Ionic liquids at electrified interfaces

Until recently, “room-temperature” (<100–150 °C) liquid-state electrochemistry was mostly electrochemistry of diluted electrolytes(1)–(4) where dissolved salt ions were surrounded by a considerable amount of solvent molecules. Highly concentrated liquid electrolytes were mostly considered in the narrow (albeit important) niche of high-temperature electrochemistry of molten inorganic salts(5-9) and in the even narrower niche of “first-generation” room temperature ionic liquids, RTILs (such as chloro-aluminates and alkylammonium nitrates).(10-14) The situation has changed dramatically in the 2000s after the discovery of new moisture- and temperature-stable RTILs.(15, 16) These days, the “later generation” RTILs attracted wide attention within the electrochemical community.(17-31) Indeed, RTILs, as a class of compounds, possess a unique combination of properties (high charge density, electrochemical stability, low/negligible volatility, tunable polarity, etc.) that make them very attractive substances from fundamental and application points of view.(32-38) Most importantly, they can mix with each other in “cocktails” of one’s choice to acquire the desired properties (e.g., wider temperature range of the liquid phase(39, 40)) and can serve as almost “universal” solvents.(37, 41, 42) It is worth noting here one of the advantages of RTILs as compared to their high-temperature molten salt (HTMS)(43) “sister-systems”.(44) In RTILs the dissolved molecules are not imbedded in a harsh high temperature environment which could be destructive for many classes of fragile (organic) molecules

Nanostructured α-Fe2O3 platform for the electrochemical sensing of folic acid

10.1039/c3an00070bAnalyst13861779-1786ANAL

Scanning electrochemical microscopy activity mapping of electrodes modified with laccase encapsulated in sol-gel processed matrix

Electrodes modified with sol-gel encapsulated laccase (isolated from Cerrena unicolor) exhibiting mediated or mediatorless bioelectrocatalytic dioxygen reduction activity were inspected using confocal laser scanning microscopy, atomic force microscopy and scanning electrochemical microscopy. Potential-driven leaching of the redox mediator 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonate) from carbon ceramic electrodes covered by hydrophilic silicate-encapsulated laccase was detected during electrocatalytic action. Strongly non-homogeneous lateral distribution of the activity towards dioxygen reduction was found by redox competition mode of scanning electrochemical microscopy using a similar electrode with syringaldazine as redox mediator. Hydrogen peroxide formation at these electrodes is detected at potentials lower than 0.05 V. It is ascribed to the electrochemical oxygen reduction at the carbon material while laccase-catalyzed oxygen reduction occurs below 0.35 V without hydrogen peroxide formation. The scanning electrochemical microscopy images of electrodes consisting of single-walled carbon nanotubes non-covalently modified with pyrenesulfonate and laccase encapsulated in a sol-gel processed silicate film confirm direct electron transfer electrocatalysis in redox competition mode experiments and show that the enzyme is evenly distributed in the composite film. In conclusion scanning electrochemical microscopy proved to be useful for mapping of enzyme activity on different materials

Microphase voltammetry of diluted and undiluted redox liquids deposited on sol-gel ceramic carbon electrodes

Ceramic carbon electrodes (CCEs) modified with microphases of diluted and undiluted redox liquids were prepared and studied. The electrodes consisting of graphite powder, homogeneously dispersed in a hydrophobic silica matrix, were prepared by reaction of a methyltrimethoxysilane-based sol and graphite powder following a sol-gel methodology. The electrode surface was modified with different amounts of redox liquids (pure t-butylferrocene, solutions of t-butylferrocene in 2-nitrophenyloctylether, and N,N,N',N'-tetraoctyl-1,4-phenylenediamine) using hexane solutions and a solvent evaporation approach. For comparison, a glassy carbon electrode modified analogously with t-butylferrocene was also prepared and studied. The electrochemical behaviour of the electrodes was examined by cyclic voltammetry in aqueous salt solutions. The electrodes exhibited anticipated electroactivity connected with the presence of redox liquids. The shape of voltammograms and the degree of conversion were very different for processes on CCEs compared to those observed on glassy carbon. Presumably due to the promotion of formation of microphases, the magnitude of the current responses obtained with CCEs modified with t-butylferrocene is substantially larger than that obtained with GC electrodes modified with the same amount of redox liquid. In contrast to CCEs modified with diluted and undiluted t-butylferrocene where after 5-10 scans stable voltammetric curves were obtained, glassy carbon failed to give stable cyclic voltammograms. The results can be explained by the extent of triple interface formation in the CCE silicate network. Due to the electrode microstructure, the voltammetric response of CCEs modified with microphases of N,N,N',N'-tetraoctyl-1,4-phenylenediamine shows similar enhancement effects. (C) 2004 Elsevier Ltd. All rights reserved