Acidic Electrolyte Solution Research Articles

Decolorization Treatment of Copper Phthalocyanine Textile Dye Wastewater by Electrochemical Methods

Electrochemical decolorization and degradation treatment of aqueous copper phthalocyanine reactive dye solutions was comparatively studied by electrocoagulation, electrooxidation and electro-Fenton processes. In the electrocoagulation process with aluminum electrodes the colored aqueous solutions of initial pH 6.4 containing 50 mg L-1 copper phthalocyanine and 6 g L-1 NaCl were treated at applied current densities of 2.5 and 5 mA cm-2. Fast and 100% decolorization was achieved in 4 and 2 minutes of electroprocessing respectively. The indirect electrooxidation process was conducted in acidic electrolyte solutions containing 50 mg L-1 copper phthalocyanine and 6 g L-1 NaCl with Ti/Pt and graphite plate electrodes at the applied current density of 10 mA cm-2. Even after 90 minutes of electrolysis time the dye remained by 23 and 18.8 % respectively undegradable. By the direct and indirect electrooxidation with the same amount of Na2SO4 electrolyte and added H2O2 respectively and using the same electrodes, the copper phthalocyanine dye was not or was only barely degraded respectively. In the electro-Fenton process with Fe electrodes and added amounts of H2O2 at pH 3 and an applied current density of 5 mA/cm2 complete degradation of copper phthalocyanine occurred in 15 minutes.

Significant sensitivity improvement of alternating current driven-liquid discharge by using formic acid medium for optical determination of elements

A method has been developed to improve the performance of alternating-current electrolyte atmospheric liquid discharge (ac-EALD) optical emission spectrometry for the determination of elements. Significant enhancement of emission intensity was achieved by adding organic substance into the nitric acid electrolyte solutions. Under the optimized conditions, 3% (v/v) formic acid in nitric acid (pH 1.0) produced 13 times enhancement for Ag and 7% (v/v) formic acid resulted in 17 times enhancement for Cd. The emission of Pb was even enhanced 78 times in the presence of 3% formic acid. In addition, the signal stability was also improved compared with that in the absence of organic substances. Repeatability was 0.8% for 0.1mgL−1 Ag, 0.7% for 0.2mgL−1 Cd and 2.6% for 1mgL−1 Pb standard solutions (n=5). The limits of detection of Ag, Cd and Pb were 1, 17 and 45μgL−1, respectively. The accuracy of the method was demonstrated by determination of elements in simulated natural water samples (GBW(E)080402 and GBW(E)080399).

Peptide mapping using capillary electrophoresis offline coupled to matrix‐assisted laser desorption ionization time of flight mass spectrometry

This article reports the results of a study carried out to evaluate the offline hyphenation of capillary zone electrophoresis with matrix-assisted lased desorption ionization time of flight mass spectrometry (MALDI-TOF-MS) for the analysis of low-abundant complex samples, represented by the tryptic phosphorylated peptides of phosphoproteins, such as α-casein, β-casein, and fetuin. The proposed method employs a latex-coated capillary and consists in the online preconcentration of the tryptic peptides by a pH-mediated stacking method, their separation by capillary zone electrophoresis, and subsequent deposition of the separated analytes onto a MALDI target for their MS analysis. The online preconcentration method allows loading a large sample volume (∼150 nL), which is introduced into the capillary after the hydrodynamic injection of a short plug of 1.0 M ammonium hydroxide solution and is sandwiched between two plugs of the acidic background electrolyte solution (BGE) filling the capillary. The sample spotting of the separated analytes onto the MALDI target is performed either during or postseparation using an automatic spotting device connected to the exit of the separation capillary. The proposed method allows the separation and identification of multiphosphorylated peptides from other peptides and enables their identification at femtomole level with improved efficiency compared with LC approaches hyphenated to MS.

Synthesis and characterization of polyhedral and quasi-sphere non-polyhedral Pt nanoparticles: effects of their various surface morphologies and sizes on electrocatalytic activity for fuel cell applications

In this article, polyhedral and non-polyhedral Pt nanoparticles were prepared by modified polyol method using AgNO3 as a good structure-modifying agent. Their TEM and HRTEM images showed the particle size in the range of 8–16 nm for both the above cases. The structures and properties of the surfaces of Pt nanoparticles were investigated through cyclic voltammetry in dilute perchloric acid (HClO4) electrolyte solution. A comparison of the electrocatalytic property in methanol electrooxidation was made. Here, the effects of polyhedral and non-polyhedral morphologies on their catalytic properties were studied. The results revealed that the special catalytic activity of quasi-sphere non-polyhedral Pt nanoparticles is higher than that of polyhedral Pt nanoparticles. In addition, Pt nanoparticles of un-sharp and quasi-sphere morphologies exhibit the tolerance to poisoning species better than that of Pt nanoparticles of sharp and polyhedral morphologies due to the various morphologies of the catalyst surfaces in the chronoamperometric plots. Therefore, these experimental evidences showed the morphology-dependent catalytic property according to the various morphologies and complexity of their catalyst surfaces.

Electrochromic properties of NiOOH thin films prepared by reactive sputtering in an H2O atmosphere in various aqueous electrolytes

Nickel oxyhydroxide (NiOOH) thin films were prepared by reactive sputtering using H2O as a reactive gas, and the electrochromic (EC) properties of these thin films were investigated in alkaline, neutral, and acidic aqueous electrolyte solutions. A stable EC cycling of up to 100 cycles was obtained for the NiOOH thin films in electrolyte solutions with a wide pH range of 4.1–13.5. However, the EC cycling degraded drastically after several tens of cycles in an electrolyte with pH=2.0. In the stable pH region, the NiOOH films exhibited a large transmittance change from approximately 30–90%, although the response speed slowed with decreasing pH of the electrolytes.

Electrodeposition and Characterization of p-type Sb_xTe_y Thermoelectric Thin Films

The electro-deposition of compound semiconductors has been attracting more attention because of its ability to rapidly deposit nanostructured materials and thin films with controlled morphology, dimensions, and crystallinity in a costeffective manner (1). In particular, low band-gap <TEX>$A_2B_3$</TEX>-type chalcogenides, such as <TEX>$Sb_2Te_3$</TEX> and <TEX>$Bi_2Te_3$</TEX>, have been extensively studied because of their potential applications in thermoelectric power generator and cooler and phase change memory. Thermoelectric <TEX>$Sb_xTe_y$</TEX> films were potentiostatically electrodeposited in aqueous nitric acid electrolyte solutions containing different ratios of <TEX>$TeO_2$</TEX> to <TEX>$Sb_2O_3$</TEX>. The stoichiometric <TEX>$Sb_xTe_y$</TEX> films were obtained at an applied voltage of -0.15V vs. SCE using a solution consisting of 2.4 mM <TEX>$TeO_2$</TEX>, 0.8 mM <TEX>$Sb_2O_3$</TEX>, 33 mM tartaric acid, and 1M <TEX>$HNO_3$</TEX>. The stoichiometric <TEX>$Sb_xTe_y$</TEX> films had the rhombohedral structure with a preferred orientation along the [015] direction. The films featured hole concentration and mobility of <TEX>$5.8{\times}10^{18}/cm^3$</TEX> and <TEX>$54.8\;cm^2/V{\cdot}s$</TEX>, respectively. More negative applied potential yielded more Sb content in the deposited <TEX>$Sb_xTe_y$</TEX> films. In addition, the hole concentration and mobility decreased with more negative deposition potential and finally showed insulating property, possibly due to more defect formation. The Seebeck coefficient of as-deposited <TEX>$Sb_2Te_3$</TEX> thin film deposited at -0.15V vs. SCE at room temperature was approximately 118 <TEX>${\mu}V/K$</TEX> at room temperature, which is similar to bulk counterparts.

Electrodeposition of p-Type Sb x Te y Thermoelectric Films

Thermoelectric SbxTey films were potentiostatically electrodeposited in aqueous nitric acid electrolyte solutions containing different concentrations of TeO2. Stoichiometric SbxTey films were obtained by applying a voltage of −0.15 V versus saturated calomel electrode (SCE) using a solution consisting of 2.4 mM TeO2, 0.8 mM Sb2O3, 33 mM tartaric acid, and 1 M HNO3. The nearly stoichiometric Sb2Te3 films had a rhombohedral structure, \( R\bar{3}m \), with a preferred orientation along the (015) direction. The films had hole concentration of 5.8 × 1018/cm3 and exhibited mobility of 54.8 cm2/Vs. A more negative potential resulted in higher Sb content in the deposited SbxTey films. Furthermore, it was observed that the hole concentration and mobility decreased with increasingly negative deposition potential, and eventually showed insulating properties, possibly due to increased defect formation. The absolute value of the Seebeck coefficient of the as-deposited Sb2Te3 thin film at room temperature was 118 μV/K.

Electrochemical properties of ruthenium metallopolymer: Monolayer-protected gold cluster nanocomposites

Nanocomposite polymer films of [Ru(bpy) 2(PVP) 10] 2+ metallopolymer and gold monolayer-protected clusters (MPCs) have been formed. Cyclic voltammetry of the films has been performed in both acidic (0.1 M H 2SO 4) and neutral (0.1 M Na 2SO 4) pH electrolyte solution. In acidic electrolyte, the protecting monolayers is desorbed as the gold surface is oxidized. Transmission electron microscopy of the nanocomposite following electrochemical cycling reveals aggregates of “naked” MPCs. In sharp contrast, in neutral pH electrolyte, the MPCs are stable towards voltammetric cycling and no gold oxide formation is evident in the voltammetry. The homogeneous charge-transfer diffusion coefficient, D CT , was determined for a range of nanocomposite films as the MPC mole fraction is systematically varied. When acidic electrolyte is used, D CT decreases from 2.8 ± 0.5 × 10 −10 to 1.5 ± 0.1 × 10 −11 cm 2 s −1 as the MPC mole fraction is increased from 0 to 0.45. In contrast, the D CT determined in neutral electrolyte is universally lower than that determined in acidic electrolyte, it increases by over two orders of magnitude from 2.6 ± 0.9 × 10 −15 to 4.0 ± 0.5 × 10 −13 cm 2 s −1 as MPC mole fraction increases from 0.05 to 0.5.

Pilot laboratory electrolyzer for electrosynthesis of hydrogen peroxide in acid and alkaline solutions

Results of a preparative electrosynthesis of hydrogen peroxide by cathodic reduction of oxygen in a carbon black gas-diffusion electrode in acid and alkaline electrolyte solutions in a versatile pilot laboratory three-chamber electrolyzer are presented.

Scanning electrochemical microscopy as an etching tool for ITO patterning

This work presents a new patterning technique of Indium Tin Oxide (ITO) thin films using the microelectrode of a Scanning Electrochemical Microscope (SECM). With the development of new display technologies, patterned indium tin oxide (ITO) films have enormous growth potential and can find applications in any device that requires transparent and conductive electrodes. To optimize the performances of such devices, a clean patterning technique providing straight sidewalls and control of surface chemistry and physical properties is needed. We report here a simple and one-step patterning technique of ITO using scanning electrochemical microscopy as a soft etching tool. This electrochemical wet-lithographic technique provides a fast and low cost patterning process and is performed in an aqueous acid electrolytic solution. This maskless technique leads to a clean etching with straight walls and no redeposition of the ablated part. The subjacent substrate (glass or polymer) is not damaged by this technique and the electrical and/or optical properties of the remaining ITO film are preserved.

A Comparative Spectroelectrochemical Study of the Redox Electrochemistry of N-(Polyvinylamine)-Substituted-o-Nitroaniline

The electrochemistry and spectroelectrochemistry of polyvinylamine (PVAm) and N-(polyvinylamine)-substituted-o-nitroaniline at a polycrystalline gold electrode in contact with different electrolyte solutions (0.1 M HClO4 and 0.1 M KClO4) have been investigated with cyclic voltammetry and surface enhanced Raman spectroscopy (SERS). Cyclic voltammograms recorded with in acidic electrolyte solution showed formation of N-(polyvinylamine)-o-phenylenediamine in the negative going potential scan; in neutral solution reduction proceeds only to N-(polyvinylamine)-o-phenylhydroxylamine. Vibrational modes are discussed and assigned to monomer-surface interactions of adsorbates at the gold surface in both electrolyte solutions. A variety of adsorption behaviors of these polymers at a gold surface is concluded; they apparently depend on the applied electrode potential, pH of electrolyte (acidic or neutral), type and mole percentage of the o-nitroaniline moiety. The adsorption at the gold surface is strongly enhanced with 12.7 mole% of o-nitroaniline moiety, respectively, at its PVAm-backbone. The direct coordination of these polymers with the gold surface occurred via the nitro-group of the o-nitroaniline moiety and primary amino-groups located at the polymer backbone.

Spatially Resolved ATR‐FTIRS Study of the Formation of Macroscopic Domains and Microislands during CO Electrooxidation on Pt

Electrooxidation of CO in CO-saturated sulfuric acid electrolyte solutions with controlled mass transport is investigated with spatially resolved attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy under galvanostatic and potentiostatic conditions. The reaction conditions are chosen such that steady states with intermediate current densities and intermediate average CO coverages are accessible. We demonstrate that under these conditions the reaction never proceeds uniformly on the electrode surface. Instead, macroscopic domains form spontaneously, composed of areas with high CO coverage and areas essentially free of adsorbed CO molecules. The average coverage within the CO-covered domains depends on the electrolyte concentration and the applied potential and can vary between saturation coverage and a few tenths of a monolayer. However, the absence of a red-shift of the CO vibrational band points to a further substructuring of the domains in densely packed CO microislands. These microislands most likely also form in the boundary layer between the CO-rich and CO-free electrode domains. This hierarchical patterning of the electrode surface is attributed to the interplay of autocatalytic reaction steps, spatial coupling through migration or the galvanostatic control of the experiment, and molecular interactions between molecules co-adsorbed on the electrode surface.

Electroplating of Cu(Ag) thin films for interconnect applications

Electromigration effects in interconnect metallizations cause a need for materials with superior resistance against electromigration failure but with adequate electrical properties. In principle, Cu(Ag) alloys are potential candidates to become an interconnect material of the next generation of microelectronic devices. Therefore, in the following paper the electroplating of such Cu(Ag) alloys from a sulfuric acid electrolyte solution with varying silver content in a home built deposition tool is presented. Besides the general deposition characteristics, the growth mode of the films and the deposition into trenches will be discussed. The investigations show that Cu(Ag) alloys can be deposited with adequate homogeneity of the film thickness by electroplating. Furthermore, the electrical resistivity is low enough to assure a use of these films for interconnect applications. However, distinct island growth and insufficient trench filling capabilities lead to the fact that the additive composition needs to be optimized for Cu(Ag) thin film electroplating.

Double layer supercapacitor properties of onion‐like carbon materials

AbstractThis paper describes the electrochemical performance of carbon onions as electrode materials in electrical double layer capacitors with water electrolytes. Onion‐like carbon (OLC) species were produced by vacuum annealing of detonation nanodiamonds (NDs) powder at 1170–2170 K. The material capability of the charge accumulation in the electric double layer was estimated using the voltammetric technique. The correlations between specific capacitance, surface area and conductivity were found. Charge‐discharge measurements revealed a dependence of the specific capacitance of OLC on the degree of diamond particle graphitization and defectness of particle surfaces. Promising capacitance values, ranging within 20−40 F g–1 and within 70−100 F g–1 were found for the OLC materials operating respectively in acid electrolytic solution (1 M H2SO4) and alkaline electrolytic solution (6 M KOH). (© 2008 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Carbon black supported gold nanoparticles for oxygen electroreduction in acidic electrolyte solution

Oxygen reduction in acidic electrolyte solution has been studied at various Au/C catalysts with different support materials and different gold particle sizes. The peak potential in cyclic voltammogramms (CVs) during oxygen reduction depends on the potential applied to the catalyst during electrochemical pre-treatment. This effect is attributed to a shift of oxide reduction on the nanoparticles to more negative potentials compared to bulk gold, as can be seen from CV. Quantitative assessment of the oxygen reduction activity has been carried out with rotating disc electrode (RDE) measurements. A catalyst with a gold loading of 0.5 wt% gold turned out to be the most active in terms of mass specific activity. However, the surface specific activity was neither dependent on the particle size in the range 2.7–42.3 nm nor on the support material. It has been found the average number of electrons transferred per oxygen molecule is two to three, independent on gold particle size.

Spectroelectrochemical studies of self assembled monolayers of biphenyl ethynyl thiols on gold electrodes

Adsorbate layers of 4-trimethylsilylethinyl-4′-thioacetyl-1,1′-biphenyl, 4-ethinyl-4′-thioacetyl-1,1′-biphenyl, and 4-trimethylsilylethinyl-1,1′-biphenyl-4′-thiol were formed on a roughened polycrystalline gold surface in contact with an acidic electrolyte solution. The degree of coverage of the SAMs on the gold electrode was examined with cyclic voltammetry. Results of surface enhanced Raman spectroscopy (SERS) suggest that the obtained SAMs adopt different adsorption orientations with respect to the gold surface depending on the terminal group. Vibrational modes assigned to the adsorbate–metal interaction of the molecule through the S atom or the C C group are found. Vibrational wavenumbers were calculated for the investigated biphenyl ethynyl thiols with DFT at the B3LYP level using the 6–31G* basis set. The data obtained from vibrational frequency calculations are used to assign vibrational bands obtained in infrared and Raman spectroscopy as well as in surface enhanced Raman spectroscopy of the studied molecules.

Surface coatings for improvement of bone cell materials and antimicrobial activities of Ti implants

Ti surface was modified to simultaneously improve bone cell materials and antimicrobial activities. Titanium surface was first anodized in sodium fluoride and sulfuric acid electrolytic solution to form titania nanotube on the surface to improve the biocompatibility of the surface. Silver was electrodeposited on the titania nanotube surface at 5 V. Silver added titania nanotube surface was tested for compatibility with bone-cell materials interactions using human osteoblast bone cells. The antibacterial effect was studied using Pseudomonas aeruginosa. Our results show that silver-treated titania nanotube surface may provide antibacterial properties to prevent implants against postoperative infections without interference to the attachment and proliferation of bone tissue on titanium, which is commonly used in dental and orthopedic surgical procedures.

Electrochemical Energy Generation and Storage. Fuel Cells and Lithium-Ion Batteries

Abstract We illustrate our current work for electrochemical energy generation and storage (i.e., fuel cells and lithium-ion batteries, respectively). In fuel cell research, we have been developing Pt-based ordered intermetallic compounds as electrocatalysts towards anodic reactions of liquid fuels such as methanol, ethanol, and formic acid for proton-exchange membrane fuel cells (PEMFCs). Development of the intermetallic compounds ranges from bulk materials to nanoparticles. In our work, we have employed a combinatorial method to achieve rapid screening of a large number of potential electrocatalysts. Multi-element sputtering was employed to generate films with different compositions including most of a phase diagram and the resulting libraries were screened using a fluorescence assay. For portable applications, we have also developed a planar microfluidic membraneless fuel cell (PMMFC) device, which eliminates the need for a polyelectrolyte membrane (PEM) and takes advantage of the laminar flow of fuel and oxidant streams. Particularly, in order to increase power density (cell voltages) of a PMMFC device, we have focused on the development of a dual electrolyte PMMFC in which alkaline and acid electrolyte solutions are employed for fuel and oxidant streams, respectively. In lithium-ion battery research, we have been designing new cost-effective organic materials with high energy densities as cathode electroactive materials, targeting large applications such as electrically powered automotives. In particular, we have focused on organosulfur-based polymers, involving the redox chemistry of thiolates (RS−), capable of higher energy density than conventional lithium metal oxides such as LiCoO2. By combining electrochemical techniques with computational methods and organic synthesis, we have tried to establish an efficient procedure to develop novel organic-based electroactive materials suitable for the demands of energy storage materials for rechargeable lithium-ion batteries.

Quasi-Reversible Chloride Adsorption/Desorption through a Polycationic Organic Film on Cu(100)

Combined cyclic voltammetry and in situ scanning tunneling microscopy studies were employed to gain information about the interfacial structure of a chloride modified Cu(100) electrode surface exposed to an acidic electrolyte solution that contained redox-active dibenzylviologens (DBV, 1,1‘-dibenzyl-4,4‘-bipyridinium molecules). A particular focus of this contribution lies in the structural characterization of the electrode surface under nonequilibrium reactive conditions, for example, during the occurrence of an electron-transfer reaction. Typically, two pairs of clearly distinguishable current waves denoted as P1/P1‘ and P2/P2‘ appear in the cyclic voltammogram of Cu(100) in a mixture of 10 mM HCl and 0.1 mM DBVCl2, provided the cathodic potential limit remains restricted to values of Ework > −425 mV vs reversible hydrogen electrode. Systematic variations of the DBV solution concentration and the nature of the counterion strongly suggest that P1 has to be assigned to the first electron-transfer reaction...

Redox properties of phenosafranine at zeolite-modified electrodes—Effect of surface modification and solution pH

Redox properties of cationic dye phenosafranine (3,7-diamino-5-phenylphenazenium chloride) (PS +) were studied at zeolite-modified electrodes using Zeolite-Y and NaZSM-5. The peak current and peak potential of phenosafranine-adsorbed zeolite were found to be influenced by the pH of the electrolyte solution. Observation of a second redox couple is suggested to be due to formation of new species at low concentration from the reduced phenosafranine at the zeolite-modified electrodes. Titanium dioxide nanoparticles encapsulated in the cavities of the zeolite or anchored on the external surface of the zeolite do not seem to affect the redox properties of adsorbed PS +. When the cyclic voltammograms are recorded immediately after the electrode is immersed into the solution, the redox potential of PS + is found to be sensitive to the nature of the zeolite surface. The peak potential shifts towards positive region under continuous cycles as the surface hydroxyl groups get protonated in acidic electrolyte solution thereby forcing the movement of dye molecules from the zeolite surface to the zeolite electrode solution interface. The electron transfer rate constants for the adsorbed dye at the electrode are calculated to be 2.5 ± 0.2 s −1 and 3.5 ± 0.2 s −1 for the zeolite-Y electrode and the ZSM-5 electrode, respectively by the Laviron equation.