Elektrochemische Methode zur quantitativen und kontinuierlichen Bestimmung von Ozon in Gasgemischen

The method is based on the measurement of the diffusion controlled limiting current obtained with the cathodic reduction of ozone according to O₃ + 2H⁺ + 2e^? → H₂O + O₂ in sulphuric acid. The electrolyte is vigorously mixed with the gas containing ozone and circulated through the electrolytic cell by the ascending gas flow operating as a gas-lift pump. The solution saturated with ozone moves along a cylindric electrode consisting of a smooth platinum foil in laminar flow. A constant potential is maintained at the electrode by means of a potentiostat in such a way, that the electrochemical reaction is proceeding under limiting current conditions. A lead anode of high capacitiy is used as a counter- and reference electrode. The current recorded continuously is directly proportional to the concentration of ozone in gas.     

Rate determination of the catalytic oxidation of methane and propane in an electrochemical solid-electrolyte reactor

The possibility of using a solid-electrolyte reactor in kinetic studies of the catalytic oxidations of hydrocarbon with molecular oxygen was investigated. A theoretical analysis of processes in a catalytically asymmetric gas-diffusion cell in N₂ + O₂ + CH₄ and N₂ + O₂ + C₃H₈ gas mixtures was performed. Analytical expressions are presented for calculating the oxygen, methane, and propane concentrations and the methane and propane oxidation rates in the inner space of the cell from the emf of the latter. The potentiometric response was studied experimentally after the addition of methane and propane in the gas mixture in a reactor with silver electrodes and samples with applied catalytic materials. The concentrations of the components in the inner space of the reactor and the oxidation rates of hydrocarbons were calculated from the experimental data.     

Electrode Potentials of Cells with an Electrolyte Based on Zirconium Dioxide in Gas Mixtures N2+ O2+ CO2+ CO: A Platinum Electrode

Steady-state potentials of various platinum electrodes are measured in cells containing electrolyte ZrO₂+ Y₂O₃(10 mol %) in the temperature range 673–773 K in binary equilibrium gas mixtures N₂+ O₂and CO + CO₂, as well as in four-component nonequilibrium gas mixtures N₂+ O₂+ CO₂+ CO containing 0–3 vol % CO and 0–10 vol % O₂. Adding CO to a gas mixture makes the electrode potential deviate from equilibrium, which is explained by chemisorption of CO on the electrode. The oxygen, which is adsorbed on platinum, interacts with CO; as a result, CO₂undergoes desorption and the surface concentration of CO drops.     

Effect of oxygen activity and water partial pressure to degradation rate of Ni cermet electrode contacting Zr<Subscript>0.84</Subscript>Y<Subscript>0.16</Subscript>O<Subscript>1.92</Subscript> electrolyte

The time curves of full polarization resistance of Ni cermet electrode modified with CeO_{2 − δ} additive were studied by means of impedance spectroscopy in binary gas mixtures x% H₂ + (100 − x)% H₂O, 10% CO + 90% CO₂ and multicomponent gas mixtures H₂ + CO₂ + H₂O + CO + Ar of various composition at the temperature of 900°C. The Ni cermet electrode degradation rate in binary gas mixtures H₂ + H₂O was shown to increase sharply at the partial water pressure over 45%. The Ni cermet electrode degradation rate in the mixture of 10% CO + 90% CO₂ was significantly lower than that in 10% H₂ + 90% H₂O. The major changes in the electrode characteristics upon long exposure in working conditions were accounted for by changes in the high-frequency partial polarization resistance. In the course of long testing, the electrode microstructure was not significantly changed. In the presence of hydrogen-containing components (H₂ and H₂O), the carbon-containing components (CO and CO₂) were shown to make an insignificant contribution to the current generation processes in Ni cermet electrode. It was suggested that strong degradation of Ni cermet electrode was caused by poisoning its reaction sites with strongly linked adsorption forms of water (hydroxyls) at the positive charge of electrode.     

Oxygen isotope exchange between the gas-phase and the electrochemical cell O<Subscript>2</Subscript>, Pt | YSZ | Pt,O<Subscript>2</Subscript> under conditions of applied potential difference

The kinetics of oxygen isotope exchange between gas-phase oxygen and the electrochemical cell O₂, Pt | ZrO₂ + 10 mol % Y₂O₃ (YSZ) | Pt, O₂ with applied potential difference (ΔU = ±1.2 V) is studied in the temperature range of 600–800°С and the oxygen pressure interval of 3–13 kPa. An original design of a vacuum electrochemical cell with the separated gas space is put forward for studying how the potential difference on the electrochemical cell influences the kinetics of interaction of gas-phase oxygen with the gas electrode O₂, Pt | YSZ in the electrochemical cell. It is shown that the oxygen interphase exchange rate is the higher the more negative the charge on the electrode studied; moreover, the mechanism of gas-phase oxygen exchange with the gas electrode O₂, Pt | YSZ in the electrochemical cell depends fundamentally on the electrode charge sign. The possible reasons for the revealed differences are discussed; the corresponding models are proposed.     

Catalytic effects of metal submonolayers formed by faradaic adsorption on the anodic oxidation of ascorbic acid at a platinum electrode

The catalytic effects of metal ions on the anodic oxidation of ascorbic acid on a Pt electrode in 1 M HClO₄ were studied by linear sweep voltammetry. The anodic peak due to a two-electron oxidation of ascorbic acid shifts to the negative potential side on the addition of Bi³⁺. This indicates the accelerating effect of Bi³⁺ on the oxidation of ascorbic acid. The presence of other metal ions, such as Pb²⁺, Hg²⁺, Tl⁺, Ag⁺ and Sb³⁺, also exerts similar effects. These metal ions were adsorbed on a Pt electrode at underpotentials and the adsorbed metals (denoted as M_ad) still remain on the electrode surface until the electrode potential goes up to and beyond the peak potential of the oxidation of ascorbic acid. On the other hand, metal ions forming no adsorbed layer on Pt, such as Co²⁺, Zn²⁺, Fe³⁺ and Ni²⁺, exhibit no catalytic effect. These facts suggest that the presence of a M_ad on Pt is essential for the promotion of the anodic oxidation of ascorbic acid. However, there is a difference in the catalytic action among the M_ad, for example, Cu_ad, Cd_ad, In_ad, Sn_ad and Mo_ad display no catalytic action.The catalytic activity depends on the degree of surface coverage by the M_ad. The maximal effect of the M_ad is attained in the submonolayer region. The effects of metal ions were discussed on the basis that the M_ad plays its major role in the removal of the adsorbed ascorbic acid occupying active sites on the electrode surface, and provides effective sites for the activation of adjacent water molecules. Furthermore, from the ¹³C NMR spectra for the oxidation products, the adsorbed water on the M_ad appears to function by promoting the subsequent hydration steps, following the electron-transfer step of ascorbic acid.     

Open-circuit polarization of a porous platinum electrode in an atmosphere with a changing oxygen content: Diffusion model and equation for polarizing flux

A diffusion-kinetic model for an open-circuit polarization of a porous platinum electrode is considered. The electrode is situated on the surface of a solid-electrolyte cell of 0.9ZrO₂ + 0.1 Y₂O₃ in an atmosphere containing oxygen, inert gas, and carbon dioxide or water vapor. Deceased.     

Gas diffusion hindrances on Ni cermet anode in contact with Zr<Subscript>0.84</Subscript>Y<Subscript>0.16</Subscript>O<Subscript>1.92</Subscript> solid electrolyte

The electrochemical behavior of Ni cermet electrode with CeO_{2 ? x} additive in contact with YSZ electrode was studied by means of impedance spectroscopy in H₂, H₂O, CO₂, CO, He, and Ar gas media of various composition within the temperature range of 700 to 950°C. Near the equilibrium potential, the electrochemical impedance spectra of the studied electrodes indicate to three stages of electrode reaction. The polarization conductivity of the low-frequency stage of electrode reaction (σ_lf) is characterized with the following regularities: (a) temperature dependence of σ_lf has a positive slope in Arrhenius coordinates; (b) σ_lf increases upon replacement of gas mixture with lower mutual diffusion coefficient by mixture with higher mutual diffusion coefficient, while polarization conductivity values of other stages remain practically invariable; (c) concentration relationships of 1/σ_lfrecorded for constant activity of oxygen in the gas phase are linear in the 1/σ_lf vs. 1/P _{CO 2} (P _CO) coordinates; (d) no low-frequency stage of the electrode reaction is observed upon electrochemical inflow (outflow) of the gas reagents (reaction products) to (from) the test electrodes (current passing through closely pressed specimens and central specimen impedance measurement); and (e) no change in the gas flow rate affects σ_lf value. The observed regularities were explained by assuming the gas diffusion nature of the low-frequency stage of the electrode reaction. The gas diffusion layer thickness was estimated.     

Hydrogen Isotope Exchange Reactions in an Atmospheric Pressure Discharge Utilizing Water as Carrier Gas

Allowing water/hydrogen or water/hydrogen/He gas mixture to flow through micro- hollow type of electrodes and applying 60 Hz AC power between the electrodes made it possible to sustain large area and atmospheric pressure discharge. The electrode assembly was constructed by sandwiching a dielectric spacer with two thin metal sheets and boring an array of micro holes through them. Another variation of the assembly was prepared by stacking thin metallic sheets so that the stack functions as an electrode through which the gas mixture flows for generating dielectric barrier discharge. A large volume of the gas mixture, while producing plasma, underwent instantaneous hydrogen isotope exchange reactions between H₂O and D₂O or between D₂O and H₂ gas molecules. The efficiency of the atmospheric pressure discharge was assessed by measuring the extent of the exchange reactions at a given flow rate of the gas mixture.     

Open-circuit polarization of a porous platinum electrode in an atmosphere with a changing oxygen content: Comparing a polarization equation to experimental results

The dependence of overpotential on emf of a porous platinum electrode polarized under open-circuit conditions is analyzed on the basis of a polarization equation. The electrode is situated on the surface of a solid-electrolyte cell of 0.9ZrO₂ + 0.1Y₂O₃ in an atmosphere containing oxygen, inert gas, and carbon dioxide or water vapor. A comparison with the experiment is performed. Deceased.     

Two‐Dimensional Spatial Resolution of Concentration Profiles in Catalytic Reactors by Planar Laser‐Induced Fluorescence: NO Reduction over Diesel Oxidation Catalysts

Planar laser‐induced fluorescence (PLIF) enables noninvasive in situ investigations of catalytic flow reactors. The method is based on the selective detection of two‐dimensional absolute concentration maps of conversion‐relevant species in the surrounding gas phase inside a catalytic channel. Exemplarily, the catalytic reduction of NO with hydrogen (2 NO+5 H₂→2 H₂O+2 NH₃) is investigated over a Pt/Al₂O₃ coated diesel oxidation catalyst by NO PLIF inside an optically accessible channel reactor. Quenching‐corrected 2D concentration maps of the NO fluorescence above the catalytic surface are obtained under both, nonreactive and reactive conditions. The impact of varying feed concentration, temperature, and flow velocities on NO concentration profiles are investigated in steady state. The technique presented has a high potential for a better understanding of interactions of mass transfer and surface kinetics in heterogeneously catalyzed gas‐phase reactions.     

Preparation of an Electrode Modified with an Electropolymerized Film as a Mediator of NADH Oxidation and Its Application in an Ethanol/O2 Biofuel Cell

This paper reports a novel mediator for the oxidation of β‐nicotinamide adenine dinucleotide (NAD⁺/NADH), an electropolymeric film (pAPRu) of [Ru(NH₂‐phen)₃]²⁺. A pAPRu‐modified electrode was prepared via electropolymerization and exhibited catalytic activity toward the electrochemical oxidation of NADH due to the imine moieties of pAPRu. The electrochemical oxidation of ethanol was observed using an alcohol dehydrogenase (ADH)‐immobilized electrode. A compartmentless ethanol/O₂ biofuel cell composed of an ADH anode and a bilirubin oxidase cathode was constructed. The maximum current density and the maximum power density of the biofuel cell were 190 µA cm^?2 and 31 µW cm^?2 (at 0.29 V), respectively.     

Product Determination of Gaseous Radical Reactions Using Matrix Isolation-Ftir Detection

The matrix isolation technique with Fourier transform infrared detection has been applied to determine the products of gaseous radical reactions. The gas phase reactions were carried out in a discharge flow system and about 1% of the gas mixture was deposited onto a low temperature target through a pinhole. A differential pumping scheme was employed to maintain the pressure of the cryosystem below 10^?5 torr while that of the flow system was kept at about 2 torr. Species including HO₂ (from the H+O₂ reaction), ClO₂ (from the Cl+O₂ reaction) and ClO (from the Cl+O₃ reaction) have been produced in the gas phase and were successfully trapped in matrices and detected with an FTIR spectrometer. In addition, both HCl and HOCl have been detected as the reaction products from the gaseous ClO+HO₃ reaction. The production of HCl from the ClO+HO₂ reaction may have a significant impact on catalytic ozone destruction in the atmosphere.     

Electrochemical Synthesis of Chitosan‐co‐polyaniline/WO3⋅nH2O Composite Electrode for Amperometric Detection of NO2 Gas

An electrode of hydrated tungsten oxide (WO₃?nH₂O) embedded chitosan‐co‐polyaniline (CHIT‐co‐PANI) composite was electrochemically prepared on an indium tin oxide (ITO) coated glass surface using mineral acid as a supporting electrolyte. The resulting CHIT‐co‐PANI/WO₃?nH₂O/ITO electrode was characterized using ultraviolet‐visible spectroscopy (UV‐vis), Fourier transform infrared spectroscopy (FTIR), cyclic voltammetry (CV), and scanning electron microscopy (SEM). The composite electrode exhibited a three‐dimensional nanofibrous structure with the diameter of the nanofibers ranging from 20 to 100 nm. The CHIT‐co‐PANI/WO₃?nH₂O/ITO electrode allowed for the low potential detection of NO₂ gas in acidic medium. The NO₂ gas sensing characteristics were studied by measuring change in the current with respect to concentration and time. Using the CHIT‐co‐PANI/WO₃?nH₂O/ITO electrode, NO₂ gas was detected electrochemically without interference at pH 2.0 and 0.25 V vs. Ag/AgCl. The current of the electrochemical cell with the CHIT‐co‐PANI/WO₃?nH₂O/ITO electrode decreased linearly with an increase in NO₂ gas concentration in a range from 100 to 500 ppb with a response time of eight seconds.     

Anodic reactions of the halides in dimethyl sulfoxide at the pyrolytic graphite electrode

The anodic reactions of the halide ions in dimethyl sulfoxide at the pyrolytic graphite electrode have been studied. The iodide ion demonstrates a 3-step oxidation; the bromide, a 2-step oxidation and chloride, a 1-step oxidation. The electrode reaction (X^-→$\text{1}\text{2}$ X₂ + e^-) is complicated by a catalytic reaction occurring after the electrode reaction. The catalytic reaction is important for only bromide and chloride causing a considerable diffusion current enhancement. The αn_a value for all 3 primary reactions is of the order of 0.5.     

Quartz crystal microbalance monitoring of density changes in mesoporous TiO2 phytate films during redox and ion exchange processes

Nanofilm deposits of TiO₂ nanoparticle phytates are formed on gold electrode surfaces by ‘directed assembly’ methods. Alternate exposure of a 3-mercapto-propionic acid modified gold surface to (i) a TiO₂ sol and (ii) an aqueous phytic acid solution (pH 3) results in layer-by-layer formation of a mesoporous film. Ru(NH₃)₆³⁺ is shown to strongly adsorb/accumulate into the mesoporous structure whilst remaining electrochemically active. Scanning the electrode potential into a sufficiently negative potential range allows the Ru(NH₃)₆³⁺ complex to be reduced to Ru(NH₃)₆²⁺ which undergoes immediate desorption. When applied to a gold coated quartz crystal microbalance (QCM) sensor, electrochemically driven adsorption and desorption processes in the mesoporous structure become directly detectable as a frequency response, which corresponds directly to a mass or density change in the membrane. The frequency response (at least for thin films) is proportional to the thickness of the mass-responsive film, which suggests good mechanical coupling between electrode and film. Based on this observation, a method for the amplified QCM detection of small mass/density changes is proposed by conducting measurements in rigid mesoporous structures.     

Elektrochemische Methode zur quantitativen und kontinuierlichen Bestimmung von Ozon in Gasgemischen

Zusammenfassung Die vorgeschlagene Methode zur Ozonbestimmung beruht auf der Messung des Diffusionsgrenzstromes bei der kathodischen Reduktion von Ozon nach O₃ + 2H⁺ + 2e^– H₂O + O₂ in Schwefelsäure. Der Elektrolyt wird in der elektrochemischen Meßzelle intensiv mit dem ozonhaltigen Gas durchmischt und durch den aufsteigenden Gasstrom nach dem Prinzip der Mammutpumpe kontinuierlich im Kreislauf transportiert. Die mit Ozon gesättigte Lösung fließt in laminarer Strömung über eine zylindrische Meßelektrode aus glattem Platin. An dieser Elektrode wird mittels eines elektronischen Potentiostaten ein solches Potential konstant eingestellt, daß die elektrochemische Reaktion stets im Grenzstrombereich abläuft. Als Gegen- und Bezugselektrode wird eine Bleianode mit hoher Kapazität eingesetzt. Der mit einem Schreiber registrierte Strom ist dem Ozongehalt im Gas direkt proportional.

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Electrochemical method for quantitative and continuous determination of ozone in gas mixtures

The method is based on the measurement of the diffusion controlled limiting current obtained with the cathodic reduction of ozone according to O₃ + 2H⁺ + 2e^– H₂O + O₂ in sulphuric acid. The electrolyte is vigorously mixed with the gas containing ozone and circulated through the electrolytic cell by the ascending gas flow operating as a gas-lift pump. The solution saturated with ozone moves along a cylindric electrode consisting of a smooth platinum foil in laminar flow. A constant potential is maintained at the electrode by means of a potentiostat in such a way, that the electrochemical reaction is proceeding under limiting current conditions. A lead anode of high capacitiy is used as a counter- and reference electrode. The current recorded continuously is directly proportional to the concentration of ozone in gas.

     

Reversible Solid Oxide Fuel Cell for Power Accumulation and Generation

The anodic and cathodic polarization dependences for the oxygen electrode based on lanthanum-strontium manganite and the fuel Ni-cermet electrode are studied in the temperature range of 700–900°С in gas media that correspond to working conditions of a reversible fuel cell. The temporal behavior of these electrodes is studied in the course of periodic polarity changes of current with the density of 0.5 A/cm². The electrode overvoltage is shown to be about 0.1 V in modes of power generation and water electrolysis at 900°С and the current density of 0.5 A/cm². A single electrolyte supported tubular solid-oxide fuel cell was fabricated and tested in the fuel-cell and hydrogen-generation modes. It is found that at 900°С and overvoltage of 0.7 V, the cell generates the specific electric power of 0.4 W/cm² when the 50% H2 + 50% H₂O gas mixture is used as the fuel and air is used as the oxidizer. At the water electrolysis with the current density of 0.5 A/cm², which under normal conditions corresponds to generation of about 0.2 and 0.1 L/h of hydrogen and oxygen, respectively, the consumed power is about 0.55 W/cm². The efficiency of the conversion cycle electric power–hydrogen–electric power is 70–75%.     

Ni/ZSM‐5 Zeolite Modified Carbon Paste Electrode as an Efficient Electrode for Electrocatalytic Oxidation of Formaldehyde

In this study, we prepared a modified carbon paste electrode consisting of Nickel entrapped in synthesized ZSM‐5 zeolite (Ni/ZMCPE). Then Ni(II) ions were incorporated to electrode by immersion of modified electrode in 1 M Ni(II) ion solution. Cyclic voltammetry and chronoamperometry experiments were used for electrochemical study of this modified electrode; a good redox behavior of Ni(OH)₂/NiOOH couple at the surface of electrode can be observed, the excellent capability of this modified electrode for catalytic oxidation of formaldehyde was demonstrated during the anodic potential sweep in alkaline solution. The amount of transfer coefficient (α), surface coverage (Γ*) of the redox species and catalytic chemical reaction rate constant (k) for formaldehyde were evaluated. Thus, it can be a candidate as an anode for fuel cell application.     

Nickel‐Catalyzed Facile [2+2+2] Cyclotrimerization of Unactivated Internal Alkynes to Polysubstituted Benzenes

A catalytic [2+2+2] cyclotrimerization of unactivated internal alkynes providing cyclotrimerization products in excellent yields with high regioselectivity is described. The transformation is accomplished by using a simple catalytic mixture comprising Ni(acac)₂, an imidazolium salt and a Grignard reagent at room temperature or 60 °C for 20 min or 1 h.