Electrochemical behavior of high-molecular-weight poly(ferrocenylsilane) films in aqueous electrolyte solutions

The electrochemical behavior of high-molecular-weight poly(ferrocenyldimethylsilane) films and poly(ferrocenylmethylphenylsilane) films, which contained about 2.8 × 10⁻⁶ mol cm⁻² ferrocene sites in eight kinds of aqueous electrolyte solutions, was investigated with cyclic voltammetry (CV). In some aqueous electrolyte solutions, the CV peak currents diminished gradually with an increase in the scanning times, whereas in other aqueous electrolyte solutions, stable and repeated cyclic voltammograms were obtained. The polymer films were poor-solvent-swollen in aqueous electrolyte solutions, and this resulted in a high resistivity of mass transfer and a slow rate of electrode reaction; therefore; quasireversible or irreversible CV processes were obtained. The kinetic parameters of the film-electrode processes, such as the surface transfer coefficient, the apparent diffusion coefficient, and the standard rate constant for electron transfer, for the two films in aqueous LiClO₄ solutions were measured, and the electrode process mechanism of the films was examined. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2245–2253, 2004     

Facile cation electro-insertion into layer-by-layer assembled iron phytate films

Molecular layer-by-layer assembly from pre-saturated aqueous solutions of Fe³⁺ and phytate is employed to build up iron phytate deposits on tin-doped indium oxide (ITO) electrodes. Globular films with approximately 1 nm growth per layer are observed by AFM imaging and sectioning. In electrochemical experiments the iron phytate films show well-defined voltammetric responses consistent with an immobilised Fe(III/II) redox system in aqueous (LiClO₄, NaClO₄, KClO₄, phosphate buffer) and in ethanolic (LiClO₄, NaClO₄, NBu₄ClO₄) electrolyte solutions. The Fe(III/II) redox system is reversible and cation insertion/expulsion occurs fast on the timescale of voltammetric experiments even for more bulky NBu₄⁺ cations and in ethanolic solution. Peak shape analysis and scan rate dependent midpoint potentials suggest structural changes accompanying the redox process and limiting propagation. Iron phytate is proposed as a versatile and essentially colourless cation electro-insertion material and as a potential energy storage material.     

Electrochemical behaviour of V2O5 xerogel in aqueous LiNO3 solution

By dissolving crystalline V₂O₅ in hydrogen peroxide and drying at elevated temperature, the V₂O₅ xerogel was obtained. Its electrochemical behaviour was examined in aqueous solution of LiNO₃ by both cyclic voltammetry and galvanostatic charging/discharging cycling. Peak-to-peak potential separation observed at the cyclovoltammograms indicated fast Li⁺ intercalation/deintercalation reactions. Initial discharge capacity amounted to 69 mAhg^?1, and after 100 charging/discharging cycles, capacity fade amounted to 11% only. This presents a remarkable improvement in comparison with the behaviour of crystalline, vanadium oxide based, lithium intercalates in aqueous electrolytes.     

IR spectroelectrochemical studies of Fe2V4O13, FeVO4 and InVO4 thin films obtained via sol-gel synthesis

In this paper we generalize the IR spectroscopic properties of M³⁺VO₄ (M=Fe, In) orthovanadate and Fe₂V₄O₁₃ films. The films were prepared using the sol-gel synthesis route from M³⁺ nitrates and vanadium oxoisopropoxide. The vibrational bands in the IR absorbance spectra of the films are classified in terms of terminal V-O stretching (1050–880 cm^–1), bridging V-O^...Fe and V^...O^...Fe stretching (880–550 cm^–1), mixed V-O-V deformations and Fe-O stretching (<550 cm^–1) modes. Ex situ IR spectra of films were measured after consecutive charging/discharging to various intercalation coefficients x and correlated to the current peaks in the cyclic voltammetry curves measured in 1 M LiClO₄/propylene carbonate electrolyte. We classified the ex situ IR spectra of charged/discharged films according to their vibrational band changes. The results reveal that, for small values of the intercalation coefficient, crystalline FeVO₄, InVO₄ and Fe₂V₄O₁₃ films exhibit a simultaneous decrease in the intensity of all IR bands while the band frequencies remain unaffected. For the higher intercalation levels, IR mode frequencies are shifted, signaling the presence of reduced vanadium. Further charging leads to an amorphization of the film structure, which was established from the similarity of the IR spectra of charged films with those of amorphous films prepared at lower annealing temperatures. The results confirm that ex situ IR spectroelectrochemical measurement is an effective way to assess the structural changes in films with different levels of intercalation. Electronic Publication     

Iridium Anodic Oxidation to Ir(III) and Ir(IV) Hydrous Oxides

Iridium oxide films (IROFs) are known to have an enhanced or the so‐called super‐Nernstian (<59 mV/pH) pH‐sensitivity. The intention in the present study was to find out the reasons of such behavior and also to elucidate the nature of iridium anodic oxidation processes. The methods employed were combined cyclic voltammetry and chronopotentiometry. Iridium layers of 0.1 to 0.2 μm thickness, deposited thermally on titanium or gold‐plated titanium substrates, were used for investigations. IROFs on the surface of working electrodes were formed anodically by applying a constant potential in deaerated and oxygen‐containing solutions of 0.5 M H₂SO₄, 0.1 M KOH and 0.5 M H₃PO₄+KOH. Linear pH‐dependences of the stationary open‐circuit potential with the slopes close to 59 mV/pH were found for iridium electrode oxidized at 0.4 V–0.8 V (RHE) in deaerated and at 0.8 V–1.2 V (RHE) in O₂‐containing solutions. They were attributed to reversible Ir/Ir(OH)₃ and Ir/ IrO₂?nH₂O metal‐oxide electrodes, respectively. It has been suggested that the main current peaks seen in the voltammograms of iridium electrode in acid and alkaline solutions are of different nature. The difference between iridium electrode surface states in acid and alkaline solutions has been presumed to be the main reason of super‐Nernstian pH‐sensitivity of the IROFs. On the basis of the results obtained standard potential of Ir/Ir(OH)₃ electrode and the solubility product of Ir(OH)₃ have been evaluated: =0.78±0.02 V and K_sp=3.3×10^?64.     

Characterization and Electrocatalytic Properties of Composite Poly(new fuchsin) and Phosphomolybdate Films

Organic/inorganic hybrid films of poly(new fuchsin) and phosphomolybdate (PMo₁₂O ) have been prepared in acidic aqueous solutions. These new combination films are stable, electrochemically active, and can be produced on glassy carbon, platinum, gold, and transparent semiconductor tin oxide electrodes. An electrochemical quartz crystal microbalance along with cyclic voltammetry and UV‐visible absorption spectroscopy were used to study the in situ growth of the hybrid films. The hybrid poly(new fuchsin) and PMo₁₂O films showed four obvious redox couples, and when transferred to various acidic aqueous solutions, the formal potentials of the four redox couples were found to be pH dependent. The electrocatalytic reduction of ClO , BrO , IO , SO , S₂O , H₂O₂, and NO by the hybrid poly(new fuchsin) and PMo₁₂O films was achieved in acidic aqueous solutions. In an aqueous solution at pH 1.5, a hybrid poly(new fuchsin) and PMo₁₂O film showed a higher electrocatalytic reduction activity of IO than BrO or ClO , and the order of electrocatalytic activity was IO >BrO >ClO . The order of electrocatalytic reduction of SO , S₂O , H₂O₂, and NO by hybrid poly(new fuchsin) and PMo₁₂O films in an aqueous solution at pH 1.5 was NO >H₂O₂>S₂O and SO . The electrocatalytic reactions of the poly(new fuchsin) and PMo₁₂O films were investigated using the rotating ring‐disk electrode method.     

EQCM Study of Iridium Anodic Oxidation in H2SO4 and KOH Solutions

In the present study anodic oxidation of iridium layer formed thermally on a gold‐sputtered quartz crystal electrode has been investigated by electrochemical quartz crystal microgravimetry (EQCM) in the solutions of 0.5 M H₂SO₄ and 0.1 M KOH. The emphasis here has been put on the microgravimetric behavior of iridium as a metal, because a few previous EQCM studies reported in literature have been devoted to iridium oxide films (IROFs). The objective pursued here has been to elucidate the nature of the main voltammetric peaks, which occur at different ranges of potential in the solutions investigated. It has been found that anodic oxidation of iridium electrode in 0.5 M H₂SO₄ and 0.1 M KOH solutions is accompanied by irregular fluctuations of the electrode mass at 0.4 V<E<0.8 V followed by regular increase in mass at 0.8 V<E<1.2 V. The cathodic process initially, at 1.2 V>E>0.9 V, proceeds without any or with slight increase in electrode mass, whereas at E<0.8 V a regular decrease in mass is observed. It has been found that mass to charge ratio characterizing the processes of interest is 2 to 3 g F^?1in acidic medium, whereas in the case of alkaline one it is 4 to 6 g F^?1. The main pair of peaks seen in the voltammograms of Ir electrode in alkaline medium at E<0.8 V is attributable to redox transition Ir(0)→Ir(III), whereas those observed in the case of acidic medium at E>0.8 V should be related to the redox process Ir(0)→Ir(IV) going via intermediate stage of Ir(III) formation. As a consequence of these redox transitions, the gel‐like surface layer consisting of Ir(III) or Ir(IV) hydrous oxides forms on the electrode surface.     

Dioxouranium(VI) Hydrolysis at 75 and 100 °C in 3.6 mol⋅kg<Superscript>−1</Superscript> LiClO<Subscript>4</Subscript> Aqueous Medium

This work is concerned with the acidic properties of the uranyl ion, UO₂²⁺, at 75 and 100 °C in 3.6 mol⋅kg⁻¹ LiClO₄ aqueous medium. The investigation was carried out with a coulometric-potentiometric technique. Direct and reverse acid-base titrations were carried out in order to check whether equilibrium had been reached. Moreover, in order to determine whether or not the solutions were oversaturated, a further check was carried out with fresh saturated hydrolyzed solutions.     

Synthesis of nanoporous activated iridium oxide films by anodized aluminum oxide templated atomic layer deposition

Iridium oxide (IrOx) has been widely studied due to its applications in electrochromic devices, pH sensing, and neural stimulation. Previous work has demonstrated that both Ir and IrOx films with porous morphologies prepared by sputtering exhibit significantly enhanced charge storage capacities. However, sputtering provides only limited control over film porosity. In this work, we demonstrate an alternative scheme for synthesizing nanoporous Ir and activated IrOx films (AIROFs). This scheme utilizes atomic layer deposition to deposit a thin conformal Ir film within a nanoporous anodized aluminum oxide template. The Ir film is then activated by potential cycling in 0.1 M H₂SO₄ to form a nanoporous AIROF. The morphologies and electrochemical properties of the films are characterized by scanning electron microscopy and cyclic voltammetry, respectively. The resulting nanoporous AIROFs exhibit a nanoporous morphology and enhanced cathodal charge storage capacities as large as 311 mC/cm².     

Influence of addition of lithium salt solution into PEDOT:PSS dispersion on the electrochemical and spectroscopic properties of film electrodes

The present work has studied electrochemical and optical properties of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) film electrodes drop-casted from commercial PEDOT:PSS aqueous dispersion with preliminary addition and without addition of LiClO₄ electrolyte (further denoted as PEDOT:PSS/LiClO₄ and PEDOT:PSS). Cyclic voltammetry measurements showed the significant increase in capacitance of PEDOT:PSS/LiClO₄ film electrodes in comparison to PEDOT:PSS. Furthermore, the improved charge transport in PEDOT:PSS/LiClO₄ films was demonstrated by electrochemical impedance spectra. In situ spectroelectrochemical measurements revealed that preliminary addition of LiClO₄ into PEDOT:PSS aqueous dispersion allows to increase amount of free charge carriers (polaron and bipolaron states) in the resulting film during electrochemical oxidation in LiClO₄ propylene carbonate solution. This increase was attributed to ion-induced charge screening between positively charged PEDOT and negatively charged PSS in polyelectrolyte structure, which was supported by structural investigations of both types of film electrodes by using FTIR, SEM, and XPS measurements. Charge screening results from a more open structure that allows conformational relaxation of PEDOT molecules during charge transport, which leads to partial separation of oppositely charged PSS and PEDOT molecules and facilitating the increase of electrochemical activity.

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The electrocatalytic reactions of adenine, guanine, H2O, H2O2, N2H4, and l -cysteine catalyzed by poly(Ni(4-TMPyP)) film-modified electrodes

Electrochemical preparation of poly(nickel tetrakis(N-methyl-4-pyridyl)porphyrin) tetratosylate (poly-Ni(4-TMPyP)) produces stable and electrochemically active films in strong and weak basic aqueous solutions. These films were produced on glassy carbon and gold electrodes. The electrochemical quartz crystal microbalance and cyclic voltammetry were used to study the in situ growth of poly(Ni(4-TMPyP)) films. The electrochemical properties of poly(Ni(4-TMPyP)) films indicate that the redox process was confined in to the immobilized film. The electrochemical quartz crystal microbalance results showed an ion exchange reaction for the redox couple. The polymer films showed one new redox couple when transferred to strong and weak basic aqueous solutions and the formal potential was found to be pH dependent. The electrocatalytic oxidation of H₂O by a nickel tetrakis(N-methyl-4-pyridyl)porphyrin film-modified electrode was also performed. The mechanism of oxygen evolution was determined by cyclic voltammetry, chronoamperometry and rotating ring disc electrode methods. The oxygen evolution was determined by a bicatalyst system using hemoglobin, and iron tetrakis (N-methyl-2-pyridyl)porphyrin as catalyst to detect the oxygen by electrocatalytic reduction. The electrocatalytic oxidations of adenine, guanine, H₂O₂, N₂H₄, NH₂OH, and l-cysteine by the film-modified electrode obtained from water-soluble nickel porphyrin were also investigated.     

The single crystal metal-non-aqueous solvent interface: Underpotential deposition of Cd on Ag (111) in propylene carbonate

The underpotential deposition of cadmium on Ag (111) in propylene carbonate using either lithium perchlorate or tetra-n-butylammonium perchlorate as supporting electrolytes has been found to yield sharp and well defined voltammetric peaks. The results obtained in aqueous LiClO₄ and tetraethylammonium perchlorate solutions for the same UPD-host metal system were, however, found to be different from those in propylene carbonate, particularly in the case of LiClO₄ for which the voltammetry was characterized by broad and ill-defined features. This novel solvent-induced effect has been attributed to differences in the extent of specific adsorption of the perchlorate anion in water and PC and/or to solvent-metal substrate interactions.     

Electrochemical Properties of Poly-3-methylthiophene Films: A Cyclic Voltammetry and Chronoamperometry Study

The charge transfer in poly-3-methylthiophene films in 0.05–0.5 M LiClO₄ solutions in acetonitrile is studied by cyclic voltammetry and chronoamperometry. An analysis of data on the current relaxation following a film perturbation by a low-voltage pulse reveals two constituents of the current relaxation, both exponentially dependent on time. Dependence of parameters of the empirical equation derived for the current relaxation on experimental variables is studied.     

Ionic conductivity of hybrid films composed of polyacrylonitrile,ethylene carbonate,and LiClO4

The electrical conductivity of hybrid films consisting of polyacrylonitrile (PAN), ethylene carbonate (EC), and LiClO₄ was investigated. In these films, EC and LiClO₄ are found to be molecularly dispersed in PAN, forming solid solutions over a wide composition range. The ionic character of the electrical conductivity is demonstrated. The conductivity is not correlated with the content of LiClO₄ or of PAN, but primarily with the mole ratio [EC]/[LiClO₄] in the films. An increase in the [EC]/[LiClO₄] ratio enhances the conductivity. When the ratio is about 2, the conductivity attains 10^?4–10^?5 S cm^?1 at 25°C. This change in conductivity results from a change in carrier mobility. PAN makes the films solid without decreasing the carrier mobility. In the hybrid films, the carrier mobility and the macroscopic viscosity are not related by Walden's rule. The high conductivity is due to regions in the film characterized by a low microscopic viscosity. This is determined by the mole ratio [EC]/[LiClO₄] and largely controls the carrier mobility.     

Charging and discharging rate studies of polypyrrole films in AlCl3: 1-methyl-(3-ethyl)-imidazolium chloride molten salts and in CH3CN

The chronocoulometric charging and discharging of polypyrrole films in basic AlCl₃/1-methyl-(3-ethyl)-imidazolium chloride molten salts and CH₃CN have been investigated. Both processes follow a t^{$\text{1}\text{2}$} time dependence and are significantly faster in the molten salts. Comparison with redox polymer and porous electrode models shows that neither model is satisfactorily applicable over the entire potential region studied. The charging and discharging rates are limited by ion migration in the polymer and for potential steps in the “double layer charging” region polypyrrole behaves as a porous electrode material. In this region there is a good correlation between the charging/discharging rates and the solvent conductivity.     

Metal Oxide Film Anodes in the Electrolysis of Water or Brine

Metal (M) oxide (M: Ir, Os, Pd, Pt, Rh, Ru) together with MaO₂ and MnO₂ alone, were coated on SnO₂ films and the anode behavior was examined in 1.0 N H₂SO₄, 1.0 N NaOH and 1.0, N NaCl aqueous solutions at 25°. The results are compared with those of DSA and of metallic Pt.     

Mass tranfer of ions and solvent at redox processes in poly-3,4-ethylenedioxythiophene films

The work presents the data on mass transfer at the interface of the poly-3,4-ethylenedioxythiophene film with different propylene carbonate electrolyte solutions (TBAPF₆, LiClO₄, NaClO₄, TBAClO₄, TBABF₄) obtained using the quartz microgravimetry method in combination with cyclic voltammetry. It is shown that two parts of different nature can be observed in the region of electric activity of poly-3,4-ethylenedioxythiophene films on Δm, ΔQ curves. They evidence the change in mass transfer conditions at achieving different film oxidation degrees.     

Electrodepositions and capacitive properties of hybrid films of polyaniline and manganese dioxide with fibrous morphologies

Electrocodepositions were conducted in solutions of aniline and MnSO₄ through potential cycling to afford hybrid films of polyaniline (PANI) and manganese dioxide (PANI/MnO₂). The films obtained displayed characteristic redox peaks of PANI on cyclic voltammograms in acidic aqueous solution. While in 1.0 M NaNO₃ at pH 1, the films showed pseudocapacitive behaviors from 0 to 0.65 V vs. SCE. MnO₂ was detected through XRD and XPS measurements on the films. The codeposition of PANI with MnO₂ had dramatic effects on morphologies of the obtained hybrid films that displayed fibrous morphologies instead of granular one of PANI. Hybrid film PM50 obtained in the presence of 50 mM Mn²⁺ displayed a specific capacitance of 532 F g⁻¹ at 2.4 mA cm⁻² discharging current, 26% higher than that of similarly prepared PANI. It showed a coulombic efficiency (η) of 97.5% over 1200 cycles with 76% specific capacitance maintained.     

Voltammetric Determination of BHT Antioxidant at Gold Electrode in Biodiesel

The voltammetric determination of synthetic antioxidant 2,6‐di‐tert‐butyl‐4‐methylphenole (BHT) was studied using linear‐sweep voltammetry (LSV) and cyclic voltammetry (CV) with a gold electrode and performed in isopropanol media containing either 0.1 mol L^?1 H₂SO₄ or 0.1 mol L^?1 LiClO₄ as supporting electrolyte. The results obtained have revealed that the most reliable detection was acquired in acidic media (isopropanol–H₂SO₄) whereas the use of isopropanol? LiClO₄ solution exhibited poorer reproducibility due to possible passivation of the electrode. Real samples of biodiesel mixture were analyzed without any special sample treatment or separation and results were compared with those obtained by FTIR‐spectroscopy.     

Solid‐State Electrochemical Method for Determining Core and Shell Size in Pd@PdO Nanoparticles

Electrochemical characterization of palladium nanoparticles surrounded by a palladium oxide shell (Pd@PdO) is described from a combination of voltammetry plus electrochemical quartz crystal microbalance experiments at nanoparticle deposits on graphite electrodes in contact with aqueous H₂SO₄ and NaOH solutions. A method for determining the metal core size and oxide shell thickness of the Pd@PdO nanoparticles, based on a combination of conventional voltammetry of nanoparticles in DMSO solution and voltammetry of nanoparticle deposits in contact with 0.10 M aqueous NaOH solution, is described.