Anodic Potential Window Research Articles

Electrochemical Corrosion Behavior of Heat-Treated HVOF Coatings on ASTM SA213-T22 Steel

Herein the electrochemical corrosion behavior of pre- and post-heat-treated composite coatings of NiCrMoFeCoAl-30%SiO2 and NiCrMoFeCoAl-30%Cr2O3 on ASTM SA213-T22 boiler tube steel by a high-velocity oxygen fuel (HVOF) spraying technique are reported. The samples were subjected to hot molten salt (Na2SO4–60%V2O5) corrosion environment in a tubular furnace at 700°C under thermocyclic conditions. The microscopic, structural, and electrochemical investigations of post-heat-treated specimens reveal NiCrMoFeCoAl-30%Cr2O3 composite HVOF coating exhibits a superior corrosion resistance compared to NiCrMoFeCoAl-30%SiO2 composite coating and bare ASTM SA213-T22 steel boiler tube steel in neutral electrolyte. The room-temperature potentiodynamic and impedance investigations of heat-treated samples suggest high interfacial charge transfer resistance for HVOF coatings over a wide anodic potential window. This could be ascribed to the protective nature of the chromium-oxide-containing coatings on high-temperature treatment. AC impedance analysis reveals NiCrMoFeCoAl-30%Cr2O3 coating exhibits very high resistive behavior with very high charge transfer resistance, in the order of 106 Ω higher than the NiCrMoFeCoAl-30%SiO2 coating and uncoated ASTM SA213-T22 steel boiler tube steel. Furthermore, the high-temperature-induced formation of metal chromates/chromites along with the presence of Cr2O3 provides good resistance toward corrosion.

Organometallic Au(III) Based Electrochemical Sensor with Wide Anodic Potential Window for Sensitive and Selective Detection of Ochratoxin A

AbstractHerein, an organometallic Au(III) catalyst was easily prepared via self‐assembly method using chloroauric acid (HAuCl4) and cetyltrimethylammonium bromide (CTAB). The electrode fabricated by the catalyst not only shows extended anodic potential window compared to that of Au nanoparticle‐based electrode, but also possess the high electrocatalytic activity in the selective oxidation of Ochratoxin A. Under optimized conditions, the modified electrode exhibits a wide linearity range from 1.0×10−7 to 1.0×10−5 mol/L and a low detection limit of 2.9×10−8 mol/L (S/N=3). Furthermore, the electrochemical sensor possesses good recoveries between 93.5 % and 98.2 % in real sample analysis, indicating high accuracy in real sample analysis.

Platinum nanoparticles/Ti3C2Tx (MXene) composite for the effectual electrochemical sensing of Bisphenol A in aqueous media

Abstract This paper evaluates the electrochemical performance of platinum nanoparticles/Ti3C2Tx nanocomposite (Pt@Ti3C2Tx) towards environmental sensing applications. The nanocomposite was prepared by self-reduction of Pt salt to Pt nanoparticles (PtNPs) on the surface of delaminated Ti3C2Tx nanosheets, in which Ti3C2Tx simultaneously acted as reducing agent as well as conductive matrix. The Pt@Ti3C2Tx nanocomposites with different Pt loading have been electrochemically characterized and it was found that 10%Pt@Ti3C2Tx has the highest electrochemical activity in the anodic potential window. Hence, 10%Pt@Ti3C2Tx has been used to develop an electrochemical sensor for the detection of Bisphenol A (BPA), which is one of the common environmental pollutants. At the optimal conditions, the oxidation peak of BPA was proportional to the analyte concentration from 50 nM to 5 μM with a detection limit of 32 nM. The practical application of the proposed sensor was successfully evaluated in drinking water and fresh milk samples.

Extension of Anodic Potential Window of Ester-Based Electrolyte Solutions for High-Voltage Lithium Ion Batteries

A stability against oxidation of ester-based electrolyte solution was highly improved by a tandem preparation method, i.e., increasing concentration of lithium salt and diluting with a miscible diluent. The resultant saturated electrolyte solution offered a wide anodic potential window and allowed a LiNi0.5Mn0.2Co0.3O2 positive electrode to deliver charge/discharge capacities over 200 mAh g–1 up to 4.6 V almost without capacity fading after 50 cycles. The solution structure was studied to clarify the stabilizing mechanism of the electrolyte solution. On the basis of the results, this study presents a viable strategy to design an electrolyte solution with a wide potential window for various electrochemical systems.

Indium Tin Oxide Film Characteristics for Cathodic Stripping Voltammetry.

The combination of conductivity, optical transparency, and wide anodic potential window has driven significant interest in indium tin oxide (ITO) as an electrode material for electrochemical measurements. More recently, ITO has been applied to the detection of trace metals using cathodic stripping voltammetry (CSV), specifically manganese (Mn). However, the optimization of ITO fabrication for a voltammetric method such as CSV is yet to be reported, nor have the microstructural properties of ITO been investigated for CSV. Furthermore, CSV does not require optical transparency, thereby allowing nontransparent substrates to be used for deposition. This enables microfabrication procedures to be expanded and simplified compared to glass or quartz. Combining this with the profound importance of sensitive, selective detection of toxic metal ions in environmentally and biologically relevant samples makes ITO especially attractive. In this work, we report a thorough investigation of ITO deposition and processing on silicon (Si) substrates for CSV analysis using Mn as the model analyte. Several ITO process parameters were examined such as heated deposition and post-process annealing. Each ITO film was characterized using a variety of surface, bulk (X-ray diffraction), and electrochemical measurements. Although each ITO film type showed electrochemical activity, the heated and annealed (HA) ITO fabrication process yielded superior results for Mn CSV; a limit of detection (LOD) of 0.1 ppb (1.8 nM) was obtained. This work exemplifies new applications of ITO as an electrode material while providing a baseline for trace detection of toxic metals and other contaminants amenable to detection by CSV.

Facet‐Resolved Electrochemistry of Polycrystalline Boron‐Doped Diamond Electrodes: Microscopic Factors Determining the Solvent Window in Aqueous Potassium Chloride Solutions

AbstractA systematic examination of the microscopic factors affecting the aqueous solvent (electrolyte) window of polycrystalline (p) boron‐doped diamond (BDD) electrodes in chloride‐containing salt solutions is undertaken by using scanning electrochemical cell microscopy (SECCM) in conjunction with electron backscatter diffraction (EBSD) and Raman microscopy. A major focus is to determine the effect of the local boron doping level, within the same orientation grains, on the solvent window response. EBSD is used to select the predominant (110) orientated areas of the surface with different boron‐doped facets, thereby eliminating crystallographic effects from the electrochemical response. Voltammetric SECCM is employed, whereby a cyclic voltammogram is recorded at each pixel mapped by the meniscus‐contact SECCM cell. The data obtained can be played as an electrochemical movie of potential‐resolved current maps of the surface to reveal spatial variations of electroactivity, over a wide potential range, including the solvent (electrolyte) window. Local heterogeneities are observed, indicating that the solvent window is mainly linked to local dopant levels, with lower dopant levels leading to a wider window, that is, slower electrode kinetics for solvent/electrolyte electrolysis. Furthermore, the effects of O‐ and H‐surface termination of the BDD surface are investigated for the same electrode (in the same area). The surface termination is a particularly important factor: the solvent window of an H‐terminated surface is wider than for O‐termination for similar boron dopant levels. Furthermore, the anodic potential window of the O‐terminated surface is greatly diminished due to chloride electro‐oxidation. These studies provide new perspectives on the local electrochemical properties of BDD and highlight the importance of probing the electrochemistry of BDD at the level of a single crystalline grain (facet) to unravel the factors that control the solvent (aqueous) window of these complex heterogeneous electrodes.

Highly stable Ti3C2Tx (MXene)/Pt nanoparticles-modified glassy carbon electrode for H2O2 and small molecules sensing applications

Electrochemical performance of a 2D Ti3C2Tx (MXene, where T: O, OH, F) sheets modified with Pt nanoparticles (PtNPs) was investigated. The results showed that Ti3C2Tx/PtNP nanocomposite deposited on the surface of GCE showed much better and stable redox behavior in an anodic potential window as compared to the GCE modified with pristine Ti3C2Tx MXene. For example, the H2O2 sensor of Ti3C2Tx/PtNP on GCE offered LOD of 448 nM with a potential at which reduction starts of ∼+250 mV (vs. Ag/AgCl) in comparison to values of 883 μM and ∼−160 mV observed for Ti3C2Tx modified GCE. Moreover, the Ti3C2Tx/PtNP sensor could detect small redox molecules such as ascorbic acid (AA), dopamine (DA), uric acid (UA) and acetaminophen (APAP) at a potential higher than +250 mV with high selectivity and LOD down to nM level. We proved that selectivity of detection of such molecules (AA, DA, UA and APAP) could be modulated to high extent using external membranes.

Physical and Electrochemical Properties of Ionic Liquids Based on Quaternary Phosphonium Cations and Carboxylate Anions as Electrolytes

A new group of ionic liquids based on tetraethylphosphonium and tetrabutylphosphonium cations together with several carboxylate anions is proposed and presented in this report. In obtained ionic liquids, tetrabutylphosphonium formate and tetrabutyl-phosphonium lactate became room temperature ionic liquids. It was found that the phosphonium ionic liquids showed the typical VTF-type convex curve behaviors. The phosphonium ionic liquids also had a high cathodic stability similar to those of the TFSA- and FSA-anion based phosphonium ionic liquids. On the other hand, relatively low anodic potential window was observed. The thermal stability of the phosphonium ionic liquids showed higher thermal stabilities than those of the corresponding ammonium ionic liquids.

Physical and Electrochemical Properties of Ionic Liquids Based on Quaternary Phosphonium Cations and Carboxylate Anions As Electrolytes

Ionic liquids (ILs) have been developed for a wide variety of electrochemical applications due to their unique physicochemical properties such as favorable solubility of organic and inorganic compounds, relatively high ionic conductivity, no measurable vapor pressure, high thermal stability, low flammability, etc. Another advantage of ILs is a designability of the ion structures. Although many kinds of ILs have been already investigated, phosphonium-based ILs have rarely been proposed. We have previously designed and synthesized the phosphonium ILs together with typical anion species such as bis(trifluoromethylsulfonyl)amide (TFSA) and bis(fluorosulfornyl)amide (FSA) anions.1,2 On the other hand, interests in ILs consisting of carboxylic acid based anions have been increasing in recent years. In this work, we synthesize the ILs based on quaternary phosphonium cations (tetraethylphosphonium, P2222 +, and tetrabutylphosphonium, P4444 +) in combination with carboxylate anions such as formate (HCO2 -), acetate (MeCO2 -) and propionate (EtCO2 -), characterizing the physicochemical and electrochemical properties of the ILs as a new family of IL-based electrolyte.The preparation of the phosphonium ILs was carried out by neutralization reactions of the precursor phosphonium hydroxides with the carboxylic acids. The obtained ILs were dried under high vacuum for at least 10 h at 60◦C. We also prepared the corresponding ammonium salts by the same procedure for comparison. The physicochemical and electrochemical properties such as conductivity (ac impedance method), viscosity (a cone-plate type viscometer), density, melting point (DSC), thermal decomposition temperature (TGA) and electrochemical window (linear sweep voltammetry using a conventional three-electrode cell) were measured under dry argon atmosphere. Table 1 summarizes the physicochemical properties of the ILs obtained in this work. The almost compounds were low-melting white solids; however only P4444-HCO2 became a liquid at ambient temperature. The conductivity and viscosity of P4444-HCO2 depended on temperature, showing the Arrhenius-type convex curve behaviors. This means a typical electrolyte behavior generally observed in IL media. P4444-HCO2 showed the lowest viscosity and highest conductivity in the three P4444-based phosphonium salts, which might be attributed to the anion sizes of the three phosphonium salts. It should be noted that the thermal decomposition temperatures of the phosphonium salts were much higher than those of the corresponding ammonium salts, revealing the high thermal stability of the carboxylic anion based phosphonium ILs (Fig. 1). In the electrochemical measurements, it was found that P4444-HCO2 had a high cathodic stability similar to those of the TFSA- and FSA-anion based phosphonium ILs. On the other hand, relatively low anodic potential window up to 0.7 V vs. Ag/Ag+ was observed, which seems likely to be due to the anodic oxidation of formate anion.

Electrochemical and spectroelectrochemical properties of new metal free, nickel(II), lead(II) and zinc(II) phthalocyanines

The new metal free, nickel(II), lead(II) and zinc(II) phthalocyanines containing 2-[2-(4-allyl-2-methoxyphenoxy)ethoxy]ethoxy groups were synthesized and structurally characterized by using IR, 1H NMR, 13C NMR, UV–vis and elemental analysis spectral data. Redox properties of the complexes were determined with voltammetric and in situ spectroelectrochemical measurements in different electrolytic systems, tetrabutylammonium perchlorate (TBAP) dissolved dichloromethane (DCM) and dimethylsulfoxide (DMSO). All complexes gave two reversible reduction couples in the cathodic sides of the voltammograms in TBAP/DCM. While two oxidation processes were observed for all complexes in DCM, these processes were recorded as broad and split waves. All of the redox processes of the complexes shifted to the negative potentials and behaved more reversible in TBAP/DMSO electrolyte. Due to the narrow anodic potential window of DMSO, only one oxidation process was recorded in DMSO, while third reduction processes could be observed at more negative potentials for all complexes. Changing of the metal center of the complexes caused to shifting of the redox processes due to the different effective nuclear charge on the metal ions of the complexes. It can be easily concluded that the results of the voltammetric and in situ spectroelectrochemical supported the proposed structure of the complexes.

Permanganate-Route-Prepared Electrochemically Reduced Graphene Oxides Exhibit Limited Anodic Potential Window

Graphene-related materials have been of significant interest in the field of electrochemical sensing and biosensing. Four main methods of synthesizing large quantities of graphene from graphite via graphene oxide have been used to date, using either chlorate (Staudenmaier and Hofmann methods) or permanganate (Hummers and Tour methods) oxidants and strong mineral acids to generate graphite oxide with subsequent reduction. In electrochemical applications, electrochemical reduction is often used to prepare reduced graphenes so as to eliminate any electrochemically reducible groups on the surface of graphene oxides which could interfere with the analytical signals. Here, we show that electrochemical reduction of oxygen-containing groups at graphene oxide surfaces indeed results in materials without inherent electrochemistry for chlorate-based graphene oxides; however, permanganate-based electrochemically reduced materials exhibited significant limitation in the anodic region, starting from ∼+0.1 V (vs Ag/AgCl...

Electrochemically reduced graphene nanoribbons: Interference from inherent electrochemistry of the material in DPV studies

Graphene nanoribbons (GNRs) are attracting the interest of scientific community due to the outstanding versatility of their properties and applications. One of the most successful routes for the production of GNRs is the oxidative unzipping of carbon nanotubes followed by electrochemical reduction of oxygen functionalities. Electrochemically reduced graphene nanoribbons may present a reduced anodic potential window due to the intrinsic reversible chemistry of oxygen functionalities. Here we show that the oxidation signal obtained for caffeine on GNRs is strongly influenced by the inherent background signal of the reduced graphene nanoribbon material. Our findings provide important insight into the origin of the electrochemical signal obtained in the anodic region when using electrochemically reduced graphene nanoribbons as platform for sensing and biosensing. This insight bears high importance for future use of electrochemically reduced graphene nanoribbons in electroanalysis.

Transparent nanoporous tin-oxide film electrode fabricated by anodization

A transparent nanoporous tin oxide film electrode was fabricated by anodizing a tin film on a fluorine-doped tin oxide (FTO) film electrode. The resulting anodized nanoporous tin oxide (ANPTO) film has columnar-type pore channels with around 50 nm in diameter and is optically transparent. Electrochemical measurements with Fe(CN) 6 3− as a redox probe clearly revealed that the ANPTO film could be used for a working electrode with a large internal surface area. Moreover, it was found that ANPTO film had a wider anodic potential window (> ca. 2.0 V) than conventional metal oxide electrodes, such as FTO and indium tin oxide film electrodes (> ca. 1.3 V). The wide anodic potential window improves applicability of a transparent metal oxide electrode for various electrochemical oxidation reactions, which are often interfered by oxygen evolution in water. These results conclude that the ANPTO film can be used as an advanced transparent nanoporous film electrode.

Interfacing Boron Doped Diamond and Biology: An Insight on Its Use for Bioanalytical Applications

AbstractBoron doped diamond (BDD) films are promising materials for electroanalysis and bioelectroanalysis. This contribution gives a short review on BDD functionalization by chemical and biochemical entities and on the applications of BDD electrodes to electroanalysis of chemical compounds of biological interest. This review is illustrated by the developments on BDD interfaces in both these areas carried out in our group. BDD electrodes were prepared by means of microwave plasma‐assisted CVD onto silicon substrate giving rise to H‐terminated BDD films. Anodic polarization of BDD electrodes in aqueous media generates hydrophilic oxidized surfaces and extended electrochemical window in aqueous media. We took advantage of this enlarged electrochemical window together with the hydroxylated surface for the functionalization of BDD electrode surfaces with biomolecules and for bioelectroanalysis. We have designed a novel route of BDD functionalization using OH terminations of the anodized surface. The modification of the BDD surface with biotin groups will be presented here as biologically active model. Furthermore, as the anodic potential window of BDD increases upon electrochemical activation, 2′‐deoxyguanosine (1.2 V vs. Ag/AgCl) and 2′‐deoxyadenosine (1.5 V vs. Ag/AgCl) could be detected electrochemically with an acceptable signal to noise ratio. The electrochemical signature of each oxidizable base was assessed using differential pulse voltammetry (DPV). These experiments pointed towards adsorption of the oxidized products, which were investigated macroscopically by DPV and at the microscopic level by SECM (scanning electrochemical microscopy).

Dinuclear and Dendritic Polynuclear Ruthenium(II) and Osmium(II) Polypyridine Complexes: Electrochemistry at Very Positive Potentials in Liquid SO2

The electrochemistry in liquid SO2 of RuII and OsII dendritic polynuclear complexes (two hexanuclear species, having as the core a bis-chelating ligand, and one decanuclear species, built around a metal core) has been performed together with that of several of their lower-nuclearity analogues (five dinuclear and one trinuclear species), which can be considered as components of the larger dendritic species. All of the compounds contain 2,3- or 2,5-bis(2-pyridyl)pyrazine (2,3- or 2,5-dpp) as bridging ligands and 2,2‘-bipyridine (bpy) as terminal ligands. The identification of the redox sites for the compounds with high nuclearity was made possible by a bottom-up approach based on an extensive comparison of their electrochemical behavior with that of the simpler species. Owing to the large anodic potential window of liquid SO2 (to ∼4.3 V vs SCE under our experimental conditions) in conjunction with tetrabutylammonium hexafluoroarsenate as supporting electrolyte, several metal- and ligand-centered oxidations ...