0000000000049708
AUTHOR
Jerónimo Agrisuelas
The role of lithium, perchlorate and water during electrochemical processes in poly(3,4-ethylenedioxythiophene) films in LiClO4 aqueous solutions
Abstract Thin films of poly(3,4-ethylendioxythiophene) (PEDOT) were electrochemically deposited on gold electrodes in aqueous media. The role of perchlorate, lithium, and water during the charge/discharge of PEDOT films was investigated by cyclic voltammetry together with EQCM, vis − NIR spectroscopy, and acoustic impedance, also by means of ac-electrogravimetry in a 0.1 M LiCl O 4 aqueous solutions. In this way, it has been possible to correlate the electrical, mass, color and electromechanical properties changes during the electrochemical reactions of this polymer. Both, hydrated lithium cations and perchlorate anions can act as counterions during the electrochemical reactions, however, a…
An approach to the electrochemical activity of poly-(phenothiazines) by complementary electrochemical impedance spectroscopy and Vis–NIR spectroscopy
Abstract The electroactivity of two poly-(phenothiazine), the poly-(Azure A) and the poly-(Methylene Blue), has been compared in this work. The spectroelectrochemical results prove clearly the existence of two electroactive moieties integrated in the polymeric lattice, the phenothiazine ring (detected by changes of absorbance at 590 and 685 nm) and the newly formed covalent links which fixes the monomers in the backbone of the polymer (detected by changes of absorbance at 460 and 875 nm). Differences in the electrochemical response of both polymers are due to differences in this covalent link. However in both polymers, the charge balance during electrochemical reactions takes place by the e…
Electronic Perspective on the Electrochemistry of Prussian Blue Films
The derivative of the voltabsommetric scans, together with previous nano-electrogravimetric and X-ray diffraction results, allow different electrochemical processes to be distinguished during the Prussian blue (PB) voltammetric scan. Potassium, proton, and hydrated proton counterions involved in PB electrochemistry are related here to the electrochemical reactions of specific Fe sites. Potassium counterions show two different sites for their insertion: one located in the crystalline framework and another in ferrocyanide vacancies. From the monitoring of electroactive Fe sites, the covalent-exchange model is suggested as one of the first approaches to explain the origin of the PB magnetic or…
Effects of anions size on the redox behavior of poly(o-toluidine) in acid solutions. An in situ vis-NIR cyclic spectroelectrogravimetry study
International audience; The combination of different in situ techniques allows a more complete analysis combining several physical and chemical processes of polymer-modified electrodes to be obtained. The hybrid technique -cyclic electrogravimetry coupled with visible-near infrared spectroscopy- was used to study in depth the electrochemistry of poly(o-toluidine) (POT) thin films. In this work, a POT modified electrode was polarized between the pernigraniline and leucoemeraldine forms in 0.5 M HNO3 and 0.5 M HClO4 solutions. The electrochromic properties of View the MathML sourcePOT-CIO4− and View the MathML sourcePOT-NO3− were localized in the experimental potential range associated to the…
Interfacial role of Cesium in Prussian Blue Films
The simultaneous measurement of current, mass, motional resistance and absorbance magnitudes allows the electrochemical cation insertion process to be explained during successive voltammograms around the Prussian Blue ⇄ Everitt's Salt system in CsCl aqueous acid solutions. Two different ways for the entrance of cesium to the porous structure of Prussian Blue have been observed. Firstly, Cs+ is spontaneously absorbed as CsCl into the interstitial cluster of water of the channels formed by the Fe(II)low spinCNFe(III)high spin structural units of the crystal. This chemical absorption involves a spontaneous substitution of inner water molecules of the interstitial water cluster. Finally, Cs+ …
Alternating current electrogravimetry of copper electrodissolution in a sulfuric acid solution
Abstract Copper electrodissolution processes have been studied by means of electrochemical impedance spectroscopy and ac-electrogravimetry (mass impedance). During ac-electrogravimetry acquisition, mass decreases or increases due to the electrodissolution or the electrodeposition of copper, respectively. As a result, this continuous mass drift makes impossible obtaining a true ac-electrogravimetry response unless a numerical correction was applied. It has been compared the electrochemical behavior of copper layers previously treated and other freshly deposited on the gold electrode of the quartz crystal microbalance. The simultaneous analysis of both impedance functions has allowed separati…
Innovative Combination of Three Alternating Current Relaxation Techniques: Electrical Charge, Mass, and Color Impedance Spectroscopy. Part I: The Tool
Technical details concerning the simultaneous acquisition of three impedance functions (electrochemical impedance spectroscopy, alternating current electrogravimetry or mass impedance, and alternating current colorimetry or color impedance) are presented. The analysis of each type of impedance function gives interesting information about the species participating during the electrochemical processes. Furthermore, obtaining three impedance functions in situ allows the crossed impedance functions to be calculated. These functions are especially useful in detecting delays between the color, mass, and electrical charge response of the system to the same perturbation, and it allows species parti…
An Electronic Perspective On The Electrochemical Changeover In Prussian Blue-Like Materials
Derivative voltabsometric scans together with previous electrogravimetric results allow to distinguish between the different electrochemical processes due to Fe-sites located into the Prussian Blue crystalline framework and other located next to ferrocyanide vacancies. The potassium, proton and hydrated proton counterions involved in these reactions are correlated to changes in near-UV/VIS/near-IR spectra. Potassium counter-ions show two different sites for insertion: one located into the crystalline framework and the other into ferrocyanide vacancies. From the monitoring of electroactive Fe-sites, it is possible to assume that the reduction of all Fe-sites located next to ferrocyanide vaca…
Quantification of electrochromic kinetics by analysis of RGB digital video images
A new, rapid, and practical procedure to obtain quantitative kinetic information of electrochromic materials is proposed. When the transition between two colors on a colored electrode surface is monitorized by digital video, the analysis of pixel color intensity (I) in sequential RGB digital images allows us to precise the half-life time (t1/2) of the color change since a maximum value of the standard deviation of the pixel intensity (σ(I)) is reached. We simulated and analyzed the evolution of standard deviation during an electrochromic transition in different circumstances (kinetic and diffusion control). As an example of application, electrochromic transitions of a thin film model, the P…
Usefulness of F(dm/dQ) Function for Elucidating the Ions Role in PB Films
The conversion process of "insoluble" prussian blue (PB) films into the "soluble" structure has been followed by the simultaneous measurement of current and mass changes during voltammetric experiments and focusing on the possibilities of the use of the instantaneous mass/electrical charge ratio at each potential. A similar procedure was used for the analysis of the mechanism of reduction of PB films to the Everitt's salt form and to follow the partial dissolution of iron species during the oxidation to the prussian yellow form. The possibility of covering PB films by Nafion membranes, which make difficult the transport of anions through it, allows us to discern the role of anions in the so…
Identification of electroactive sites in Prussian Yellow films
Abstract Prussian Blue films were electrogenerated on the surface of the transparent ITO electrodes. The electrochemical oxidation to the Prussian Yellow form was investigated by means of in situ voltammetry and vis–NIR spectroscopic techniques. Changes of the whole spectra between 400 and 950 nm were analyzed and three characteristic wavelengths were selected to in situ follow the electrochemical changes of the films. Voltammetric peaks and absorbance derivative curves at these three wavelengths were deconvoluted and were interpreted such as the overlapping of different electrochemical processes. The correlation between these overlapped processes has allowed proposing three different elect…
Ionic and Free Solvent Motion in Poly(azure A) Studied by ac-Electrogravimetry
International audience; This work is focused on the mechanistic aspects of the redox behavior of poly(azure A) taking advantage of the controlled modulation of their oxidation states by ac-electrogravimetry. The originality of this technique is its ability to discriminate between cation and anion involved in the charge compensation process and the accompanying free solvent transfer, directly or indirectly. Two processes were proposed where the faster ionic exchange is considered to be the participation of the anion species acting as counterions whereas the slower one is related to the proton transfer. The proton is implied as reactants for the two electroactive sites identified in the polym…
Viscoelastic potential-induced changes in acoustically thin films explored by quartz crystal microbalance with motional resistance monitoring
Abstract Viscoelastic properties of intrinsically conducting polymers depend on different factors, among them polymer structure, ionic and solvent population and film thickness. During a voltammetric cycle, electrochemical reactions involve changes of these factors. Consequently, the viscoelastic properties are expected to be changed. Electrochemical quartz crystal microbalance with motional resistance monitoring were employed to calculate the instantaneous resonant frequency/motional resistance ratio (d f r / d R m ) during the electrochemical processes of acoustically thin films of poly(o-toluidine). d f r / d R m is defined as the energy dissipation factor and shows values around ∼10 Hz …
Effects of anion size on the electrochemical behavior of H2SO4-structured poly(o-toluidine) films. An ac-electrogravimetry study in acid solutions
International audience; ac -Electrogravimetry has allowed an easy separation of kinetic information to be evaluated for all the transferred species in three different H2SO4-structured poly(o-toluidine) or POT films, View the MathML sourcePOT-NO3−, View the MathML sourcePOT-ClO4− and POT-Cl− films when they are polarized between the pernigraniline (oxidized) and leucoemeraldine (reduced) forms. It is clear that larger anions slow down the electrochemical transitions of POT films, but the effects of anion transfer on hydrated protons and free solvent transfers are affected. For the same polymeric structure of a POT film, the kinetics of all specie transfers have been evaluated considering the…
Electrochemistry and electrocatalysis of a Pt@poly(neutral red) hybrid nanocomposite
Abstract Platinum nanoparticles have been deposited on a scaffold of electrosynthetized phenazine-type polymer, the poly(neutral red). This work discusses the role of poly(neutral red) in the electrochemistry and electrocatalysis properties of the hybrid nanocomposite. In situ combination of electrochemical quartz crystal microbalance and visible-near infrared spectroscopy (cyclic Vis-NIR spectroelectrogravimetry) and a combination of electrochemical impedance spectroscopy and mass impedance spectroscopy ( ac -electrogravimetry) were employed. Two electrochemical processes have been identified in our experimental conditions. On the one hand, the radical cations (polarons) localized in the i…
Kinetics of Surface Chemical Reactions from a Digital Video
In the last few years, the color analysis of the studied surface has been regarded as a nonexpensive way to obtain not only the spectrochemical data but also the spatiotemporal information of the entire surface. Mean color intensities and standard deviation calculated from the red, green, and blue color histograms of digital images of surfaces have been considered particularly useful for the chemical understanding of surface kinetics. The shape of curves, the maximum of peaks, or the half-peak widths depend on the kinetic constants and on the kinetic order of the surface chemical process. Some strategies used for obtaining the kinetics from RGB color intensities and their standard deviation…
Identification of Processes Associated with Different Iron Sites in the Prussian Blue Structure by in Situ Electrochemical, Gravimetric, and Spectroscopic Techniques in the dc and ac Regimes
The physicochemical properties of Prussian blue films are strongly dependent on the ratio Fe3+/Fe2+ in the structure. This ratio can be modulated by electrochemical techniques such as cyclic voltammetry, and some information about physicochemical properties can be extracted from in situ auxiliary techniques. Prussian blue films have been studied by the use of in situ vis–NIR spectroscopy, quartz crystal microbalance, and electrochemical techniques (cyclic voltammetry and electrochemical impedance spectroscopy). By cyclic voltammetry + absorbance derivative curves + mass derivative curves, it has been possible to identify at least three different processes during the reduction of Prussian bl…
Vis/NIR spectroelectrochemical analysis of poly-(Azure A) on ITO electrode
Electrochromic behavior of poly-(Azure A) on indium–tin oxide electrode is analyzed in an aqueous potassium nitrate solution. The dependence of the absorbance on the applied potential during cyclic voltammograms proves very interesting at two selected characteristic wavelengths: at 925 nm, attributed to an intermediate species and another at 735 nm, attributed to the oxidized form of the polymer. Molar absorptivity coefficients for both species have been calculated from the relationship between current and the derivative of absorbance with respect to time. Voltammograms of formation of the intermediate are simulated from spectroelectrochemical results. Keywords: Poly-(Azure A), Spectroelect…
Electrochromic Performances of Poly(Azure A) Films from Digital Video-Electrochemistry (DVEC)
Poly(Azure A) (PAA) films doped with sodium dodecyl sulfate (SDS) were grown on transparent indium tin oxide (ITO) glass substrates by cyclic voltammetry. The electrochromism of PAA was investigated by digital video-electrochemistry (DVEC). DVEC consists of the acquisition of sequential digital images during the electro-stimulated changes of PAA color. The evolution of red, green, and blue (R, G, B) colors intensity (I) of analyzed pixels provides enough sensitivity to detect changes of some nmol cm−2 of electroactive centers. Besides, the different time evolution of these color intensities can serve to discern among different electroactive centers activated in the polymer. For the first ti…
Evidence of Magnetoresistance in the Prussian Blue Lattice during a Voltammetric Scan
This manuscript reports evidence of magnetoresistance effects in the Prussian Blue lattice during a voltammetric scan at room temperature. Accordingly, the PB is a well-known semiconductor that becomes surprisingly an almost metallic conductor in the presence of an internal magnetic field induced during the voltammetric scan. This offers appealing perspectives for the control of this interesting phenomenon from electrochemical techniques that could be used for the fabrication of the recent phase-change computational memories, which are electronically configurable. Herein, the PB magnetic properties have been monitored in situ by means of resonating magnetic microsensors based on the shift i…
RGB video electrochemistry of copper electrodeposition/electrodissolution in acid media on a ternary graphite:copper:polypropylene composite electrode
Abstract Galvanostatic copper electrodeposition and electrodissolution on graphite:copper:polypropylene composite electrodes in acidic media have been investigated to extend the technological applicability of ternary composites. Both electrochemical processes were monitored by RGB video electrochemistry. The analysis of digital images allowed the color changes on the electrode surface to be investigated. We estimate the growth rate of the copper layer in two different electrode geometries. The relatively high resistance of this composite causes a gradient of the electric resistance along the electrode involving a non-homogeneous electrodeposit growth in CuSO4/H2SO4 aqueous solutions. Copper…
Kinetic and Mechanistic Aspects of a Poly(o-toluidine)-Modified Gold Electrode. 1. Simultaneous Cyclic Spectroelectrochemistry and Electrogravimetry Studies in H2SO4 Solutions
International audience; Electrodeposited poly(o-toluidine) (POT) on gold electrodes was investigated in a 0.5 M H2SO4 aqueous solution using cyclic electrogravimetry with in situ vis-NIR spectroscopy. This coupling of different techniques allows the electrical, color, and mass changes during the electrochemical reactions of these polymers to be correlated. Therefore, this is a powerful tool to obtain valuable information on the physical models of polymer films and their electrochemical properties. The accurate analysis of the results from these techniques showed the contribution of three different redox transitions (leucoemeraldine-polaron transition, polaron-bipolaron transition, and bipol…
A Comparative Study of Poly(Azure A) Film-Modified Disposable Electrodes for Electrocatalytic Oxidation of H₂O₂: Effect of Doping Anion.
In the present paper, poly(azure A) (PAA) films were electrosynthetized in the presence of different doping anions on disposable screen-printed carbon electrodes (SPCEs). The anions used included inorganic monoatomic (chloride and fluoride), inorganic polyatomic (nitrate and sulfate) and organic polyatomic (dodecyl sulfate, DS) species. The coated electrodes thus obtained were characterized by electrochemical techniques and SEM. They showed improved electrocatalytic activities towards hydrogen peroxide oxidation compared to that of a bare SPCE. In particular, the insertion of DS anions inside PAA films provided a special sensitivity to the electrocatalysis of H2O2, which endowed these elect…
An electromechanical perspective on the metal/solution interfacial region during the metallic zinc electrodeposition
The difficulty of studying the metal/solution interfacial region makes the use of non-conventional measurement techniques indispensable. In this way, a careful in situ study by means of acoustic impedance techniques coupled with nano-electrogravimetric techniques allowed this interface to be monitored during the metallic zinc electrodeposition process. This paper proves the formation of a viscoelastic layer consisting of ultra-hydrated Zn(II)/Zn(I) salts as a key step in the metallic zinc electrodeposition mechanism in sulfate aqueous solutions. Surprisingly, this layer is located in the metal/solution interfacial region and not on the reaction substrate. The chloride ions effect on the met…
Insights on the Mechanism of Insoluble-to-Soluble Prussian Blue Transformation
The electrochemical transformation of the soluble form of Prussian blue (PB) material from the insoluble form was monitored using electrochemical, gravimetric, acoustic, and spectroscopic techniques simultaneously. The described combination of in situ techniques represents an innovative tool for measurement in electrochemistry, which provides complementary information on the electrochemical systems. The insoluble-to-soluble PB transformation process takes place during the successive voltammetric cycles between the mixed valence form (PB) and the fully reduced form [Everitt's salt (ES)]. One of the processes that takes place is the exit of free Fe(CN) 4- 6 ions occluded in the vacancies of t…
Electrochemical performance of activated screen printed carbon electrodes for hydrogen peroxide and phenol derivatives sensing
Screen-printed carbon electrodes (SPCEs) are widely used for the electroanalysis of a plethora of organic and inorganic compounds. These devices offer unique properties to address electroanalytical chemistry challenges and can successfully compete in numerous aspects with conventional carbon-based electrodes. However, heterogeneous kinetics on SPCEs surfaces is comparatively sluggish, which is why the electrochemical activation of inks is sometimes required to improve electron transfer rates and to enhance sensing performance. In this work, SPCEs were subjected to different electrochemical activation methods and the response to H2O2 electroanalysis was used as a testing probe. Changes in to…
About the Insoluble to the Soluble Prussian Blue Transformation
Figure 1 shows firstly an increase of the motional resistance during the first scan of the transformation process, denoting an increase of the viscoelasticity of this structure. Soluble Prussian Blue have a localized changeover in the properties of these films just when Fe(III) fraction reaches the characteristic value. Secondly, this Figure shows an increase of motional resistance in zone 2 of the voltammetric scan, proving more evident for the last cycles than for the first ones. The increase of the motional resistance in zone 2 records an increase of the PB coercive field which at the same time, is due to an interesting changeover in the PB physiochemical properties localized at this pot…
Polymer dynamics in thin p-type conducting films investigated by ac-electrogravimetry. Kinetics aspects on anion exclusion, free solvent transfer, and conformational changes in poly(o-toluidine)
A new transfer model is proposed to explain ac-electrogravimetry response of p-doped films. This model takes into account the exclusion effect occurring as a result of the anion transfer. The insertion/expulsion of anions inside a film involves simultaneously the expulsion/insertion of free solvent molecules. The number of solvent molecules excluded depends on the volume of anion transferred. Solvent transfer stimulated by the conformational changes of films constitutes the remaining electrogravimetric response when the exclusion process cannot explain by itself this response. Consequently, the kinetics of this free solvent transfer can be directly related to the kinetics of conformational …
Design and Characterization of Effective Ag, Pt and AgPt Nanoparticles to H2O2 Electrosensing from Scrapped Printed Electrodes
The use of disposable screen-printed electrodes (SPEs) has extraordinarily grown in the last years. In this paper, conductive inks from scrapped SPEs were removed by acid leaching, providing high value feedstocks suitable for the electrochemical deposition of Ag, Pt and Ag core-Pt shell-like bimetallic (AgPt) nanoparticles, onto screen-printed carbon electrodes (ML@SPCEs, M = Ag, Pt or AgPt, L = metal nanoparticles from leaching solutions). ML@SPCEs were characterized by scanning electron microscopy, cyclic voltammetry and electrochemical impedance spectroscopy. The results were compared to those obtained when metal nanoparticles were synthesised using standard solutions of metal salts (MS@…
Evaluation of the electrochemical anion recognition ofNO3−-imprinted poly(Azure A) inNO3−/Cl−mixed solutions by ac-electrogravimetry
Abstract During the reversible electrochemical reactions of the intrinsically conducting polymer (ICP) films, ions are inserted in them to balance the inner charge site of the polymer. For this reason, doped ICP films with anions or cations can be good candidates for the electrochemical removal of contaminant ions from wastewater. In this work, a polymer of a phenothiazine derivative (poly(Azure A or PAA)) was electrosynthesized by cyclic voltammetry in aqueous solutions using nitrate ions as a structural template. After that, PAA film was repeatedly cycled in identical conditions in a monomer-free solution. The electrochemical anion recognition of the nitrate-imprinted poly(Azure A) ( N O …
Kinetic and Mechanistic Aspects of a Poly(o-Toluidine)-Modified Gold Electrode. 2. Alternating Current Electrogravimetry Study in H2SO4 Solutions
International audience; Electrodeposited poly(o-toluidine) (POT) on gold electrodes was investigated in 0.5 M H2SO4 aqueous solutions using alternating current electrogravimetry (simultaneous electrochemical impedance and mass transfer functions). The kinetic aspects of the three different redox transitions proposed for this polymer (leucoemeraldine-polaron transition, polaron-bipolaron transition, and bipolaron-pernigraniline transition) and the species involved, cation (hydrated proton), anion (bisulfate ion), and free solvent (water), are studied by means of the mass impedance technique. An ionic transfer model is proposed with coherent results where anion transfer is the fastest process…
Innovative Combination of Three Alternating Current Relaxation Techniques: Electrical Charge, Mass, and Color Impedance Spectroscopy. Part II: Prussian Blue ⇆ Everitt’s Salt Process
The simultaneous recording of three impedance functions (electrochemical impedance, color, and mass impedance) allows the role of different species to be distinguished easily during electrochemical processes in conducting and electrochromic films. Herein, this technique has been applied to the study of the Prussian blue films at several potentials between the blue form (Prussian blue) and the colorless form (Everitt’s salt). At these potentials, these electrochemical reactions take place by means of exchange of different ions. Thus, the exchange of potassium cations is related to the changes of absorbance at 690 nm, whereas the exchange of protons does not introduce color changes at this wa…
Usefulness of the Instantaneous Mass-charge Ratio for Elucidating the Ions Role in the Stabilization and Dissolution Processes in Prussian Blue Films
The conversion process of 'insoluble' Prussian Blue films into the 'soluble' structure has been followed by the simultaneous measurement of current and mass changes during voltammetric experiments and focusing on the possibilities of the use of the instantaneous mass/electrical charge ratio at each potential. A similar procedure was used for the analysis of the mechanism of reduction of Prussian Blue films to the Everitt's Salt form and to follow the partial dissolution of iron species during the oxidation to the Pussian Yellow form. The possibility of covering Prussian Blue films by Nafion membranes which make difficult the transport of anions through it allows to discern the role of anion…
Oscillatory Changes of the Heterogeneous Reactive Layer Detected with the Motional Resistance during the Galvanostatic Deposition of Copper in Sulfuric Solution.
Metallic copper was galvanostatically deposited on quartz|gold resonant electrodes by applying a constant current in a 0.5 M CuSO4/0.1 M H2SO4 aqueous solution. Galvanostatic copper deposition is one of the best methodologies to calibrate the electrochemical quartz crystal microbalances (EQCM), a gravimetric sensor to evaluate changes in mass during the electrochemical reactions through the Sauerbrey equation. The simultaneous measurement of mass, current density, and motional resistance by an EQCM with motional resistance monitoring allows us to characterize the processes occurring on the electrode surface and at the interfacial regions with unprecedented detail. During the galvanostatic c…
Spatiotemporal colorimetry to reveal electrochemical kinetics of poly(o-toluidine) films along ITO surface
Abstract Sheet resistance of transparent conducting electrodes can affect dramatically the electrochromic response of surface confined active species in any electrochromic device. The generated gradient of effective potential on the electrode surface has a direct impact on the electrochemical kinetics of these species. In this work, the electrochromic poly (o-toluidine) (POT) film, a derivative polyaniline, was deposited along a narrow, long transparent indium tin oxide (ITO) supporting electrode with a sheet resistivity of 30 Ω cm−1. This configuration was used as a model to simulate a surface electrical conduction from the external metallic contact to the opposite extreme of ITO with an i…
Electrochemically induced free solvent transfer in thin poly(3,4-ethylenedioxythiophene) films
International audience; In dynamic intrinsically conducting films, counterions transfer and conformational movements stimulated by the electrochemical reactions affect the free water molecules transfer. Poly(3,4-ethylenedioxythiophene) or PEDOT is included in this category. Here, p-doping of PEDOT immersed in LiClO4 aqueous solution was explored by ac-electrogravimetry. Electrochemical impedance spectroscopy combined with mass impedance spectroscopy proves useful for species identification and kinetics. For PEDOT, new equations have been developed to analyze the ac -electrogravimetry response. Quantitatively, faster free water transfer and slower coupled View the MathML sourceClO4−/free wat…
Digital video-electrochemistry (DVEC) to assess electrochromic materials in the frequency domain: RGB colorimetry impedance spectroscopy
Abstract This work is the first one allowing the characterization of electrochromic devices simultaneously at various parts on their surface and different rates of color change. We describe a new proficient and affordable methodology for reporting electrochromic parameters such as coloration efficiency, optical contrast, and switching time based on the use of digital video-electrochemistry (DVEC) in the ac regime, namely RGB colorimetry impedance spectroscopy. Simultaneously with the electrochemical impedance spectroscopy, the RGB color changes of an electrochromic electrode were recorded by a CCD digital camera at 120 digital images per second. In such conditions, RGB electrochromic change…
Highly activated screen-printed carbon electrodes by electrochemical treatment with hydrogen peroxide
An easy effective method for the activation of commercial screen-printed carbon electrodes (SPCEs) using H2O2 is presented to enhance sensing performances of carbon ink. Electrochemical activation consists of 25 repetitive voltammetric cycles at 10 mV s−1 using 10 mM H2O2 in phosphate buffer (pH 7). This treatment allowed us to reach a sensitivity of 0.24 ± 0.01 μA μM−1 cm−2 for the electroanalysis of H2O2, which is 140-fold higher than that of untreated SPCEs and 6-fold more than screen-printed platinum electrodes (SPPtEs). Electrode surface properties were characterized by SEM, EIS and XPS. The results revealed atomic level changes at the electrode surface, with the introduction of new ca…
Motional Resistance Evaluation of the Quartz Crystal Microbalance to Study the Formation of a Passive Layer in the Interfacial Region of a Copper|Diluted Sulfuric Solution
A hyphenated technique based on vis–NIR spectroscopy and electrochemical quartz crystal microbalance with motional resistance monitoring was employed to investigate the dissolution of copper in acid media. Changes in motional resistance, current, mass, and absorbance during copper dissolution allow the evolution of the interfacial region of copper|diluted sulfuric solution to be understood. In particular, motional resistance is presented in this work as a useful tool to observe the evolution of the passive layer at the interface. During the forced copper electrodissolution in sulfuric solution, SO4(2–) favors the formation of soluble [Cu(H2O)6]2+. On the contrary, OH– involves the formation…
Use of RGB digital video analysis to study electrochemical processes involving color changes
Color changes on an electrode surface during the course of electrochemical processes were monitored by in situ digital video recording. The evolution of standard red, green and blue (sRGB) intensity channels extracted from digital images showed a close relationship with the electrochemical processes taking place. In particular, the derivative of the sRGB mean intensity with respect to time (dI−/dt) gave useful insights into the electrochemical mechanism. The standard deviation (std) of the sRGB intensity provided information about the color homogeneity of the studied region on the electrode surface. We selected poly(o-toluidine) electrochromism on a transparent electrode and anodic copper d…
Correction of mass drift in ac-electrogravimetry of Prussian Yellow films. Mass impedance under apparently non-steady state condition
Abstract Mass impedance spectroscopy allows the modulated response of mass of a resonant electrode to be followed at different perturbation frequencies during electrochemical impedance spectroscopy experiments (ac-electrogravimetry). However, some difficulties appear if a continuous mass change takes place foreign to the mass changes due to the ac-modulated electrochemical processes. A new strategy is proposed to solve this limitation. Both, mass and potential analog signals are recorded frequency by frequency from 100 Hz up to the lowest frequencies. Then, a numerical procedure based on a multiparametric fitting of raw data against the elapsed time allows the contribution due to the modula…