Electrochemical Potential Cycling Research Articles

Compositional changes in unusually stabilized Prussian blue by CTAB surfactant: Application to electrocatalytic reduction of H 2O 2

We report here for the first time the ex situ Mossbauer and ESR identification of tetrahedrally coordinated high spin Fe 3+ ions incorporated in the interstitial position of Prussian blue (PB) lattice of the PB–CTAB composite material prepared in pH = 1.7 (0.02 M HCl + 0.1 M KCl) solution in presence of CTAB surfactant during film preparation by electrochemical potential cycling method. The PB–CTAB composite film electrode, which possesses enhanced film growth, efficient and rapid charge transfer, and also extremely high stability, has been advantageously employed as an amperometric sensor for H 2O 2 estimation with extended linearity, and low detection limit, compared to an unmodified PB film electrode. The presently developed surfactant stabilized PB film electrode possesses the best sensitivity towards H 2O 2 ca. 9.79 A M −1cm −2, highest ever found for PB-based H 2O 2 probes, and also holds some of the better qualities than the well-known H 2O 2 sensors.

Preparation and characterisation of monomeric molybdate(VI) anion-doped polypyrrole electrodes

Stable monomeric molybdate(VI) anion-doped polypyrrole composites [Ppy(Mo)] have been prepared from sulfuric acid solution containing Mo(VI) by an electrochemical potential cycling method. Ppy(Mo) films exhibit redox waves inherent to the polypyrrole moiety only, and the built-in Mo(OH)5O− is found to be electroinactive. X-ray photoelectron spectroscopic examination of oxidised and reduced Ppy(Mo) films confirms this phenomenon.

Electrochemically- and Photo-Induced IR Absorption of Low Band-Gap Polydithienothiophenes: A Comparative Study

ABSTRACTPoly(dithieno[3,4-b:3',4'-d]thiophene) (pDTT1), poly(dithieno[3,4-b:3',2'-d]thiophene (pDTT2) and poly(dithieno[3,4-b:2',3'-d]thiophene) (pDTT3) are low band-gap polymers that undergo both p- (oxidation) and n- (reduction) type electrochemical reversible doping in organic electrolytes. In this work we report on the in-situ IR spectroscopic characterization of both doping types using attenuated total reflection (ATR) FTIR spectroelectrochemistry. Thin polymer films were prepared on Ge reflection elements by electrosynthesis. During electrochemical potential cycling experiments in a spectroelectrochemical cell, the evolution of infrared active vibrational (IRAV) modes, correlated with the generation of charge within the polymer chain, was studied. In addition to electrochemical doping, the polymers exhibit also charged excitations by photodoping. FTIR spectra recorded by illumination/dark cycles show photoinduced IRAV bands which are similar to those found for the electrochemically p-doped materials. The infrared spectroscopic results are compared with Raman spectra of the neutral polymers. The relationship between vibrational properties and structure of the polymers is discussed in terms of different contribution of the φ-electrons within the repeating units to the electronic structure of the conjugated backbone.

Microgravimetric monitoring of transport of cations during redox reactions of indium(III) hexacyanoferrate(III,II)

We demonstrate here that, primarily, electrolyte cations but also, to some extent, anions are capable of penetrating indium hexacyanoferrate films during redox reactions. We find from electrochemical quartz crystal microbalance measurements that the electrolyte cation (K+) undergoes sorption and desorption during the system's reduction and oxidation, respectively. The formal potential, which has been determined from the system's well-defined voltammetric peaks recorded with the use of an ultramicroelectrode, decreases ∼40 mV per decade of decreasing K+ concentration. The latter value is lower than the 60 mV change expected for the involvement of a cation in the reaction mechanism according to the ideal Nernstian dependence. We also demonstrate, using 35-S labelled sulfate, that anion penetrates the reduced film and its concentration markedly increases during oxidation. Careful examination of cyclic voltammetric responses of the system shows that, in addition to the well-defined peaks, capacitance-like currents appear during oxidation. During reduction anion is largely expelled from the film. This complex ionic penetration and transport in indium hexacynoferrate may be explained in terms of formation of two forms: ‘soluble’, KInIII[FeII(CN)6], and ‘insoluble’ (‘normal’), InIII4[FeII(CN)6]3, during the electrochemical growth or potential cycling of the films. These forms would require cations and anions, respectively, to provide charge balance during reactions. Regardless of the actual mechanism, penetration of anions cannot be neglected completely in the discussion of charging of indium hexacyanoferrate.

I n s i t u scanning tunneling microscopy of platinum (111) surface with the observation of monatomic steps

I n situ scanning tunneling microscopy was applied to single-crystal platinum (111) surfaces both before and after electrochemical potential cycling in an aqueous sulfuric acid solution. Steps observed on a Pt(111) facet were usually located on nearly parallel straight lines or on the directions forming an angle of close to 60°, as expected for a surface with threefold symmetry. The height of each step was in accord with the monatomic step height of 0.238 nm on the Pt(111) surface. Randomly oriented islands a few atoms in height were clearly observed on the terraces after five potential cyclings. It was suggested that Pt adatoms produced by the reduction of the oxide are coagulated on the terraces.

In situ scanning tunnelling microscopy of a platinum {111} surface in aqueous sulphuric acid solution

An in situ scanning tunnelling microscope was applied, for the first time, to a single-crystal platinum {111} surface both before and after electrochemical potential cycling in aqueous sulphuric acid solution. The single-crystal Pt{111} was annealed in a flame near 1100 °C for 1 min and then quickly brought into contact with pure water. It was not possible to see any particular structures on the fire-annealed single crystal. It is shown that the fire-annealing procedure can produce an almost completely atomically flat surface on a single crystal. The flat {111} surface of the Pt crystal was roughened by the electrochemical potential cycling. Semi-spherical domains have predominantly been observed on the single crystal. These domains seem to be randomly distributed over the surface. The diameter and height of the semi-spherical domains were in the ranges 20–30 and 5–10 A, respectively.