Electrosynthesis of poly(neutral red) incorporated with ferrocenesulfonic acid

The electrochemical oxidation of neutral red in 0.5 mol dm⁻³ sulfuric acid and 0.2 mol dm⁻³ ferrocenesulfonic acid solution was carried out using repeated potential cycling between −0.20 and 1.40 V (versus SCE). The polymer film was electrochemically deposited on a platinum anode and had an electrochemical activity in the solution of 0.5 mol dm⁻³ Na₂SO₄ with pH ≤ 7.0. The result from the X-ray photoelectron spectroscopy (XPS) experiment shows that the anions can be doped into the polymer film during the electrochemical polymerization reaction of neutral red. The scanning electron microscopy (SEM) micrograph shows that the surface of the resulting polymer film formed on the platinum foil is covered with a compact surface consisting of micro fibers. The visible spectrum and infrared spectrum (IR) of the polymer are different from those of the corresponding monomer. A possible chemical structure of the resulting polymer was also proposed.     

Formation of porous anodic titanium oxide films in hot phosphate/glycerol electrolyte

The present study reveals the formation of porous anodic films on titanium at an increased growth rate in hot phosphate/glycerol electrolyte by reducing the water content. A porous titanium oxide film of 12 μm thickness, with a relatively low content of phosphorus species, is developed after anodizing at 5 V for 3.6 ks in 0.6 mol dm⁻³ K₂HPO₄ + 0.2 mol dm⁻³ K₃PO₄/glycerol electrolyte containing only 0.04% water at 433 K. The growth efficiency is reduced by increasing the formation voltage to 20 V, due to formation of crystalline oxide, which induces gas generation during anodizing. The film formed at 20 V consists of two layers, with an increased concentration of phosphorus species in the inner layer. The outer layer, comprising approximately 25% of the film thickness, is developed at low formation voltages, of less than 10 V, during the initial anodizing at a constant current density of 250 A m⁻². The pore diameter is not significantly dependent upon the formation voltage, being ∼10 nm.     

Electropolishing of NiTi shape memory alloys in methanolic H2SO4

The electropolishing of NiTi shape memory alloys was surveyed electrochemically. Anodic polarization of NiTi up to 8 V was performed in various aqueous and methanolic H₂SO₄ solutions. The passivity could be overcome in methanolic solutions with 0.1 mol dm−3≤CH₂SO₄≤7 mol dm−3. The dissolution kinetics was studied in dependence of the polarization potential, the H₂SO₄-concentration, the water concentration and the temperature. For lower concentrations of sulfuric acids (CH₂SO₄≤0.3 mol dm−3) electropolishing conditions were not observed for potentials up to 8 V. The dissolution remained under Ohmic control. In the concentration range from 1 to 7 mol dm⁻³ a potential independent limiting current was registered depending linearly on the logarithm of concentration. The best results were obtained with a 3 mol dm⁻³ methanolic sulfuric acid at 263 K which yielded an electropolishing current of 500 A m⁻² at a potential of 8 V. Surface roughness as well as current efficiency showed an optimum under these conditions.     

Investigation of the properties of Ti/[IrO2-Nb2O5] electrodes for simultaneous oxygen evolution and electrochemical ozone production, EOP

A systematic investigation of the influence of Ti/[IrO₂-Nb₂O₅] electrode composition ([IrO₂]=40, 45 and 50 mol%) on electrochemical ozone production (EOP), was conducted in 3.0 mol dm⁻³ H₂SO₄ in the presence and absence of 0.03 mol dm⁻³ KPF₆. “In situ” characterisation revealed all oxide layer presented similar structures, except for the 50 mol% IrO₂ nominal composition which showed a higher porosity/roughness. The introduction of KPF₆ in the electrolyte resulted in an inhibition of the oxygen evolution reaction (OER) at high current densities, improving ozone generation efficiency at i > 0.4 A cm⁻², while reducing overpotential for OER. When normalised for the area, the ozone current efficiency presented a good performance of the system. However, improvement of the electrode service life is necessary in order to support the drastic conditions observed during EOP.     

Novel PVA-based polymers showing an anti-Hofmeister Series property

A series of poly(vinyl alcohol)-trimellitate (PVA-T) polymers with different esterification degrees (ED: 82, 61, and 32 mol%) were prepared through the esterification of PVA and trimellitic anhydride (TA). Solubilities of these polymers and the swelling properties of PVA-T hydrogels, which were prepared by crosslinking with ethylene glycol diglycidyl ether (EGDGE), were investigated in various salt solutions comprising of SO₄²⁻, Cl⁻, SCN⁻ and Li⁺, Na⁺, K⁺, Cs⁺. The PVA-T polymers proved to have larger solubilities in salt solutions (1 M) than in pure water, and the ionic “salting-in” effect was significant in order of SO₄²⁻ > SCN⁻ > Cl⁻ for anions, and Li⁺ > Na⁺ > K⁺ > Cs⁺ for cations, regardless of their ED values. The PVA-T hydrogels also showed corresponding swelling properties; they significantly swelled in sulfate solutions of medium concentration (0.1-1 M), while in other salt solutions no appreciable swelling occurred. The marked salting-in effects exerted by sulfate anion, which is otherwise a typical “salting-out” agent, means that PVA-T polymers have an “anti-Hofmeister Series” (anti-HS) property. This is naturally ascribed to the trimellitic acid group because the degree of swelling in sulfate solutions was more significant for PVA-T with higher ED values; the combination of π-electron system and acidic protons seems to be essential to endow polymers with the anti-HS property.     

Polypyrrole and La1−xSrxMnO3 (0≤ x ≤0.4) composite electrodes for electroreduction of oxygen in alkaline medium

Composite G/PPy/PPy(La_1−xSr_xMnO₃)/PPy electrodes made of the perovskite La_1−xSr_xMnO₃ embedded into a polypyrrole (PPy) layer, sandwiched between two pure PPy films, electrodeposited on a graphite support were investigated for electrocatalysis of the oxygen reduction reaction (ORR). PPy and PPy(La_1−xSr_xMnO₃) (0≤ x ≤0.4) successive layers have been obtained on polished and pretreated graphite electrodes following sequential electrodeposition technique. The electrolytes used in the electrodeposition process were Ar saturated 0.1 mol dm⁻³ pyrrole (Py) plus 0.05 mol dm⁻³ K₂SO₄ with and without containing a suspension of 8.33 g L⁻¹ oxide powder. Films were characterized by XRD, SEM, linear sweep voltammetry, cyclic voltammetry (CV) and electrochemical impedance (EI) spectroscopy. Electrochemical investigations were carried out at pH 12 in a 0.5 mol dm⁻³ K₂SO₄ plus 5 mmol dm⁻³ KOH, under both oxygenated and deoxygenated conditions. Results indicate that the porosity of the PPy matrix is considerably enhanced in presence of oxide particles. Sr substitution is found to have little influence on the electrocatalytic activity of the composite electrode towards the ORR. However, the rate of oxygen reduction decreases with decreasing pH of the electrolyte from pH 12 to pH 6. It is noteworthy that in contrast to a non-composite electrode of the same oxide in film form, the composite electrode exhibits much better electrocatalytic activity for the ORR.     

Electrosyntheses of poly(neutral red), a polyaniline derivative

The electrochemical oxidation of neutral red in 0.5 mol dm⁻³ H₂SO₄ solution was carried out by using repeated potential cycling between −0.20 and 1.20 V (versus SCE). The polymer film was electrochemically deposited on a platinum anode and had an electrochemical activity in the solution of 0.5 mol dm⁻³ Na₂SO₄ with pH ≤ 4.0. The result from the X-ray photoelectron spectroscopy (XPS) experiment shows that the anions can be doped into the polymer film during the electropolymerization reaction of neutral red. The scanning electron microscopy (SEM) micrograph shows the surface of poly(neutral red) film deposited on the platinum foil is covered with a micro-structured network of mass interwoven fibers with a diameter of 2-4 μm. A straight fiber of the unsystematic micro-fibers is longer than 0.4 mm. The UV-vis spectrum and infrared spectrum (IR) of the polymer are different from those of the monomer.     

In situ radiotracer and voltammetric study of the formation of surface adlayers in the course of Cr(VI) reduction on polycrystalline and (1 1 1) oriented platinum

This paper is focused on the in situ radiotracer and voltammetric studies of the induced HSO₄⁻/SO₄²⁻ adsorption at Pt(poly) and Pt(1 1 1) surfaces in 0.1 mol dm⁻³ HClO₄ solution in the course of Cr(VI) electroreduction. Besides this, the sorption behavior of HSO₄⁻/SO₄²⁻ ions on bare Pt(poly) and Pt(1 1 1) electrodes is compared and discussed. From the experimental results it can be stated that: (i) although the extent of bisulfate/sulfate adsorption is strongly dependent upon the crystallographic orientation of Pt surfaces, the maximum coverage on the Pt(1 1 1) does not exceed 0.2 monolayer; (ii) the Cr(VI) electroreduction on both poly- and (1 1 1) oriented platinum proceeds via a ce (chemical-electron-transfer) mechanism to yield Pt surfaces covered with intermediate surface adlayers containing Cr(VI) particles (and reduced Cr-containing adspecies) and ‘strongly bonded’ HSO₄⁻/SO₄²⁻ ions; (iii) while the coverage of platinum surfaces by the intermediate complexes formed in the course of Cr(VI) electroreduction at E > 0.20 V is basically independent of the crystallographic orientation of the Pt electrode, the onset for rapid Cr(VI) reduction is highly affected by the nature and crystallographic orientation of the electrode.     

Electrochemical polymerization and initial corrosion properties of polyaniline-benzoate film on aluminum

Electrochemical synthesis of polyaniline (PANI) on aluminum electrode from aqueous solution of 0.25 mol dm⁻³ aniline and 0.2 mol dm⁻³ sodium benzoate has been investigated under potentiodynamic and galvanostatic conditions. Initial corrosion behavior of aluminum and PANI coated aluminum electrode exposed to 3% NaCl has been investigated using electrochemical potentiodynamic and impedance spectroscopy technique (EIS). It was shown that PANI coating initially provide corrosion protection of aluminum, decreasing the corrosion current density at least 15 times.     

The stability of an acidic tin methanesulfonate electrolyte in the presence of a hydroquinone antioxidant

The electrodeposition of tin at a (0.28 cm²) copper surface from 0.014 mol dm⁻³ SnSO₄ and 12.5 vol.% methanesulfonic acid (MSA 1.93 mol dm⁻³) at 296 K was studied. Hydroquinone concentrations of 0.005, 0.05 and 0.5 mol dm⁻³ (corresponding to a molar concentration ratio of hydroquinone to stannous ions of 0.36, 3.6 and 36, respectively) were used. Cyclic and linear sweep voltammetry served to characterise the electrochemical behaviour of tin deposition and stripping. The effects of potential sweep rate and electrode rotation speed on the voltammetry were studied. The stability of the electrolyte with storage time was quantified by changes in the limiting current density for tin deposition at a smooth rotating disc electrode and the peak current density at a static disc electrode. The influence of hydroquinone on mass transport controlled tin deposition and suppression of hydrogen evolution was evaluated.     

Mass transportation in diethylmethylammonium trifluoromethanesulfonate for fuel cell applications

To use the protonic mesothermal fuel cell without humidification, mass transportation in diethylmethylammonium trifluoromethanesulfonate ([dema][TfO]), trifluoromethanesulfuric acid (TfOH)-added [dema][TfO], and phosphoric acid (H₃PO₄)-added [dema][TfO] was investigated by electrochemical measurements. The diffusion coefficient and the solubility of oxygen were ca. 10⁻⁵ cm² s⁻¹ and ca. 10⁻³ M (=mol dm⁻³), respectively. Those of hydrogen were a factor of 10 and one-tenth compared to oxygen, respectively. The permeability, which is a product of the diffusion coefficient and solubility, of oxygen and hydrogen were almost the same for the perfluoroethylenesulfuric acid membrane and the sulfuric acid solution; therefore, these values are suitable for fuel cell applications. On the other hand, a diffusion limiting current was observed for the hydrogen evolution reaction. The current corresponded to ca. 10⁻¹⁰ mol cm⁻¹ s⁻¹ of the permeability, and the diffusion limiting species was the hydrogen carrier species. The TfOH addition enhanced the diffusion limiting current of [dema][TfO], and the H₃PO₄ addition eliminated the diffusion limit. The hydrogen bonds of H₃PO₄ or water-added H₃PO₄ might significantly enhance the transport of the hydrogen carrier species. Therefore, [dema][TfO] based materials are candidates for non-humidified mesothermal fuel cell electrolytes.     

Effects of specific adsorption of copper (II) ion on charge transfer reaction at the thin film LiMn2O4 electrode/aqueous electrolyte interface

This study investigated the effect of a specific adsorption ion, copper (II) ion, on the kinetics of the charge transfer reaction at a LiMn₂O₄ thin film electrode/aqueous solution (1 mol dm⁻³ LiNO₃) interface. The zeta potential of LiMn₂O₄ particles showed a negative value in 1 × 10⁻² mol dm⁻³ LiNO₃ aqueous solution, while it was measured as positive in the presence of 1 × 10⁻² mol dm⁻³ Cu(NO₃)₂ in the solution. The presence of copper (II) ions in the solution increased the charge transfer resistance, and CV measurement revealed that the lithium insertion/extraction reaction was retarded by the presence of small amount of copper (II) ions. The activation energy for the charge transfer reaction in the solution with Cu(NO₃)₂ was estimated to be 35 kJ mol⁻¹, which was ca. 10 kJ mol⁻¹ larger than that observed in the solution without Cu(NO₃)₂. These results suggest that the interaction between the lithium ion and electrode surface is a factor in the kinetics of charge transfer reaction.     

Diffusion coefficients of aluminium chloride in aqueous solutions at 298.15, 303.15 and 315.15 K

Mutual diffusion coefficients (interdiffusion coefficients) have been determined for aluminium chloride in water at 298.15, 303.15 and 310.15 K at concentrations from 0.002 to 0.010 mol dm⁻³ together with molar conductivity values. The diffusion coefficients were obtained by using a conductimetric open-ended capillary cell. The experimental data were discussed on the basis of the Onsager-Fuoss model. The Nernst diffusion coefficients derived from diffusion 1.208 × 10⁻⁹ and 1.701 × 10⁻⁹ m² s⁻¹ and from conductance 1.238 × 10⁻⁹ and 1.692 × 10⁻⁹ m² s⁻¹, at two temperatures 298.15 and 310.15 K, respectively, agree well each other.     

Interactions of cobalt chloride with saccharose in aqueous solutions at 298.15 K

Mutual diffusion coefficients (interdiffusion coefficients) and molar electrical conductivities have been measured for cobalt chloride aqueous solutions in the absence and the presence of saccharose at different concentrations (from 0.01 to 0.3 mol dm⁻³) and 298.15 K. The diffusion coefficients were measured by using the conductimetric method. For these aqueous solutions, limiting molar conductivity values have been calculated. The value of λ⁰(Co²⁺) = 105.36 × 10⁻⁴ S m² mol⁻¹, obtained at 298.15 K in pure water solution, agrees well with that reported in the literature. The Nernst diffusion coefficient values derived from diffusion (1.301 × 10⁻⁹ m² s⁻¹) and from conductance (1.295 × 10⁻⁹ m² s⁻¹) are also in good agreement.The dependence of diffusion coefficients and electrical conductivity of CoCl₂ on the concentration of saccharose is discussed by considering the effect of the carbohydrate on the electrolyte dehydration, as well as on the ion-pairs and complexes (CoCl₂-saccharose and ions-saccharose) formation.     

Electropolishing of AISI-304 stainless steel using an oxidizing solution originally used for electrochemical coloration

Chemical polishing or electropolishing, instead of mechanical polishing, are recommended for the attainment of metallic surface polishes without the introduction of contaminants or tensions in the surface layers of the metal. The fundamental difference between the chemical and electrochemical polishing processes is that in the latter anodic currents/potentials are used to help in the dissolution and passivation of the metal. In this paper, the use of an oxidizing electrolytic solution (2.5 mol L⁻¹ CrO₃ + 5.0 mol L⁻¹ H₂SO₄) originally employed in electrochemical coloration processes is reported for the electropolishing of AISI-314 stainless steel. Parameters involved in this electropolishing process, such as temperature, current density and time, were optimized so as to attain the best possible results evaluated by the obtained surface brightness measured by reflectance spectra. Surface analyses by scanning electron microscopy allowed a clear correlation between obtained brightness and surface smoothing. The best conditions obtained for the electropolishing process are: temperature of 45 °C, electrolysis time of 10 min and current density of around 25 A dm⁻². It should be pointed out that an electropolishing process signature (periodic oscillations of the cell potential) was established; this may be an important tool for optimizing and monitoring electropolishing processes.     

In situ scanning tunneling microscopy study of selective dissolution of Au3Cu and Cu3Au (0 0 1)

We present an electrochemical study of Au₃Cu (0 0 1) single crystal surfaces in 0.1 mol dm⁻³ H₂SO₄ and 0.1 mol dm⁻³ H₂SO₄ + 0.1 mmol dm⁻³ HCl, and of Cu₃Au (0 0 1) in 0.1 mol dm⁻³ H₂SO₄. The focus is on in situ scanning tunneling microscopy experiments. The changes of the surface morphology, which are time- and potential-dependent, have been observed, clearly resolving single atomic steps and mono-atomic islands and pits. Chloride additives enhance the surface diffusion and respective morphologies are observed earlier. All surfaces have shown considerable roughening already in the passive region far below the critical potential.     

Effect of Ni content on the corrosion behavior of Cu-Ni alloys in neutral chloride solutions

The effect of systematic increase of Ni content on the electrochemical behavior of the Cu-Ni alloys in neutral chloride solutions was investigated. The pitting corrosion behavior of Cu-Ni alloys with different Ni contents, namely, 5, 10, 30 and 65 mass% Ni, in a stagnant 0.6 mol dm⁻³ NaCl solution of pH 7.0 was studied. The effect of chloride ion concentration on the electrochemical behavior of these alloys was also investigated. The results show that the increase in nickel content decreases the corrosion rate of the alloys in the neutral chloride solution. The increase of chloride concentration up to 0.3 mol dm⁻³ increases the corrosion rate. At higher concentrations ([Cl⁻] > 0.3 mol dm⁻³) the corrosion rate decreases due to the hydrolysis of Cu(I) chloride to form the passive Cu(I) oxide film. The breakdown potential depends on the chloride ion concentration and the nickel content of the alloy. For these investigations conventional electrochemical techniques and electrochemical impedance spectroscopy (EIS) were used. The impedance measurements have shown that the increase of the Ni content and the immersion time of the alloys in the chloride solution increase the corrosion resistance of the alloys. The experimental impedance data were fitted to theoretical values according to a proposed equivalent circuit model.     

Mechanism and kinetics of wollastonite fibre dissolution in the aqueous solution of acetic acid

The dissolution of fibrous wollastonite (CaSiO₃) in the aqueous solution of acetic acid (3 mol dm^− 3) was investigated in the temperature interval from 25 to 50 °C using mixed batch-type reactor. An incongruent dissolution of wollastonite proceeds under applied acidic condition. The pH of solvent was increasing during leaching of calcium and its actual value depended on the concentration of Ca²⁺ ions in the solution according to the Henderson buffer equation. That enabled the monitoring of dissolution kinetics via concentration of Ca in the dispersion medium of suspension of wollastonite measurement. The kinetic parameter of the process was evaluated from measured dissolution rates of wollastonite at constant temperature using the empirical Arrhenius equation. The apparent activation energy and pre-exponential factor estimated from the Arrhenius plot are 47 ± 1 kJ mol^− 1 and (1.8 ± 0.9) × 10³ s^− 1. The kinetics analysis of the process indicates that the process is driven by the stationary two-dimensional diffusion (D₂).     

Solubility of blue CoAl2O4 ceramic pigments in water and diethylene glycol media

The chemical stability of blue CoAl₂O₄ ceramic pigment in aqueous and non-aqueous suspension was investigated. Distilled water and diethylene glycol (DEG) were used as media. The isoelectric points (IEP) for the commercial and synthesised CoAl₂O₄ pigment were determined to be 4.9 and 8.5, respectively. The IEP shifts toward acidic pH values for the commercial pigment with respect to the synthesised pigment due to the existence of the quartz phase. In water, the cobalt ion concentration was low (2.5 mg dm⁻³), and this concentration did not change with time. However, the aluminium ion concentration was initially high and then decreased to ∼10 mg dm⁻³ at pH 9 and 11 due to the precipitation of Al³⁺ ions as an Al(OH)₃ phase. In DEG, the dissolution of pigment particles with higher ion concentrations (>800 mg dm⁻³) was more significant than that of the aqueous medium, implying that CoAl₂O₄ pigment has insufficient chemical stability in DEG medium with respect to aqueous suspensions.