Effect of Cl ions and benzylideneacetone/ethanol on the underpotential deposition of zinc in acidic media: cyclic voltammetry and EQCM studies

The influence of chloride ions and a benzylideneacetone (BDA)/ethanol (EtOH) mixture on the underpotential deposition (UPD) of Zn²⁺ ions on Pt electrodes in acidic media was investigated by cyclic voltammetry and electrochemical quartz crystal microbalance (EQCM). In the potential region of the UPD of H and Zn, the surface coverage of Zn adatoms on Pt was evaluated based on the correspondence between charge and mass for several different solutions. In the absence of Cl⁻ ions and BDA/EtOH, the maximum surface coverage of the Zn deposited by UPD was 0.29. In addition, in the presence of Cl⁻ ions, the UPD of Zn²⁺ ions occurred simultaneously with the adsorption of Cl⁻, and the presence of Cl⁻ did not modify the quantity of Zn deposited by UPD. In the presence of Cl⁻ ions and BDA/EtOH, the maximum surface coverage of the Zn deposited by UPD was 0.16. The partial inhibition of the UPD of Zn²⁺ ions is associated with the adsorption of BDA/EtOH or products of the decomposition of BDA/EtOH during the UPD process.     

An EQCM study of polyethyleneglycol 8000 adsorption and its coadsorption with Cl ions on Pt in perchloric acid solutions

The adsorption of the additive polyethyleneglycol 8000 (PEG8) and its coadsorption with Cl⁻ ions was investigated by cyclic voltammetry and linear potential scans in conjunction with simultaneous measurements of the frequency change of an electrochemical quartz crystal microbalance (EQCM). Data obtained from the studies of EQCM for solutions of HClO₄ containing PEG8, shows the formation of a peak (IcI) in the potential range from 0.2 to 0.4 V during the cathodic potential scan, which is due to the adsorption of PEG8 onto Pt. Analysis of simultaneously recorded massograms and voltammograms revealed that the adsorption of PEG8 occurs via a non-Faradaic process, and that no adsorption of PEG8 is observed at the open circuit potential. As the concentration of PEG8 in the solution was increased over the range  M, the degree of coating by PEG8 on the Pt surface increased to 0.21. The presence of Cl⁻ ions in the solution inhibited PEG8 adsorption, and the degree of inhibition gradually increased with increasing Cl⁻ concentration.     

Influence of halide ions on the adsorption of diphenylamine on iron in 0.5 M H2SO4 solutions

Halide ions are found to enhance the inhibition performance of amines due to enhanced adsorption of amines by the adsorbed halide ions on the metal surface. In this work, the synergistic action of halide ions on the corrosion inhibition of iron in 0.5 M H₂SO₄ by diphenylamine has been found out by electrochemical impedance and polarization methods. Analysis of impedance data has been made with equivalent circuit with constant phase angle element for calculation of double layer capacitance values. Experiments have been carried out in the concentration range of 100-1000 ppm of diphenylamine in the presence of 0.5-1.0 × 10⁻³ M of halide ions. Diphenylamine is found to be a cathodic inhibitor and the inhibition efficiency of about 65% is obtained at 1000 ppm. The anodic and cathodic Tafel slopes in the presence of diphenylamine alone and with halide ions are 65 ± 5 and 105 ± 5 mV, respectively. Diphenylamine inhibits corrosion by adsorption and the surface coverage values are increased considerably in the presence of halide ions. In the presence of iodide ions, the inhibition efficiency of diphenylamine at 100 ppm is increased to more than 90%. In the case of other halide ions, the inhibition efficiency of diphenylamine in increased to 80% at 1000 ppm. The order of synergism of halide ions is I⁻ ? Br⁻ > Cl⁻. The highest synergistic effect of iodide ions is due to chemisorption with metal surface due to its larger size and ease of polarizability.     

EQCM study of the ECL quenching of the tris(2,2′-bipyridyl)ruthenium(II)/tris-n-propylamine system at a Au electrode in the presence of chloride ions

Significant effect of chloride ions on the electrogenerated chemiluminescence (ECL) behavior of the ruthenium(II)tris(2,2′-bipyridine) (Ru(bpy)₃²⁺)/tri-n-propylamine (TPrA) system at a Au electrode was reported. At low concentrations (e.g., [Cl⁻] < 5 mM), the ECL was enhanced; at relatively high concentrations, however, the ECL intensity decreased with the increase of the [Cl⁻]. At [Cl⁻] = 90 mM, ∼50% and 100% ECL inhibition was observed for the first and the second ECL wave, respectively. The electrogenerated gold-chloride complexes (AuCl₂⁻ and AuCl₄⁻) which were verified using an electrochemical quartz-crystal microbalance (EQCM) method were found to be responsible for the ECL inhibition. This study suggests that care must be taken when a Au working electrode is used for ECL studies in chloride-containing buffer solutions (widely used in DNA probes) and/or with the commonly used chloride-containing reference electrodes since in these cases the ECL behavior may significantly disagree with that obtained using other electrodes and reaction media.     

Influence of chloride ions on the stability of PtNi alloys for PEMFC cathode

The dependence of the rate of Ni dissolution from PtNi alloys on the chloride concentration was studied electrochemically in 0.5 M HClO₄ at room temperature. Electrodeposited PtNi catalysts were subjected to extensive potential cycling between 20 mV and 1.3 V at various Cl⁻ concentrations and the cyclic voltammograms (CV) response and the oxygen reduction reaction (ORR) activity of the catalysts were determined at different intervals. Energy dispersive X-ray spectroscopy (EDS) and inductively coupled plasma spectroscopy (ICP) analyses were carried out to determine the elemental composition of the alloys and the amount of dissolved Ni at different stages of the potential cycling. It was found that the presence of Cl⁻ increases the rate of Ni dissolution and by this accelerates the dealloying process relative to potential cycling in chlorine-free solutions. Dealloying is most pronounced during the initial stages of potential cycling. Already a small amount of Cl⁻ is sufficient to dissolve the majority of the non-noble metal from the alloys. Even then, under oxygen reduction conditions, the blockage of Pt surface by Cl⁻ is less pronounced for the alloys than for pure Pt catalysts, leading to marginally improved ORR activity for the PtNi alloys at low Cl⁻ concentrations. From a practical point of view, the effect of chloride ion leakage from a commercially available saturated KCl reference electrode on the electrocatalytic activity was also investigated.     

Effect of hydroxyl ions on chloride penetration depth measurement using the colorimetric method

In this paper, the effect of hydroxyl ions on chloride penetration depth measurement using the colorimetric method was studied. Equivalent silver nitrate solution (i.e. Ag⁺ = Cl⁻) was added to the NaCl + NaOH solution with different concentrations, then the amount of precipitated silver chloride and silver oxide were determined by chemical methods, and the color of the precipitated products was examined. Results show that the amount of silver chloride formed decreases linearly as OH⁻ to Cl⁻ ratio (r) increases. Thus, the chloride concentration at color change boundary changes with the pH value of the concrete. AgCl has a white color, while Ag₂O has a dark brown color. When the value of r exceeds 4, the color of the mixture looks brown, and color change boundary cannot be easily distinguished.     

A voltammetric and nanogravimetric study of Te underpotential deposition on Pt in perchloric acid medium

This work describes the study of Te underpotential deposition on Pt in acid media using cyclic voltammetry, rotating ring-disc electrode and electrochemical quartz crystal microbalance techniques. The voltammetric results indicate the presence of two dissolution peaks in the positive scan with a total charge density of 420 μC cm⁻². These phenomena are attributed to the deposition of one Te monolayer with the occupancy of two active Pt sites by each ad-atom. This is confirmed by rotating ring-disc electrode results. The electrochemical quartz crystal microbalance (EQCM) experiments yielded the small mass variation of −32 ng cm⁻² (while the theoretical one is −140.4 ng cm⁻² for a complete Te monolayer). This low value can be attributed to the simultaneous adsorption of water, perchlorate anions and the formation of platinum oxide.     

Electrochemical behavior of thin polycrystalline rhodium layers studied by cyclic voltammetry and quartz crystal microbalance

Electrochemical behavior of thin polycrystalline Rh layers has been studied in 0.5 M H₂SO₄ solution by cyclic voltammetry (CV) and the electrochemical quartz crystal microbalance (EQCM). The properties of surface oxide formed on freshly electrodeposited Rh are different than on electrochemically aged Rh. The analysis of frequency changes in both hydrogen and oxygen regions is presented. It is suggested that hydrogen desorption occurs simultaneously with the adsorption of HSO₄⁻ ions, whose maximum surface coverage reaches ca. 8%. The EQCM results indicate that RhO is the main species formed during Rh surface oxidation. Metal dissolution proceeds during electrode cycling to sufficiently high potentials. The amount of dissolved metal increases with an increase in potential and a decrease in scan rate.     

Surface-enhanced IR spectroscopy investigation on the electro-oxidation of CO adlayer at a polycrystalline Pt film electrode in Cl-containing HClO4

The electro-oxidation of CO adlayer on Pt electrode in Cl⁻-containing 0.1 M HClO₄ has been investigated with in situ attenuated-total-reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS). Two potentials were selected for predosing CO on the Pt electrode: one is in the H-UPD region, i.e., 0.1 V (vs. RHE) and the other is in the double-layer region, i.e., 0.45 V (vs. RHE). The broadening of the prewave and the main peak for the CO oxidation is observed, in addition to the positively shifted oxidation potentials. The spectroelectrochemical data suggest the specific adsorption of Cl⁻ starts at a potential as negative as 0.1 V which may compete with the adsorption of OH at CO-unoccupied sites (including but not limited to defect sites) and/or hinder the diffusion of CO to OH adsorption sites on Pt electrode, slowing down the CO oxidation. This competitive Cl⁻ adsorption at lower potentials disrupts the interfacial free H₂O structure on the top of CO adlayer, signaled by a reduced OH stretching band intensity.     

Electrocatalytic reduction of NO2: Platinum modified glassy carbon electrode

Platinum particles were electrochemically deposited over glassy carbon (GC) to prepare GC-Pt electrodes. The electrocatalytic behaviors of this electrode have been compared with that of an ordinary polycrystalline(OPC) Pt and GC electrode in reducing NO₂⁻ at neutral medium. The as prepared GC-Pt electrode reduced NO₂⁻, exhibiting double-peak reduction waves. The reduction performance of this electrode was noticed at least 7.8 times higher than that of an OPC Pt electrode. The sensitivity of the GC-Pt electrode was found to be enhanced by the temperature rise. A consecutive mechanism, NO₂⁻ → NO → NH₄⁺, over the as prepared GC-Pt electrode has been investigated.     

Electrochemistry of thorium in LiCl-KCl eutectic melts

This work presents a study of the electrochemical properties of Th chloride ions dissolved in a molten LiCl-KCl eutectic, in a temperature range of 693-823 K. Transient electrochemical techniques such as cyclic voltammetry, chronopotentiommetry and chronoamperometry have been used in order to investigate the reduction mechanism on a tungsten electrode and the diffusion coefficient of dissolved Th ions. All techniques showed that only one valence state was stable in the melt. The reduction into Th metal was found to occur according to a one-step mechanism, through a nucleation-controlled process which requires an overpotential of several 100 mV. At 723 K, the diffusion coefficient is D_Th(723 K) = 3.15 ± 0.15 × 10⁻⁵ cm² s⁻¹. EMF measurements indicated that, at 723 K, the standard apparent potential is (723 K) = −2.582 V versus Cl₂/Cl⁻, and the activity coefficient γThCl₄ (723 K) = 4.6 × 10⁻⁴ on the mole fraction scale (based on a pure liquid reference state).     

Nanotribology at single crystal electrodes: Influence of ionic adsorbates on friction forces studied with AFM

We present friction force measurements on Au(1 1 1) single crystal electrode surfaces performed under electrochemical conditions using an atomic force microscope (AFM). At monoatomic steps friction is increased in both scan directions. In 0.05 M sulfuric acid an increase of friction is observed with the increase of adsorbed sulfate. Friction force increases non-linearly with load. Cu UPD also increases friction in presence of sulfate. However, in presence of 4 × 10⁻⁴ M chloride friction is much smaller for all deposited Cu coverages - ranging from a submonolayer up to bulk copper compared to the solution without chloride. After dissolution of bulk copper clusters deposited on Au(1 1 1) we observed an area with higher friction forces due to the formation of an alloy between gold and copper.     

Enhancement of filling performance of a copper plating formula at low chloride concentration

In this work, microvia filling was performed by copper electroplating using two plating formulas with and without a leveler at a low concentration of chloride. The base plating solution contained CuSO₄, H₂SO₄, polyethylene glycol (PEG), bis (3-sulfopropyl) disulfide (SPS) and Cl⁻. When the Cl⁻ concentration was lower than 30 ppm, the plating formula without a leveler became dead for bottom-up filling, resulting in conformal deposition. The addition of 1 ppm Alcian Blue, used as a leveler, could effectively recover the filling performance of the plating formula with low chloride concentration. Electrochemical analyses revealed possible mechanisms. The results demonstrate that the usage of Alcian Blue can widen the operation window of chloride concentration, since it can assist PEG in competing with SPS in adsorption at low chloride concentration.     

Voltametry and EQCM study of copper oxidation in acidic solution in presence of chloride ions

Cyclic voltametry experiments coupled with electrochemical quartz crystal microbalance (EQCM) measurements showed the corrosion mechanism of electrodeposited copper in presence of chloride ions. The oxidation of copper in acidic solution containing high concentration of Cl⁻ begins with formation of Cu⁺ ions. The Cu⁺ concentration at the vicinity of the electrode increasing, the small solubility product of CuCl is then exceeded, leading to a CuCl precipitation on the gold covered quartz crystal used as working electrode. For highest anodic potentials, the oxidation of electrodeposited copper or CuCl precipitate phases could occur. A combination with structural techniques like SEM, EDAX, AFM and DRX gives insight into the morphology and the nature of these CuCl precipitates.     

Finely dispersed Pt nanoparticles in conducting poly(o-anisidine) nanofibrillar matrix as electrocatalytic material

A new approach based on stepwise oxidation of o-anisidine is explored for generating nanoporous films of poly(o-anisidine), POA and loading of Pt nanoparticles that are subsequently used for electrocatalysis of methanol oxidation are presented and compared with bulk Pt. POA film can easily be prepared by stepwise electro-oxidation procedure with very high porosity consisting of nanofibrillar structure using without templates. Controlled sizes of Pt nanoparticles were entrapped into POA matrix by a two-step process in which first PtCl₆²⁻ ions are sorbed into the pores of polymer matrix followed by electroreduction at −0.55 V in a 0.5 M H₂SO₄ solution. Loading of Pt nanoparticles (10-200 μg/cm²) onto POA matrix were accomplished by varying the concentration (2-10 mM) of the sorbate, i.e., H₂PtCl₆. The sizes of the Pt nanoparticles were determined from TEM analysis and Pt particles were found to be in the range of 10-20 nm. The crystallite phase of Pt particles in POA was examined from XRD pattern. AFM image further supports Pt particles embedded in POA matrix.     

Effect of metals on silver electrodeposition: Application to the detection of cisplatin

In the present work, the influence of several metals (Co, Ru, Pd, Os, Pt, Cu, Pb), deposited on a carbon paste electrode, towards silver electrodeposition was tested. First, adequate conditions for the electrodeposition of metals on the electrode were found. Then, the cyclic voltammograms registered (silver deposition curves and analytical signals) showed that Co, Cu, Pt and Pd were able to accelerate silver electrodeposition. Finally, a valid methodology for the detection of cisplatin was established. It is based on the deposition of silver on a Pt (from cisplatin) modified electrode and the analytical signal corresponds to the anodic stripping of the deposited silver. A limit of detection of 3.2 × 10⁻⁹ mol dm⁻³ (1 ng cm⁻³) cisplatin was obtained.     

Effect of reduction conditions on electrocatalytic activity of a ternary PtNiCr/C catalyst for methanol electro-oxidation

The effect of reduction conditions on a Pt₂₈Ni₃₆Cr₃₆/C catalyst was investigated by using two different reduction methods: hydrogen reduction and NaBH₄ reduction. In hydrogen reduced catalysts, dissolution of metallic Ni and Cr was observed during cyclic voltammetry (CV) tests, and a larger amount of Ni and Cr was dissolved when reduced at higher temperatures. For methanol electro-oxidation, the highest specific current density of 1.70 A m⁻² at 600 s of the chronoamperometry tests was observed in the catalyst reduced at 300 °C, which was ∼24 times that of a Pt/C catalyst (0.0685 A m⁻²). In NaBH₄ reduced catalysts, formation of an amorphous phase and a more Pt-rich surface was observed in X-ray diffraction and CV results, respectively, with increasing amounts of NaBH₄. When reduced by 50 times of the stoichiometric amount of NaBH₄, the PtNiCr/C catalyst (PtNiCr-50t) showed a current density of 34.1 A g_{noble metal}⁻¹, which was 81% higher than the 18.8 A g_{noble metal}⁻¹ value of a PtRu/C catalyst at 600 s of the chronoamperometry tests. After 13 h of chronoamperometry testing, the activity of the PtNiCr-50t (15.0 A g_{noble metal}⁻¹) was 110% higher than the PtRu/C catalyst (7.15 A g_{noble metal}⁻¹). The PtNiCr/C catalyst shows promise as a Ru-free methanol oxidation catalyst.     

A test method for measuring chloride diffusion coefficients through partially saturated concrete. Part II: The instantaneous plane source diffusion case with chloride binding consideration

A test method is proposed for measuring chloride diffusion coefficients through partially saturated concrete specimens with well characterized water contents. It includes an experimental procedure for supplying a limited amount of Cl⁻ to the tested concrete surface, and two mathematical models for processing the experimental Cl⁻ content profiles obtained at selected diffusion times. The use of the more refined model, taking into account the chloride binding by concrete, allows to increase the reliability of the determined diffusion coefficients. For the two tested Portland cement concretes, (water/cement ratios 0.6 and 0.5), the Cl⁻ diffusion coefficient decreases about two orders of magnitude, from 6 · 10^− 12 to 2 · 10^− 14 m²/s, when the relative humidity of the atmosphere in equilibrium with concrete is lowered from 95% to 54% approximately.     

Participation of the dissolved O2 in the passive layer formation on Zn surface in neutral media

The composition of the passive layers formed on Zn electrode in naturally aerated and de-aerated 0.1 M KClO₄ solution were studied using X-ray photoelectron spectroscopic measurements (XPS). A correlation between the presence of dissolved O₂ and the formation of an interior passive layer was carried out. Librated Cl⁻ from the perchlorate reduction reaction was detected in its solutions during Zn electrode polarization. The librated Cl⁻ concentration reached its maximum value at −1.4 V. Moreover, in the studied potential range the perchlorate reduction rate increases in absence of dissolved oxygen. Chrono-amperometry and electrochemical impedance spectroscopy (EIS) were performed for the stationary and the rotating disc Zn electrodes in naturally aerated and de-aerated 0.1 M KClO₄ solution. EIS technique showed a change in the electrode impedance with the experimental conditions as a result of changing the reactions occurring in the electrode vicinity. The obtained data were fitted to three different equivalent circuits depending on the electrode potential. The protective nature of the passive layers formed in different experimental conditions was found to decrease with rotating the electrode and de-aerating the solution.     

Model experiments on electrochemical formation of nano-dimensioned noble metal-oxide-semiconductor junctions at Si(1 1 1) surfaces

The recently introduced nanoemitter concept allows photovoltaic and photoelectrocatalytic energy conversion. Device functioning is presently based on metallic nanoemitters that are embedded in passivating films on Si absorbers. Model experiments on the electrodeposition of nanoscale noble metal islands onto n-type H:Si(1 1 1) are presented. Besides electrochemical methods such as impedance spectroscopy and cyclic voltammetry, atomic force microscopy (AFM), transmission electron microscopy (TEM) and synchrotron radiation photoelectron spectroscopy (SRPES) have been applied to elucidate the surface chemistry and electronics. The electrodeposition profiles of the reduction current under depletion condition indicate electron exchange via occupied surface states which strongly influence the deposition rate and the surface site selectivity of the nucleation process. SRPES at photon energies adjusted to high surface sensitivity shows formation of an ultrathin silicon dioxide film in the course of the reduction of the noble metal chloride complexes. The presence of this interfacial oxide is confirmed by high resolution TEM experiments. Step bunching at the Si surface upon electrodeposition is observed by AFM and analyzed in detail using (i) metal chloride complex containing solutions and (ii) chloride-ion solutions. A model for Si etching in chloride-ion containing solutions is presented that is also based on impedance measurements which show that Cl⁻ is adsorbed at the Si surface. Finally, the successive steps of Pt electrodeposition from the hexachloro complex PtCl₆²⁻ onto Si(1 1 1) are outlined.