Contact Electric Resistance Technique Research Articles

First experimental evaluation of partial charge transfer during anion adsorption

The partial charge transfer during anion adsorption cannot be measured in electrochemical experiments or reliably estimated by ab initio quantum-chemical and DFT calculations. However, it is directly involved in the adsorbate charge that is experimentally accessible by in situ contact electric resistance technique. We present the first quantitative evaluation of charge transfer during halides adsorption on silver from aqueous solutions in dependence on the electrode potential. Partial charge transfer from adsorbed bromide and iodide ions to the silver electrode increases with the positive potential shift and may reach complete charge transfer resulting in adatom creation. Chloride adsorption on silver occurs with much lower charge transfer, but on some stainless superalloys it proceeds with substantial charge transfer owing to their specific electronic structure.

Recent trends in experimental and theoretical investigations of chemisorption on metal-electrolyte interface. II. Contact electric resistance method

New trends in experimental and theoretical investigations of chemisorption on electrodes are considered on examples of in situ spectroscopic studies and the density functional theory calculations. The partial charge transfer during ionic and molecular adsorption from aqueous solutions on coinage and platinum metals and the thermodynamic uncertainty regarding the direction of the charge transfer are discussed. The contact electric resistance technique (CER) was shown to offer a new approach to considering these problems. This technique provides information on the coefficient and direction of the charge transfer, the kinetics of the transformation of the electrode surface during the conversion of adsorbed ions to adatoms, and the role of competitive adsorption of water. It was examined how the charge transfer is related to the electrosorption valence of anions and what the role plays the tunneling of electrons in the generation of the CER signal. The CER was demonstrated to be dependent on the potential E, the coverage, and the residence charge of the adsorbate. For the adsorption of halide ions from aqueous solutions on 1B metals, the bell shaped CER vs. E dependences were obtained. The maxima in these dependences correspond to the onset of substantial charge transfer, their position and amplitudes being determined by the nature of the metal and anion and the concentration of the latter. At E < Emax, halide ions are adsorbed without appreciable charge transfer; within the range Emax (Emax + 0.1 V), the charge transfer for silver and gold approaches 1, being far less for copper. For a given metal, Emax increases in the series I− < Br− ≪ Cl− while for a given anion, Emax increases in the series Au < Ag ≪ Cu. Based on the measured CER-E dependences, a quantitative criterion of the substantial charge transfer during ionic and molecular adsorption was proposed. This criterion was demonstrated to be consistent with the published data on charge transfer in various adsorbate-adsorbent systems. In particular, it shows that the hydrophilicity and electronic properties of 1B metals differently influence charge transfer during ionic and molecular adsorption. New electrosorption equations have been proposed describing the partial charge transfer and screening of the adsorbate charge due to partial ionization of the surface atoms. An experimental approach to solve the “anion problem” in the density functional theory has been developed basing on the CER-measured values of Emax in corresponding electrochemical systems.

Kinetics of chloride ion adsorption on stainless alloys by in situ contact electric resistance technique

Abstract As the primary reason for pitting of stainless alloys, chloride adsorption is not adequately studied, e.g. kinetic investigations of chloride adsorption are actually absent. We discuss and partly reconsider some well-known facts (e.g. halides order: Cl− > Br− > I−), disputed points (chloride penetration in passive film), and still unknown aspects of chloride adsorption. For the first time, we report kinetic studies of chloride adsorption on stainless alloys by in situ contact electric resistance technique. The peak-like character of kinetic curves has been found for all studied stainless alloys, but not for pure iron and nickel. This has been considered as a sequence of the substantial charge transfer during chloride adsorption. Opposite to typical d metals, stainless materials are alloys of early and late transition metals having unfilled d-bands with increased number of d-electron vacancies. Such electronic structure is favorable for adsorption of electron donating adsorbates like halide ions. Experimental data of this work are more compatible with possibility of chloride penetration into the passive films on stainless alloys that also might involve a transformation of primary oxy-hydroxide films into oxy-chloride films.

Effects of Environmental Factors on the Electronic Properties of Interfacial Oxide Film on 304L Stainless Steel in High Temperature Pure Water

The electronic properties of the interfacial oxide film formed on 304L stainless steel in high temperature water are investigated by contact electric resistance (CER) measurements. Tests are performed in pure water with a wide range of dissolved oxygen (DO) content at 200, 250, and 288°C. The electrochemical potential (ECP) moves in the noble direction and CER increases when increasing DO. Results show that DO content has a dominant effect on the electronic properties of oxide film. The change of oxide film properties can also be attributed to the variation of the electrochemical potential, which is directly affected by DO content. Critical potentials exist for the formation and reduction of oxide films in high temperature water. Multiple steps are found for the reduction of oxide films due to de-aeration in 200, 250, and 288°C water, implying the presence of multiple-layer interfacial oxide films. The film reduction process is relatively slower than the film formation process. Present results show that even in high purity water, a moderate change of DO content can result in different surface conditions. Dissolved hydrogen has a moderate effect on interfacial surface films in deaerated water. In-situ monitoring of the oxide film properties by CER technique provides information on the interfacial reactions that are related to the SCC behavior of materials in high temperature water environments.

Ion transport investigations of polypyrroles doped with different anions by EQCM and CER techniques

The ion transfer in redox processes of conducting polypyrrole doped with various anions, such as 1-naphthalenesulfonate, 10-camphorsulfonate, p-toluenesulfonate, dodecylbenzenesulfonate was investigated by electrochemical quartz crystal microbalance (EQCM), contact electric resistance (CER), and cyclic voltamperometry in situ techniques. By using this setup, the doping levels of the synthesized PPy films and mobility of charge carries in these materials in KCl aqueous solution under linear potential scan were determined.

Conduction Mechanism of the Passive Film on Iron Based on Contact Electric Impedance and Resistance Measurements

The application of a mixed conduction model and a new contact electric impedance (CEI) technique to predict quantitatively the electronic and ionic transport properties of oxide films on iron in a nearly neutral tetraborate solution is discussed. The mixed-conduction model emphasizes the coupling between the ionic defect structure and the electronic conductivity in an anodic film. Conventional electrochemical techniques have not been sufficient to characterize properly the electronic and ionic properties of anodic films on metals. The CEI technique makes it possible to distinguish between processes taking place at different rates within oxide films. Using this technique together with the contact electric resistance technique, we have found that the diffusion coefficient for the electronic conduction in the anodic film on iron is several orders of magnitude higher than that for the ionic transport. This shows that the passive film on iron is predominantly an electronic conductor. The fitting of the experimental results to the mixed conduction model gives a good agreement and thus supports the validity of this model in the present case. © 2001 The Electrochemical Society. All rights reserved.

In-situ characterization of the polypyrrole films by EQCM and CER techniques

A novel setup for the investigation of ion moving processes occurring in polymer films is proposed. The special crystal holder capsule was created to include EQCM (Electrochemical Quartz Crystal Microbalance) into CER (Contact Electric Resistance) equipment and provide its reliable operation. The dependence of the resistance and the mass change of the polypyrrole films on the polarisation potential in potassium iodide aqueous solutions were investigated combining the EQCM and CER techniques. The CER method reinforced with the EQCM technique gives us a helpful tool for the better understanding of the polymeric films preparation processes with well-defined physical and chemical properties.

Localized corrosion of stainless steel in chloride, sulfate and thiosulfate containing environments

Localized corrosion behavior of UNS S30403 type stainless steel was studied by cyclic polarization scans, scratch tests and Contact Electric Resistance (CER) technique in simulated paper-mill environments at pH 3 or 5 (55 or 65°C) containing varying amounts of chloride, sulfate and thiosulfate. Polarization scans, scratch tests and CER technique gave similar results on thiosulfate related pitting and crevice corrosion.

Conduction Mechanism of the Anodic Film on Fe‐Cr Alloys in Sulfate Solutions

The passive state of Fe‐12% Cr and Fe‐25% Cr alloys in 1 M sulfate solutions of pH 0 and 5 was studied with a combination of electrochemical techniques: impedance spectroscopy, photoelectrochemistry, and dc resistance measurements by the contact electric resistance technique. The investigations were supported by studies on pure metal constituents (Fe, Cr) in the same solutions. As a result, the steady‐state passive film on the alloys (and on pure Cr) can be described as a thin, essentially insulating layer. Polarization of the steady‐state metal/anodic film/electrolyte system to negative and positive potentials away from the potential region corresponding to the highest electronic resistance was concluded to lead to the generation of lower or higher valency defects at the interfaces via solid‐state electrochemical reactions. These reactions result in a substantial increase of the conductivity in the first layers adjacent to either the metal/film or the film/electrolyte interface. At very negative (or very positive) potentials the film is transformed into a conductor allowing active (or transpassive) dissolution to take place. A quantitative physical model of the conduction mechanism on the basis of the surface charge approach is proposed and compared with experimental data. © 1999 The Electrochemical Society. All rights reserved.

Synthesis, electropolymerization and electrochemical characterization of some new acrylate substituted thiophene derivatives

In this work, three new acrylate substituted thiophene monomers, (3-thienyl) methylacrylate, 6-(3-thienyl)methoxy-hexylacrylate and 11-(3-thienyl)methoxy-undecylacrylate were synthesized and electropolymerized. Electrochemical polymerisation by a potential step technique leads to the formation of an electroactive film on a Pt electrode in each case. The polymerization involves evidently only the thiophene ring, as no sign of polyacrylate formation could be detected. The oxidation of each polymer was studied by in situ external reflectance FTIR spectroscopy, which showed several bands assigned to (bi)polaron type charge carriers in the region 1500–1000 cm−1. The evolution of the conductivity was studied in situ by the contact electric resistance technique. The conductivity of poly(3-thienyl methacrylate) was found to be higher in aqueous solutions than in acetonitrile. The surface of poly((3-thienyl) methacrylate) was found to have a granular structure observed for many polythiophenes, as studied by atomic force microscopy (AFM).

Combination of Different Electrochemical Techniques to Characterize the Anodic Behaviour of Chromium

A literature survey on the active dissolution and passive state of pure chromium in acidic solutions revealed that there is considerable discrepancy concerning the properties of the anodic passive film on Cr. The conclusions concerning especially the type of conductivity of the anodic film at different potentials were contradictory. This work was undertaken to clarify the anodic behaviour of Cr using a combination of several experimental techniques, including in situ dc resistance measurements with the contact electric resistance (CER) technique. Rotating ring disk electrode measurements in the active dissolution region showed that release of soluble Cr species proceeds in solutions with a pH of 5, in contradiction with earlier reports which had indicated that active dissolution occurs only at pH 0.7 V, i.e. at potentials approaching the transpassive region. Photocurrent measurements pointed to an almost opposite behaviour as a function of potential, and the change in the sign of the photocurrent was dependent on the initial oxidation potential. Measurements performed using the CER technique indicated that irreversible changes in the film properties take place at high potentials in the passive region. This lead us to suggest that different layers of the film determine the photoresponse and the capacitive behaviour of the electrode.

Contact Electric Resistance (CER) Technique for In-Situ Characterisation of Surface Films

In this paper a new in situ contact electric resistance (CER) technique for the measurement of electric resistance of surface films is described in detail. The applicability of this technique to characterise electrochemical phenomena is evidenced. Also the complementary nature of the CER technique to other electrochemical techniques is shown. The CER measurement enables monitoring of e.g. adsorption, oxide growth and reduction processes. It can also be applied at negative potentials where hydrogen evolution occurs and in electrolytes which contain a redox-couple having a significant exchange current density. The application areas of the CER technique include e.g. investigation of the role of adsorption in electrocatalysis, characterisation of conducting polymers, optimisation of electroplating processes, investigation of the effectiveness of inhibitors and monitoring of the kinetics of oxide growth in high temperature water. Correlation of CER results with practical corrosion phenomena such as weight gain and stress corrosion cracking susceptibility have been established. In this paper CER results on AISI 316 stainless steel in a borate buffer solution at 200°C are compared with a current-voltage curve and capacitance measurements in the same environment. As another example the electric resistance of the surface film on nickel and Inconel 600 are shown as a function of time in a high temperature (320°C) aqueous environment with varying dissolved hydrogen content.

The Mechanism of the Transpassive Dissolution of Chromium in Acidic Sulfate Solutions

The transpassivity of chromium in 1 M sulfate solutions (pH 0 and 5) was studied by steady‐state polarization, rotating ring‐disk electrode voltammetry, and impedance spectroscopy in combination with the contact electric resistance technique. Ring‐disk electrode measurements in the transpassive region indicated the dissolution of Cr mainly as Cr(VI) and partly as Cr(III). The conductivity of the anodic film strongly increased in the transpassive potential range, probably due to the formation of Cr(VI) species. A kinetic model for the transpassive process was advanced to explain the observed experimental features. It comprises two dissolution paths of Cr as Cr(VI) and one as Cr(III). The formation of a Cr(IV) intermediate and a continuous change in the valence state of Cr at the film/solution interface are considered. Kinetic equations for both steady state and impedance response were derived and compared to experimental results to determine the reaction rate constants.

Characterization of a poly(3-methyl thiophene) film by an in-situ dc resistance measurement technique and in-situ FTIR spectroelectrochemistry

Abstract The newly developed in-situ dc resistance measurement technique called the contact electric resistance (CER) technique as well as in-situ external reflectance FTIR spectroscopy were applied for studying the conductivity and redox behaviour of poly(3-methyl thiophene) (PMeT) in acetonitrile and aqueous solutions. The maximum conductivity as well as the effect of the thickness of the film on the evolution of the conductivity were observed to depend on whether the PMeT films are electrochemically synthesized and studied in the presence of Bu 4 NClO 4 or Bu 4 NPF 6 in acetonitrile. The maximum conductivity was 10 −2 S cm −1 for the former and 10 −1 S cm −1 for the latter system. The deactivation of PMeT began in acetonitrile solutions at about 1.4 V. In accordance with this the in-situ IR spectra showed that the number of (bi)polarons started to decrease. The aqueous solutions were observed to decrease the maximum conductivity by 2–3 decades depending on the anion and to cause a much slower resistance response to an applied potential when compared with the results in acetonitrile. The FTIR measurements proved that in aqueous solution (bi)polarons similar to those observed in acetonitrile are formed in the film during anodic oxidation. The CER technique was found to be well suited for measuring the in-situ resistance of conducting polymers.

Application of in situ UV-vis spectroscopy and an in situ dc resistance measurement technique to the study of a poly(thiophene-3-methanol) film

The evolution of the UV-vis optical absorption of poly(thiophene-3-methanol) (PTM) has been followed as a function of applied potential in Bu4NClO4 and Bu4NPF6 in acetonitrile. The UV-vis spectra at 310 to 820 nm show similar features to many polythiophenes of higher degrees of conjugation. The behaviour of the absorbance maxima corresponding to interband transition and (bi)polaron bands have also been registered during linear sweeps and potential step measurements in order to characterize the response of the PTM to applied potential, and the recovery of the polymer film during reduction. The evolution of the absorbance shows differences in the behaviour of the films synthesized and studied in the presence of the two anions. These correlate with our previous in situ FTIR measurements. The study of a conductive polymer by the newly developed contact electric resistance (CER) technique is reported for the first time. This in situ dc resistance measurement technique has been applied for determining the behaviour of the resistance of PTM during linear sweep measurements as well as for estimation of the maximum conductivity of the PTM, which was about 10−4 S/cm. The results obtained by UV-vis spectroscopy and CER technique are compared.