Effects of K<Subscript>4</Subscript>Fe(CN)<Subscript>6</Subscript> on electroless copper plating using hypophosphite as reducing agent

K₄Fe(CN)₆ was used to improve the microstructure and properties of copper deposits obtained from hypophosphite baths. In electroless copper plating solutions using hypophosphite as the reducing agent, nickel ions (0.0038 M with Ni²⁺/Cu²⁺ mole ratio 0.12) was used to catalyze hypophosphite oxidation. However, the color of the copper deposits was dark or brown and its resistivity was much higher than that obtained in formaldehyde baths. The effects of K₄Fe(CN)₆ on the deposit composition, resistivity, structure, morphology and the electrochemical reactions of hypophosphite (oxidation) and cupric ion (reduction) have been investigated. The deposition rate and the resistivity of the copper deposits decreased significantly with the addition of K₄Fe(CN)₆ to the plating solution and the color of the deposits changed from dark-brown to copper-bright with improved uniformity. The nickel and phosphorus content in the deposits also decreased slightly with the use of K₄Fe(CN)₆. Smaller crystallite size and higher (111) plane orientation were obtained by addition of K₄Fe(CN)₆. The electrochemical current–voltage results show that K₄Fe(CN)₆ inhibited the catalytic oxidation of hypophosphite at active nickel sites and reduced the reduction reaction of cupric ions on the deposit surface by adsorption on the electrode. This results in lower deposition rate and a decrease in the mole ratio of NaH₂PO₂/CuSO₄ consumed during plating.     

Investigation on conductivity of mixed surfactants reverse microemulsion

P-octyl polyethylene glycol phenyl ether (Triton X-100) and cetyltrimethylammonium bromide (CTAB) were mixed to be used as surfactant for preparing reverse microemulsion with n-hexane, n-hexanol and water. Effects of weight ratio of the two surfactants, temperature, concentrations of water and cosurfactant on the conductivity were studied. The results indicate that the conductivity of the mixed surfactants reverse microemulsion is greatly higher than that of the single surfactant system. The reverse microemulsion has been modified to be with good conductivity. The weight ratio of the two surfactants, temperature, concentrations of water and cosurfactant have obvious effects on the conductivity of the reverse microemulsion. Furthermore, the electrochemical behavior of potassium ferricyanide [K₃Fe(CN)₆] in the mixed surfactants reverse microemulsion was investigated by cyclic voltammetry. The result shows that the redox processes of \textFe( \textCN ) ₆ ^3- / \textFe( \textCN ) ₆ ^4- {{\text{Fe}}\left( {\text{CN}} \right)_{ 6}}^{ 3- } / {{\text{Fe}}\left( {\text{CN}} \right)_{ 6}}^{ 4-} present good reversibility and are controlled by diffusion in the system.     

Rhodium stabilized Prussian Blue-modified graphite electrodes for H<Subscript>2</Subscript>O<Subscript>2</Subscript> amperometric detection

Graphite electrodes chemically modified with Prussian Blue (G/PB) were obtained by spreading, on the electrode surface, appropriate volumes of 100 mM K₃[Fe(CN)₆] and 100 mM FeCl₃ solutions, both containing 10 mM HCl. In order to improve the electrochemical response stability, the potential of G/PB electrodes was cycled (in the domain where PB exhibits electrochemical activity) in 0.1 M KCl solution (G/PB-K), as well as in 2 mM RhCl₃ solution, containing 0.05 M KCl (G/PB-Rh). Compared with G/PB-K, the G/PB-Rh modified electrodes showed: (i) higher relative stability of the PB electrochemical response; (ii) better analytical parameters for H₂O₂ amperometric detection; (iii) slightly lower rate constant corresponding to the second order electrocatalytic reaction for H₂O₂ amperometric detection; (iv) an electrocatalytic activity not affected by the H₂O₂ concentration.     

Cathodic behaviour of CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript> spinel electrodes in alkaline medium

Spinel type CoFe₂O₄ thin films have been prepared, on stainless steel supports, by thermal decomposition of aqueous solutions of mixed cobalt and iron nitrates in 1:2 molar ratio at 400 °C. The electrochemical behaviour of the CoFe₂O₄/1 M KOH interface was investigated by cyclic voltammetry, chronoamperometry and impedance techniques. The studies allowed finding out the redox reactions occurring at the oxide surface. The results were compared with colloidal electrodes prepared by alkaline precipitation of Fe(II) or Fe(III) hydrous oxi-hydroxides on platinum electrodes. In addition, it has been concluded that the processes are diffusion-controlled and the diffusion of the hydroxide ion, through the oxide, acts as the rate-determining step. The diffusion coefficient of OH⁻ through the oxide film was determined using cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy techniques.     

Solid medium for conventional electrochemical measurements

Polysaccharide solids containing a large amount of water were used as a medium for conventional electrochemical measurements instead of liquid water. It was succeeded to prepare a tight and elastic solid by applying very carefully a microwave, when solubilizing the polysaccharide in water. It was successfully shown that the cyclic voltammogram (CV) of K₄Ru(CN)₆ in the tight 2 wt.% agarose or carrageenan solid containing excess water was almost the same as in a liquid water. The apparent diffusion coefficients of the molecule (D_app) shows similar values in the solid as well as in a liquid water indicating that the complex can diffuse in the solid the same as in a liquid water. Similar results were also obtained for the redox molecules, K₄Fe(CN)₆, methylviologen (MV²⁺) and Ru(bpy)₃²⁺, but for larger size molecules, on increasing their concentration, diffusion is suppressed showing a possible control of molecular diffusion by designing its size and the kind of the solid matrix including their concentrations. The electrochemical response of a modified electrode, in the present case prussian blue (PB)-coated electrode, could be measured in these solids the same as in liquid water indicating that the resistance between the PB film and the polysaccharide solid is almost the same as the interface between PB and water.     

Characterization of boron-doped diamond electrodes by electrochemical impedance spectroscopy

Charge transfer on boron doped diamond (BDD) electrodes was studied by cyclic voltammetry and electrochemical impedance spectroscopy. The diamond films of 5 μm thickness and boron content between 200 ppm and 3000 ppm were prepared by the hot filament CVD technique on niobium substrate and mounted in a Teflon holder as rotating disk electrodes. The electrochemical measurements were carried out in aqueous electrolyte solutions of 0.5 M Na₂ SO ₄ + 5 mM K₃[Fe(CN)₆]/K₄[Fe(CN)₆]. Significant deviation in the redox behaviour of BDD and active Pt electrodes was indicated by a shift of the peak potentials in the cyclic voltammograms with increasing sweep rate and lower limiting diffusion current densities under rotating disk conditions. In the impedance spectra an additional capacitive element appeared at high frequencies. The potential and rotation dependence of the impedance spectra can be described quantitatively in terms of a model based on diffusion controlled charge transfer on partially blocked electrode surfaces. Direct evidence for the non-homogeneous current distribution on the diamond surface was obtained by SECM measurements.     

Electropolymerization of pyrrole in ionic liquid microemulsion

The direct electropolymerization of pyrrole in [BMIM]PF₆ microemulsion was investigated for the first time. The H₂O/TX-100/[BMIM]PF₆ (W/IL), bicontinuous (BC), [BMIM]PF₆/TX-100/H₂O (IL/W) subregions can be used as electrolytes for pyrrole electropolymerization. The use of IL microemulsion remarkably reduces the amount of IL. Furthermore, electrochemical measurements indicated that W/IL microemulsion was the optimal medium and its polymerization rate was the fastest. Compared with molecular solvent system (0.25 mol L⁻¹ [BMIM]PF₆/acetonitrile) and neat [BMIM]PF₆, the resultant films electrodeposited in W/IL microemulsion possessed excellent electrochemical activity and uniform morphology. All the results indicated that the H₂O/TX-100/[BMIM]PF₆ microemulsion as electrolyte medium is the most suitable for electropolymerization of pyrrole. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Synthesis and electrochemical evaluation of carbon coated Cu<Subscript>6</Subscript>Sn<Subscript>5</Subscript> alloy-graphite composite lithium battery anodes

With a view to minimize the unavoidable large volume changes of tin based Cu₆Sn₅ alloy anodes, a composite Cu₆Sn₅/graphite anode has been prepared via. a mechanical alloying process and subsequently coated with disordered carbon through pyrolysis of PVC. Phase pure products with better crystallinity and preferred surface morphology were obtained, as evident from PXRD and SEM respectively. Upon electrochemical charge-discharge, the intermetallic Cu₆Sn₅ alloy-graphite composite anode was found to exhibit an enhanced initial discharge capacity of 564 mAh g⁻¹ followed by significant capacity fade (>20%) especially after five cycles. On the other hand, carbon coated Cu₆Sn₅ alloy-graphite composite demonstrated promising electrochemical properties such as steady reversible capacity (∼200 mAh g⁻¹), excellent cycle performance (<5% capacity fade) and high coulombic efficiency (∼98%) via. significant reduction of volume changes. The carbon coating offers buffering and conductive actions on the anode active material and thereby enhances the electrochemical behavior of carbon coated Cu₆Sn₅ alloy/graphite composite anode material.     

Effects of surface area on electrochemical performance of Li[Ni<Subscript>0.2</Subscript>Li<Subscript>0.2</Subscript>Mn<Subscript>0.6</Subscript>]O<Subscript>2</Subscript> cathode material

The effect of surface area on the electrochemical properties and thermal stability of Li[Ni_0.2Li_0.2Mn_0.6]O₂ powders was characterized using a charge/discharge cycler and DSC (Differential Scanning Calorimeter). The surface area of the samples was successfully controlled from ~4.0 to ~11.7 m² g⁻¹ by changing the molar ratio of the nitrate/acetate sources and adding an organic solvent such as acetic acid or glucose. The discharge capacity and rate capability was almost linearly increased with increase in surface area of the sample powder. A sample with a large surface area of 9.6–11.7 m² g⁻¹ delivered a high discharge capacity of ~250 mAh g⁻¹ at a 0.2 C rate and maintained 62–63% of its capacity at a 6 C rate versus a 0.2 C rate. According to the DSC analysis, heat generation by thermal reaction between the charged electrode and electrolyte was not critically dependent on the surface area. Instead, it was closely related to the type of organic solvent employed in the fabrication process of the powder.     

Synthesis and Characterization of Ferromagnetic BaFe<Subscript>2</Subscript>O<Subscript>4</Subscript> Nanocrystals Using Novel Ionic Precursor Complex [Fe(opd)<Subscript>3</Subscript>]<Subscript>2</Subscript>[Ba(CN)<Subscript>8</Subscript>]

The following investigation reports the synthesis of novel complex [Fe(opd)₃]₂[Ba(CN)₈] and preparation of BaFe₂O₄ nanoparticles through thermal decomposition without using any surfactant. The complex was characterized via Furrier transform infrared spectroscopy (FT-IR), ultra violet-visible spectroscopy (UV–vis), conductivity measurement and elemental analysis. The synthesized crystals of inorganic precursor complex was transferred to furnace, where they were calcined under normal atmosphere condition at 900 °C for 4 h. Formation of BaFe₂O₄ was supported by FT-IR and energy-dispersive X-ray analysis. Hexagonal structure of nano-oxide was confirmed on powder X-ray diffraction. Furthermore, uniform morphology of nanocrystals were reported by scanning electron microscopy. The saturation magnetization (22 emu/g), remanent magnetization (6 emu/g) and coercivity (400 Oe) reported on vibrating sample magnetometer curve illustrates the promising industrial and medicinal applications of prepared mixed oxide.     

Еlectrochemical hydriding/dehydriding of nanocrystalline Mg<Subscript>2−<Emphasis Type="Italic">x</Emphasis></Subscript>Sn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Ni (<Emphasis Type="Italic">x</Emphasis> = 0, 0.1, 0.3)

The electrochemical hydriding/dehydriding under galvanostatic conditions of nanostructured Mg_2-x Sn _x Ni (x = 0,0.1,0.3) were studied at different temperatures in the range 28–45 °C. The discharge capacity, cycle life and electrochemical impedance of the alloys were found to depend on the presence of Sn. Tin decreases the maximum electrochemical capacity, but essentially improves the cycle life of Mg₂Ni. Intensive corrosion of surface Mg was found to take place during the first 2–3 charge/discharge cycles to a much larger extent for Mg₂Ni, compared to the tin containing alloys. Sn decreases the electron density around the Mg atoms and therefore impedes magnesium oxidation. It was also found that Sn hampers charge transfer but reduces the hydrogen diffusion resistance in Mg₂Ni based alloys.     

Phase behavior and structural properties for the triton X-100/<Emphasis Type="Italic">n</Emphasis>-C<Subscript>n</Subscript>H<Subscript>2n+1</Subscript>COOH/H<Subscript>2</Subscript>O system

In the Triton X-100/n-C_nH_2n+1COOH/H₂O system, n-C_nH_2n+1COOH can be used as a cosurfactant. As its chain length increases, the regions of the microemulsions showing oil-in-water (O/W), water-in-oil (W/O), and bicontinuous structures decrease and at the same time, the region of the lamellar liquid crystal increases. In the O/W region, the distribution coefficient K of n-C_nH_2n+1COOH between Triton X-100 micellar phase and water phase increases with the chain length of saturated unbranched monocarboxylic acid. The relationship between the standard solubilization Gibbs free energy of saturated unbranched monocarboxylic acid and the number of methylene groups in the saturated unbranched monocarboxylic acid is given by the equation: ΔG _m ⁰=−2.364−2.818 n(CH₂) kJ·mol⁻¹ in the Triton X-100 micellar system. In the lamellar liquid crystal region, small-angle X-ray diffraction shows that the thickness of the bilayer d ₀ is independent of the weight ratio of n-C_nH_2n+1COOH to Triton X-100, but the volume of the solvent penetrating from the solvent layer to the amphiphilic bilayer increases with the weight ratio of n-C_nH_2n+1COOH to Triton X-100. Furthermore, the d ₀ value increases with the chain length of saturated unbranched monocarboxylic acid, which will contribute to the formation and stabilization of the lamellar liquid crystal.     

Direct electrochemical reduction of Dy<Subscript>2</Subscript>O<Subscript>3</Subscript> in CaCl<Subscript>2</Subscript> melt

The electrochemical reduction of Dy₂O₃ in CaCl₂ melt was studied. The cyclic voltammetry, chronoamperometry, AC impedance and constant voltage electrolysis were employed. A single cathodic current peak in the cyclic voltammogram and one response semicircle in the AC impedance spectrum were observed, supporting a one-step electrochemical reduction mechanism of Dy₂O₃. No intermediates were observed by XRD, which confirmed the following electrochemical reduction sequence: Dy₂O₃ → Dy. The charge transfer resistances and the activation energies involved in the electrochemical reduction step of Dy₂O₃ were obtained by simulating the AC impedance spectra with equivalent circuits. The electrochemical reduction reaction of Dy₂O₃ is controlled by the charge transfer process at a low voltage range and by the diffusion process at a high voltage range.     

Hydrothermal synthesis of MnO<Subscript>2</Subscript>/CNT nanocomposite with a CNT core/porous MnO<Subscript>2</Subscript> sheath hierarchy architecture for supercapacitors

MnO₂/carbon nanotube [CNT] nanocomposites with a CNT core/porous MnO₂ sheath hierarchy architecture are synthesized by a simple hydrothermal treatment. X-ray diffraction and Raman spectroscopy analyses reveal that birnessite-type MnO₂ is produced through the hydrothermal synthesis. Morphological characterization reveals that three-dimensional hierarchy architecture is built with a highly porous layer consisting of interconnected MnO₂ nanoflakes uniformly coated on the CNT surface. The nanocomposite with a composition of 72 wt.% (K_0.2MnO₂·0.33 H₂O)/28 wt.% CNT has a large specific surface area of 237.8 m²/g. Electrochemical properties of the CNT, the pure MnO₂, and the MnO₂/CNT nanocomposite electrodes are investigated by cyclic voltammetry and electrochemical impedance spectroscopy measurements. The MnO₂/CNT nanocomposite electrode exhibits much larger specific capacitance compared with both the CNT electrode and the pure MnO₂ electrode and significantly improves rate capability compared to the pure MnO₂ electrode. The superior supercapacitive performance of the MnO₂/CNT nancomposite electrode is due to its high specific surface area and unique hierarchy architecture which facilitate fast electron and ion transport.     

Modulation of the interfacial electrochemistry of surfactant-functionalised polypyrrole chemical sensor systems

The redox properties of electro-polymerized polypyrrole (Ppy) doped with different surfactants were studied in acid medium. It was found out that the addition of different surfactants affect the redox properties as evidenced by diffusion coefficients and rate constants calculated from experimental data obtained from cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Three different surfactants were incorporated into polypyrrole matrix to form homogeneous composites i.e. anionic surfactant polyvinylsulphonic acid (PVSA) as well as non-ionic surfactants (polyethylene glycol p-(1,1,3,3-tetramethylbutyl)-phenyl ether (Triton-X 100) and polyoxyethylene (20) sorbitan monolaurate (Tween 20). CV and EIS experiments were carried in the presence of the redox probe K₃[Fe(CN)₆]. Diffusion coefficient was interpreted as a measure of electron movement within the composite polymer structure and rate constant was interpreted as a measure of the rate of oxidation and reduction of the redox probe. The highest value for diffusion coefficient and rate constant was obtained for Ppy/PVSA as 8.16 × 10⁻¹² cm² s⁻¹ and 1.05 × 10⁻⁵ cm s⁻¹ respectively. The values obtained by CV and EIS were in good agreement.     

Temperature programmed desorption of oxygen from Pd films interfaced with Y<Subscript>2</Subscript>O<Subscript>3</Subscript>-doped ZrO<Subscript>2</Subscript>

The origin of the effect of non-faradaic electrochemical modification of catalytic activity (NEMCA) or Electrochemical Promotion was investigated via temperature-programmed-desorption (TPD) of oxygen, from polycrystalline Pd films deposited on 8 mol%Y₂O₃–stabilized–ZrO₂ (YSZ), an O²⁻ conductor, under high-vacuum conditions and temperatures between 50 and 250 °C. Oxygen was adsorbed both via the gas phase and electrochemically, as O²⁻, via electrical current application between the Pd catalyst film and a Au counter electrode. Gaseous oxygen adsorption gives two adsorbed atomic oxygen species desorbing at about 300 °C (state β₁) and 340–500 °C (state β₂). The creation of the low temperature peak is favored at high exposure times (exposure >1 kL) and low adsorption temperatures (T_ads < 200 °C). The decrease of the open circuit potential (or catalyst work function) during the adsorption at high exposure times, indicates the formation of subsurface oxygen species which desorbs at higher temperatures (above 450 °C). The desorption peak of this subsurface oxygen is not clear due to the wide peaks of the TPD spectra. The TPD spectra after electrochemical O²⁻ pumping to the Pd catalyst film show two peaks (at 350 and 430 °C) corresponding to spillover O_ads and according to the reaction:

Influence of surface inhomogeneities of boron doped CVD-diamond electrodes on reversible charge transfer reactions

The electrochemical behaviour of reversible charge transfer reactions on boron doped diamond (BDD) was studied by cyclic voltammetry and electrochemical impedance spectroscopy using rotating disc electrodes under defined convection. Diamond films of 5 m thickness with doping levels of 200, 3000 and 6000 ppm were prepared by hot filament chemical vapour deposition on niobium substrate. The electrochemical measurements were carried out on BDD electrodes in deaerated 0.5 M Na₂SO₄ + 5 mM K₃[Fe(CN)₆]/K₄[Fe(CN)₆] solution at rotation frequencies 0 < f _rot < 4000 rpm. Comparative measurements were carried out on an active Pt electrode. The BDD electrodes exhibit distinct irreversibilities indicated by a larger peak potential difference in the cyclic voltammograms, lower diffusion limiting current densities and an additional impedance element at high frequencies. Mechanical polishing with carbon fleece and SiC paper strongly affects the irreversible behaviour of the BDD electrodes. The experimental results are explained by a partial blocking of the diamond surface with reversible charge transfer at active sites. The impedance spectra are analysed quantitatively using a transport impedance model for reversible reactions on partially blocked electrode surfaces.     

The impedance of fast charge transfer reactions on boron doped diamond electrodes

Reversible charge transfer on boron doped diamond (BDD) electrodes was studied using cyclic voltammetry and electrochemical impedance spectroscopy. Polycrystalline diamond films of 5 μm thickness with 200 and 3000 ppm boron content were prepared by chemical vapour deposition on niobium substrate. The samples were mounted in a Teflon holder and used as rotating disk electrodes (RDE) with rotation frequencies between 0 and 4000 rpm. The electrochemical measurements were carried out in aqueous electrolyte solutions of 0.5 M Na₂SO₄ + 5 mM K₃[Fe(CN)₆]/K₄[Fe(CN)₆] and 0.1 M KCl + 5 mM [Ru(NH₃)₆]Cl₂/[Ru(NH₃)₆]Cl₃. The electrochemical redox behaviour of the BDD electrodes was found to differ significantly from that of an active Pt electrode. The deviations are indicated by a large peak potential difference and a shift of the peak potentials in cyclic voltammograms with increasing sweep rate. At rotating electrodes lower limiting current densities are found and the impedance diagrams exhibit an additional capacitive impedance element at high frequencies. The results are described quantitatively by an impedance model which is based on partial blocking of the diamond surface.     

Improved electrochemical properties of Li(Ni<Subscript>0.7</Subscript>Co<Subscript>0.3</Subscript>)O<Subscript>2</Subscript> cathode for lithium ion batteries with controlled sintering conditions

Improved electrochemical properties of Li(Ni_0.7Co_0.3)O₂ cathode material are reported. Samples were synthesized by the co-precipitation method with various sintering conditions, namely temperature, time and atmosphere. Li(Ni_0.7Co_0.3)O₂ sintered at 850 °C for 14 h in air exhibited the lowest unit cell volume accompanied with relatively higher values of c/a and I ₁₀₃/I ₁₀₄ reflection peaks ratios. This also exhibited superior electrochemical properties, such as high charge–discharge capacity, high Coulombic efficiency, and low irreversible capacity loss. This can be attributed to improved hexagonal ordering, crystallinity and morphology. The electrochemical cell parameters were better than the reported ones, probably due to controlled sintering conditions.     

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.