53rd Meeting of the International Society of Electrochemistry

Russian Journal of Electrochemistry -     

Hydrogen Oxidation on a Platinum Microelectrode: Effect of Carbon Monoxide Impurities

The kinetics of the hydrogen oxidation and the CO adsorption on a Pt (ultra)microelectrode is studied in a 0.5 M H₂SO₄ solution saturated with a mixture of gaseous H₂ and CO at partial CO pressures p _CO = 10–500 ppm. The balance between rates of diffusion and adsorption of CO at different adsorption times is studied. Studied is the effect of CO impurities in H₂ on steady-state polarization curves for the hydrogen ionization and nonsteady-state curves of the oxidation current decay with time at 0.02–0.05 V. Conditions under which in a certain time interval and at a certain CO concentration the slope of an I vs. t curve is proportional to p _CO are determined. The obtained dependence may be used when designing a technique for monitoring CO impurities in technical hydrogen.     

Adsorption and Electrochemical Behavior of Cobalt Tetra(p-methoxyphenyl)porphyrin at Anisotropic Pyrographite

The electrochemical behavior and electrocatalytic activity of cobalt tetra(p-methoxyphenyl)porphyrin (CoTMPP) adsorbed at anisotropic pyrographite in the reaction of oxygen electroreduction in 0.5 M H₂SO₄ is studied by cyclic voltammetry. Dependences of voltammogram parameters (currents and potentials of maximums of the Co^3+/2+TMPP redox reaction, numbers of adsorbed and working molecules, values of uncompensated layer resistance) on the adsorbate concentration (10^–6 to 10^–3 M) in chloroform are analyzed. It is concluded that adsorbed molecules change their orientation from a flat to an inclined position at c _CoMPP> 5 × 10^–5 M. The optimum, as to the effectiveness of CoTMPP in the oxygen reduction, is the adsorption layer thickness close to the thickness of a monolayer of flatly-oriented molecules.     

Sorption of water vapor on cation-substituted vermiculite

Deformations of Na, Ca, and Ba vermiculites upon sorption of water vapor have been determined by a dilatometric method. Sequential stages in the hydration of interlayer exchange cations have been identified. The experimental results have been compared with data obtained in studies using adsorptive, calorimetric, and x-ray methods.Institute of Physical Chemistry, Russian Academy of Sciences, 117915 Moscow. Institute of Colloid Chemistry and the Chemistry of Water, Academy of Sciences of the Ukraine, Kiev. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 1, pp. 34–39, January, 1992.     

Special features in the chemical structure of phosphorus isocyanates

The UV and IR absorption spectra and the NMR and NQR spectra of certain isocyanates of three- and four-coordinated phosphorus have been investigated. The reciprocal effect of the phosphorus atom and the NCO group is discussed on the basis of spectral analysis, quantum chemical calculations of the electron systems, and calculations of the normal vibrational forms. Comparison of the (PO) frequencies in the IR spectra of the phosphorus isocyanates with the Taft gives a linear relationship which testifies to the predominant inductive effect of the NCO group on the P(O)R₁R₂ grouping. A similar relationship is observed between the resonance frequency _res in the NMR spectra and for C1P(O)R₁R₂ compounds. The effect of the phosphorus atom on the electronic system in the NCO group is shown by the hypsochromic shift of the absorption band in the210-m region and an appreciable increase in its intensity, compared with alkyl isocyanates. This fact, which agrees with the NMR spectral data and the quantum chemical calculations, indicates the presence of conjugation in the P-N bond. We found the order of the P-N bond to be approximately 1.2. This partial double-bond nature of the P-N bond results from the interaction of the p electrons of nitrogen in the NCO group with the d orbitals of the phosphorus atom.We are grateful to our colleagues at the Kazan Physicotechnical Institute AS USSR A. I. Rivkind, S. G. Salikhov, and I. A. Safin for recording the spectra.     

Adsorption studies of organosubstituted laminated silicates

The hysteresis of sorptive deformation of sorbents has been studied for the first time. Based on the results obtained, it is assumed that the deformation of sorbents could be the universal reason for the sorptive hysteresis.For Part 1, see Ref. 1.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1477–1479, August, 1995.     

Mediated Bioelectrocatalytic Oxidation of Glucose on a Glucose Oxidase-Containing Composite

A composite material, which includes glucose oxidase (GOD), finely divided colloidal graphite, ferrocene, and Nafion, is developed and investigated. Kinetic parameters of redox conversions of GOD and flavin adenine dinucleotide, which is present in the active center of GOD, indicate that GOD in the composite retains molecular integrity and enzymic activity. Ferrocene in the composite undergoes reversible oxidation and is reduced on the electrode. Bioelectrocatalytic oxidation of glucose on the composite occurs via a mediator path, and the half-wave potential of a polarization curve recorded on the electrode in the presence of glucose coincides with the redox potential of ferrocene, which is equal to 0.32 V (Ag/AgCl). Effect of the ferrocene amount in the composite and the glucose concentration in the bulk solution on the glucose oxidation is studied. The results are used to optimize the composite's composition to ensure a stable operation of the enzyme electrode and effective glucose oxidation.     

Microcalorimetric Study of Water Adsorption on Initial and Polyfluoroalkylated Silicas

Water adsorption on initial and modified Silochrom samples was studied by the adsorption calorimetry. Integral heats of immersional wetting by water were measured simultaneously. It was shown that hydroxyl groups both free and sterically screened by a modifier remain on the modified Silochrom surface. Concentrations of these groups and OH groups chemically interacted with the modifier were estimated. The heat of reaction of water molecules with a free surface OH groups of modified sorbents was determined (≈60 kJ/mol). It was found that the modifying layers of the sorbents are getting loose under the effect of adsorbed water, and water molecules gain access to the sterically screened OH groups; the heat of water interaction with these groups is 54–55 kJ/mol. The energy is consumed for getting the modifying layers loose and the rupture of point contacts between Aerosil particles of the secondary structure of both initial and modified Silochrom that significantly affects the heat of immersion, the differential heat of adsorption, the form of the heat release curve, and the dependence of the differential heat on the adsorption value.     

Ion-exchange equilibria and exchange heats on clinoptilolite involving singly-charged cations

Isotherms and integral heats of exchange of alkali metal, ammonium, and silver cations on sodium clinoptilolite were measured. Exchange involving K₊, NH₄ ⁺, Cs⁺, and Ag⁺ displacing cations was found to be exothermic for all occupancies of the clinoptilolite exchange sites. Exchange was exothermic for Li₊ cations up to = 0.15. The dependence of the differential ion-exchange heats on was determined. Clinoptilolite was found to have two types of exchange sites with different heats of ion exchange. The experimental data were used to calculate the selectivity coefficients, thermodynamic constants, and ion-exchange entropy. These findings are discussed relative to the differences in the cation properties and structural features of clinoptilolite.A. V. Dumanskii Institute of Colloid Chemistry and the Chemistry of Water, National Academy of Sciences of Ukraine, 42 Prospekt Akademika Vernadskogo, 252680 Kiev-142, Ukraine. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 32, No. 5, pp. 315–319, September–October, 1996. Original article submitted February 12, 1996.