DNA hybridization biosensor using chitosan–carbon nanotubes composite film as an immobilization platform and [Cu(bpy)(MBZ)2(H2O)] (bpy = 2,2′-bipyridine, MBZ = p-methylbenzoate) as a novel redox indicator

In this paper, a new DNA hybridization detection strategy was developed based on the immobilization of capture probe DNA on a chitosan (CS)–carbon nanotubes (CNTs) composite modified glassy carbon electrode (CS–CNTs/GCE) and the use of a copper complex, [Cu(bpy)(MBZ)₂(H₂O)] (bpy = 2,2′-bipyridine, MBZ = p-methylbenzoate), as a new redox hybridization indicator. The electrochemical characterization experiments showed that the nanocomposite film of CS–CNTs could effectively immobilize the capture probe DNA and greatly improve the electron-transfer reactions of the electroactive molecules. Electrochemical and fluorescent spectroscopic analysis revealed that the polypyridyl copper complex of [Cu(bpy)(MBZ)₂(H₂O)] bound to DNA via a typical intercalation mode. Surface studies further showed that the copper complex can discriminate between double-stranded and single-stranded DNA that immobilized on the surface of CS–CNTs/GCE. When being utilized as a redox indicator for the detection of hybridization for short DNA species related to phosphinothricin acetyltransferase (PAT), the indicator showed good specificity for recognizing the complementary, three-base mismatched and non-complementary DNA. Under the optimized conditions, the oxidation peak currents of the copper complex enhanced linearly with increases in the concentration of the complementary sequence in the range from 5.0 × 10⁻¹⁰ to 1.0 × 10⁻⁸ M. A detection limit of 5.0 × 10⁻¹⁰ M was also obtained based on the constructed DNA biosensor.     

Spectroelectrochemistry of poly(o-phenylenediamine): Polyaniline-like segments in the polymer structure

A comparative discussion of the electrochemical and spectroelectrochemical properties of poly(o-phenylenediamine) POPD, an aromatic diamine, is presented. In situ conductance measurements show that POPD shows some conductance around the redox peak potentials, i.e. = −0.02 < E_SCE < 0.00 V. In situ UV–vis and Raman spectroelectrochemical results suggest that radical cations of polyaniline (PANI)-like segments in POPD backbone might be responsible for imparting conductance to this otherwise nonconducting polymer (as commonly supposed in the literature). The presence of radical cations was confirmed by in situ Raman spectra showing a band at 1390 cm⁻¹ characteristic of a C–N⁺-stretching vibration having an intermediate single/double bond character and being coupled to quinoid rings/polaronic form of PANI segments in the polymer. Results also reveal that POPD shows a close correlation between its electrochemical and spectroelectrochemical properties in the range of −0.02 < E_SCE < 0.00 V, and provide support for the suggested presence of doped PANI-like segments in said potential range.     

Electrochemical properties of N-doped hydrogenated amorphous carbon films fabricated by plasma-enhanced chemical vapor deposition methods

Nitrogen-doped hydrogenated amorphous carbon thin films (a-C:N:H, N-doped DLC) were synthesized with microwave-assisted plasma-enhanced chemical vapor deposition widely used for DLC coating such as the inner surface of PET bottles. The electrochemical properties of N-doped DLC surfaces that can be useful in the application as an electrochemical sensor were investigated. N-doped DLC was easily fabricated using the vapor of nitrogen contained hydrocarbon as carbon and nitrogen source. A N/C ratio of resulting N-doped DLC films was 0.08 and atomic ratio of sp³/sp²-bonded carbons was 25/75. The electrical resistivity and optical gap were 0.695 Ω cm and 0.38 eV, respectively. N-doped DLC thin film was found to be an ideal polarizable electrode material with physical stability and chemical inertness. The film has a wide working potential range over 3 V, low double-layer capacitance, and high resistance to electrochemically induced corrosion in strong acid media, which were the same level as those for boron-doped diamond (BDD). The charge transfer rates for the inorganic redox species, Fe^2+/3+ and Fe(CN)₆^4−/3− at N-doped DLC were sufficiently high. The redox reaction of Ce^2+/3+ with standard potential higher than H₂O/O₂ were observed due to the wider potential window. At N-doped DLC, the change of the kinetics of Fe(CN)₆^3−/4− by surface oxidation is different from that at BDD. The rate of Fe(CN)₆^3−/4− was not varied before and after oxidative treatment on N-doped DLC includes sp² carbons, which indicates high durability of the electrochemical activity against surface oxidation.     

Iron role in the electrochemical cyclopropanation reaction of activated olefins and halogenated compounds

The electrochemical procedure for cyclopropanation reaction between benzal chloride (BC) and dimethyl itaconate (DMI), using Cu(I) salt, iron rod as sacrificial anode, and low temperature (−10 °C < T < −5 °C), was investigated by cyclic voltammetry and electrolysis. The variation of the experimental parameters of electrolyses, such as the absence or the presence of CuBr during the pre-electrolysis step, or its substitution by an initial amount of iron salt (FeCl₂, FeBr₂ or FeI₂), and pyridine addition to the reaction medium showed that the presence of dissociated Fe(II) is essential to the cyclopropanation process. The Cu(I) salt is deposited on the cathode surface during the pre-electrolysis, providing the accumulation of Fe(II) in solution, which does not act as catalyst in the electrochemical process. The best cyclopropanation yield (81%) was reached in DMF/pyridine (9:1) in the presence of FeI₂ salt. A cyclopropanation mechanism involving two possible pathways was suggested, implying both an anionic and a radical BC intermediates.     

Electrosynthesis of conducting polymer films from the azo dye methoxy red

Anodic polymerization of the azo dye methoxy red (4-methoxybenzene azo-1,3-diaminobenzene) on platinum electrodes in 1 M HCl in 50% v/v ethanol/water was found to yield thin and stable polymeric films. The films were electroactive in acidic solutions and the activity diminished as the acidity decreased. The pair of symmetrical redox peaks at a formal redox potential, (E )_pH=0 = 0.61 V vs SCE, with a Nernstian slope dE/dpH = 0.06 V, is attributed to a 1:1 proton + electron elimination (on oxidation)/addition (on reduction) at the amino/imino linkages which connect the aromatic nuclei. Chronocoulometric plots indicated that the transport of the solvated protons, and probably Cl^– ions, through the film is the rate-determining step of the above redox processes. The rate of electron transfer reactions of the redox couple [Fe(CN)₆]^3–/4– on poly-methoxy red-covered platinum electrodes decreased by a factor of more than two orders of magnitude, compared to the bare electrodes.     

Determination of the kinetic parameters of oxygen reduction on copper using a rotating ring single crystal disk assembly (RRDCu(h k l)E)

The kinetics of the oxygen reduction reaction (orr) on Cu(h k l) surfaces are investigated in perchloric acid and sulfuric acid solutions using rotating ring disk electrode (RRD_Cu(h k l)E). Parameters, such as reaction order, kinetic current, rate constant, Tafel slopes as well as the number of electrons transferred are determined. The variation in the activity and reaction pathway with the crystal faces in different electrolytes is related to the surface characteristics of Cu(h k l) and the structure-sensitive inhibiting effect of the adsorbed anions on their surfaces. In 0.1 M HClO₄, the difference in activity is clearly observed on Cu(h k l) surfaces (Cu(1 0 0) > Cu(1 1 1) although it is relatively small). The higher activity of Cu(1 0 0) arises from its more open characteristics which may facilitate the co-adsorption of O₂. On the other hand, the adsorption of oxygenated species on Cu(1 1 1) at E > −0.35 V induces a 2 e⁻ pathway; while a 4 e⁻ reduction is observed on Cu(1 0 0) in the entire potential region (−0.70 V < E < −0.10 V). In 0.5 M H₂SO₄, the sequence in activity between Cu(1 1 1) and Cu(1 0 0) varies with the potentials, i.e., Cu(1 0 0) is initially more active than Cu(1 1 1) at −0.35 V < E < −0.15 V, however, the reversal in the activity between Cu(1 1 1) and Cu(1 0 0) is observed at more negative potentials (−0.45 V < E < −0.35 V). The desorption of strongly adsorbed (bi)sulfate anions on Cu(1 1 1) induces the 2 e⁻ reduction via peroxide formation, however, a 4 e⁻ reduction is dominant on the Cu(1 0 0) surfaces. The major effect of (bi)sulfate anions and oxygenated species on the orr kinetics and reaction pathway on Cu(h k l) surfaces is the blocking of active copper sites for the adsorption of O₂ molecules.     

An electrochemical DNA biosensor developed on novel multinuclear nickel(II) salicylaldimine metallodendrimer platform

An electrochemical DNA biosensor (EDB) was prepared using an oligonucleotide of 21 bases with sequence NH₂-5′-GAGGAGTTGGGGGAGCACATT-3′ (probe DNA) immobilized on a novel multinuclear nickel(II) salicylaldimine metallodendrimer on glassy carbon electrode (GCE). The metallodendrimer was synthesized from amino functionalized polypropylene imine dendrimer, DAB-(NH₂)₈. The EDB was prepared by depositing probe DNA on a dendrimer-modified GCE surface and left to immobilize for 1 h. Voltammetric and electrochemical impedance spectroscopic (EIS) studies were carried out to characterize the novel metallodendrimer, the EDB and its hybridization response in PBS using [Fe(CN)₆]^3−/4− as a redox probe at pH 7.2. The metallodendrimer was electroactive in PBS with two reversible redox couples at E°′ = +200 mV and E°′ = +434 mV; catalytic by reducing the E_pa of [Fe(CN)₆]^3−/4− by 22 mV; conducting and has diffusion coefficient of 8.597 × 10⁻⁸ cm² s⁻¹. From the EIS circuit fitting results, the EDB responded to 5 nM target DNA by exhibiting a decrease in charge transfer resistance (R_ct) in PBS and increase in R_ct in [Fe(CN)₆]^3−/4− redox probe; while in voltammetry, increase in peak anodic current was observed in PBS after hybridization, thus giving the EDB a dual probe advantage.     

Electrochemical determination of the diffusion coefficient of cations into Chevrel phase-based electrochemical transfer junction by potential step chronoamperometry and impedance spectroscopy

The molybdenum chalcogenides Mo₆X₈ (X = S, Se) offer the possibility of intercalation/de-intercalation processes by chemical or electrochemical way. Besides the different applications of so-called Chevrel phases, we have proposed an electrochemical transfer junction for selective recovery of metallic cations in the perspective of recycling of industrial liquid mineral wastes. Thus, the knowledge of the diffusion properties of cations in the Chevrel phases is essential. Here we report on the electrochemical determination of diffusion coefficients of Co²⁺, Ni²⁺, Fe²⁺, Cd²⁺, Zn²⁺, Mn²⁺ and Cu²⁺ for Mo₆S₈ and Mo₆Se₈ matrices. Experiments were realized on samples with compactness of 50% and 96–98%. They point out that the lower compactness is unfavorable to the mobility of the cobalt ions. From potential step chronoamperometry and electrochemical impedance spectroscopy, the diffusion coefficients were found around 10⁻⁹ cm² s⁻¹, even 10⁻⁶ cm² s⁻¹ for copper. These results confirm the high mobility of transition metal ions in studied phases and complete the data for Co, Fe or Mn–Mo₆S₈ system and Mn–Mo₆Se₈ system. For the sulfide phase, the following sequence for is observed Ni < Co < Fe < Cd < Zn < Mn ? Cu and can be explained in regards with structural considerations and repulsion effects for copper.     

The characterization and bioelectrocatalytic properties of hemoglobin by direct electrochemistry of DDAB film modified electrodes

Direct electrochemistry of hemoglobin can be performed in acidic and basic aqueous solutions in the pH range 1-13, using stable, electrochemically active films deposited on a didodecyldimethylammonium bromide (DDAB) modified glassy carbon electrode. Films can also be produced on gold, platinum, and transparent semiconductor tin oxide electrodes. Hemoglobin/DDAB films exhibit one, two, and three redox couples when transferred to strong acidic, weak acidic and weak basic, and strong basic aqueous solutions, respectively. These redox couples, and their formal potentials, were found to be pH dependent. An electrochemical quartz crystal microbalance and cyclic voltammetry were used to study the in situ deposition of DDAB on gold disc electrodes and hemoglobin deposition on DDAB film modified electrodes. A hemoglobin/DDAB/GC modified electrode is electrocatalytically reduction active for oxygen and H₂O₂, and electrocatalytically oxidation active for S₂O₄²⁻ through the Fe(III)/Fe(II) redox couple. In the electrocatalytic reduction of S₄O₆²⁻, S₂O₄²⁻, and SO₃²⁻, and the dithio compounds of 2,2′-dithiosalicylic acid and 1,2-dithiolane-3-pentanoic acid, the electrocatalytic current develops from the cathodic peak of the redox couple at a potential of about −0.9 V (from the Fe(II)/Fe(I) redox couple) in neutral and weakly basic aqueous solutions. Hemoglobin/DDAB/GC modified electrodes are electrocatalytically reduction active for trichloroacetic acid in strong acidic buffered aqueous solutions through the Fe(III)/Fe(II) redox couple. However, the electrocatalytic current developed from the cathodic peak of the redox couple at a potential of about −0.9 V (from the Fe(II)/Fe(I) redox couple) in weak acidic and basic aqueous solutions. The electrocatalytic properties were investigated using the rotating ring-disk electrode method.     

Hexacyanoferrate ion adsorbed on propylpyridiniumsilsesquioxane polymer film-coated SiO2/Al2O3: use in an electrochemical oxidation study of cysteine

Hexacyanoferrate ion, [Fe(CN)₆]⁴⁻, was immobilized by an ion-exchange reaction on the propylpyridiniumsilsesquioxane chloride polymer thin-film-coated SiO₂/Al₂O₃ surface. The amount of [Fe(CN)₆]⁴⁻ immobilized was 0.22 mmol g⁻¹ with a surface coverage of 9.6×10⁻⁶ mmol cm⁻². A carbon paste electrode made with this material was prepared and its electrochemical properties studied. The electrode presented two well-defined redox peaks with midpoint potentials, E_m, of 0.152 V vs SCE. This potential was not significantly affected by pH changes between 2 and 9.5. The electrode showed much reproducible responses and was successfully used to study the electrochemical oxidation of cysteine.     

Faradaic impedance titration and control of electron transfer of 1-(12-mercaptododecyl)imidazole monolayer on a gold electrode

In this work, we studied interfacial proton transfer of the self-assembled monolayer (SAM) of 1-(12-mercaptododecyl)imidazole on a gold electrode by faradaic impedance titration method with Fe(CN)₆³⁻ as an anionic redox probe molecule. The surface pK_1/2 was found to be 7.3, which was nearly the same as that of 1-alkylimidazole in solution. We also investigated the electrochemical properties of the SAM-modified electrode by cyclic voltammetry. Cyclic voltammetry was performed (1) in the solution containing Fe(CN)₆³⁻ with repeated alternation of pH values to investigate the electrostatic interaction of the protonated or deprotonated imidazole with Fe(CN)₆³⁻ and (2) in the acidic or basic electrolyte containing Ru(NH₃)₆³⁺ as a cationic redox probe to verify the effect of the polarity of a redox probe. We observed the reversible adsorption/desorption of Fe(CN)₆³⁻ and concluded that the adsorbed Fe(CN)₆³⁻ catalyzed the electron transfer of both Fe(CN)₆³⁻ itself and cationic Ru(NH₃)₆³⁺.     

Strategies for the determination of the convective-diffusion limiting current from steady state linear sweep voltammetry

The limiting current is an important parameter for the characterization of mass transport in electrochemical systems operating under convective-diffusion control. Four methods to determine the limiting current from current (I) vs. potential (E) plots are considered. Strategies to determine the limiting current values include: (1) direct measurement from I vs. E curves, (2) estimation from the current value at E _L = ΔE/2 where ΔE is the length of the limiting current plateau, (3) evaluation of the first derivative dI/dE in the I vs. E curve and (4) from plots of E/I vs. I ⁻¹. The electrode reactions chosen to demonstrate the different strategies are: Cu(II) → Cu(I) and Cu(I) → Cu(0) in 1.5 mol dm⁻³ NaCl (pH 2) at a platinum rotating disc electrode and in 1 mol dm⁻³ NaOH at a 60 ppi reticulated vitreous carbon electrode (RVC).     

A study of ion exchange at the poly(butyl viologen)-electrolyte interface by SECM

In this work, the ion exchange characteristics of poly(butyl viologen) (PBV) thin films on a platinum electrode has been investigated by cyclic voltammetric (CV) scans. Since ferrocyanide anions (Fe(CN)₆⁴⁻) were added during the polymerization of the PBV thin-film for its stability, Fe(CN)₆⁴⁻ could form charge transfer complex with monomer and co-deposited with polymer. Scanning electrochemical microscopy (SECM) was used to probe the released Fe(CN)₆⁴⁻ ions from PBV film with Os(bpy)₃Cl₂ as a mediator for the approaching process in 0.5 M KCl medium. Mass changes during the redox process of the film were also monitored in-situ by electrochemical quartz crystal microbalance (EQCM). The ion exchange and transport behavior was observed during CV cycling of the film of the SECM and EQCM. The insertion and extraction of anions were found to be potential-dependence. Moreover, the decrease in tip current of released Fe(CN)₆⁴⁻ with increasing cycle number accounted for the ion exchange between Fe(CN)₆⁴⁻ and Cl⁻ in the KCl electrolyte. However, the Fe(CN)₆⁴⁻/Fe(CN)₆³⁻ redox couple was found to be highly stable between 0.0 and 0.5 V (vs. Ag/AgCl/saturated KCl) in the phosphate buffer solution. Therefore, the electrochemical property of Fe(CN)₆⁴⁻/Fe(CN)₆³⁻ redox couple was studied at different scan rates using CV technique. The peak currents were directly proportional to the scan rate as predicted for a surface confined diffusionless system. The surface coverage (Γ) and the concentration of Fe(CN)₆⁴⁻ were determined to be 1.88 × 10⁻⁸ mol/cm² and 0.641 mol/dm³, respectively. By neglecting cations incorporation during redox reaction of the PBV film and also based on the results obtained from energy-dispersive X-ray spectroscopy for the films of as-deposited, reduced and oxidized states, an ion exchange mechanism was proposed.     

Electrochemical studies with a Cu-5wt.%Ni alloy in 0.5 M H2SO4

The electrochemical behavior of the annealed Cu-5wt.%Ni alloy in 0.5 M H₂SO₄ was studied by means of open-circuit potential (E_OCP) measurements, cyclic voltammetry, electrochemical impedance spectroscopy (EIS), and quasi-stationary linear potential sweep. The hydrodynamics of the system was also studied. This material is constituted by a single α₁ phase. The anodic behavior of a Cu-Ni alloy in H₂SO₄ consists fundamentally on the electrodissolution of Cu, its main component, and the formation of a sulfur-containing passive layer. The presence of Ni decreases the rate of Cu oxidation, mostly at high positive potentials. The impedance spectra, obtained for the unrotating electrode, can be interpreted in terms of a simple charge-transfer reaction across a surface layer. When the electrode is rotated, the occurrence of an inductive loop evidenced the existence of an adsorbed layer. All the resistance estimated from the proposed equivalent circuits diminished with the electrode rotation rate, emphasizing the influence of ion transport in the overall electrode process. The system presented two anodic Tafel slopes: 40 mV dec⁻¹ for E<255 mV and 67 mV dec⁻¹ for E>275 mV. A Tafel slope of 40 mV dec⁻¹ evidences that copper dissolution can be interpreted in terms of the mechanism proposed by Mattsson and Bockris. The second Tafel suggests that at potentials more positive than 275 mV, copper dissolves according to a mechanism that considers the disproportionation of adsorbed Cu(I) species.     

Surface immobilisation of transition metal substituted Krebs type polyoxometalates, [X2W20M2O70(H2O)6] (X = Bi or Sb, M = Co or Cu), by the layer by layer technique

A series of transition metal (i.e. Cu²⁺ and Co²⁺) substituted Krebs type polyoxometalates (POMs), of the general formula [X₂W₂₀M₂O₇₀(H₂O)₆]ⁿ⁻, X = Sb or Bi, M = Co(II) or Cu(II), have been successfully immobilised onto carbon electrode surfaces through the employment of the layer-by-layer (LBL) technique. This involved the construction of alternating anionic POM, [X₂W₂₀M₂O₇₀(H₂O)₆]ⁿ⁻, layers and the cationic metallodendrimer, Ru(II)-metallodendrimer as the cationic layers, in addition to a [poly(diallyldimethylammonium chloride)] PDDA base layer. Stable multielectron redox couples associated with the W–O framework, for the Krebs type POMs, and the Ru(III/II) for the metallodendrimer, were clearly observed upon layer construction and redox switching within the pH domain of 2–6.5. The constructed multilayer assemblies exhibited pH dependent redox activity and thin layer behaviour up to 100 mV s⁻¹. The porosity and permeability of the individual multilayer assemblies towards an anionic probe were determined by AC impedance and cyclic voltammetry. The surface morphology of each multilayer was also determined by Atomic Force Microscopy (AFM).     

Spectroelectrochemical characterisation of copper salen-based polymer-modified electrodes

Electrogenerated polymers based on copper salen-type complexes were characterised electrochemically and by in situ UV-vis and ex situ EPR spectroscopy. The films, poly[Cu(salen)] and poly[Cu(saltMe)], exhibit reversible oxidative electrochemical behaviour in a wide potential range (0.0-1.5 V). Different regimes for charge transport behaviour are accessed by manipulation of film thickness and experimental time scale: thin films (surface concentration, Γ < ca. 80 nmol cm⁻²) show thin-layer/surface behaviour in the scan rate range used (0.020-2.0 V s⁻¹), whereas thicker polymers (Γ > ca. 90 nmol cm⁻²) exhibit a changeover from thin-layer to diffusion control regime at a critical scan rate that depends on polymer and film thickness: 0.15-0.20 V s⁻¹ for poly[Cu(salen)], 90 < Γ < 130 nmol cm⁻² and 0.20-0.30 V s⁻¹ for poly[Cu(saltMe)], 170 < Γ < 230 nmol cm⁻².UV-vis and EPR spectroscopies have allowed the characterisation of electronic states in the reduced and oxidised forms. The role of the copper atom during film oxidation was probed by combining UV-vis data with EPR on copolymers of the copper and nickel complexes. Data from both techniques are consistent and indicate that polymerisation and redox switching are associated with ligand-based processes. EPR of Ni-doped Cu polymers provided evidence for the non-involvement of the metal centre in polymer oxidation; like the analogous nickel polymers, copper polymers behave like delocalised π-system (‘conducting’) rather than discrete site (‘redox’) polymers.     

The effect of Fe/Cu ratio in the synthesis of mixed Fe,Cu,Al-clays used as catalysts in phenol peroxide oxidation

Mixed Fe,Cu,Al-clays (Fe,Cu,Al-MM) were prepared from Ca-montmorillonite (Mukhortala, Buryatia) at OH/(Fe + Cu + Al) 2.4 and Al/(Fe + Cu) 10/1. Effect of Fe/Cu ratio of Fe,Cu,Al-containing pillaring solution on structural properties of Fe,Cu,Al-MM was examined. Characterization studies were performed by use of XRD, FTIR, DR-UV–vis and N₂-adsorption/desorption analysis. The increase in copper loading leads to the decrease in total surface area, micropore volume and interlay distance of Fe,Cu,Al-MMs. It was found that the decrease in Fe/Cu ratio is favourable for the formation of oligomeric iron species. The relationships between preparation conditions, iron state, catalytic activity and stability to leaching were revealed in wet phenol oxidation with H₂O₂. The introduction of copper ions results in catalytic reaction acceleration that was interpreted in terms of the increase of radical generation rate.     

The mediation reaction between the external couple Ferri/Ferrocyanide and Os(II) bipyridile poly-vinylpyridile films coated onto glassy carbon electrodes

The oxidation-reduction of the Ferri/Ferrocyanide couple in solution onto modified glassy carbon Rotating Disk Electrodes (RDE) covered by Os(II) bipyridile poly-vinylpyridile (OsBPP) polymer was studied at room temperature. Steady state polarization curves were carried out as a function of the rotation speed, the polymer thickness and the concentration of redox centers within the polymer. This system has the characteristic that the formal redox potentials of both the external redox couple (E⁰′(Fe(CN)₆^3−/4−) = + 0.225 V vs. SCE) and the mediator polymer (E⁰′(OsBPP) = 0.260 V vs. SCE) lie very close. It is demonstrated that diffusion of the Ferri/Ferrocyanide inside the polymer can be ruled out. Since the processes of charge transfer at the metal/polymer and the mediating reaction are fast, the experimental results can be interpreted in terms of a kinetics in which the charge transport in the polymer or the diffusion in the solution may be the rate determining step, according to the experimental conditions. A simple model is considered that allows interpreting the experimental results quantitatively. Application of this model allows the determination of the diffusion coefficient of the electrons within the film, D_e ≈ 10⁻¹⁰ cm² s⁻¹.     

Iodide/triiodide electrochemistry in ionic liquids: Effect of viscosity on mass transport, voltammetry and scanning electrochemical microscopy

The electrochemistry of I⁻/I₃⁻ was studied in ionic liquids using a combination of cyclic voltammetry, chronoamperometry and scanning electrochemical microscopy (SECM). The electrolytes were 1-alkyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide [C_nC₁Im][Tf₂N], ionic liquids (where n = 2, 4 and 8) and I⁻ was typically added at a concentration of approximately 11 mM. During cyclic voltammetry, two sets of peaks were observed in each ionic liquid due to oxidation and reduction of the I⁻/I₃⁻ redox couple and oxidation/reduction of the I₃⁻/I₂ redox couple. The diffusion coefficients of I⁻ and I₃⁻, as determined using chronoamperometry, increased with increasing temperature and decreased with increasing ionic liquid viscosity. The effect of ionic liquid viscosity on ultramicroelectrode (UME) voltammetry was also determined using the I⁻/I₃⁻ redox couple. Steady-state behaviour was observed at 1.3 μm UMEs at slow voltammetric scan rates and steady-state SECM feedback approach curves were also obtained at a 1.3 μm Pt SECM tips, provided that the tip approach speed was sufficiently low.     

Electrochemical behavior of several iron complexes in hydrophobic room-temperature ionic liquids

The electrochemical behavior of FeCp₂⁺/FeCp₂ (Cp⁻, cyclopentadienyl), FeCl₄⁻/FeCl₄²⁻, FeBr₄⁻/FeBr₄²⁻ and Fe(CN)₆³⁻/Fe(CN)₆⁴⁻ couples was studied in the hydrophobic room-temperature ionic liquids based on bis(trifluoromethylsulfonyl)imide (TFSI⁻) with 1-n-butyl-1-methylpyrrolidinium (BMP⁺) and other quaternary ammonium cations. The cyclic voltammetric data indicated that these complexes were stable in BMPTFSI and that the redox reactions between trivalent and divalent iron species of these complexes are electrochemically reversible. The diffusion coefficients of these complexes were found to be affected mainly by the size of the species. On the other hand, the redox potential of Fe(CN)₆³⁻/Fe(CN)₆⁴⁻ couple depended on organic cations reflecting the difference in the acceptor properties of the organic cations.