was built and showed a 4-fold improvement in the power delivered at 1 mA. [Copyright &y& Elsevier]

Memory effects in Li-ion battery materials have been explained on the basis of the thermodynamics of many-particles body, however the role of the (de-)intercalation kinetics is not yet clear. We demonstrate that kinetic aspects, specifically Li-ion mobility, are determining the magnitude of the memory effect in TiO2 by studying samples with different levels of oxygen vacancies. [ABSTRACT FROM AUTHOR]

Abstract: AFM-SECM measurements using alternating current mode SECM (AC–SECM) were performed at an AFM tip with an integrated recessed ring microelectrode. Measurements were carried out in a three-electrode arrangement at 14.92kHz and 110mVpp in 1mM KCl solution. Combined AFM–AC–SECM enables the detection of electrochemical surface properties with high lateral resolution without addition of a redox mediator, thereby providing images on topographical changes along with chemical information. For demonstrating the capabilities of this method, simultaneously recorded data on the topography and the surface conductivity of gold/glass structures and of microelectrode arrays are discussed. [Copyright &y& Elsevier]

The results of testing a new enzyme, anionic tobacco peroxidase (TOP), in various amperometric biosensors are summarized. The biochemical and electrochemical properties of the enzyme are briefly characterized. As compared to the commonly used cationic peroxidase from horseradish roots, TOP exhibits a wider optimum stability pH range, higher stability to inactivation with hydrogen peroxide, and higher efficiency in direct electron-transfer processes. The enzyme immobilized by adsorption on graphite is effective in determining aminophenols and aromatic diamines under flow conditions with a detection limit of 10 nM. Upon immobilization on graphite by incorporation into a gel of a redox-active polymer (crosslinked polyvinylimidazole with osmium 4,4′-dimethylbipyridinium chloride), TOP exhibited sensitivity and stability comparable to those of horseradish peroxidase and a wider linearity range. Upon immobilization on a self-assembled thiol monolayer at a gold electrode, TOP was much superior to horseradish peroxidase in the sensitivity of determining hydrogen peroxide, regardless of the charge of the monolayer. Prospects for the further use of the native enzyme and its genetically engineered unglycosylated form are considered. [ABSTRACT FROM AUTHOR]

This communication aims at the investigation of NiTi shape memory alloys (nitinol) with respect to visualisation of localised corrosion phenomena. Alternating current scanning electrochemical microscopy (AC-SECM) has been used as an approach to detect inhomogeneities in the passive oxide layer of nitinol with high spatial resolution. The appearance of microscopic corroding spots on the surface can be imaged due to the decreasing solution resistance between the sample and the used scanning tip. These spots bear a high reactivity towards the onset of pitting corrosion. [Copyright &y& Elsevier]

Scanning ion conductance microscopy (SICM) takes advantage of the increase in the resistance which occurs if a glass microelectrode is closely approached to a poorly conducting membrane (Science 243 (1989) 641) and has been shown to be a promising technique to study membranes of living cells (Biophys J 73 (1997a) 653; J Microsc 188 (1997b) 17). Based on a newly designed set-up on top of an inverted light microscope in combination with a speed optimized low noise intracellular amplifier, a novel mode for control of the distance between the probe and surface has been developed. By application of current pulses, the change in the resistance is monitored independently from electrode drift and parasitic DC currents. We demonstrate the applicability by showing first high-resolution images of neural cells produced with the pulse-mode operated SICM. [Copyright &y& Elsevier]