Low Cathodic Potentials Research Articles

Electrodeposition of Silicon Thin Films from Ionic Liquids

The possibility of obtaining Si thin films by electrodeposition from the oxygen and water stable N-butyl-N-methyl-pyrrolidinium bis(trifluoromethyl-sulfonyl)amide ionic liquid at room temperature was investigated. The results obtained using SiCl4 and SiBr4 as precursors and aluminium and nickel as substrates were compared. Cyclic voltammetry, square wave voltammetry and chronoamperometry were used to characterize the electroreduction step of the silicon species. The results showed that the growth of the silicon layer is very slow, yielding only clusters of silicon at low cathodic potentials and short electrolysis times. At higher electrodeposition potentials and/or longer deposition times, the films became rougher and cracks appeared in the layers. This was mainly due to the accumulation of tensile strains during growth. The layers were very reactive to air and humidity, probably due to the high porosity of the film. In some cases, contamination of the layers by S and F was also observed

Behaviour of Al–Ga alloy during cathodic polarization

The effect of the addition of small quantities of gallium to high-purity aluminium (99.999 wt%) on its electrochemical behaviour at high cathodic potentials (up to −2.0 V versus SCE), has been investigated using the potentiostatic pulse method. After cathodic polarization, anodic current was traced versus time to determine the quantity of charge necessary for oxidation of substances formed. Anodic current responses to the return to the E OCP were also recorded in the period of 1 s. Time responses of the cathodic and anodic currents were analyzed. The cyclic voltammetry method was used to determine the hydration potential. The range of low and high cathodic potentials (LCP, HCP) was defined for all the samples. It has been established that the oxide film retains its properties in the LCP range, while in the HCP range cathodic breakdown and hydration of the oxide take place. Electrochemical methods complemented the SEM and EDAX analysis before and after the cathode pulse of −1.9 V versus SCE.

Influence of temperature and applied potential on the electrochemical behaviour of nickel in LiBr solutions by means of electrochemical impedance spectroscopy

The effects of temperature, applied potential and hydrogen generation on the passive behaviour of nickel were investigated in lithium bromide aqueous solution using different electrochemical techniques: open circuit potential (OCP), potentiodynamic and potentiostatic measurements, and electrochemical impedance spectroscopy (EIS). From the polarization curves, it is observed that localised corrosion resistance decreases with temperature, the repassivation of nickel is more difficult at 75 °C and the hydrogen evolution reaction is favoured with an increase in temperature. Impedance results showed that the most suitable corrosion mechanism of nickel in LiBr solutions includes the double layer and the passive film formed on the nickel surface. The passive film of nickel partially disappears when a low cathodic potential is applied.

Electron Fluxes in a Microbial Fuel Cell Performing Carbon and Nitrogen Removal

The electron recovery in microbial fuel cells (MFCs) is decreased by processes like methanogenesis, bacterial growth, and the accumulation of intermediates. Using a suite of analytical techniques, including electrochemical monitoring, chemical analysis, microsensor analysis, and Titration and Off-Gas Analysis (TOGA), this study aimed to (a) identify and quantify the electron losses occurring at the anode and the cathode of a MFC removing acetate and nitrate (NO3-), respectively, and (b) to investigate the impact of the operational characteristics of the cathode on the denitrification process. Our results show that methane (CH4) production and estimated biomass formation at the anode and nitrous oxide (N2O) accumulation at the cathode were responsible for the reduction of Coulombic efficiency (epsilon) during continuous feeding conditions. At the anode, up to 40.1% of the acetate consumed was released as methane at closed circuit. At the cathode, N2O accumulation represented instead the main loss accounting for up to 10.0 +/- 2.1% of the oxidation capacity of the electron acceptor provided as NO3-. Batch experiments at controlled potentials and currents revealed that for a given current the fraction of electron transferred and released as N2O is significantly reduced by low cathodic potentials.

Spectroscopic evidences of the presence of hydrogenated species on the surface of copper during CO 2 electroreduction at low cathodic potentials

Carbon dioxide electroreduction on copper electrode was studied by surface enhanced Raman scattering (SERS) in K 2SO 4 aqueous solutions with different pH values. CO 2 was bubbled into the solution at 0 V vs. Ag/AgCl, i.e., on an oxidized copper surface. In acidic solutions (pH around 2.5), at −0.2 V, bands indicative of the presence of ethylene on the electrode surface were detected. Although ethylene is knowledgably a product of CO 2 electroreduction on copper, it was not experimentally identified on the electrode’s surface at such a low cathodic potential in prior works. In solutions with pH around 2.5, CO bands were not observed, suggesting that hydrocarbons could be formed by a pathway that does not occur via adsorbed CO. In solutions with higher pHs, a complex spectral pattern, between 800 and 1700 cm −1, was observed at approximately −0.4 V. The observed spectrum closely resembles those reported in the literature for adsorption of monocarboxylic acids with small chains. The spectral features indicate the presence of a structure containing a double C C bond, a carboxyl group, and C–H bonds on the electrode’s surface. SERS spectra obtained in CO-saturated solution are also presented. However, in this case, no SERS bands were observed in the region between 800 and 1700 cm −1 at low cathodic potentials.

Poly (3, 4-ethylendioxithiophene) (PEDOT) oxidation: activation energy and conformational energy

The oxidation kinetics of films of the conducting polymer PEDOT-C1O4 after electrochemical reduction by polarization at increasing cathodic potential was studied by potential steps. The response i/t presents a maximum at intermediate oxidation times. At the maximum the reaction occurs under chemical kinetic control following the expected current variations from the Chemical and Electrochemical Kinetics, when reactant concentrations or temperatures are changed. The obtained activation energy of the oxidation present two ranges as a function of the cathodic potential of prepolarization: constant values after prepolarization at low cathodic potentials and a lineal variation after prepolarization at increasing high cathodic potentials. According with the conformational relaxation model during electrochemical reduction the polymer shrinks, closes and packs the conformational structure. The activation energy for the subsequent oxidation includes two terms: the constant chemical activation energy and the conformational energy required to relax the packed polymeric structure. The conformational energy only appears after prepolarization at more cathodic potentials than the closing potential where more packed conformations were obtained. The conformational activation energy accounts the energetic requirements to relax and unfold the polymeric chains generating the required free volume to lodge balancing counterions; meanwhile the chemical activation energy accounts the energetic requirements for the electrochemical reaction to occur.

Electrodeposition of Cu from acidic sulphate solutions containing cetyltrimethylammonium bromide (CTAB)

In this paper we report a study of the electrodeposition of Cu from an acidic sulphate solution containing cetyltrimethylammonium bromide (CTAB). This investigation is based on cyclic voltammetry, in situ surface-enhanced Raman spectroscopy (SERS), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). Adsorption of CTAB over a wide range of cathodic potentials was proved spectroelectrochemically, encompassing both conditions where compact and loose Cu grows (up to −0.4 and between −0.4 and −1 V vs. Ag/AgCl, respectively). Furthermore, we found that CTAB tends to react cathodically, undergoing the loss of the aliphatic tail at lower cathodic potentials and the formation of an allylic product at higher polarisations. CTAB deeply impacts the Cu growth mode: ordered ridges of compact Cu crystallites form at low cathodic potentials—where the electrodeposition process is strongly inhibited by CTAB adsorption—and nanoparticles grow under hydrogen-evolution conditions.

Electron Capture Dissociation Implementation Progress in Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

Successful electron capture dissociation (ECD) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) applications to peptide and protein structural analysis have been enabled by constant progress in implementation of improved electron injection techniques. The rate of ECD product ion formation has been increased to match the liquid chromatography and capillary electrophoresis timescales, and ECD has been combined with infrared multiphoton dissociation in a single experimental configuration to provide simultaneous irradiation, fast switching between the two techniques, and good spatial overlap between ion, photon, and electron beams. Here we begin by describing advantages and disadvantages of the various existing electron injection techniques for ECD in FT-ICR MS. We next compare multiple-pass and single-pass ECD to provide better understanding of ECD efficiency at low and high negative cathode potentials. We introduce compressed hollow electron beam injection to optimize the overlap of ion, photon, and electron beams in the ICR ion trap. Finally, to overcome significant outgassing during operation of a powerful thermal cathode, we introduce nonthermal electron emitter-based electron injection. We describe the first results obtained with cold cathode ECD, and demonstrate a general way to obtain low-energy electrons in FT-ICR MS by use of multiple-pass ECD.

Electrodeposition of CoWP film: IV. Effect of applied potential and current density

CoWP films were electrochemically deposited on copper-coated silicon wafers from citrate electrolytes containing cobalt sulphate, sodium tungstate and sodium hypophosphite by both potentiostatic and galvanostatic methods and the effects of applied potential and current density on composition and microstructure of the films were studied. Surface compositional analysis using XPS shows that the films contained elemental cobalt, tungsten and phosphorus, cobalt hydroxide, and oxides of cobalt and tungsten. The thickest film with highest amount of cobalt (65 at.%) was obtained at an applied potential of −1.0 V versus AgCl/Cl reference electrode. It was observed that larger variation of compositions (cobalt from 36 to 57 at.%, tungsten from 31 to 59 at.% and phosphorus from 5 to 12 at.%) could be achieved by changing the deposition current density between −1 and −9 mA cm −2. XRD and SEM examinations revealed that the films deposited at low cathodic potentials and current densities were crystalline with larger crystallites, whereas films plated at higher cathodic potentials and current densities were amorphous with smaller crystallites.

Poly(3-methylthiophene) oxidation under chemical control. Rate coefficients change with prepolarization potentials of reduction

Abstract A kinetic study based on the potentiostatic oxidation of poly(3-methylthiophene) is presented. The influence of different initial states obtained by the reduction of the film at rising cathodic potentials for the same prepolarization time was studied. At the chronoamperometric maxima, the oxidation occurs under chemical control as shown by the semilogarithmic relationships between current and chemical concentrations. The oxidation rate coefficient changes as a function of both the oxidation overpotential, as for any other electrochemical oxidation, and the reduction potential of prepolarization. This dependence on the cathodic prepolarization shows two ranges: constant rate coefficients were obtained after reduction by prepolarization at low cathodic potentials and an exponential decrease of the rate coefficient after reduction at increasing cathodic prepolarizations. The conformational relaxation model allows a good description and quantification of these results.

Electrocatalytic dehalogenation of α-bromoketones in the presence of Cp2TiCl2

Processes of direct and electrocatalytic (in the presence of electrochemically reduced Cp2TiCl2) reduction of three α-bromoketones containing the C(sp3)-Br or C(sp2)-Br bond, viz., 2-bromo-and 2,6-dibromo-4,4-dimethylcyclohexa-2,5-dien-1-ones and α-bromo-acetophenone, were studied by cyclic voltammetry and preparative electrolysis. In all cases, the dissociative electron transfer proceeds via the concerted mechanism. Preparative electrolysis of these α-bromoketones in the presence of Cp2TiCl2 affords the reductive debromination products in 40–80% yield at low cathodic potentials (−0.85 V vs. Ag/AgCl/KCl). In the case of 2,6-dibromo-4,4-dimethylcyclohexa-2,5-dien-1-one in the potentiostatic regime, only one bromine atom can be eliminated selectively.

The effects of a magnetic field on the morphologies of nickel and copper deposits: The concept of "effective overpotential"

The morphologies of nickel and copper deposits obtained without applied magnetic fields, and with both parallel and perpendicular applied magnetic fields were examined by the scanning electron microscopy (SEM) technique. Changes in the morphologies of the metals caused by the effect of the magnetic fields are explained by the concept of "effective overpotential". The morphologies of the nickel and copper deposits obtained under parallel oriented magnetic fields were similar to those obtained at some lower cathodic potentials without an applied magnetic field. The magnetic field with a perpendicular orientation to the electrode surface increased the dispersity of the nickel and copper deposits. Nickel and copper deposits obtained under this orientation of the magnetic field were similar to those obtained at some higher cathodic potentials without an applied magnetic field. .

Effect of potential on the early stage of nucleation and growth during aluminum electrocrystallization from molten salt (AlCl3–NaCl–KCl)

Electrodeposition of aluminum onto graphite from a molten electrolyte containing AlCl3–NaCl–KCl was studied by the method of chronoamperometery. In the early stage of the deposition and at low cathodic potentials two-dimensional (2D) nucleation and growth proceeding through instantaneous and a multitude of progressive steps followed the initial double layer charging. The processes are manifested as peaks on a decaying chronoamperogram. Non-linear fitting methods were applied to obtain the kinetic parameters in the light of Bewick, Fleischmann and Thirsk (BFT) theory. Under more cathodic potentials, transition from 2D to three-dimensional (3D) processes have been observed as manifested in the form of plateau on decaying chronoamperograms. The kinetic parameters associated with 3D progressive growth mechanism was obtained as above but using the Armstrong, Fleischmann and Thirsk (AFT) model.

Models of hypoxia activated prodrugs: Co(iii) complexes of hydroxamic acids

Co(III) complexes of simple hydroxamic acids have been evaluated as models of hypoxia activated prodrugs containing MMP inhibitors. The complexes are based upon a proposed carrier system comprising the tripodal tetradentate ligand tris(2-methylpyridyl)amine (tpa) with the hydroxamate functionality occupying the remaining coordination sites of the Co centre. Acetohydroxamato (aha), propionhydroxamato (pha), and benzohydroxamato (bha) complexes were synthesised and characterised by single crystal X-ray diffraction. For aha and pha both the hydroxamato and hydroximato (deprotonated) forms were obtained and were readily interconverted by pH manipulation; for bha only the hydroximato complex was obtained as a stable species. Electrochemical analysis was used to probe the redox chemistry of the complexes and assess their ease of reduction. All of the complexes displayed irreversible reduction and had low cathodic peak potentials. This suggests that the Co-tpa carrier system would provide a suitably inert framework to deliver the drugs to target sites intact yet would release the ligands upon reduction to the more labile Co(II) oxidation state.

Cathodic breakdown of anodic oxide film on Al and Al–Sn alloys in NaCl solution

The effect of cathodic polarisation on stability of defined oxide films on Al and Al–Sn alloys (with up to 0.40% Sn) has been investigated in a 0.5 M NaCl solution using the potentiostatic pulse method. The dependence of the cathodic current on time (in the period of 1, 10 and 100 s) was recorded on Al and Al–Sn alloys when subjected to a potential pulse from E OCP to different negative values (up to −2.0 V). Anodic current responses to the return to the E OCP were also recorded at three different time scales (1, 10 and 100 s). It has been established that the cathodic polarisation of passivated Al and Al–Sn alloys in a chloride solution is characterized by two regions of potentials with distinctly different phenomena: the range of low and high cathodic potentials (LCP and HCP). In the LCP range, the oxide film retains its properties, while in the HCP range cathodic breakdown and hydration of the oxide take place. The boundary between these two potential ranges shifts towards more negative potential values when the percentage of Sn in the alloy increases. The longer the duration of the cathodic pulse, the more positive the potentials at which the oxide film breakdown takes place. This shift is more marked with alloys containing higher percentage of Sn. Cathodic polarisation (duration of 100 s) activates alloys with 0.20% and 0.40% Sn for anodic dissolution.

Electrochemical study of imipenem's primary metabolite at the mercury electrode: Voltammetric determination in urine

Imipenem shows a fast chemical conversion to the more stable imin form (identical to that from biochemical dehydropeptidase degradation) in aqueous solutions that shows a wave at lower cathodic potential than the imipenem one. The aim of this work is the study of the electrochemical behaviour of the primary metabolite of imipenem (M1) and the proposal of electrochemical methods for the determination of M1 in human urine samples. Electrochemical studies were realized in phosphate buffer solutions over pH range 2.0–8.0 using differential pulse polarography, dc-tast polarography, cyclic voltammetry and linear sweep voltammetry (staircase). In acidic media, a non-reversible diffusion-controlled reduction involving two electrons and two protons occurs and the mechanism for the reduction was suggested. A differential pulse polarographic method for the determination of M1 in the concentration range 10 −6 to 10 −4 M with a detection limit of 4.5 × 10 −7 M was proposed. Also, a method based on controlled adsorptive pre-concentration of M1 on the hanging mercury drop electrode (HMDE) followed by linear sweep voltammetry allows its determination in the concentration range 2 × 10 −9 to 4 × 10 −8 M with a detection limit of 1.05 × 10 −9 M. The proposed methods have been used for the direct determination of M1 in spiked human urine and real human-derived urine with good results and should be appropiate for monitoring purposes.

Investigation of hydrogen adsorption behaviours in the presence of methanol and dissolved oxygen using electrochemical quartz crystal microbalance

In the presence of methanol and dissolved oxygen, hydrogen adsorption and reduction behaviours on electrodeposited Pt electrode were investigated with cyclic voltammetry and in situ electrochemical quartz crystal microbalance. Specific hydrogen adsorptions occur at two different cathodic potentials and its adsorption at low cathodic potential is suppressed by oxygen adsorption. After methanol oxidation occurred on Pt electrode, part of Pt surface is covered with reaction intermediate, CO, which blocks the adsorption of hydrogen and oxygen. Measurement of reaction currents and mass changes during cyclic voltammetry and potentiostatic oxygen reduction suggested that the amount of hydrogen adsorption decreases significantly and specific hydrogen adsorption steps are altered, which resulted in the decrease of oxygen reduction.

Electrodeposition of p–i–n type CuInSe2 multilayers for photovoltaic applications

Copper indium diselenide polycrystalline thin films of p-, i- and n-type electrical conductivity were grown using a one-step electrodeposition process in a single bath. The bulk structure and the stoichiometry of the layers were determined using X-ray diffraction and X-ray fluorescence. The material composition was correlated with the electrical conductivity type variation, detected by the photoelectrochemical cell. Atomic force microscopy analysis showed copper-rich films deposited at low cathodic potentials (0.6 V vs Ag/AgCl) are of spherical and granular morphology and the grain sizes were 0.3–0.5 μm, while stoichiometric CIS films deposited at 1.0 V vs Ag/AgCl have grain sizes of 0.1–0.4 μm. The initial studies of optoelectronic properties (Voc, Jsc and FF) of the four-layer solar cell devices (glass/FTO/n-CdS/n-CIS/i-CIS/p-CIS/Au) are presented.

Initial stages of Ni–P electrodeposition: growth morphology and composition of deposits

The evolution of growth morphology and composition of deposits during the initial stages of Ni–P electrodeposition is studied using atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). Combined electrochemical and surface analytical measurements show that the deposition process starts at relatively low cathodic potentials by instantaneous formation and growth of hemispherical centres. The phosphorus content of deposits in the initial deposition stages is found to increase gradually with the deposition time. Additional electrochemical and XPS measurements, carried out on Ni substrates under same polarisation conditions in a Ni 2+ ion free electrolyte solution, show the occurrence of a time dependent Ni–P surface alloy formation indicating a strong Ni–P interaction. It is suggested that the very early stages of Ni–P electrodeposition involve a primary instantaneous nucleation of Ni followed by a Ni–P alloy formation induced by the strong Ni–P interaction. AFM images show that in advanced deposition stages the coalescence of growing Ni–P centres leads to formation of larger growth mounds. The evolution of the resulting surface roughness is analysed on the basis of the so-called dynamic scaling concept. The estimated values for the roughness exponent and the growth exponent ( α=1.07±0.05 and β=0.28±0.05) correspond to a model involving a smoothing of the growing surface driven by surface diffusion.

Electrochemical arylation of cobalt and nickel chelates with diphenyliodonium salts

Electrochemical arylation of cobalt chelates with diphenyliodonium salts occurs at low cathodic potentials (viz., potential of the first reduction wave of the diphenyliodonium salt) and affords the phenyl derivatives of CoIII chelates containing the σ-Co—C(sp2) bond. Nickel complexes should be arylated at higher cathodic potentials because it is necessary to generate paramagnetic NiI complexes.