Influence of bovine immunoglobulin G on faradaic reactions at electrodes

The effect of bovine immunoglobulin G (IgG), adsorbed on different electrode materials, on faradaic reactions of hexacyanoferrate(III)-hexacyanoferrate(II), hydroquinone-benzoquinone, nicotinamide adenine dinucleotide, reduced from (NADH), and phenol is described and discussed. The reactions are partially inhibited by IgG, but the current and peak potentials reach protein-independent values for higher concentrations of IgG. The hydroquinone-benzoquinone couple can be used for detection purposes at IgG-covered electrodes in electrochemical immunoassays.     

Carbon materials for supercapacitor application

The most commonly used electrode materials for electrochemical capacitors are activated carbons, because they are commercially available and cheap, and they can be produced with large specific surface area. However, only the electrochemically available surface area is useful for charging the electrical double layer (EDL). The EDL formation is especially efficient in carbon pores of size below 1 nm because of the lack of space charge and a good attraction of ions along the pore walls. The pore size should ideally match the size of the ions. However, for good dynamic charge propagation, some small mesopores are useful. An asymmetric configuration, where the positive and negative electrodes are constructed from different materials, e.g., activated carbon, transition metal oxide or conducting polymer, is of great interest because of an important extension of the operating voltage. In such a case, the energy as well as power is greatly increased. It appears that nanotubes are a perfect conducting additive and/or support for materials with pseudocapacitance properties, e.g. MnO(2), conducting polymers. Substitutional heteroatoms in the carbon network (nitrogen, oxygen) are a promising way to enhance the capacitance. Carbons obtained by one-step pyrolysis of organic precursors rich in heteroatoms (nitrogen and/or oxygen) are very interesting, because they are denser than activated carbons. The application of a novel type of electrolyte with a broad voltage window (ionic liquids) is considered, but the stability of this new generation of electrolyte during long term cycling of capacitors is not yet confirmed.     

Hybrid materials for supercapacitor application

In the present study, a manganese oxide obtained by the acid treatment of LiMn₂O₄ spinel has been used as a positive electrode of supercapacitor. Removal of lithium from a spinel allowed to obtain MnO₂ compound with the pores partly distributed in atomic scale, hence, an efficient use of its pseudocapacitive properties could be reached. On the other hand, residual lithium remaining in the structure preserved layered framework of MnO₂ with pathways for ions sorption. Physical properties, morphology, and specific surface area of electrode materials were studied by scanning and transmission electron microscopy, and nitrogen sorption measurements. Voltammetry cycling, galvanostatic charge/discharge, and impedance spectroscopy measurements performed in two- and three-electrode cells have been applied in order to measure electrochemical parameters. Neutral Li₂SO₄ aqueous solution has been selected for electrolytic medium. Extension of operating voltage for supercapacitor has been realized through asymmetric configuration with an activated carbon as a negative electrode. The asymmetric capacitor was operating within a voltage range up to 2.5 V (limited to 2.0 V for cycling tests) and was able to deliver a specific capacitance of 60 Fg⁻¹ per capacitor at 100 mA g⁻¹ current density. High specific energy of 36 Wh kg⁻¹ was reached but with a moderate power density.     

可逆反应的热静力学研究法

本文建立了一种新的可逆反应的热静力学研究方法, 并利用本法研究了18-冠-6与钾离子、钡离子在水中的配位反应。实验测得的这两种反应的平衡常数和焓变与文献值很好吻合。本法适用于平衡常数大于1而小于10^4的反应体系。     

Detailed equilibrium principle in reversible bimolecular diffusion-controlled reactions

The expressions for the observed rate constants of the forward bimolecular and back monomolecular reactions have been obtained using the boundary conditions imposed upon the reaction surfaces of each reagent particle. The rate, equilibrium and thermodynamical parameters of the back dissociation reactions of phenoxy radical dimers have been measured. The resultant values of k^obs_?1 as a function of solvent viscosity are accurately described by theoretical relationships obtained in the present work.     

Electrochemical supercapacitor application of pervoskite thin films

We have explored electrochemically deposited pervoskite nanocrystalline porous bismuth iron oxide (BiFeO₃) thin film electrode from alkaline bath for electrochemical supercapacitors. The pervoskite BiFeO₃ nanocrystalline thin film electrode showed comparable specific capacitance of 81 F g⁻¹ and electrochemical supercapacitive performance and stability in an aqueous NaOH electrolyte to that of commonly used ruthenium based pervoskites.     

On-line FFT faradaic admittance measurements application to A.C. cyclic voltammetry

A measurement approach is described and data are presented which demonstrate the ability to effect a.c. cyclic voltammetric measurements with the on-line digital FFT approach to faradaic admittance data acquisition. The equipment utilized enables complete faradaic admittance spectra to be obtained at an effective spectrum acquisition rate of 10 s^?1, so that the d.c. potential range encompassed by a typical cyclic wave can be encompassed with adequate resolution in the E_dc dimension in ≥6 s, approximately. The instrument features dynamic, computerized measurement and compensation of the non-faradaic ohmic resistance and double-layer capacitance contributions to the acquired total cell admittance. Measurements with quasi-reversible systems yield the expected faradaic admittance and phase angle responses over a quite generous bandwidth. Applications to mercury and platinum electrodes are illustrated.     

Nanotubes based composites rich in nitrogen for supercapacitor application

Exceptional conducting and mechanical properties of multiwalled carbon nanotubes (Nts) used for carbonisation a polymer blend of melamine (M) and formaldehyde (F) enabled to prepare a unique Nt-composite rich in nitrogen. Using a different proportion of Nts and a polymer blend, a series of composites with a comparable texture (surface area of ca. 400 m²/g) but variable N content ranging from ca. 7 to 20 wt% has been obtained without any activation process. A detailed analysis of physicochemical properties of composites has been performed and correlated with supercapacitor characteristics. Composite with ca. 12 wt% of nitrogen showed the best charge propagation, its mesoporous network allowed a pseudocapacitance effect of nitrogen to be efficiently used.     

Kinetic equation for reversible heterogeneous catalytic reactions

It is demonstrated that when operating far from equilibrium, despite the non-linearity of a complex reaction system, the overall rate of a heterogeneous catalytic reaction is expressed by a classical equation, where the equilibrium constant is determined by the ratio of constants of the forward and reverse reaction, which do not include the lateral interactions in the adsorbed layer.     

Plasmonic response of electrified metal-liquid interfaces during faradaic and non-faradaic reactions by enhanced optical transmission

Thin Au films, patterned by focused ion beam (FIB) milling to contain an array of subwavelength nanopores, exhibit enhanced optical transmission (EOT) via front-back resonance coupling. The films also serve as working electrodes capable of controlling the local potential, allowing electrochemical processes to be monitored using wavevector-resolved spectral mapping. The precise value of the surface plasmon resonance (SPR) wavevector can be extracted from the enhanced optical transmission signal and correlated with several distinct classes of electrochemical processes: double layer reorganization, faradaic adsorption/desorption, heterogeneous electron transfer, and anion adsorption. Specifically, the protonation/deprotonation reaction of an adsorbed monolayer of 4-mercaptobenzoic acid, the adsorption/desorption reaction of dodecanethiol to Au, the solution-phase reaction of ferri-ferrocyanide, and sulfate adsorption/desorption are investigated. A simple model is presented that encompasses both the EOT signal and electrochemical processes and produces semi-quantitative agreement with the SPR spectral wavevector mapping observed experimentally.     

Non-isothermal two-membrane reactors for reversible gas phase reactions

The performance of a non-isothermal two-membrane reactor for reversible chemical reactions in gas phase has been analyzed by numerical simulation. The analyzed reactions were of the form: aA = bB + cC. Two membranes, that are permeable to all the components of the reaction mixture, are supposed to be the most permeable to one of the two reaction products, satisfying the condition of reverse products permselectivities. The reactant is taken to be the slowest permeating component. A negative temperature influence on the permeabilities of components has been assumed. Co-current plug flow pattern has been accepted. It has been shown that it is possible to enhance reactant conversion above that of a conventional reactor for both endothermic and exothermic reversible reactions, including adiabatic and non-adiabatic case. By using a two-membrane reactor, considerable lowering of feed temperatures is enabled for an endothermic reaction. For endothermic reactions, there is the optimum feed temperature, whereas for exothermic reactions, the higher the temperature, the lower is the attained conversion. In reactor design, the optimal external heat exchange for both endothermic and exothermic reactions can be determinated.     

Thermoanalytical studies of the kinetic of reversible reactions

A method is described for determination of the kinetic parameters of reversible reactions under isothermal and non-isothermal conditions in thermal analysis. Reversible reactions of the first and second orders and of mixed types are considered. The kinetic parameters of the forward and reverse reactions are determined on the basis of the initial integral data of the thermoanalytical experiment. The results of processing a computerized experiment demonstrated that the suggested method is satisfactorily applicable.

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Zusammenfassung Es wurde eine Methode zur Bestimmung kinetischer Parameter von reversiblen Reaktionen unter isothermen bzw. nicht-isothermen Umständen in der Thermoanalyse beschrieben. Umkehrbare Reaktionen erster Ordnung, zweiter Ordnung sowie Reaktionen vom Mischtyp wurden betrachtet. Die kinetischen Parameter der Hin- bzw. Rückreaktionen wurden auf der Grundlage der Anfangsintegrale der termoanalytischen Experimente bestimmt. Die Ergebnisse eines computermodellierten Experimentes zeigen, dass die vorgeschlagene Methode befriedigend angewendet werden kann.

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The regularities of reversible chain reactions in the equilibrium state

The characteristics of dynamic equilibrium states in the experimentally studied reversible chain reactions of quinoneimines with hydroquinones and in some reversible chain reactions with similar mechanisms are discussed. The concentrations of radicals and non-radical participants were calculated. The equilibrium concentrations of the same reaction participants depend only on the initial reactant concentrations, being independent of the number of chain initiation-chain termination steps in the reaction mechanism. The results of mathematical modeling of reversible chain reactions using the experimentally determined rate constants for elementary steps of a reaction in the quinoneimine-hydroquinone system are presented. Expressions relating the equilibrium constants of elementary steps to each other and to the equilibrium constant of the total stoichiometric reaction are derived. Examples of other actual reversible chain reactions are presented, indicating that such reactions are widespread.     

Role of reversible dimerization in reactions of amphoteric aziridine aldehydes

Unprotected aziridine aldehydes belong to the amphoteric class of molecules by virtue of their dual nucleophilicity/electrophilicity. The dimeric nature of these molecules, brought together by a weak and reversible aminal "connection", was found to be an important element of reactivity control. We present evidence that reversible dimer dissociation is instrumental in aziridine aldehyde transformations. We anticipate further developments that will unveil other synthetic consequences of remote control of selectivity through forging reversible covalent interactions.     

Nitrogen-doped carbon aerogel synthesis by solvothermal gelation for supercapacitor application

Journal of Solid State Electrochemistry - Nitrogen-doped mesoporous carbon aerogel having high surface area and high nitrogen content was synthesized by sol–gel method for supercapacitor...