Dissipative structures formed in the layer of magnetic suspension upon the action of rotating elliptically polarized magnetic field

Structural transformations that take place in an ensemble of spherical particles suspended in a liquid layer with finite thickness are studied upon the action of rotating elliptically polarized magnetic field with the polarization plane perpendicular to the plane layer. Results of physical and numerical studies of the transformation of dissipative structure upon variations in the polarization ellipse of magnetic field are reported.     

Design and application of a magnetic field gradient electrode

A platinum coated electrode, which creates a magnetic field of 25 mT and a field gradient of order 10⁵ T m⁻¹ within 100 nm of the electrode surface is produced by embedding an array of CoPt nanowires in an alumina membrane. There is an enhancement by up to a factor of three for a model oxygen reduction reaction in an alkaline medium when the nanowires in the electrode are in a magnetized state. We suggest that the enhancement of the oxygen reduction current is associated with an increase of concentration of ${\text{HO}}_2^{-}$ on the surface of the electrode by the magnetic field gradient.     

Desorption of hydrogen from the electrode surface under influence of an external magnetic field

The effect of a uniform magnetic field in perpendicular-to-electrode configuration, on the hydrogen evolution reaction was investigated during the deposition of Fe and CoFe alloys. It was found that the desorption of hydrogen is supported in a magnetic field. This effect is discussed in details with respect to the micro-magnetohydrodynamic convection, which arises due to the fluctuation of the current distribution close to the H₂ bubble.     

Interaction between a stationary mercury electrode and a hydrogen bubble in an aqueous sodium dodecyl sulphate solution

The stability and rupture of thin liquid films formed from an aqueous solution of Na₂SO₄ (0.05 mol dm⁻³) in the presence of 5 × 10⁻⁵ mol dm⁻³ sodium dodecyl sulphate between a stationary mercury electrode and a hydrogen bubble has been investigated as a function of electrode potential. The electrostatic component of disjoining pressure has been calculated using the results of capacity measurement for the mercury-solution interface. Special attention has been paid to films formed on positively charged mercury surfaces. In this case, despite the positive electrode polarization, the outer Helmholtz plane potential is found to be negative due to the high surface activity of the dodecyl sulphate anion. The van der Waals component of disjoining pressure has been calculated on the basis of a double sheath model of the two interacting surfaces, taking into consideration the orientation of the adsorbed surfactant layers at the interfaces. Calculations of the total disjoining pressure can explain film stability at negative mercury potentials, but do not explain film rupture when the polarization of the mercury is positive. The existence of a hydrophobic attractive interaction is postulated in the latter case.     

Electrochemical reduction of oxygen to hydrogen peroxide in a gas-diffusion electrode based on mesoporous carbon

Mesoporous carbon prepared by template synthesis using SBA-15 mesostructured silicate material was tested as an electrocatalyst for electrochemical synthesis of Н₂О₂ from О₂ in a two-layer gas-diffusion electrode. Preparative syntheses of Н₂О₂ in 0.06 to 2.0 M aqueous solutions of various electrolytes (pH 2–8) were performed at current densities in the interval 0.05–0.19 A cm^–2. Solutions with an Н₂О₂ concentration of 1–2.8 M were prepared with 46–70% current efficiency. Thus, the material tested shows promise as an electrocatalyst of two-electron reduction of oxygen to Н₂О₂.     

Semiclassical self-consistent field perturbation theory for the hydrogen atom in a magnetic field

A recently developed perturbation theory for solving self-consistent field equations is applied to the hydrogen atom in a strong magnetic field. This system has been extensively studied using other methods and is therefore a good test case for the new method. The perturbation theory yields summable large-order expansions. The accuracy of the self-consistent field approximation varies according to field strength and quantum state but is often higher than the accuracy from adiabatic approximations. A new derivation is presented for the asymptotic adiabatic approximation, the most useful of the adiabatic approaches. This derivation uses semiclassical perturbation theory without invoking an adiabatic hypothesis. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 69: 183–192, 1998     

Electrosynthesis of hydrogen peroxide from oxygen in a gas-diffusion electrode in solutions of mineralized exometabolites

The electrosynthesis of H₂O₂ in aqueous solutions (pH 1–9) of mineralized liquid and solid bio-wastes (exometabolites) for their processing in closed life-support systems was studied. It was shown that H₂O₂ can be obtained in these solutions by electrochemical reduction of oxygen in carbon black gas diffuse electrodes to concentrations of over 2 M with current efficiency 80%. The composition of the solution was found to affect the accumulation of H₂O₂ during the synthesis. The solutions can be concentrated further to 19 M H₂O₂. The results showed that the electrolytic method is promising for preparing H₂O₂ for closed life-support systems.     

Thin layer gas electrode and its application to measurement of dissolved oxygen

A novel thin layer cell equipped with thin layer gas electrode (TLGE) was studied as electrochemical gas sensor for the measurement of dissolved oxygen in water or aqueous solutions. The working electrode (TLGE) is a hydrophobic gas diffusing electrode placed between the cell electrolyte and the solution to be tested. The hydrophobic pores in TLGE serve as a gas chamber. After the sampling period, in which the partial pressure of dissolved oxygen in test solution becomes in equilibrium with that in the gas chamber, the TLGE is polarized with square wave or linear potential signal. Then the Faradaic charge (Q) consumed in depletion of the oxygen contained in pores of TLGE is measured. The main merits of this system are good linearity between the partial pressure of dissolved oxygen in test solution and Q, low zero-reading, negligible liquid-gas difference, convenient calibration and very low temperature coefficient (ca. 0.5%/°C). This technique can also be applied to the measurement of oxygen partial pressure in gas phases.     

Electrochemical noise analysis of the effects of a magnetic field on cathodic hydrogen evolution

The effect of a static magnetic field on the evolution of hydrogen gas from a small platinum electrode in an aqueous electrolyte has been studied by recording the noise spectrum of overpotential voltage fluctuations at a constant current density of ?50 mA mm^?2. A 1/f² variation of the power spectrum characteristic of droplet coalescence is found for frequencies >10 Hz. The overpotential for hydrogen evolution decreases with applied field. When the production of gas bubbles is quasiperiodic, there is a threshold field of 0.5 T beyond which the size of the bubbles released is approximately doubled. This is explained by enhanced coalescence of small bubbles swept across the electrode surface by forced convection due to the Lorentz force.     

Solid particle in the boundary layer of a rising bubble

The hydrodynamic interaction of a solid particle and the boundary layer around a rising bubble is analyzed in the before-contact state (BCS) of a flotation act. The lagging of the particle behind the basic outer flow is accounted for. The forces acting on the particle are qualitatively examined. A new term is introduced in the force balance — the migration force. An expression for the collision efficiency is proposed that concerns a particle already entrained in the bubbles boundary layer.     

Effect of trialkylammonium salts and current density on the electrosynthesis of hydrogen peroxide from oxygen in a gas-diffusion electrode in acid solutions

The influence exerted by the nature of cation of a supporting electrolyte and by the current density on the electroreduction of oxygen to hydrogen peroxide in acid K₂SO₄ solutions (pH 0.9–1.4) in gas-diffusion hydrophobized carbon black electrodes with varied electrolyte porosity was studied.     

The dynamics of a bubble ensemble in a cavitation field

A system of equations was obtained to describe the dynamics of bubbles in a cavitation cloud taking into account the interaction of pulsating bubbles involved in translational motion. The kinetics of cavitation bubble concentration changes, changes in the compressibility of the liquid, and phase transitions within a cavitation bubble and in the neighboring volume of the liquid were taken into account. The role played by bubble deformation in a cavitation cloud was considered. The Bernoulli pressure effect was shown to be negligible. The interaction of cavitation bubbles was a substantial factor that strongly influenced the dynamics of bubbles. It was suggested that there was at least one more mechanism that reduced sonoluminescence intensity from the multiple-bubble cavitation field, namely, a fairly high efficiency of sonoluminescence quenching could additionally be related to the arrival of a cumulative liquid stream at the central cavitation bubble region, where the concentration of active species was high. The dynamics of bubbles in the cavitation field is not only related to the expansion and compression of cavitation bubbles in the acoustic field, but also governed to a great extent by their interaction, translational motion, deformation, and the influence of cumulative streams penetrating the bubbles.     

Regularity and chaos in the center of mass motion of the hydrogen atom in a magnetic field

What does the center of mass motion of the hydrogen atom in a magnetic field look like? Is it similar to the uniform straight-lined motion of the field-free case or does is perform only tiny vibrations? We show that there is a great variety in the center of mass motion. For regular electronic motion only a bounded range of phase space is available for the center of mass coordinate. There exist many different types of regular center of mass behavior according to the values of the magnetic field strength, energy and angular momentum. At the onset of chaos in the electronic motion a prominent transition to chaos in the center of mass motion is observed. In the fully chaotic regime the trajectories of the center of mass exhibit many properties of a random motion and fill up the unbounded coordinate space. In particular, we obtain a linear diffusion law for the spreading of an ensemble of center of mass trajectories.     

A new structure of water layer on Cu(111) electrode surface during hydrogen evolution

A layered structure of water molecules formed on a Cu(111) electrode surface during hydrogen evolution in sulfuric acid solution was studied by surface X-ray diffraction and infrared reflection absorption methods. Water molecules in the surface layers take a closest pack-like stacking structure with nearest-neighbor oxygen-oxygen distances in intra-(0.322(5) nm) and inter-(0.275(15) nm) layers of multi-domains; the infrared spectra of the layered water on the Cu electrode surface showed the existence of free OH(OD) and hydrogen-bonded OH(OD) of water molecule.     

Kinetic considerations on the electrogenerated luminescence of luminol at platinum electrode in the presence of hydrogen peroxide and oxygen

The ECL behavior of the luminol/H2O2 and luminol/O2 systems was evaluated at Pt electrode by using different electroanalytical techniques such as chronoamperometry, cyclic and rotating disk electrode (RDE) voltammetry. Diffusive and kinetic parameters such as the diffusion coefficient of luminol, D, the number of exchanged electrons, n, and the apparent heterogeneous rate constant, kap, were determined in the maximum light emission conditions achieved at pH 11, at an electrode potential of 750 mV vs. SCE. The experimental order of reaction were determined from the relation between the reactant concentrations and the emitted light intensity.     

Nanoscale membrane electrode assemblies based on porous anodic alumina for hydrogen–oxygen fuel cell

In this paper, we demonstrate that nanoscale membrane electrode assemblies, functioning in a H₂/O₂ fuel cell, can be fabricated by impregnation of anodic alumina porous membranes with Nafion® and phosphotungstic acid. Porous anodic alumina is potentially a promising material for thin-film micro power sources because of its ability to be manipulated in micro-machining operations. Alumina membranes (Whatman, 50 μm thick, and pore diameters of 200 nm) impregnated with the proton conductor were characterized by means of scanning electron microscopy, X-ray diffraction, and thermal analysis. The electrochemical characterization of the membrane electrode assemblies was carried out by recording the polarization curves of a hydrogen–oxygen 5 cm² fuel cell working at low temperatures (25?÷?80 °C) in humid atmosphere. Our assemblies realized with alumina membranes filled with phosphotungstic acid and Nafion® reach respectively the peak powers of 20 and 4 mW/cm² at room temperature using hydrogen and oxygen as fuel and oxidizer.     

Summation of the perturbation series for the energy levels of a hydrogen atom in a magnetic field

A new method to sum divergent power series is developed and applied to the calculation of the energy levels of the hydrogen atom in a uniform magnetic field. Analytical expressions for the first two eigenstates obtained in this way are shown to agree closely with accurate numerical calculations in the whole range of field strengths.     

The porous CuO electrode fabricated by hydrogen bubble evolution and its application to highly sensitive non-enzymatic glucose detection

The porous Cu film was deposited on a Pt/Ti/Si substrate by electrochemical deposition accompanied by hydrogen evolution at very high current densities. CuO films with similar morphologies were obtained by subsequent annealing of the porous copper films. The morphology, composition and structure of the porous Cu and porous CuO were investigated by FE-SEM, EDS and XRD methods. The complete transformation of Cu to CuO after annealing was indicated. The sensing performances of the porous CuO film were evaluated in alkaline solution with the porous CuO film showing a wide linearity range from 1 μM to 2.5 mM with sensitivity of 2.9 mA cm⁻² mM⁻¹, and detection limit of 0.14 μM. The sensor showed good selectivity to conventional intermediates such as AA and UA and long term stability.     

Measurements of the hyperfine structure of hydrogen dimers in zero magnetic field

Measurements of the zero magnetic field hyperfine spectra of the ortho—para and the ortho—ortho hydrogen dimers are presented. Comparison with the theoretical spectra yields expectation values for the intermolecular separation, rotational constant and anisotropic intermolecular interaction strengths in the dimers.