Interaction of BSA protein with copper evaluated by electrochemical impedance spectroscopy and quartz crystal microbalance

The interaction of bovine serum albumin (BSA) protein with copper in phosphate buffer solution has been studied by a combination of electrochemical impedance spectroscopy (EIS) close to the open circuit potential, with simultaneous monitoring by the electrochemical quartz crystal microbalance (EQCM), in order to throw light on BSA adsorption. Copper films were electroplated onto gold quartz crystals and mounted in the EQCM. Experiments were conducted in the presence and absence of dissolved oxygen and of BSA and the results show the influence of O₂ on the protein/metal interaction and also show specific interactions between BSA and copper. The good reproducibility obtained in these experiments suggests future application to other systems and which should lead to a better understanding of the use of such types of protein as corrosion inhibitors.     

Study of the adsorption process of bovine serum albumin on passivated surfaces of CoCrMo biomedical alloy

Adsorption of bovine serum albumin (BSA) on CoCrMo surface was studied by electrochemical techniques in order to determine the mechanism of protein adsorption at different surface conditions (which are reached by considering different passivation times) in phosphate buffered solution (PBS). At open circuit potential (OCP), adsorption kinetic was influenced by surface passivation when passivation time was lower than 1 h, whereas, at higher passivation times, no apparent modification in the kinetic mechanisms of adsorption was observed. On the other hand, at a passive applied potential, the BSA addition decreased the passivation kinetics of the process at all the passivation times.     

Effect of physico-chemical properties of simulated body fluids on the electrochemical behaviour of CoCrMo alloy

The behaviour of the CoCrMo alloy was studied under different experimental conditions of solution pH, chemical composition (phosphate buffer solution with and without addition of bovine serum albumin) and aeration (presence and absence of oxygen in the solution). With this purpose, electrochemical techniques such as open circuit measurements (OCP), potentiodynamic curves, potentiostatic tests and electrochemical impedance spectroscopy (EIS) were employed.The results show that the general corrosion behaviour of CoCrMo alloy depends on the solution pH. Thus, the effect of BSA and the aeration conditions are related to the solution pH. At pH 3 no influence of BSA was observed in deoxygenated solutions which imply that BSA acts over the oxygen reduction reaction in acidic media. On the contrary, a noticeable influence of BSA addition was observed at pH 7.4 (independently on the gas content). Finally, at pH 10, the influence of BSA was only significant in oxygenated solution. It was found that H₂PO₄⁻ favours the formation of passivating compounds which improves the resistance of the CoCrMo alloy to passive dissolution. Therefore, when the concentration of the H₂PO₄⁻ increases (when pH decreases) the polarization resistance of the alloy also increases. On the other hand, the oxygen (aerated conditions) decreases the polarization resistance of the alloy in all the studied conditions.     

Study of passivation of Al and Al-Sn alloys in borate buffer solutions using electrochemical impedance spectroscopy

Properties of thin oxide films on Al and Al-Sn alloys (with Sn content of 0.02, 0.09, 0.20 and 0.40 wt.%) formed either naturally or anodically in borate buffer solutions were investigated by means of electrochemical impedance spectroscopy. Equivalent circuits have been proposed that completely illustrate the Al(Al-Sn alloy)/oxide film/electrolyte systems examined, and properties of oxide films were determined. The stability (thickness and resistance) of oxide films has been found to increase with increased Sn content in the alloy, with increased passivation potential, and with longer time of anodising. The increase in temperature of anodising significantly reduces impedance in systems observed.     

Characterization by electrochemical impedance spectroscopy of magnetite nanoparticles supported on carbon paste electrode

Magnetite nanoparticles were supported on carbon paste electrode and characterized by low scan rate voltammetry and electrochemical impedance spectroscopy (EIS) to obtain mechanistic information related to its oxidation and reduction in acid media.The voltammograms showed only one reduction and one oxidation peak for the supported magnetite, which were attributed to formation of ferrous ion and ferric oxide, respectively. Both peaks are fairly wide, indicating complex mechanisms.Using EIS, a mechanism showing up to three time constants, capacitive all of them, was evidenced, both in anodic and cathodic domain. These were attributed to charge transfer at the highest frequencies, adsorption of generated species at intermediate frequencies, and proton adsorption at low frequencies. Discussion about the nature of the adsorbed species and the concerned mechanism for each domain is developed.     

Electrochemical behaviour of PANi/polyurethane antifouling coating in salt water studied by electrochemical impedance spectroscopy

Electrochemical behaviour of polyaniline–polyurethane (PANi–PU) antifouling coating in 3.5 wt% NaCl is studied by electrochemical impedance spectroscopy (EIS). A thick coating (∼1 mm) of 10, 15 and 20% PANi in marine grade PU, is cast over corrosion resistant aluminium alloy 2024 and its impedance characteristics are measured by EIS and compared with neat PU. On addition of 10% PANi, the impedance of the coating drastically comes down from 10⁹ to 10⁷ Ω. 20% is the maximum processable amount of PANi for the selected PU system. The coatings are exposed to 3.5 wt% NaCl and its impedance characteristics are monitored as a function of time. Changes in the impedance characteristics of the systems were found to occur as a function of the exposure time in all cases, though their evolution with time showed marked differences with PANi content. Water sorption and break down frequency are derived from the experimental results and analysed.     

Effect of thermal treatment and applied potential on the electrochemical behaviour of CoCrMo biomedical alloy

CoCrMo alloy are one of the most important biomaterials for orthopaedic applications, widely used in total joint replacements. The thermal treatments applied to CoCrMo alloys modifies the microstructure of the alloy and change the electrochemical and mechanical properties of the biomaterial. Thus, the aim of this research is to characterize the electrochemical behaviour of CoCrMo alloy depending on the thermal treatment at different applied potentials (according to the cathodic, anodic and transpassive electrochemical domains of the alloy).Metallographic study and electrochemical techniques such as potentiodynamic curves, potentiostatic tests at different potentials (selected according to the electrochemical regions of the potentiodynamic curves) and electrochemical impedance spectroscopy (EIS) are employed to characterize the CoCrMo alloy after three different thermal treatments in simulated body fluid (bovine serum solution).The same corrosion mechanisms were observed for the CoCrMo alloy under the three thermal treatments at different applied potentials, however, the rate of the corrosion reactions which take place on the metallic surfaces depends on those thermal treatments and it is related to the amount of carbide inclusions. At passive potentials the study reveals that the properties of the passive layer depend on the microstructure of the alloy. EIS results show that the resistance of the passive layer in bovine serum solution increased with the carbides solubilisation.     

Influence of ultrasound irradiation on the adsorption of bovine serum albumin on copper

The effect of irradiation by power ultrasound on the adsorption of proteins on copper has been investigated, using bovine serum albumin (BSA) as a model protein in pH 7 phosphate buffer solution. Open circuit potential measurements, cyclic voltammetry and electrochemical impedance spectroscopy were used to characterise the copper/solution interface. Electrochemical impedance measurements at potentials close to the open circuit potential showed that pulsed ultrasound irradiation removes the naturally formed copper oxide films in phosphate buffer solution, and that their re-formation can lead to an oxide film with different electrical characteristics. Adsorption of BSA blocks the surface, decreasing or increasing the interfacial resistance, depending on the applied potential and the oxide characteristics, as well as changing the interfacial capacitance. This study augurs well for application of the combination of electrochemical impedance plus ultrasound to other systems. Special issue dedicated to Prof. Tony Wragg.     

Corrosion behaviour of Ti-6Al-7Nb and Ti-6Al-4V ELI alloys in the simulated body fluid solution by electrochemical impedance spectroscopy

The corrosion behaviour of Ti-6Al-7Nb and Ti-6Al-4V ELI (extra low interstitial) was investigated as a function of immersion hours in simulated body fluid (SBF) condition, utilizing potentiodynamic polarisation and electrochemical impedance spectroscopy (EIS) techniques. Polarisation experiments were conducted after 0, 120, 240 and 360 h of immersion in SBF solution. From the polarisation curves, very low current densities were obtained for Ti-6Al-7Nb alloy compared to Ti-6Al-4V ELI, indicating a formation of stable passive layer. Impedance spectra were represented in the form of Bode plots and it was fitted using a non-linear least square (NLLS) fitting procedure, in which it exhibited a two time constant system suggesting the formation of two layers. The surface morphology of the titanium alloys have been characterized by SEM and EDAX measurements.     

An electrochemical impedance spectroscopy and scanning electron microscopy study of the influence of positive plate compression on the electrochemical behaviour of lead-acid batteries

This study has developed an electrochemical impedance spectroscopy (EIS) method for the in situ investigation of the influence of positive plate compression on the electrochemical behaviour of lead-acid batteries during charge/discharge cycling. The EIS data for a fully charged and fully discharged battery are internally consistent with the expected kinetics of a battery in the opposite states of charge, and demonstrate that EIS measurements may be recorded with a high level of reproducibility. Furthermore, this study has necessitated the development of a special cell incorporating horizontally orientated battery plates that can be subjected to elevated pressure through the stacking of lead bricks on top of the cell, as well as a physically robust reference electrode system that can withstand the application of pressure. For this purpose, a platinum-wire pseudo-reference electrode has been developed, and has been shown to exhibit sufficient electrode stability over the period of an EIS recording, enabling the measurement of reproducible and meaningful EIS data. Additionally, the influence of positive plate compression on the behaviour of the lead-acid battery has been investigated by using scanning electron microscopy (SEM). Clearly, the experimental data show that plate compression enhances significantly the kinetics and concomitant performance of the lead-acid battery, and this is related to the enhanced reactivity of the active material, as rationalized by using the agglomeration-of-spheres (AOS) model.     

Mechanism of anodic oxidation of molybdenum in nearly-neutral electrolytes studied by electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy

Anodic oxidation of molybdenum in weakly acidic, nearly neutral and weakly alkaline electrolytes was studied by voltammetric and electrochemical impedance spectroscopic measurements in a wide potential and pH range. Current vs. potential curves were found to exhibit two pseudo-Tafel regions suggesting two parallel pathways of the dissolution process. Electrochemical impedance spectra indicated the presence of at least two reaction intermediates. X-ray photoelectron spectroscopic (XPS) results pointed to the formation of an oxide containing Mo(IV), Mo(V) and Mo(VI), the exact ratio between different valence states depending on potential and pH of the solution. A physico-chemical model of the processes is proposed and a set of kinetic equations for the steady-state current vs. potential curve and the impedance response are derived. The model is found to reproduce quantitatively the current vs. potential curves and impedance spectra at a range of potentials and pH and to agree qualitatively with the XPS results. Subject to further improvement, the model could serve as a starting point for the optimization of the electrochemical fabrication of functional molybdenum oxide coatings.     

First insights into the borohydride oxidation reaction mechanism on gold by electrochemical impedance spectroscopy

Direct borohydride fuel cells (DBFC) exhibit some potential regarding the powering of small portable electronic devices, thanks to their high energy density as well as the facile and safe storage of borohydride salts. However, DBFC are hindered because (i) the borohydride oxidation reaction (BOR) is complex, (ii) its mechanism imperfectly determined yet and (iii) no practical electrocatalyst exhibits both fast BOR kinetics and high faradaic efficiency. In this context, we characterized the BOR mechanism for polycrystalline bulk gold (a classical model BOR electrocatalyst) in the rotating disk electrode (RDE) setup. Modeling cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) data, we propose a simplified reaction pathway, the theoretical behavior of which agrees with the experimental findings. This pathway includes at least a first irreversible electrochemical step (E) for BH₄⁻ oxidation, which competes with the electrochemical adsorption reaction (EAR) of OH⁻ anions at high potentials.     

Review study of electrochemical impedance spectroscopy and equivalent electrical circuits of conducting polymers on carbon surfaces

Electrochemical impedance spectroscopy (EIS) is an experimental method for characterizing electrochemical systems. This method measures the impedance of the concerned electrochemical system over a range of frequencies, and therefore the frequency response of the system is determined, including the energy storage and dissipation properties. The aim of this article is to review articles focusing on electrochemical impedance spectroscopic studies and equivalent electrical circuits of conducting polymers, such as polypyrrole, polycarbazole, polyaniline, polythiophene and their derivatives, on carbon surfaces. First, the conducting polymers are introduced. Second, the electrochemical impedance spectroscopic method is explained. Third, the results of EIS applications using equivalent electrical circuits for conducting polymers taken from the literature are reviewed.     

Characterization of active pigments in damage of organic coatings on steel by means of electrochemical impedance spectroscopy

Active anticorrosive pigments are solid additives for primers which can give further protection for areas with coating damage in addition to their barrier effect. These pigments are expected to prevent corrosion of metal substrate in coating damage by build-up of permanently passive conditions at the metal surface (electrochemical protection) and/or by build-up of solid compounds which plug the coating damage (chemical protection). Electrochemical Impedance Spectroscopy (EIS) was applied to characterize the corrosion protection behaviour of alkyd primers containing different pigments. Impedance spectra were recorded in the frequency range 50 mHz f 50 kHz at the open-circuit potential as a function of the type of pigment and the exposure time in different corrosive media. In general, two different parts can be distinguished in the impedance diagrams. The higher frequency part is related to the insulating properties of the primer and the lower frequency part can be attributed to electrochemical processes taking place within the coating defects. The parameters derived from EIS results show that the low frequency data can be used for characterization of the protective properties of anticorrosive pigments in the presence of defects in organic coatings.     

Analysis of high temperature polymer electrolyte membrane fuel cell electrodes using electrochemical impedance spectroscopy

An electrochemical impedance spectroscopy (EIS) study of electrodes in a phosphoric acid loaded polybenzimidazole (PBI) membrane fuel cell is reported. Using EIS, the effect of electrode parameters such as Pt catalyst wt%, acid doping in PBI and PTFE baesd electrodes and catalyst heat treatment on kinetic and mass transport characteristics is characterised. The influence of cell parameters of current load, temperature and oxidant gas on response is demonstrated and interpreted using an equivalent circuit model. For polarisable electrodes under small to medium steady-state current operation, the model was capable of identifying electrodes with the best kinetic or mass transport behaviour and classifying behaviour in terms of relative performance.     

Chemical reactivity of thermo-hardenable steel weld joints investigated by electrochemical impedance spectroscopy

The chemical reactivity of oxide-free weld joints made of thermo-hardened carbon steel in different electrolytes was investigated by chronopotentiometry, electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM). The objective was to identify the role of different electrolyte constituents on the electrochemical behaviour of the different materials constituting the weld joint, namely the weld material, the heat affected zone (HAZ) and the base carbon steel. Hardness measurements by Vickers and nano-indentation techniques indicated that the weld material is harder than the heat affected zone and the base carbon steel due to a Widmanstätten ferrite-type structure of the weld. Electrochemical measurements were performed on polished cross-sections on these weld joints in four electrolytes containing different additives. The weld joints are active in all tested electrolytes and the composition of the electrolytes dictates the dissolution even though the main chemical reactivity mechanism remains unaffected. A balanced presence of oxidative agent, inhibitor and HF in the electrolyte is necessary to obtain a homogeneous chemical attack on weld joint and Si-rich inclusion removal in weld material, while avoiding excessive attack roughening and/or pitting of the carbon steel.     

Cyclability study of silicon–carbon composite anodes for lithium-ion batteries using electrochemical impedance spectroscopy

The effects of carbonization process and carbon nanofiber/nanotube additives on the cycling stability of silicon–carbon composite anodes were investigated by monitoring the impedance evolution during charge/discharge cycles with electrochemical impedance spectroscopy (EIS). Three types of Si–C anodes were investigated: the first type consisted of Si nanoparticles incorporated into a network of carbon nanofibers (CNFs) and multi-walled carbon nanotubes (MWNTs), with annealed polymer binder. The second type of Si–C anodes was prepared by further heat treatment of the first Si–C anodes to carbonize the polymer binder. The third Si–C anode was as same as the second one except no CNFs and MWNTs being added. Impedance analysis revealed that the carbonization process stabilized the Si–C anode structure and decreased the charge transfer resistance, thus improving the cycling stability. On the other hand, although the MWNTs/CNFs additives could enhance the electronic conductivity of the Si–C anodes, the induced inhomogeneous structure decreased the integrity of the electrode, resulting in a poor long term cycling stability.     

Performance degradation study of a direct methanol fuel cell by electrochemical impedance spectroscopy

A stability test of a direct methanol fuel cell (DMFC) was carried out by keeping at a constant current density of 150 mA cm⁻² for 435 h. After the stability test, maximum power density decreased from 68 mW cm⁻² of the fresh membrane-electrode-assembly (MEA) to 34 mW cm⁻² (50%). Quantitative analysis on the performance decay was carried out by electrochemical impedance spectroscopy (EIS). EIS measurement of the anode electrode showed that the increase in the anode reaction resistance was 0.003 Ω cm². From the EIS measurement results of the single cell, it was found that the increase in the total reaction resistance and IR resistance were 0.02 and 0.05 Ω cm², respectively. Summarizing the EIS measurement results, contribution of each component on the performance degradation was determined as follows: IR resistance (71%) > cathode reaction resistance (24%) > anode reaction resistance (5%). Transmission electron microscopy (TEM) results showed that the average particle size of the Pt catalysts increased by 30% after the stability test, while that of the PtRu catalysts increased by 10%.     

Mechanistic study of the reduction of copper oxides in alkaline solutions by electrochemical impedance spectroscopy

Electrochemical impedance spectroscopy was used to study the mechanism by which copper oxides are reduced in alkaline solutions. For the reductions of CuO and Cu₂O, a capacitive loop and also an inductive loop under certain conditions were observed in the complex plane. The electrochemical impedance for CuO reduction was not greatly dependent on the solution alkalinity and the kind of alkali hydroxide. However, the electrochemical impedance for Cu₂O reduction was considerably affected by the kind and concentration of alkali hydroxide. The diameter of the capacitive loop, i.e., the charge-transfer resistance (R_ct), was increased with increase in solution alkalinity. It should also be noted that R_ct was increased in the order of KOH < NaOH < LiOH. These dependences were consistent with the good separation between the reduction potentials of CuO and Cu₂O in chronopotentiometric and voltammetric measurements with strongly alkaline electrolytes containing Li⁺. The inductive loop observed for the Cu₂O reduction at higher concentrations of KOH (>6 M) and LiOH (>0.2 M) suggested the existence of an intermediate species (probably CuOH). The specific inhibitory effect of Li⁺ ions on the reduction of Cu₂O might be explained by a possible stabilization of CuOH by Li⁺ ions.     

Corrosion of 7A04 aluminum alloy under defected epoxy coating studied by localized electrochemical impedance spectroscopy

In this work, corrosion of the coated 7A04 aluminum alloy with and without ultraviolet (UV) aging was studied by salt spray test, surface observation and localized electrochemical impedance spectroscopy measurements. Results demonstrated that, in the absence of UV aging, the impedance at coating defect increases with time, indicating the formation and accumulation of corrosion product, while the impedance in the adjacent coating decreases, which is attributed to the permeation of corrosive solution from defect and the resultant disbondment of coating. Upon UV aging, the impedance values at both defected area and the coating decrease. The coating contains a significant number of wrinkles. The wrinkles provide micro-pathways where the corrosive species, such as chloride ions, could permeate and reach the aluminum alloy surface for corrosion reaction. Different from the coating without UV aging where corrosion is limited to the defected area, a layer of corrosion product would not be formed to cover the defected area when coating experiences UV aging. Therefore, corrosion occurs continuously with time.