Electrochemical Quartz Crystal Microgravimetry Research Articles

Quantitative in Situ Studies of Ionic Doping of Polypyrrole Employing Rotated Ring−Disk Electrode Voltammetry

Changes in ionic composition (i.e., doping) accompany changes in the redox level of conducting polymers such as polypyrrole. These processes are of paramount interest because they often control the polymer's charge capacity and, more importantly, its rates of oxidation and reduction (i.e., charge and discharge). The most commonly used approaches for studying polymer doping are either ex situ techniques (e.g., elemental analysis, X-ray photoelectron spectroscopy) or nonspecific techniques (e.g., electrochemical quartz crystal microgravimetry). We have developed a paradigm whereby rotated ring−disk electrode (RRDE) voltammetry can be used to quantitatively measure both anion and cation fluxes, in situ, across the conducting polymer−solution interface. This can be accomplished in real time under operational electrochemical conditions. Herein we report studies where we use RRDE voltammetry to investigate the doping behavior of electrochemically grown films of polypyrrole which are in contact with a range of d...

Ion transport in conducting polymers doped with electroactive anions examined by EQCM

Transport properties and stability of ionic species in films of conducting polymers polypyrrole (PPy) and poly(3,4-ethylenedioxythiophene) (PEDT) were examined by electrochemical quartz crystal microgravimetry (EQCM) experiments. The mobility of ions in these polymers were greatly affected by the mode of polymerization with which the polymer film was prepared, as well as by the structure of the ions. When the conducting polymers were doped with macrocyclic anions, phthalocyanine and porphyrin derivatized with sulfonate anionic groups, these anions were not expelled from the PPy or PEDT films by extensive potential cycles. Heteropolytungstate ions have partial mobility in the polymers and were expelled by negative potential sweeps applied to the films that were formed by electropolymerization at a constant potential or constant current. Polymer films formed with alternating potential programs showed drastically diminished permeability to anions. By forming a polymer film with cyclic potential sweeps or square wave potentials, it was possible to examine transport of other ions without complications due to the transport of the initial dopant ions.

Real-time stoichiometry monitoring of electrodeposited chalcogenide films via coulometry and electrochemical quartz-crystal microgravimetry with hydrodynamic control. Ag2+Se case

Abstract Potentiostatic coulometry is used in conjunction with electrochemical quartz-crystal microgravimetry (EQCM) with controlled hydrodynamics to develop a new electroanalytical protocol for in situ composition monitoring of metal chalcogenide thin films. The approach, its application scope and limitations, are illustrated using the example of electrosynthesized AgySe thin films, successfully used previously for developing ion-selective sensors for Ag(I), cyanide and Hg(II). Well-defined flowing electrolyte conditions are achieved by the EQCM/submerged wall jet (SWJ) cell arrangement. The electrolyte flow rate through the nozzle is maintained constant between 5.5 and 250 cm3 min−1. The hydrodynamic control makes it possible to extend the range of the combined EQCM/coulometric approach to greater layer thickness consistent with that of membranes practically used in sensor preparation. The stoichiometric coefficient (y) profile of AgySe is monitored in situ for comparatively thick electrodeposited films (up to 800 nm). Two distinct features are clearly distinguished in the electrochemical formation of non-stoichiometric layers: in the zone adjacent to the substrate (i.e. between 170 and 270 nm) and for greater thickness (up to 800 nm). A mean value for y=2.24±0.06 is determined for the deposited layers, which is in good agreement with the values previously obtained by ex situ energy dispersive X-ray fluorescent microanalysis (EDAX).

Application of Combined Flow Injection–Electrochemical Quartz Crystal Microgravimetry to On-line Electrodeposition and Compositional Analysis of CdSe Thin Films

This paper presents the combined application of flow injection (FI), on-line film deposition, electrochemical stripping, and electrochemical quartz crystal microgravimetry (EQCM) detection to the analysis of compound semiconductor films. The combined FI–EQCM technique and setup were first tested with experiments involving cadmium and silver deposition and the stripping of these metals. They were then used for the analysis of films comprising CdSe, free Cd, and free Se. Selective stripping of these film components with concomitant monitoring of the frequency changes in the EQCM detector facilitated compositional assay of such films. Data are presented for films electrosynthesized over a range of potentials.

Cyclic voltammetry and quartz crystal microgravimetry study of autocatalytic copper(II) reduction by cobalt(II) in ethylenediamine solutions

Abstract Cyclic voltammetry (CV) and electrochemical quartz crystal microgravimetry (EQCM) were used to study the reactions in a new type autocatalytic (electroless) copper deposition system using cobalt(II)–ethylenediamine complex as a reducing agent. The rates of Co(II) oxidation and Cu(II) reduction (partial reactions of the autocatalytic process) as well as those of Cu anodic dissolution and Co(III) reduction were measured both in separate Co(II)–En, Cu(II)–En, and in complete electroless plating systems (pH 6–8) as a function of Cu potential (from −0.4 to 0.05 V vs. SHE), in unstirred solution and under flow-through (wall-jet) conditions. The experimental results show that the autocatalytic process results from a coupling of partial electrochemical reactions of Co(II) oxidation and Cu(II) reduction on the Cu surface, some deviations from partial reactions additivity being explained by ligand (En) concentration changes at the Cu surface in the separate solutions of Co(II) and Cu(II) and in the complete system. The Co(II) oxidation rate increases with the solution pH alongside the increase in CoEn 3 2+ complex concentration in the solution. The partial reaction rate increases remarkably at solution flow conditions, this effect being related both to the transport of reacting Cu(II) and Co(II) species to the electrode, and to the removal of Co(III) species from the Cu surface. Chloride ions possibly act as a bridge between reacting complex species and the Cu electrode.

Electrochemical Quartz Crystal Microgravimetry of Gold in Perchloric and Sulfuric Acid Solutions

Electrochemical Quartz Crystal Microgravimetry of Gold in Perchloric and Sulfuric Acid Solutions

Anodic electrosynthesis of Cu2S and CuInS2 films

Abstract This paper describes the combined use of voltammetry and electrode illumination during the anodic growth of Cu2S and CuInS2 films on copper substrates in sulfide containing KOH medium. The importance of compound stoichiometry in the two systems on the quality of the photoresponse was brought out in these experiments either by varying the positive potential limit (in the Cu–S case) or by In3+ ion addition (in the Cu–In–S case) during film growth. The in situ use of electrochemical quartz crystal microgravimetry and coulometry provided further insights into the mechanistic aspects of film growth in the two systems. Further, Raman spectroscopy evidence is presented in support of a new wurtzite-type structure for the CuInS2 films grown under galvanodynamic conditions.

Electrochemical Behavior and Surface Morphologic Changes of Copper Substrates in the Presence of 2,5‐Dimercapto‐1,3,4‐thiadiazole: In Situ EQCM and Phase Measurement Interferometric Microscopy

Interaction between copper and 2,5‐dimercapto‐1,3,4‐thiadiazole (DMcT) plays a crucial role in the performance of the DMcT‐based polymer composite cathode with a copper current collector. In order to understand this interaction, we employed voltammetry combined with in situ electrochemical quartz crystal microgravimetry (EQCM) and in situ phase measurement interferometric microscope (PMIM), and investigated electrochemical behavior and surface morphologic changes of a copper substrate in nonaqueous solutions without and with DMcT. Voltammetric results show that DMcT inhibits electrodissolution of copper at potentials negative of 1.0 V vs. SSCE. EQCM results suggest that Cu may dissolve chiefly as , which may be stabilized by DMcT by forming a complex, at more positive potentials than 1.0 V. The PMIM images a.nd corresponding data demonstrate that copper dissolution is a nonuniform process and results in a roughness increase of surface in the absence of DMcT, while the presence of DMcT makes the substrate surface remain relatively smooth. Scanning electron micrographs further support the PMIM observations.

EQCM study of iron deposition from FeII/FeIII (EDTA) solutions

Abstract The complex polarisation behaviour of the Fe II (EDTA) and Fe III (EDTA) has been studied on a platinum rotating disc electrode. Iron deposition from both complexes was investigated by electrochemical quartz crystal microgravimetry (EQCM). A mass increase of the electrode, indicating iron deposition, was found at potentials below −1.0 V vs sce . The partial current of iron deposition calculated from the mass growth data was found to be close to the value of a diffusion limiting current density. Iron deposition was also confirmed by EDX analysis.

Electrosynthesis of indium sulfide on sulfur-modified polycrystalline gold electrodes

A new approach for the electrosynthesis of indium sulfide films is described. This approach uses a sulfur-modified gold substrate, and relies on the underpotential deposition of indium on it to form an indium sulfide alloy. Combined cyclic voltammetry and electrochemical quartz crystal microgravimetry scans demonstrate the veracity of this film growth approach. Photoelectrochemical measurements in a polysulfide redox medium show that the In 2 S 3 layers thus grown are photoactive and behave as an n-type semiconductor.

Autocatalytic reduction of Cu(II) to copper by Co(II) studied by electrochemical quartz crystal microgravimetry in a wall jet cell

Electrochemical Quartz Crystal Microgravimetry (EQCM) studies were carried out in a new type of electroless copper plating solution containing Co(II)-ethylenediamine species as a reducing agent for Cu(II)-ethylenediamine complex. The rates of partial reactions of Cu(II) reduction and Co(II) oxidation were studied as a function of the electrode potential (−0.3 V to 0.05 V vs. SHE) under stopped-flow and wall jet conditions. The increase in the rate of partial reactions and the overall process under wall jet conditions suggests diffusion limitations occur in the transport of reacting species (Cu(II) and Co(II)) to the electrode and/or inhibiting products of reaction (Co(III) and ethylenediamine) to the bulk of the solution. Anodic dissolution of copper starts at 0.0 V.

Electropolymerization of pyrrole and 4-(3-Pyrrolyl)butane-sulfonate on Pt substrate: An in situ EQCM study

Polypyrrole and poly(4-(3-Pyrrolyl)butane-sulfonate) films were electrodeposited potentiostatically or by potential cycling on Pt substrates. The growth behavior for electropolymerization of pyrrole and 4-(3-Pyrrolyl)butane-sulfonate was examined via an Electrochemical Quartz Crystal Microgravimetry (EQCM) in situ. The effects of pyrrole and 4-(3-Pyrrolyl)butane-sulfonate concentration on the deposition rate (g/s) and the chronoamperometric responses were investigated. Additionally, the surface morphology of conductive polymer films were observed with atomic force microscopy (AFM). The polypyrrole film deposited electrochemically by potential cycling thickens with the forward and reverse scan. However, the poly(4-(3-Pyrrolyl)butane-sulfonate) film stopped growing during the reverse scan. The deposition rate of poly(4-(3-Pyrrolyl)butane-sulfonate) is linearly dependent on the 4-(3-Pyrrolyl)butane-sulfonate concentration. However, the deposition rate of polypyrrole depends nonlinearly on the pyrrole concentration.

Deposition of Zn–Co by constant and pulsed current

The initial stages of both Zn–Co and Zn electrodeposition were investigated by electrochemical quartz crystal microgravimetry (EQCM). The initial electrode mass growth, determined under both pulse and constant current conditions, was much higher than predicted by Faraday's law. This was explained in terms of the precipitation of scarcely soluble compounds of zinc on an electrode surface. The EQCM data confirm that the hydroxide suppression mechanism explains the anomalous Zn and Co codeposition. A nonuniform adsorption of brightener (benzalaceton) on the profiled surface was concluded on the basis of plating distribution investigations. The additive adsorbs to a greater extent on the surface projections.

Electrochemical Quartz Crystal Microgravimetry Study of Zinc Electrode Behavior in a Neutral Solution by Laser Illumination

Investigations were made by quartz crystal microgravimetry into mass changes of zinc electrodes in a NaCl solution caused by laser illumination (λ = 488 nm). The mass of the dark electrode increases during zinc oxygen corrosion, which is indicative of the accumulation of corrosion products. A sudden increase in quartz oscillation frequency is observed at the beginning of illumination. This is also observed for the gold electrode. The effect of warming the solution is insufficient to cause the observed frequency increase. The rate of light‐enhanced zinc corrosion was estimated as the difference between the frequency data obtained in both aerated and deaerated solutions. The best coincidence between corrosion ratios obtained from mass measurements and from voltammetric data is when ZnO is assumed to be the corrosion product.

Study of Copper Sulfide Film Formation by Voltammetry Combined with Electrochemical Quartz Crystal Microgravimetry/Coulometry and Optical Spectroscopy

This paper describes a study of copper sulfide film formation at copper anodes in sulfide-containing aqueous NaOH media. Voltammetry along with combined electrochemical quartz crystal microgravimetry (EQCM)/coulometry showed the formation of an initial Cu2S (chalcocite) phase. Further oxidation resulted in a nonstoichiometric overlayer culminating in a surface that was CuS (covellite) in composition. The EQCM data also revealed incipient dissolution of the copper surface in the alkaline sulfide media as Cu(I) species. Chemical sulfidization of the copper surface is also shown to be an important film formation pathway. Complementary spectroscopic data were obtained in situ by visible reflectance spectroscopy and laser Raman spectroscopy. Ex situ analysis of the copper sulfide layer composition by X-ray photoelectron spectroscopy is also presented.

Electrochemical deposition and stripping of copper, nickel and copper nickel alloy thin films at a polycrystalline gold surface: a combined voltammetry-coulometry-electrochemical quartz crystal microgravimetry study

Cyclic voltammetry, anodic stripping voltammetry (ASV) and coulometry were used in conjunction with electrochemical quartz crystal microgravimetry (EQCM) and ex situ X-ray photoelectron spectroscopy (XPS) for a study of the electrodeposition and stripping of Cu, Ni and CuNi alloy thin films at a polycrystalline Au surface. A deaerated Watts bath was employed for the electrodeposition of Ni and CuNi thin films, the bath containing Cu 2+ ions (Ni:Cu = 200:1 mole ratio) in the latter case. These films showed the most satisfactory stripping in either 0.1 M HCl or 0.1 M H 2SO 4. Coulometry was used in conjunction with EQCM data for mapping the (potentiostatic) plating efficiency as a function of deposition potential in the Cu and Ni systems. For the CuNi alloy, similar data were acquired by additionally utilizing XPS compositional information and assuming current additivity in the (non-interactive) co deposition of Cu and Ni. Finally, the feasibility of employing the combined ASV-EQCM technique for analysis of CuNi/Ni bilayers is presented.

An electrochemical quartz crystal microbalance study of the deposition of mercury on graphite films

Mercury deposition onto microcrystalline graphite and glassy carbon electrodes from aqueous chloride media was studied by Electrochemical Quartz Crystal Microgravimetry (EQCM) and voltammetric techniques. After deposition of Hg(0) under controlled potential conditions, mercury continued to deposit at open circuit as a calomel film by the reaction, Hg + Hg( II) + 2 Cl − ⇄ Hg 2 Cl 2( aq) . The implications for the preparation of mercury film electrodes and for anodic stripping voltammetry are discussed.

An electrochemical quartz crystal microbalance-based investigation of the properties displayed by electroactive polypyridine films

The properties of poly-2,5-pyridine films, deposited on gold electrodes through a nickel-catalyzed cathodic polymerization route carried out in acetonitrile, were re-investigated by electrochemical quartz crystal microgravimetry in conjunction with cyclic voltammetry and coulometry. Special attention was paid to the ion transport during film reduction and ion binding of the polymer characterized by both electroactive and coordinative properties. The suitability of the electrochemical quartz crystal microbalance for the study of chemically modified electrode surfaces results in reliable information pointing out that polymeric chains in the framework are characterized by the presence of bipyridyl moieties grafted upon one another by coordinating nickel(II) ions whose coordination shell was identified. Moreover, the nickel-doped polymer turned out to undergo two cathodic processes both leading to the polymer changing from the insulating to the conductive state. The former is due to the reduction of coordinated nickel ions and is accompanied by the release of the counter anions originally present, while the uptake of cations from the supporting electrolyte is accompanied with reduction by the injection of electrons into the polymer backbone. The program developed for the simultaneous acquisition of experimental data and their processing is described.

A combined voltammetry and electrochemical quartz crystal microgravimetry study of the reduction of aqueous Se(IV) at gold

The reduction of Se(IV) in 0.5 M Na 2SO 4 is complex and does not proceed via the Se(IV) → Se(0) → Se(II-) scheme considered by most previous authors. A combined use of voltammetry and electrochemical quartz crystal microgravimetry techniques shows that the direct 6e − Se(IV) → Se(II-) reduction pathway competes with the initial four-electron process. Coupling with a subsequent (fast) chemical reaction between Se(II-) and Se(IV) results in the further deposition of Se(0) at the electrode surface. The electrochemical behavior at more negative potentials reflects a complex interplay of the four-electron and six-electron reduction processes and the chemical reaction along with the effect of Se(II-) ions stripped from the initial selenium layer. Thus the delicate balance between these is influenced by two variables, namely the potential and the Se(II-) concentration in the electrolyte. Further data in support of our mechanistic scheme are furnished by measurements with a Au disk electrode oriented “face-down” in the cell as well as by hydrodynamic voltammetry experiments.

Real-time and absolute compositional analyses of electrodeposited thin films via combined coulometry and electrochemical quartz crystal microgravimetry: application to the Cd + Se system

Real-time and absolute compositional analyses of electrodeposited thin films via combined coulometry and electrochemical quartz crystal microgravimetry: application to the Cd + Se system