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1.
Materials (Basel) ; 14(2)2021 Jan 09.
Artigo em Inglês | MEDLINE | ID: mdl-33435447

RESUMO

A graphene oxide aerogel (GOA) was formed inside a melamine sponge (MS) framework. After reduction with hydrazine at 60 °C, the electrical conductive nitrogen-enriched rGOA-MS composite material with a specific density of 20.1 mg/cm3 was used to fabricate an electrode, which proved to be a promising electrocatalyst for the oxygen reduction reaction. The rGOA-MS composite material was characterized by elemental analysis, scanning electron microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy. It was found that nitrogen in the material is presented by different types with the maximum concentration of pyrrole-like nitrogen. By using Raman scattering it was established that the rGOA component of the material is graphene-like carbon with an average size of the sp2-domains of 5.7 nm. This explains a quite high conductivity of the composite obtained.

2.
Langmuir ; 31(25): 7129-37, 2015 Jun 30.
Artigo em Inglês | MEDLINE | ID: mdl-26043143

RESUMO

The effects of electrochemical oxidation and surfactant adsorption on behavior of vertically oriented carbon-nanowall (CNW)-based electrodes are studied. Electrochemical oxidation is carried out by the electrode polarization in aqueous solutions at high anodic potentials corresponding to water electrolysis, whereas the modification of surface by surfactants is accomplished by the adsorption of molecules characterized by the cage-like structure. Using the methods of cyclic voltammetry and impedancemetry, it is shown that a substantial increase in the capacitance of CNW-based electrodes is observed in both cases (30-50-fold and 3-5-fold, respectively). The as-grown and modified electrodes are characterized by scanning electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. A substantial increase in a number of oxygen-containing functional groups is observed on the CNW surface after the electrode polarization at high anodic potentials. The kinetics of redox reactions on the CNW film surface is studied by comparing the behavior of systems [Ru(NH3)6](2+/3+), [Fe(CN)6](4-/3-), Fe(2+/3+), and VO3(-)/VO(2+). It is demonstrated that oxidation of nanowalls makes the electron transfer in the redox reaction VO3(-)/VO(2+) and the redox system Fe(2+/3+) considerably easier due to coordination of discharging ions of these systems with the functional groups; however, no such effect is observed for the redox-systems [Fe(CN)6](3-/4-) and [Ru(NH3)6](2+/3+).

3.
Phys Chem Chem Phys ; 10(17): 2390-8, 2008 May 07.
Artigo em Inglês | MEDLINE | ID: mdl-18414730

RESUMO

The multistep reduction of a binuclear Ni(ii) Robson-type complex with a multidentate template-like organic ligand (formed from 4-tert-butyl-2,6-diformylphenol and 1,3-diaminopropane), Ni(2)L, is studied using the electron photoemission technique. The number of transferred electrons corresponding to a single reduction wave is found to be 8 per complex species. This value is attributed to both complete Ni(ii) reduction (with Ni metal formation) and ligand reduction. Contributions of Ni(ii) and ligand to acceptor orbital were estimated. Three initial subsequent steps correspond to electron transfer to mixed metal-ligand orbital with comparable contributions. For more deep reduction, ligand contribution predominates. The first single-electron step is evidenced to be rate-determining, with the rate constant of 0.03 cm(2) s(-1). The latter value is discussed in the framework of a semiquantitative analysis of the rate constants estimated in the framework of quantum-mechanical electron transfer theory for different orientations of Ni(2)L in the reaction layer. The analysis includes estimations of key kinetic parameters (electronic transmission coefficient, solvent- and intramolecular contributions to the total reorganization energy) which strongly rest on the results of quantum chemical modeling. The transmission coefficients at realistic electrode-reactant distances of the closest approach are below 0.001. This means that despite of the noticeable delocalization of Ni(2)L acceptor orbital, the electron transfer is diabatic. Predominating contribution to reorganization energy results from solvent and does not exceed 0.5 eV for any reactant orientation. The highest reactivity is predicted for a planar orientation located mostly outside the compact part of electric double layer. The Ni(2)L adsorption in planar and vertical orientations on mercury is addressed as well. The results give a clear explanation of the previously observed self-inhibition of "dark" reduction of Ni(2)L on mercury and independent data on the adsorption of these species. The discovered combination of various orientation effects is compared with effects observed for other reactants.


Assuntos
Diaminas/química , Níquel/química , Compostos Organometálicos/química , Fenóis/química , Simulação por Computador , Eletroquímica , Cinética , Ligantes , Modelos Químicos , Teoria Quântica
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