Electrochemical Quartz Crystal Microbalance Analysis Research Articles

Electrochemical Quartz Crystal Microbalance Analysis of Degradation Reactions of Pt/C Cathode Catalysts for Polymer Electrolyte Fuel Cells

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Solvent Oligomerization during SEI Formation on Model Systems for Li-Ion Battery Anodes

We report the results of electrochemical quartz crystal microbalance (EQCM), and matrix assisted laser desorption ionization (MALDI) time of flight (TOF) mass spectrometry (MS) measurements along with detailed calculations examining the formation of the solid electrolyte interphase (SEI) on battery anode electrodes. EQCM analysis of Au and Sn surfaces in propylene carbonate (PC) and a 1:1 mixture of ethylene carbonate and dimethyl carbonate (EC:DMC) showed major irreversible mass uptake by the electrode surface especially during the first five cycles between +2 and 0.1 V vs. Li/Li+. MALDI-MS on emersed electrodes showed that long chain (m/z = 3000 on PC) oligomerized species were present on Au surfaces in PC and EC:DMC solvents, where oligomerized species formed in PC solutions showed higher mass ratios. The repeating units of the oligomer, visible as oscillations in the MALDI-MS, vary with the type of the solvent and electrode material. Sn surfaces initially showed formation of long chain polymers, but this material was not in evidence on electrode emersed after five cycles, which likely arises as a consequence of the catalytic involvement of Sn in decomposition of initially formed species. Density functional theory (DFT) calculations of cyclic solvent molecules suggested a radical initiated polymerization mechanism and predict oligomer subunits consistent with the experimental results.

An insight into the electrochemical behavior of Co/Al layered double hydroxide thin films prepared by electrodeposition

A detailed study aimed at clarifying the electrochemical behavior of Co/Al-LDH thin films, prepared on Pt electrode by electrodeposition at −0.9 V, has been carried out. Reproducible thin and homogeneous films with variable amounts of LDH coated on the electrode surface have been achieved by varying the electrodeposition time ( t = 5, 10, 30 and 60 s): 29.2 ± 0.7, 37.9 ± 1.4, 55.1 ± 2.1 and 62.5 ± 4.3 μg cm −2, respectively. X-ray diffraction, spectroscopic techniques and the electrochemical quartz crystal microbalance analysis have been used to give an insight into the phase changes occurring when the as-prepared Co/Al-LDH thin films were oxidized and reduced by cycling the potential between 0 and 0.6 V/SCE in 0.1 M KOH. Our experiments demonstrate that the irreversible oxidation peak observed in the first cycle corresponds to the transformation of the Co(II)/Al-LDH phase in a γ-Co(III)OOH like phase. This resulting phase is stable under cycling and shows a pseudo-capacitive behavior with an estimated specific capacitance of 500 F g −1.

Electrochemical quartz crystal microbalance analysis of the CO oxidation reaction at Pt alloy electrodes

The oxidation reactions of pre-adsorbed CO (CO ad) at pure Pt, Ru, and Pt alloy (Pt–Co, Pt–Fe and Pt–Ru) electrodes were analyzed by double-potential-step chronoamperometry (DPS-CA) with an electrochemical quartz crystal microbalance (EQCM). In a positive-going potential scan at pure Pt, Pt–Co, and Pt–Fe electrodes with CO ad ( θ CO = 1), a pre-oxidation peak was observed at 0.4–0.6 V vs. RHE before a main oxidation peak around 0.7 V. The DPS-CA at the pre-oxidation peak indicated that the elementary reactions at these three electrodes were almost the same, i.e., oxidation of weakly adsorbed CO mainly occurred after initial oxidation of a small amount of adsorbed COOH. At the main oxidation peak, CO ad was oxidized and vacant sites formed were partly occupied by water molecules and/or hydrated ClO 4 - anions. At pure Ru and the Pt–Ru alloy, one major oxidation peak was observed, where CO ad was first oxidized by Ru–OH formed by discharge of H 2O adsorbed on Ru sites (so-called bifunctional mechanism for Pt–Ru). It was found that only a small fraction of CO ad was oxidized in the first step, and subsequent oxidation of CO ad proceeded, enabled by a supply of H 2O molecules to such vacant sites.

Electrochromic Thin Film of Water-Dispersible Prussian-Blue Nanoparticles

The insoluble Prussian-blue (PB) pigment becomes possible to disperse in aqueous solution by covering their surfaces with ferrocyanide anions. The thin film fabricated with these water-dispersible PB nanoparticles shows evident electrochromic color changes between +0.8 V to -0.4 V on an ITO substrate. The mass change of the thin film during an electrochemical reaction is measured by means of electrochemical quartz crystal microbalance (EQCM). According to the EQCM analysis, the filling rate of water-dispersible PB nanoparticles in the film is 37.7% as compared with an assumed perfect crystal PB film.

In Situ Electrochemical Quartz Crystal Microbalance Measurement of Au Deposition and Dissolution in Room-Temperature Ionic Liquid Containing Chloride Ion

Abstract In-site gold electro-deposition and electro-dissolution have been examined using polycrystalline gold-coated quartz crystal electrode in a room-temperature ionic liquid of 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF4). In EMIBF4 media containing 1-ethyl-3-methylimidazolium chloride, the species of AuI (probably [AuICl2]−) resulting from the electrochemical oxidation of the Au surface was very stable and a reversible voltammetric response of the AuI/Au0 couple was observed at 0.25 V vs. Ag wire quasi-reference electrode (Ag(QRE)). In situ electrochemical quartz crystal microbalance (EQCM) technique combined with cyclic voltammetry, double potential-step chronoamperometry and double potential-step chronocoulometry has been successfully applied to investigate the cathodic deposition of AuI ion to Au metal and the anodic dissolution of Au from the Au electrode surface. It was found that the frequency change of quartz crystal electrode during the electrolysis can be interpreted in terms of rigid mass changes based on the Sauerbrey equation. The EQCM analysis of the electro-dissolution and electro-deposition of Au in the potential range of −0.60 to 0.50 V vs. Ag(QRE) gave the molecular mass equivalent of Au (197 g mol−1) corresponding to a one-electron reduction and oxidation of the AuI/Au0 redox couple.

Ac-Electrogravimetry study of ionic and solvent motion in polypyrrole films doped with an heteropolyanion, SiMo 12O 404−

One way to immobilize heteropolyanions on an electrode is to entrap them into a film of conducting polymer. In the present work, a polypyrrole film doped with a Keggin-type heteropolyanion, SiMo 12O 40 4−, obtained by electrochemical way was studied. We focus on the charge compensation process, which occurs when the heteropolyanions entrapped into the polymer are reduced or re-oxidized. First, electrochemical quartz crystal microbalance analyses were performed, then, to determine if solvent motion takes place, ac-electrogravimetry measurements were carried out. In fact, in concentrated acidic solution, only protons are involved in the charge compensation. In low acidic solution (pH 3) having a high potassium concentration (0.5 M) both proton and potassium ions are involved whereas at pH 5.2 only potassium motion takes place. These findings are in good agreement with the acido-basic properties of SiMo 12O 40 6−. In all cases, no solvent motion was pointed out.

Effect of Bath Temperature on the Electrodeposition Mechanism of Zinc Oxide Film from Zinc Nitrate Solution

film was prepared from zinc nitrate aqueous solution by the potentiostatic technique using a three-electrode system at . The film was characterized by scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. In addition, measurements of interface pH and electrochemical quartz crystal microbalance (EQCM) during the electrodeposition were carried out to elucidate the deposition mechanism. It was disclosed that the deposition scheme at the initial stage is quite different depending on bath temperature. The change in deposition mechanism with temperature is closely related to the increased thermodynamic stability of at high temperature. Based on EQCM analysis, it was suggested that the precursor of is slowly transformed to at low temperature, but the formation of is extremely rapid at high temperature, i.e., directly deposits at high temperature. Auger analysis indicated that transition from the precursor to crystal started from the bottom to the surface when the amount of precursor became larger than a critical value depending on temperature.

Electrochemical, Magnetic, and Electrical Properties of α,ω-Capped Sexithiophene Films. 2. Conduction in Sexithiophenes with α,ω-Aryl-Extended Conjugation

Thin films of tetrahexylsexithiophenes, fluorenonyl- and fluorenyl-protected at the terminal α,ω-positions, were investigated by cyclic voltammetry, electrochemical quartz crystal microbalance analysis, in situ ESR, and in situ conductivity. Reversible oxidation is composed of three separate steps, two one-electron processes and a further multielectron process. ESR indicates strong magnetic dimerization for the one-electron-oxidized species. Conductivity is redox type at the cation−dication (polaron−bipolaron) state and metal-like at doping levels higher than the bipolaron with a 20-fold increase at full oxidation. Hexyl-substituted α,ω-capped octathiophene, decathiophene, and dodecathiophene films have been similarly investigated to compare the effects of fluorenonyl and fluorenyl extension of sexithiophene with those given by additional thiophene rings. The conductivity, which increases progressively (by 3 orders of magnitude) with the oligothiophene chain length, is metal-like. In dodecathiophene the d...

Electrochemical quartz crystal microbalance analysis of the cathodic process in a lithium-ion battery

The surface processes at carbon and platinum electrodes have been studied using the electrochemical quartz crystal microbalance technique in organic electrolyte solutions for lithium ion batteries. The changes in resonance frequency were analyzed as a function of the electrode potential, indicating that the process depended not only on the electrode material but also on the cathode potential. In the solution containing LiBF4 as the electrolyte, the main product at the platinum surface was Li2CO3 and LiF, whereas formation of lithium alkylcarbonates was the primary process at the platinum and carbon electrodes in LiPF6 solution.

Investigation on Capacitance Mechanisms of Fe3O4 Electrochemical Capacitors

The capacitance mechanisms of magnetite electrochemical capacitor in , , and KOH aqueous solutions have been investigated by electrochemical quartz-crystal microbalance analysis, along with cyclic voltammetry and X-ray photoelectron spectroscopy. The oxide thin-film electrode was prepared by an electroplating method, and exhibits a capacitance of , 25, and in , , and , respectively. Strong specific adsorption of the anion species was evidenced in all solutions. Experimental results indicate that, in , the capacitive current of magnetite electrode originates from the combination of electric double-layer capacitance (EDLC) and the pseudocapacitance that involves successive reduction of the specifically adsorbed sulfite anions, from through, e.g., , and vice versa. In , the current is due entirely to EDLC. Furthermore, due to the specific adsorption behavior, magnetite exhibits high EDLC, , in both and solutions. The lowest capacitance of magnetite was observed in KOH, which is attributed to the formation of an insulating layer on the magnetite surface.

EQCM analysis of Bi oxidation mechanism on a Pt electrode

The electro-oxidation behaviours of bismuth (Bi) species adsorbed on a platinum (Pt) anode were investigated using an in situ electrochemical quartz crystal microbalance analysis in the measurement of cyclic voltammetry (CV) and electrochemical impedance spectroscopy under potentiostatic mode. In the CV of Bi modified Pt, there were four distinct features in the current–potential curves during an anodic scan: (i) the adsorption of water molecules in acidic media, (ii) the formation of Bi oxide, (iii) ionization of Bi oxide and (iv) partial desorption of Bi species. During a cathodic scan, the Bi modified Pt surface recovered to its original state via the reduction of Bi oxide and re-deposition of Bi ion. Surface mass data with electrical charge change and impedance measurements of Bi modified Pt supported the electrocatalytic oxidation of bismuth species as the responsible mechanism.

New Low-Gap Polymers from 3,4-Ethylenedioxythiophene-Bis-Substituted Electron-Poor Thiophenes. The Roles of Thiophene, Donor−Acceptor Alternation, and Copolymerization in Intrinsic Conductivity

New low-gap thiophene-based regular copolymers are produced by anodic coupling of 3,4-ethylenedioxythiophene-2,5-substituted thieno[3,4-b]pyrazine (TP), cyclopenta[2,1-b;3,4-b‘]dithiophen-4-one (CO), and 4-dicyanomethylene-4H-cyclopenta[2,1-b;3,4-b‘]dithiophene (CN). The copolymers are characterized by cyclic voltammetry, FTIR reflection−absorption and UV−vis spectroscopy, electrochemical quartz crystal microbalance analysis, and in situ p- and n-conductivity measurement. The copolymers show low optical gaps (measured at the maximum absorption) and electrochemical gaps (measured from redox potentials) in the range 0.8−1.3 eV. The CN-based polymer displays the lowest reported electrochemical gap (0.8 V). Random copolymers of CO and 3,4-ethylenedioxythiophene (EDT) have also been produced and compared with the relevant regular copolymer. Copolymerization of CO with increasing amounts of EDT decreases the gap. From an analysis of redox potential as a function of EDT fraction, it is found that the gap is limi...

A study on effect of hydrogen reduction reaction on the initial stage of Ni electrodeposition using EQCM

Electrodeposition of Ni from acidic sulfate solution with/without the addition of boric acid was studied by electrochemical quartz crystal microbalance (EQCM) to further investigate the initial stage of Ni deposition. EQCM analysis showed that nickel hydroxide was formed due to the pH increase near the electrode caused by hydrogen evolution in the absence of boric acid. In the presence of boric acid, nickel hydride was formed. EQCM was found to be a useful in-situ tool for investigating the effects of the evolution and absorption of hydrogen on metal deposition and separating the charge used for Ni deposition and for hydrogen reduction.

Temperature Dependence of Inward Diffusion of Underpotentially-Deposited Cd into a Au (100) Bulk Phase under Electrochemical Environment

We investigated the inward diffusion of underpotentially-deposited (UPD) Cd into a Au (100) substrate in 50 mol m -3 sulfuric acid solution under potential control by anodic voltammetry at the temperature range from 295 to 333 K, as well as by the electrochemical quartz crystal microbalance (EQCM) analysis and X-ray diffractmetry (XRD). The anodic voltammograms show that inward diffusion of the Cd adatoms into a Au (100) bulk phase is classified into two types of steps. One is a very fast step, which is the diffusion of UPD Cd into a Au (100) electrode at the surface layer; the activation energy of this step is ≅ 70 kJ mol -1 . The other is a much slower step; the activation energy of this step (110kJ mol -1 ) agrees well with that of Cd bulk diffusion into a Au-Cd compound. The amount of UPD Cd is calculated from EQCM analysis, and it nearly agrees with that obtained from anodic voltammetry. We found that the amount of UPD Cd increases with temperature. We confirmed the formation of β Au-Cd layer on the sample by XRD after maintained at the UPD region of -1100mV vs. Hg/Hg 2 SO 4 for 1 h at 333 K.

Solvoconductivity of Polyconjugated Polymers: The Roles of Polymer Oxidation Degree and Solvent Electrical Permittivity

The solvoconductive properties of low-defect anodically coupled polypyrroles and polythiophenes, made so they are able to be solvated by organic vapors with suitable substituents, have been studied. The investigation was performed by contemporary conductivity and electrochemical quartz crystal microbalance analysis of the polymer films as a function of the solvent vapor partial pressure. Solvoconductivity was measured at two doping levels (lightly and heavily doped) of the polymers and for a series of solvents in a wide range of dielectric constants. Lightly doped polymers are responsive to vapors whereas heavily doped polymers do no respond at all. For the sensitive polymers the response follows the electrical permittivity of the solvent es with respect to that of the polymer ep, in the sense that conductivity increases for es > ep and decreases for es < ep. A redox-type conduction model accounts for the responsive behavior of lightly doped polymers whereas a metal-like conduction model accounts for the ...

EQCM analysis of the alkali metal ion coordination properties of novel poly(thiophene)s 3,4-functionalized with crown-ether moieties

New thiophenes carrying 18-crown-6-ether ring directly linked to the 3- and 4-positions of the thiophene ring were synthesized and polymerized by anodic coupling in acetonitrile. The polymers were characterized by cyclic voltammetry (CV), UV-Vis and FTIR spectroscopy, matrix-assisted laser desorption ionization (MALDI) mass spectroscopy and in situ conductivity. Electrochemical quartz crystal microbalance (EQCM) analysis of the alkali metal coordination ability of the 18-crown-6-ether polymer films in acetonitrile has evidenced that the coordination constants (e.g. 20–80 M −1 for Na +) are ca. two orders of magnitude lower than those of polythiophenes bearing the crown substituents pendant from the polythiophene backbone. The result has been ascribed both to electronic and solid-state effects of the conjugated polythiophene chains.

Electrochemical quartz crystal microbalance analysis of CO-tolerance at PtFe alloy electrodes

An electrochemical quartz crystal microbalance (EQCM) has been applied to investigate a CO-tolerance at PtFe alloy electrodes, which exhibit excellent H 2 oxidation in the presence of 100 ppm CO. It was found that the PtFe electrodes were electrochemically stabilized by a formation of a few monolayers of Pt-skin layer during several repetitive potential sweeps in 0.1 M HClO 4 solution, i.e. a dissolution of alloy components followed by a rearrangement of thin Pt layer. In a positive-going potential scan at CO-adsorbed ( θ CO=1) electrodes of pure Pt and PtFe alloy, a pre-oxidation peak was observed at 0.3–0.5 V versus RHE before a major CO oxidation peak at 0.7 V. Based on EQCM results, each pre-peak was assigned to an oxidation of weakly-adsorbed CO at PtFe alloy and adsorbed carboxylate at pure Pt, respectively. This is consistent with our previous results by in situ FTIR, and strongly supports a modified electronic structure of the Pt-skin from that of pure Pt, which has been proposed by us.

Cathodic immobilization of π-acceptors such as aromatic ketones onto platinum interfaces under superdry conditions

Metal/electrolyte reduced phases of general stoichiometry (Pt 2 −, 2M +, X −) cathodically formed at the platinum interface in the presence of electrolyte (MX), may unexpectedly react with π-acceptors. Such an immobilization of aromatic ketones and their reduced forms has been demonstrated by coulometry and electrochemical quartz crystal microbalance analysis. This temporary immobilization at the platinum interface could orientate coupling reactions.

Are tetraalkylammonium cations inserted into palladium cathodes? Formation of new palladium phases involving tetraalkylammonium halides

The cathodic behaviour of a wide variety of tetraalkylammonium halides was studied at a polished palladium cathode in aprotic dimethylformamide. Coulometric and electrochemical quartz crystal microbalance analyses demonstrated the formation of clusters whose stoichiometry was determined, attesting to the reversible insertion of cations and anions belonging to the electrolyte into the metallic bulk.