Adsorption characteristics of electrodes containing nanostructured carbon of different morphology

The effect of camphor adsorption on the differential capacitance of electrodes of nanostructured carbon of different morphology (single-walled carbon nanotubes, filiform carbon, and columnar structures) in aqueous electrolyte solutions and also on the electrochemical reactions in these systems is studied. It is shown that irrespective of the ac frequency, the differential capacitance of the nanopaper and columnar electrodes increases 3–5-fold throughout the studied potential range. This experimental fact is explained by the substantial increase in the electrode surface accessible for electrolyte, which is a manifestation of the Rehbinder effect in electrochemistry. The revealed different kinds of effects of camphor adsorption layers formed at the nanostructured carbon/electrolyte interface on the electron transfer processes are as follows: partial inhibition of both the electron injection and the K₃[Fe(CN)₆] reduction; complete suppression of the reduction of sodium nitrate and nitrite; the absence of effects on the OH radical reduction and solvated electron oxidation.     

Hydrogen Evolution on a Mercury Electrode: The Effect of a Condensed Adsorption Layer

The electroreduction of hydrogen on a dropping mercury electrode with and without condensed adsorption layers (CAL) of organic compounds is studied by methods of classical polarography and laser photoemission. An analysis of effects CAL has on some reactions reveals that the CAL influence on the first-electron transfer and on reactions involving intermediates can retard or even completely block the process. The most profound changes occur in the processes that involve a proton donor. Possible reasons for different effects of CAL on the electron transfer processes are discussed.     

Silver Cation Reduction on a Mercury Electrode: Effect of Two-Dimensional Condensed Layer of 1-AdOH during Individual Adsorption and Coadsorption with Tetraalkyl Cations

Effect of a condensed layer (CL) of 1-adamantanol (1-AdOH) during individual adsorption and coadsorption with tetraalkyl cations on the kinetics of the electroreduction (ER) of cation Ag⁺ at a mercury electrode is studied with the aim of revealing the link between the rate of electrode processes and the structure of two-dimensional CL. It is shown that ER of Ag⁺ occurs by means of penetration of the depolarizer particles through the adsorption layer. Polarization curves are calculated under the assumption that the potential barrier for ER of Ag⁺ in the presence of CL of 1-AdOH is defined by the work for overcoming two-dimensional pressure in the layer. Satisfactory agreement between experimental and calculated dependences in the region of ascending branches of polarization curves is demonstrated. It is established that the degree of the inhibiting action of mixed adsorption layers (as compared with individual CL of 1-AdOH) on ER of Ag⁺ depends on the 1-AdOH activity in solution and the nature of the organic cation. It is assumed that the latter effect is caused by the surface activity of cations studied.     

Adsorption of compounds with the skeleton molecular structure from dimethylsulfoxide solutions on mercury electrode

The adsorption of adamantane (Ad), adamantanol (AdOH), thiocamphor (TC), and a supramolecular complex (cryptate) of sodium ion [Na⁺ ⊂ 2.2.2.] from DMSO solutions on the mercury electrode is studied by the differential capacitance method. In the considered systems, the surfactants exhibit the high surface activity, which manifests itself in different ways depending on the potential scan direction. For AdOH, TC, and [Na⁺ ⊂ 2.2.2.] that have either a dipole moment or an electrostatic charge, it is assumed that the important role is played by the adsorbate-solvent interaction at the interface, which can be the key factor determining the formation of a new adsorption layer structure in the positive potential range. The adsorption behavior of the mentioned group of surfactants radically differs from that of Ad hydrocarbon, namely, the adsorption of the latter is not accompanied by the formation of a new adsorption layer structure. The obtained results suggest that for the adsorption of surfactants from nonaqueous solvents (in contrast to aqueous solutions), the interaction between the adsorbate and the solvent molecules, which under certain condition results in the formation of two-dimensional supramolecular structures at the electrode/solution interface, acquires substantial importance.     

Kinetics of solid-phase H<Superscript>+</Superscript>/M<Superscript>+</Superscript> ion exchange on hafnium hydrogen phosphate

The kinetics of solid-phase reactions between hafnium hydrogen phosphate and alkali metal chlorides were studied by thermogravimetry with subsequent analysis of leaving gases. For sodium and potassium chlorides, the reaction occurs in two stages; the first stages produces MHHf(PO₄)₂, and the second yields the MHf₂(PO₄)₃ NASICON phosphate. For rubidium chloride, the reaction is one stage and produces Rb₂Hf(PO₄)₂. For cesium chloride, the reaction is an analogue of the reaction for rubidium chloride, but has two stages. Kinetic data were used to determine interdiffusion coefficients for hydrogen and alkali-metal ions at various temperatures and the activation energies of interdiffusion.     

Synthesis and characterization of MF-4SK + SiO<Subscript>2</Subscript> hybrid membranes modified with tungstophosphoric heteropolyacid

Composites based on MF-4K perfluorinated cation-exchange membranes doped with hydrous silica nanoparticles, which were precipitated under various conditions, and with tungstophosphoric heteropolyacid nanoparticles were synthesized. The proton conductivity of the composites was studied as a function of temperature and relative ambient humidity. As a result of modification, the water content and ion conductivity of the membranes in low humidities increase by 2.5 orders of magnitude compared to unmodified MF-4SK membranes and the material is rendered less water-dependent.     

Method for determining rate constants of processes in atoms and molecules

A variant method is proposed for determination of rate constants of elementary processes occurring within a plasma, including irradiation of the plasma by resonant radiation. In the proposed variant the radiant power is varied during experiment, but remains less than the value which causes saturation of fluorescence. It is shown that this method permits simultaneous determination of several constants. The technique is demonstrated for a C₂ molecule. The effective section for thermal excitation of the level d³_g from states (X¹ _g ⁺ + a³_u) is determined, equal to 3·10^–18 cm²±80%.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 19–23, October, 1988.     

Porphyrinylphosphonate-Based Metal–Organic Framework: Tuning Proton Conductivity by Ligand Design

A novel metal–organic framework [Zn₃(Ni-H₂TPPP)(Ni-H₄TPPP)(Ni-H₅TPPP) ⋅ 7(CH₃)₂NH₂ ⋅ DMF ⋅ 7 H₂O] (where Ni-H_xTPPP (x=2,4,5) are partially deprotonated [5,10,15,20-tetrakis(3-(phosphonatophenyl)-porphyrinato(2-))]nickel(II) species), IPCE-2Ni , with outstanding proton conductivity (1.0×10⁻² S cm⁻¹ at 75 °C and 95 % relative humidity) has been obtained. The high concentration of free phosphonate groups and compensating dimethylammonium cations bound by hydrogen bonds in the unique crystal structure of IPCE-2Ni is a key factor responsible for the observed high proton conductivity, which is one order of magnitude higher than for the corresponding MOF based on 5,10,15,20-tetrakis(4-(phosphonatophenyl)porphyrinato(2-))]nickel(II) IPCE-1Ni and comparable with that of leaders among MOFs.     

Monolayers of Supramolecular Cryptate Complexes at the Electrode/Solution Interface

Russian Journal of General Chemistry - The results of investigation of the electrochemical properties of cryptand 222 from the macropolycyclic ligands group and its complexes with cations were...