Electrochemical Quartz Crystal Microbalance Analysis Research Articles

Mechanism of mitigating organic fouling on an electro-conductive membrane under anaerobic conditions and cathodic operation

Anaerobic electroconductive membrane (ECM) bioreactors are promising wastewater treatment technology, yet their organic antifouling mechanism remains unclear. This research investigated the impact of reactive oxygen species (ROS) oxidation, pH alteration, and electrostatic repulsion on carbon nanotube-based ECM organic fouling. Using a decoupled anode–cathode filtration system ensured unbiased results from the anode while studying distinct conditions near the cathodic ECM surface. The results demonstrated a 50 % reduction in transmembrane pressure (TMP) onset applying potential due to electroosmosis, emphasizing its importance in fouling studies. Fouling experiments using alginate in synthetic wastewater solution showed substantial organic fouling at open circuit potential, −1 and −1.5 V, as the TMP increased by about 2.5 times than the initial value. Fouling decreased significantly at −2.5 V (vs. Ag/AgCl), as indicated by the stable TMP. Analysis of ROS effects and fouling experiments at pH 7–––12 found no influence on organic fouling. Simplified force balance analysis and filtration tests suggested electrostatic repulsion as the antifouling mechanism. At potentials below −2.5 V, electrostatic repulsion maximizes closer to the ECM surface, causing fouling from short-range attractive forces. Electrochemical quartz crystal microbalance analysis at 0.1 V (vs. Ag/AgCl) proposed that a smooth ECM surface can reduce organic fouling at lower potentials.

Temperature and concentration dependence of the electrochemical PtHg4 alloy formation for mercury decontamination

New and improved methods to remove toxic mercury from contaminated waters and waste streams are highly sought after. Recently, it was shown that electrochemical alloy formation of PtHg4 on a platinum surface with mercury ions from solution can be utilized for decontamination, with several advantages over conventional techniques. Herein, we examine the alloy formation process in more detail by mercury concentration measurements using inductively coupled plasma mass spectrometry in batch measurements as well as electrochemical quartz crystal microbalance analysis both in batch and in flowing water with initial mercury concentrations ranging from 0.25 to 75000 µg L−1 Hg2+. Results show that mercury is effectively removed from all solutions and the rate of alloy formation is constant over time, as well as for very thick layers of PtHg4. The apparent activation energy for the electrochemical alloy formation was determined to be 0.29 eV, with a reaction order in mercury ion concentration around 0.8. The obtained results give new insights that are vital in the assessment and further development of electrochemical alloy formation as a method for large scale mercury decontamination.

Electropolymerized Melamine on Electrochemically Reduced Graphene Oxide: Growth Mechanistics, Electrode Processing, and Amperometric Sensing of Acyclovir.

Metal-free, cost-efficient, redox-active electrode materials, combining graphene derivatives with nitrogen-rich polymelamine (PM), are widely explored as an interface layer for electrocatalysis and an electrochemical sensor platform. However, conventional chemical routes often yield derivatives of PM suffering from impaired redox behavior, restricting their electron-transfer kinetics. Herein, an optimal potentiodynamic method has been established to electrodeposit PM on electrochemically reduced graphene oxide (ErGO). A supporting electrolyte, containing Cl-, enhances the formation of intermediates NH3+ and ═NH2+ at the monomeric melamine, eventually interacting with the residual oxygenated functional groups of ErGO to form PM. In situ Raman spectrum analysis revealed the influence of the defective area and the graphitization ratio on the ErGO surface during the course of electropolymerization of melamine. Under optimal electrodeposition conditions (E = 0-1.6 V; ν = 0.1 V/s), the amount of electrodeposited PM on the ErGO surface was determined to be 16.5 μg/(cycle·cm2), using electrochemical quartz crystal microbalance analysis. An ErGO-PM-modified glassy carbon electrode (GCE) and a screen-printed electrode exhibit the direct electrooxidation of acyclovir (ACV). Amperometric analyses of ErGO-PM-modified electrodes exhibited the lowest detection limit of 137.4 pM with analytical robustness, rapid steady state, and reproducibility promising for ACV detection in complex biological matrices.

Electropolymerized methylene blue on graphene oxide framework for the direct voltammetric detection of gallic acid

Electropolymerized materials are cost efficient, sensitive and durable for sensor applications. Herein, the cationic dye, methylene blue, electropolymerized on graphene oxide framework using cyclic voltammetry and processed for voltammetric sensor platform. The surface chemistry, topology and wettability of the prepared electrode material was comprehensively studied with Raman spectroscopy, field-emission scanning electron/atomic force microscopes and contact angle measurement. The electrochemical quartz crystal microbalance analysis was done to quantify the mass adsorbed on the graphene oxide framework. Cyclic voltammetric study of the prepared methylene blue-graphene oxide framework electrode exhibits a reversible redox behavior at the electrode-electrolyte interface, following surface confined process with a coefficient determination of 0.99. Electrochemical sensing ability of the prepared electrode material was tested against the clinically important phytomedicine, gallic acid. Linear sweep voltammetric analysis enabled that methylene blue-graphene oxide framework is highly sensitive and selective toward electrooxidation of gallic acid, exerting a detection limit of 49.2 μM in the studied experimental concentration range from 50 μM to 1 mM. Real sample validation with commercial herbal tablet extracts of Euphorbia prostrata containing spiked gallic acid suggest that the prepared sensor platform could be a potential analytical probe for herbaceutical testing.

Real‐Time Mass Change: An Intrinsic Indicator to Dynamically Probe the Electrochemical Degradation Evolution in WO3

AbstractAlthough tungsten trioxide (WO3) films are considered as the most popular inorganic electrochromic cathode, the irreversible accumulation of lithium ion in it leads to the degradation of cycling stability. In situ monitoring of mass change is critical to intrinsically probe the dynamical degradation evolution of the WO3 films. Based on electrochemical quartz crystal microbalance analysis, a transfer model based on the migration of three mass carriers (lithium ion, perchlorate ion and propylene carbonate) is proposed. Higher potential can boost the migration of mass carriers, benefiting from the intensive driving force. Due to moderate intercalation of mass carriers and smallest difference in molar mass, the excellent electrochemical reversibility at 40 mV s−1 is observed. As the migration of mass carriers progresses, continuous corrosion of the WO3 films results in electrochemical degradation. It is demonstrated that electrochemical quartz crystal microbalance‐based analyses provide a valuable insight for the intercalation and extraction of mass carriers, in favor of further revealing degradation evolution induced by the irreversible intercalation of conductive ions in electrochemical devices.

Elucidating Film Loss and the Role of Hydrogen Bonding of Adsorbed Redox Enzymes by Electrochemical Quartz Crystal Microbalance Analysis.

The immobilization of redox enzymes on electrodes enables the efficient and selective electrocatalysis of useful reactions such as the reversible interconversion of dihydrogen (H2) to protons (H+) and formate to carbon dioxide (CO2) with hydrogenase (H2ase) and formate dehydrogenase (FDH), respectively. However, their immobilization on electrodes to produce electroactive protein films for direct electron transfer (DET) at the protein–electrode interface is not well understood, and the reasons for their activity loss remain vague, limiting their performance often to hour timescales. Here, we report the immobilization of [NiFeSe]-H2ase and [W]-FDH from Desulfovibrio vulgaris Hildenborough on a range of charged and neutral self-assembled monolayer (SAM)-modified gold electrodes with varying hydrogen bond (H-bond) donor capabilities. The key factors dominating the activity and stability of the immobilized enzymes are determined using protein film voltammetry (PFV), chronoamperometry (CA), and electrochemical quartz crystal microbalance (E-QCM) analysis. Electrostatic and H-bonding interactions are resolved, with electrostatic interactions responsible for enzyme orientation while enzyme desorption is strongly limited when H-bonding is present at the enzyme–electrode interface. Conversely, enzyme stability is drastically reduced in the absence of H-bonding, and desorptive enzyme loss is confirmed as the main reason for activity decay by E-QCM during CA. This study provides insights into the possible reasons for the reduced activity of immobilized redox enzymes and the role of film loss, particularly H-bonding, in stabilizing bioelectrode performance, promoting avenues for future improvements in bioelectrocatalysis.

Potential-Dependent Passivation of Zinc Metal in a Sulfate-Based Aqueous Electrolyte.

Owing to its abundance, high theoretical capacity, and low electrode potential, zinc is one of the most important metallic anodes for primary and secondary batteries such as alkaline and zinc-air batteries. In the operation of zinc-based batteries, passivation of the anode surface plays an essential role because the electrode potential of zinc is slightly below that of the hydrogen evolution reaction. Therefore, it is important to scrutinize the nature of the passivation film to achieve anticorrosion inside batteries. Herein, the potential-dependent formation and removal of the passivation film during the deposition and dissolution of zinc metal in aqueous electrolytes are detected via electrochemical quartz crystal microbalance analysis. Film formation was not noticeable in hydroxide-based electrolytes; however, sulfate-based electrolytes induced potential-dependent formation and removal of the passivation film, enabling a superior coulombic efficiency of 99.37% and significantly reducing the rate of corrosion of the zinc-metal anodes. These observations provide insights into the development of advanced electrolytes for safe and stable energy-storage devices based on zinc-metal anodes.

High Performance 2D Micro-Supercapacitor Electrode Composed of Graphene with Polydopamine As Inserts

Over the last years, graphene is deemed as one of the most promising electrode materials for EDLCs due to its large specific surface area (2600 m2·g-1), high theoretical specific capacitance (550 F·g-1) and high conductivity.1 Among all the reported approaches to achieve a graphene-like material, the most favorable route is the reduction of GO and notably the electrochemical reduction of GO that is viewed as an economic, simple, fast and eco-friendly method with production possibility at a relatively large scale.2,3 However, reduced graphene oxide (rGO) suffers from the small surface area due to the partial re-stacking of graphene sheets.4 Therefore, it is necessary to develop an effective and feasible route to avoid rGO re-stacking to obtain graphene-based electrodes with a high specific capacitance and a good stability.Herein, we report graphene-polydopamine (PDA) composites as electrodes for micro-supercapacitor devices fabricated by a facile electrochemical approach. 5 We particularly address the rGO re-stacking issue by exploiting the PDA as a “chemical insert” between the graphene sheets but also explore the impact of PDA on the interfacial charge storage properties and the cycling performance. The optimized ERGO-PDA electrode possesses combined features of excellent capacitive behavior: high gravimetric and volumetric capacitances (178 F·g-1 and 297 F·cm-3, respectively, at 10 mV·s-1). Even at a scan rate of 1V/s, its volumetric capacitance is still as high as 94 F/cm3 (versus only 39 F/cm3 for ERGO) with an excellent cycling stability. Additionally, the electrochemical quartz crystal microbalance analyses demonstrate a dominant cationic charge compensation and a very efficient interfacial transfer characteristics, since a totally reversible mass response during charge/discharge was observed for the optimized ERGO-PDA electrode. Here the favourable impact of PDA is shown to tackle rGO restacking issue, shedding light on the design of graphene based composite electrodes and can also be extended to other 2D materials for high performance electrochemical energy storage electrodes. Keywords: EDLC, reduced graphene oxide, polydopamine, composite, microsupercapacitor.

EQCM Analysis of the Insertion Phenomena in a n-Doped Poly-Alkyl-Terthiophene With Regioregular Pattern of Substitution.

In the present work, we have undertaken the study of the n-doping process in poly-3,3″-didodecyl-2,2′:5′,2″-terthiophene (poly-33″-DDTT) employing the electrochemical quartz crystal microbalance (EQCM). The present study aims at understanding how cathodic charge in n-doped poly-33″-DDTT is compensated. For this purpose, the in situ analysis of the variations of the polymeric mass has been considered. Poly-33″-DDTT was obtained as a thin coating onto a metallic substrate via the anodic coupling of the corresponding monomer 3,3″-didodecyl-2,2′:5′,2″-terthiophene (33″-DDTT). When subjected to electrochemical n-doping in the polarization interval -2.5 ≤ E appl ≤ 0 V vs. Ag/Ag+, the films of poly-33″-DDTT varied their mass according to a mechanism of cations insertion during n-doping and cations extraction during polymer neutralization. In fact, the electrochemical doping of polythiophenes requires the accompanying exchange of charged species to maintain the electroneutrality within the structure of the polymer in all states of polarization. At the end of a full electrochemical cycle (consisting of the n-doping and the successive neutralization of poly-33″-DDTT), the polymer retains a fraction of the mass acquired during n-doping, thus manifesting the phenomena of mass trapping. The combined analysis of electrochemical and microgravimetric data suggests that poly-33″-DDTT in the n-doped state undergoes (or electrocatalyzes) uncontrolled electrochemical reactions that are not accompanied by mass variations.

Ion Mobility in Thick and Thin Poly-3,4 Ethylenedioxythiophene Films-From EQCM to Actuation.

Conductive polymer actuators and sensors rely on controlled ion transport coupled to a potential/charge change. In order to understand and control such devices, it is of paramount importance to understand the factors that determine ion flux at various conditions, including the synthesis potential. In this work, the ion transport in thinner poly-3,4-ethylenedioxythiophene (PEDOT) films during charge/discharge driven by cyclic voltammetry is studied by consideration of the electrochemical quartz crystal microbalance (EQCM) and the results are compared to the actuation responses of thicker films that have been synthesized with the same conditions in the bending and linear expansion modes. The effects of polymerization potentials of 1.0 V, 1.2 V, and 1.5 V are studied to elucidate how polymerization potential contributes to actuation, as well the involvement of the EQCM. In this work, it is revealed that there is a shift from anion-dominated to mixed to cation-dominated activity with increased synthesis potential. Scanning electron microscopy shows a decrease in porosity for the PEDOT structure with increasing synthesis potential. EQCM analysis of processes taking place at various potentials allows the determination of appropriate potential windows for increased control over devices.

Perovskite oxide and polyazulene–based heterostructure for high–performance supercapacitors

AbstractSeveral types of electrode materials have been developed for high–performance supercapacitors. Most of the relevant studies have focused on the discovery of new atomic structures and paid limited attention to the effect of heterostructures in supercapacitor electrodes, which has long hindered the fundamental understanding of the use of hybrid materials in supercapacitors. In this study, a novel heterostructure based on perovskite oxide (LaNiO3) nanosheets and polyazulene was synthesized. The as–prepared heterostructure–based supercapacitor exhibited a specific capacitance of up to 464 F g−1 at a high current density of 2 A g−1 in 1–ethyl–3–methylimidazolium tetrafluoroborate. In a symmetric supercapacitor, this heterostructure delivered an energy density of up to 56.4 Wh kg−1 at a power density of 1100 W kg−1. Both LaNiO3 and polyazulene contributed pseudocapacitance and dominated the performance. Unexpectedly, electric double–layer capacitance was found to contribute in this system. Density functional theory calculations indicated that the advantage of the high electrical conductivity of the heterostructure benefited the supercapacitor operation. Electrochemical quartz crystal microbalance analysis revealed that the fast ion flux and adsorption boosted performance. The high intrinsic electrical conductivity and improved stability make this heterostructure a promising electrode material candidate for supercapacitors.

Anion Exchange and Water Dynamics in a Phosphonium-Based Alkaline Anion Exchange Membrane Material for Fuel Cells: An Electrochemical Quartz Crystal Microbalance Study.

The anion exchange and water dynamics of a phosphonium-based alkaline anion exchange membrane (AAEM) during the methanol oxidation process have been studied with the electrochemical quartz crystal microbalance (EQCM). The viscoelastic effects of the phosphonium-based AAEM in water and the optimal film thickness for EQCM analysis were identified by acoustic impedance analysis. The phosphonium-based AAEM exhibited stronger mechanical toughness in water when compared to a quaternary-ammonium-based membrane that was studied previously. From the simultaneous measurement of the electrochemical response and the frequency changes of the quartz crystal oscillator, water ingress/egress to/from the AAEM film was found to accompany the hydrogen adsorption/desorption, Pt oxidation process, and methanol oxidation process. The in situ study of AAEM films helps illustrate the critical role that water transport plays in electrochemical processes during the operation of anion exchange membrane fuel cells. The generated CO32- and HCOO-, during methanol oxidation, were absorbed into the AAEM film, replacing the OH- in the film, as shown by the decrease in frequency after one potential cycle. The exchange of OH- by CO32- and HCOO- was found to be reversible. These results provide insights into the anion exchange processes in membranes and emphasize the importance of characterizing the hydrated membranes under electrochemical conditions.

Electrochemical Synthesis of Cu-Cu2o Composite Layers and Its Catalytic Properties Towards Ethylene Generation

Recently a number of articles concerning subjects related to limitation of greenhouse gasses emission or neutralization of greenhouse gasses present in atmosphere significantly increased. Global warming negatively influences on non-failure operation of ecosystem and due to glaciers melting resulting in water volume increase causing raising of water level in seas and oceans. Large number of negative factors resulting from global warming effect creating necessity of performance of intensified investigations going to development of technologies enabling limitation of emission or neutralization of greenhouses gasses through its conversion to chemical compounds which can be applied in synthesis of other useful chemical compounds or functional materials. Other important problem beyond limitation of CO2 amount in atmosphere is related to possibilities of its conversion to chemical compounds which can be used as energy carriers. It creates possibilities for its applications in renewable energy storage oriented systems. The proposed project is focused on photoelectrochemical conversion of one of main greenhouse gas, CO2 to ethylene. The main scientific objective of performed studies was the development of methodology for electrochemical synthesis of binary composite Cu-Cu2O material. Copper is the only metal that exhibits very high selectivity for electrochemical conversion of CO2 to ethylene (1). Ren et al. observed similar effect in case of p-type Cu2O (2). Reported effects allow assumption that combination of both materials can be great solution in the frame of light supported electrochemical conversion of carbon dioxide to ethylene. Authors describe optimization of electrochemical synthesis process towards synthesis of composite coatings of wide composition range. Synthesis conditions were investigated starting from the thermodynamic analysis of the electrolyte. Conditions for synthesis were determined based on the results of voltammetric tests and electrochemical quartz crystal microbalance analyses. Synthesized coatings were characterized towards their composition, structure, morphology and catalytic properties towards electrochemical reduction of CO2 to ethylene. References Y. Kwon, Y. Lum, E. L. Clark, J. W. Ager and A. T. Bell, ChemElectroChem, 3, 1012 (2016).D. Ren, Y. Deng, A. D. Handoko, C. S. Chen, S. Malkhandi and B. S. Yeo, ACS Catalysis, 5, 2814 (2015).P. D. Tran, S. K. Batabyal, S. S. Pramana, J. Barber, L. H. Wong and S. C. J. Loo, Nanoscale, 4, 3875 (2012).

Investigation into applicability of EQCM methods at elevated temperature for ionic liquids

In this study, the dependence of the density and viscosity on the concentration of Nd(III) in an ionic liquid, triethylpentylphosphonium bis(trifluoromethylsulfonyl)amide ([P2225][TFSA]), was investigated. The density of the ionic liquid showed a linear relationship to the Nd(III) concentration, while its viscosity increased in proportion to the Nd(III) concentration. Furthermore, the Arrhenius plot of the viscosity was in good agreement with the Vogel–Fulcher–Tammann equation: η=η0T-1/2exp[B/(T-T0)].The applicability of the electrochemical quartz crystal microbalance (EQCM) in ionic liquids at elevated temperatures was proved from the relationship of the resonance frequency and the resistance to the product of the viscosity (ηL) and the density (ρL) of the ionic liquid samples. The resonance frequency shifts and the resistances were proportional to (ηLρL)1/2 at 363K and the results agreed with the theoretical equations used for EQCM analysis.

Voltammetric Electronic Tongue for Discrimination of Milk Adulterated with Urea, Formaldehyde and Melamine

We report the fabrication of a voltammetric electronic tongue for the detection and discrimination of harmful substances intentionally added to milk to increase its shelf life or imitate protein content. The electronic tongue consisted of three working electrodes composed of platinum, gold, and copper. The measurement principles involved the extraction of information from cyclic voltammograms recorded in unadulterated and adulterated milk. The extracted data were analysed using principal component analysis and the contaminants were successfully differentiated from one another in a score plot. Electrochemical quartz crystal microbalance analysis was used to investigate the electrode response in order to understand the mechanism by which the tongue could discriminate between the samples. It was found that the electrochemical formation and dissolution of platinum and gold oxides, and the reduction of a copper-melamine ionic pair formed at the surface of the copper electrode were the main factors responsible for discrimination. In addition, the electronic tongue was capable of identifying adulterations in different types of milk (whole, skimmed, and semi-skimmed) and milk from different brands. The lowest concentration of adulterant that resulted in a good discrimination was 10.0, 4.16, and 0.95 mmol·L−1 for formaldehyde, urea, and melamine, respectively.

Invited: Probing Pseudocapacitance Mechanisms in Metal-Oxide–Functionalized Carbon Nanoarchitectures with an Electrochemical Quartz Microbalance

Transition-metal oxides that exhibit “pseudo-capacitance” are challenging high-surface-area carbons as the active material of choice for next-generation electrochemical capacitors (ECs).1 The electrochemical performance of such EC-relevant metal oxides as MnOx has been extensively reported,2 yet the underlying mechanisms responsible for pseudocapacitance are still a subject of debate in the scientific literature. Spectroscopic techniques have been used to verify reversible oxidation-state cycling of metal sites in these oxides (Mn(III/IV) in MnOx; Fe(II/III) in FeOx),3,4 but less is known about the participation of charge-compensating cations from the contacting electrolyte. In the case of mild aqueous electrolytes, redox reactions that give rise to pseudocapacitance may be coupled with insertion/ deinsertion of cations from the electrolyte salt (e.g., Li+, Na+, K+), protons that are available from the H2O solvent, or combinations thereof. Electrochemical quartz crystal microbalance (EQCM) techniques provide information on changes in electrode mass during electrochemical cycling that can address questions regarding ion insertion.5 Until recently the use of EQCM has been limited to well-defined thin-film electrodes, but advancements in EQCM methods now permit analysis of a wider range of substrates, including powder-composite electrodes of EC relevance.6,7 In this paper, we will describe the application of EQCM analysis to a class of electrode architectures comprising carbon nanofoam papers8 whose exterior and interior surfaces are exhaustively coated with nanometers-thick metal oxides that exhibit pseudocapacitance.4 ,9,10,11 Carbon nanofoam papers are freestanding, device-ready electrode architectures of controllable macroscale dimensions (1–102 cm2 in area; 100–500 mm thickness) in which nanoscale dimensions of pore and solid can also be readily adjusted over a wide range (10 nm to several mm). The addition of a nanoscale metal-oxide coating to nanofoam substrates amplifies charge-storage capacity via pseudocapacitance, while the high-frequency response inherent to the nanofoam architecture is retained by ensuring that the metal oxide coating is conformal and self-limiting and that the pore network stays open in three dimensions.For EQCM analysis of these nanofoam-based electrode architectures, we attach disk-shaped pieces of native or oxide-coated carbon nanofoam paper to Au-coated quartz crystals using a carbon-based conductive epoxy. Voltammetric cycling of the resulting electrodes in an EQCM cell yields the expected pseudocapacitance response in terms of both shape and magnitude, demonstrating effective electrical contact to the nanofoam paper. Coupled to the electrochemical response, we monitor mass changes during electrochemical cycling while also varying such parameters as aqueous electrolyte composition (Li+ vs. Na+ vs. K+), average pore size of the nanofoam (10–200 nm), and the type of metal-oxide coating (MnOx vs. FeOx). Preliminary EQCM experiments show that “depletion” effects6 are observed in the presence of Li+-containing electrolytes and for MnOx-coated nanofoams with pores <40 nm, in which the pseudocapacitance mechanism switches from Li+ to NO3 – insertion/deinsertion over the most positive regions of the active potential window of MnOx. The EQCM-observed depletion effect corresponds with the slowest time response of this series of MnOx–carbon nanofoams, as previously reported.12 We compare EQCM results obtained from nanofoam-based electrode architectures with those for thin-film versions of the respective metal oxides. Monitoring mass changes during electrochemical cycling will also allow us determine the conditions under which deleterious dissolution reactions may occur.

Effect of Mn and Cu Addition on Lithiation and SEI Formation on Model Anode Electrodes

The effect of addition of Mn2+ to the electrolyte on the lithiation of a model battery anode was studied using voltammetry, electrochemical quartz crystal microbalance (EQCM), scanning electron microscopy (SEM), Auger electron spectroscopy (AES) and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). Cyclic voltammetry of a Au anode showed that the presence of one equivalent monolayer of Mn2+ in the electrolyte reduces the battery capacity by as much as 48%, a result which is recapitulated in SEM images of the anode surface after five cycles which show that the presence of Mn2+ blocks lithiation of the anode. AES demonstrates the presence or lack of Mn on the surface. EQCM analysis demonstrates greater initial mass gain on the anode with increasing concentration of Mn2+ in the electrolyte while MALDI-TOF MS shows no observable differences in the solid electrolyte interface (SEI) between the electrolyte with or without Mn2+. The addition of Cu2+ to the electrolyte exhibits an effect similar to Mn2+ addition.

Electrochemical quartz crystal microbalance analysis of the oxidation reaction of phenols found in wines at lutetium bisphthalocyanine electrodes

An electrochemical quartz crystal microbalance (EQCM) was used to investigate the processes associated with the mass changes accompanying the phenol oxidation catalysed by a lutetium bisphthalocyanine (LuPc2) film-modified Pt/quartz electrode.The study focused on the analysis of the oxidation of phenols usually found in wines, including vanillic, ferulic, caffeic and gallic acids dissolved in a hydroalcoholic solution simulating the matrix of a red wine.It has been shown that LuPc2 modified EQCM sensors immersed in hydroalcoholic solution exhibit significant mass changes upon electrochemical cycling produced by the ingress/egress of ions necessary to maintain the electroneutrality of the film.Cyclic voltammograms of LuPc2/QCM electrodes immersed in phenols also undergo mass changes associated with the ingress/egress of ions. In addition, progressive mass changes occur upon successive scans. The oxidation/reduction of monophenols produces a progressive increase in the mass, whereas ortho-diphenols show the opposite behaviour. These phenomena have been interpreted in terms of the adsorption of the phenols to the LuPc2 layer and their capability to electropolymerise at the electrode surface.The combination of cyclic voltammetry with electrochemical quartz microbalance (EQCM) has demonstrated its capability to elucidate the complex processes occurring at the surface of voltammetric sensors chemically modified with bisphthalocyanines.

EQCM Analysis of Titanium Corrosion in Peroxide- or Fluoride-Containing Solutions

Although offering superior resistance to corrosion, titanium is unable to withstand discoloration with exposure to peroxide or fluoride. The mechanism of this discoloration, however, remains to be clarified. The purpose of this study was to investigate the mechanism underlying discoloration of titanium with immersion in peroxide- or fluoride-containing solutions based on electrochemical quartz crystal microbalance (EQCM) analysis. A 9-MHz titanium-deposited quartz crystal was used as for the electrodes. Four test solutions were prepared for immersion of the electrodes: 154 mM (0.9%) NaCl; 150 mM H2O2+154 mM NaCl (pH=4 by addition of lactic acid); 150 mM H2O2+154 mM NaCl (pH=8 by addition of sodium hydroxide solution); and 48 mM (0.2%) NaF+154 mM NaCl (pH=5.0 by addition of lactic acid). A WinEchem electrochemistry software-controlled quartz crystal analyzer (QCA922) and the Potentiostat/Galvanostat (Princeton Applied Research) on Windows XP were used to measure concurrently the resonance frequency and potential of the electrodes. The EQCM data differed among solutions. In the acidulated fluoride-containing solution, the electrode showed lower open circuit potential and a gradual increase in electrode frequency, indicating a loss of mass by titanium dissolution. In the peroxide-containing solution, although open circuit potential showed no marked difference, electrode frequency showed a gentle decrease in acidic solution, indicating a gain in mass by oxidation; but an increase in alkaline solution, indicating a loss of mass by dissolution. These results confirmed that exposure to acidulated fluoride- or alkaline peroxide-containing solutions causes dissolution-induced discoloration, while that to acidulated peroxide-containing solutions resulted in the formation of an oxide film together with discoloration.

Electrochemical quartz crystal microbalance study of Si electrodeposition in ionic liquid

The electrodeposition of silicon from silicon tetrachloride in the hydrophobic room temperature ionic liquid trimethyl-n-hexyl ammonium bis-(trifluoromethylsulfonyl) imide was investigated by cyclic voltammetry and chronoamperometry. In situ electrochemical quartz crystal microbalance (EQCM) impedance spectroscopy was used to estimate the mass of films during deposition. The charge efficiency estimated from EQCM measurements is ∼190–250% for four-electron silicon reduction. However, compositional analysis by XPS shows that the EQCM current efficiency estimates are artificially high due to ionic liquid inclusion in the films. Taking the mass concentration of impurities into account, the best-case estimate of current efficiency is found to be approximately 130% for constant potential deposition, suggesting silicon may not have been completely reduced at the potentials investigated, or a chemical reaction step occurs. We also consider that the EQCM analysis may include too many deviations from assumptions for accurate estimation of mass with the conditions studied.