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The search for new hydrogen evolution reaction (HER) electrocatalysts with lower cost and higher activity and stability than noble metal catalysts is essential. In this regard cobalt phosphide is considered one of the most promising nanomaterials. The present work proposes a simple and efficient method for the synthesis of a nanocomposite of graphene–phosphorene structures decorated with CoP nanoparticles 2–5 nm in size via the electrochemical exfoliation of black phosphorus carried out in the presence of nitrogen-doped few-layer graphene structures and followed by solvothermal synthesis in a Co2+-containing solution. The obtained CoP/EEBP/N-FLGS nanocomposite demonstrates high electrocatalytic activity and stability towards HER in an alkaline medium. The nanocomposite is characterized by an overpotential of 190 mV at a current density of 10 mA cm−2 as well as a small Tafel slope (78 mV dec−1). These characteristics make the CoP/EEBP/N-FLGS nanocomposite superior to most electrocatalysts based on cobalt phosphides. The results of this study could be in demand for the future design and improvement of HER electrocatalysts.

For the first time, graphene-phosphorene structures were synthesized using the plasma-assisted electrochemical method. The catalytic activity of the composite obtained in the electrolytic plasma mode and its mixtures with few-layer graphene structures toward the hydrogen evolution reaction was studied. A substantial increase in the catalytic activity of the phosphorene structures towards the hydrogen evolution reaction was realized by mixing them with few-layer graphene structures. The catalyst demonstrates excellent activity towards the hydrogen evolution reaction in alkaline media with a low overpotential of 940 mV at a current density of 10 mA·cm−2 and a small Tafel slope of 130 mV dec−1.

A simple method for the mechanochemical synthesis of an effective metal-free electrocatalyst for the oxygen reduction reaction was demonstrated. A nitrogen-doped carbon material was obtained by grinding a mixture of graphene oxide and melamine in a planetary ball mill. The resulting material was characterized by XPS, EPR, and Raman and IR spectroscopy. The nitrogen concentration on the N-bmGO surface was 5.5 at.%. The nitrogen-enriched graphene material (NbmGO has half-wave potential of −0.175/−0.09 V and was shown to possess high activity as an electrocatalyst for oxygen reduction reaction. The electrocatalytic activity of NbmGO can be associated with a high concentration of active sites for the adsorption of oxygen molecules on its surface. The high current retention (93% for 12 h) after continuous polarization demonstrates the excellent long-term stability of NbmGO.

Current-voltage characteristics of few-layer graphene structures (FLGS) obtained by plasma-assisted electrochemical exfoliation of graphite in Na2SO4 solution were measured. FLGS are shown to possess electronic conductivity, which indicates the predominant functionalization of the edges of graphene planes and the preservation of the structure of basal planes in obtained nanostructures as in the source graphite. The effect of humidity on the conductivity of FLGS films was studied. The resistance of films was found to increase with an increase in the relative humidity of the environment due to the shielding of FLGS flakes by a film of water. The effect of different solvents on the current-voltage characteristics of FLGS was analyzed. The conductivity of films significantly decreased in vapors of polar protic solvents, while there was a minor effect of nonpolar aprotic solvents on the conductivity of FLGS films.

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.

Nondestructive method for analysis of stoichiometric ratio in metal hydrides has been developed. It is based on analysis of total neutron cross sections for hydride samples measured in the area of slow neutrons with use of neutron spectrometry time of flight method. As on titanium hydride example, it is shown, that measurement and analysis of total neutron cross sections for samples TiHn allow to evaluate the value of ratio metal-hydrogen in hydride (n) with accu¬racy ~ 1 %.

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), Ni2L, 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 cm2 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 Ni2L 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 Ni2L 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 Ni2L 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 Ni2L 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. [ABSTRACT FROM AUTHOR]

Abstract The potentialities of electrochemical and combined methods for the determination of thermodynamic characteristics and kinetic parameters of intermediates are analyzed. The electrochemical methods include polarography, versions of voltammetry, and chronopotentiometry. The combined methods combine nonelectrochemical (or indirect) generation of intermediates with electrochemical methods of their subsequent investigation: photomodulation voltammetry, method of polarography of pulsed-radiolysis products, method of indirect electrolysis, electrochemiluminescence, and a group of laser photoemission methods. Theoretical foundations and basic advantages and disadvantages of the laser photoemission methods (the measurement of photocurrents in potentiostatic conditions—method of time resolved voltammograms obtained under chopped illumination and the measurement of the kinetics of variations in the potential of an electrode after illuminating it by a pulsed laser—in coulostatic conditions) are described in detail. The potentialities of the laser photoemission methods for the determination of thermodynamic (standard potentials E0 of redox pairs R·/R-, standard adsorption free energies) and kinetic (values of rate constants W0 at an equilibrium potential, bulk lifetime of radicals R·and products of their reduction R-) characteristics of intermediates are demonstrated by studying a trifluoromethyl radical. [ABSTRACT FROM AUTHOR]

Abstract A comparative investigation of thermodynamic and kinetic properties of a number of alkylaryl intermediates (benzyl and benzhydryl radicals) and alkyl halide intermediates (chloromethyl, dichloromethyl, and trifluoromethyl radicals) is performed by methods of laser photoemission. Techniques, aimed at the determination of thermodynamic and kinetic properties of intermediates (standard potentials E0 of redox pairs R·/R-, standard adsorption free energies -?Ga(R)0, values of rate constants W0 at an equilibrium potential, as well as lifetimes (times of death in the bulk) tR of radicals R· and tX of products of their reduction R-) from a comparison of Tafel plots for quasi-reversible reduction of intermediates with calculated ones and standard potentials E0—from Tafel plots for irreversible electroreduction of intermediates, are presented. The transition from irreversible to quasi-reversible reduction in aprotic solvents at E~E0 is observed only in the case of benzyl, benzhydryl, and trifluoromethyl radicals, for which this particular collection of thermodynamic and kinetic properties is obtained, and is not observed for the chloromethyl and dichloromethyl radicals. In this case redox characteristics of intermediates (E0, W0) are estimated from absolute values of rates of their electroreduction. Possible reasons for the differences in the probability of a reversible electron transfer are discussed for the systems studied. [ABSTRACT FROM AUTHOR]

The differential capacitance and voltammograms of electrodes that contain single-walled carbon nanotubes are measured in aqueous electrolytes. The discovered dependence of the capacitance on the measurement frequency is attributed to structural features of nanomaterials used. Electrochemical characteristics of nanotube electrodes are close to those of glassy carbon electrodes, with the difference that the discharge current in the former is substantially higher at cathodic potentials in the presence of N2O. This effect is presumably caused by an autoelectron emission of electrons from nanotubes into electrolyte. [ABSTRACT FROM AUTHOR]

Photoelectrochemistry of electrodes containing single-walled carbon nanotubes is studied for the first time ever. Photoemission of electrons from such electrodes illuminated by UV light is discovered. It is established that the photocurrent amplitude as a function of the imposed potential obeys the 5/2 law and that the work function into solution for nanotubes and a mercury electrode coincide to within 0.08 eV. Similarity of electrochemical behavior of intermediates on the nanocarbon and mercury electrodes is shown with the reduction of radicals ˙CH2Cl as an example. [ABSTRACT FROM AUTHOR]

A synthesis and a study by method of measuring the differential capacitance on a stationary mercury drop of the adsorption of a number of cubane derivatives in a surface-inactive electrolyte are performed. It is established that the compounds studied exhibit a high surface activity. For bromine derivatives of cubane (4-bromomethoxycarbonylcubane, 4-bromohydroxymethylcubane) the formation of two-dimensional adsorption layers is discovered. Values of adsorption parameters for these compounds are evaluated with use made of the Frumkin isotherm. [ABSTRACT FROM AUTHOR]

Mechanism of reduction and oxidation of carboxymethyl and chlorocarboxymethyl radicals and ion-radicals adsorbed on a mercury electrode is studied by a laser photoemission method in broad ranges of potentials and solution pH. Versions of reduction and oxidation depend on the solutions" acid–base properties. In acid solutions, a metastable complex ion-radical–(radical)–proton donor undergoes reduction. In neutral and weakly alkaline solutions, the electron transfer onto an ion-radical dominates. In strongly alkaline solutions, a metastable complex ion-radical–proton donor undergoes reduction. The last complex is oxidized in neutral and alkaline solutions at anodic potentials, whereas in acid solutions carboxymethyl radicals and ion-radicals are oxidized. Kinetic parameters of metastable complexes barely depend on the presence of the chlorine atom in the radical, in contradistinction to the reduction overvoltage of ion-radicals and their complexes, which discernibly diminishes following halogenation. The experimental data are interpreted within an earlier model for electrode reactions involving intermediates, which includes two parallel channels for the electron transfer: adsorbed radical (anion-radical) to electrode and metastable complex radical (anion-radical) to donor/acceptor of protons to electrode. [ABSTRACT FROM AUTHOR]