Second-order Impedance in Electrode Kinetics

The kinetics of electrode reactions with a rather severe influence of the EDL structure is studied by nonlinear second-order impedance spectroscopy. Polarization impedance spectra and potential dependences of a nonlinear impedance are obtained for the reaction of electroreduction of the ferricyanide anion on the cadmium and bismuth electrodes in surface-inactive supporting NaF and Na₂SO₄ electrolytes. The results of measurements for the reaction Eu³⁺ + e Eu²⁺ on the bismuth and mercury electrodes are presented. It is shown that such important parameters of EDL as the potential of zero charge and the second derivative of potential with respect to the charge of the electrode surface can be determined directly from experimental curves even under conditions of occurrence of a faradaic process.     

Polarization Diagram of the Electrochemical Impedance of Second Order: A Theory that Accounts for the Diffusion of Reactants

With the aim of improving diagnostic possibilities of second-order impedance spectroscopy, a theory is put forward for a polarization diagram of a second-order impedance for reactions with charge transfer. The theory takes into account the diffusion of discharging particles in the absence of their specific adsorption.     

Second-Order Impedance Spectroscopy of an Electroreduction Reaction with Allowance for the Frumkin Correction

A theory of second-order impedance spectroscopy is developed. The theory is good for analyzing an electroreduction reaction in surface-inactive supporting electrolytes with allowance made for the structure of the electrical double layer (the Frumkin correction). According to the theory, a measured second-order impedance contains, as a factor, an effective charge transfer coefficient. The latter's dependence on potential has a minimum connected with the diffuseness of the electrical double layer. The theoretical notions are experimentally confirmed on the basis of a real system.     

Nonlinear Impedance of Liquid In–Ga Electrode in Aqueous Solutions of a Symmetrical Surface-Inactive Electrolyte

Experimental data related to the potential dependence of nonlinear characteristics of the electrical double layer at a liquid In–Ga electrode in aqueous solutions of a symmetrical surface-inactive electrolyte are obtained for the first time. It is shown that, as opposed to polycrystalline Cd and Pb electrodes, on a liquid (atomically smooth) In–Ga electrode, as on Hg, there is a clear intersection of the potential dependences of a nonlinear signal for different concentrations of a 1–1-valence surface-inactive electrolyte at one point. The intersection point exactly corresponds to the potential of zero charge of an electrode undistorted by specific adsorption of ions. It is established that, when estimating hydrophilicity of metals by a nonlinear impedance method, most information is provided by the region of average negative charges, rather than by the region near zero charge. It is shown that, as opposed to a linear impedance method, the nonlinear impedance method makes it possible to determine, directly from experiment, quantities that directly characterize the metal–solvent chemisorption interaction in a pure form; at the same time, these quantities are criteria of lyophilic nature of metals. Quantities that characterize the metal–solvent chemisorption interaction, obtained by the linear and nonlinear impedance methods are in good agreement, which confirms the validity of the approach we proposed earlier for separating the difference between reciprocal capacitances of the inner part of the electrical double layer on Hg and metal M, ^Hg _M C ^-1 _i= 1/C ^Hg _i– 1/C ^M _iinto physical (^Hg _M C ^–1)_physand chemical constituents. This coincidence also confirms correctness of numerical values obtained earlier for quantities (^Hg _M C ^–1)_phys.     

Synthetic Semiconductor Diamond Electrodes: Electrochemical Characteristics of Individual Faces of High-Temperature-High-Pressure Single Crystals

Effects of crystal structure on the electrochemistry of boron-doped high-temperature-high-pressure diamond single crystals grown from an Ni–Fe–C–B melt are studied. On the {111}, {100}, and {311} faces, the linear and nonlinear electrochemical impedance spectra and the electrochemical kinetics in the Fe(CN)₆ ^3_/4_ redox system are measured. The acceptor concentration in the diamond interior adjacent to these faces was determined from the Mott–Schottky plots and the amplitude-demodulation measurements. It varies in the 10¹⁸ to 10²¹ cm^–3 range. The difference in the electrochemical behavior of individual crystal faces is primarily attributed to different boron acceptor concentrations in the growth sectors associated with the faces.     

Adsorption Rectification and Demodulation

The electrochemical SOI of an adsorption process occurring at a finite rate is analyzed theoretically in the frequency-potential plane with the diffusion of species undergoing adsorption out of the bulk solution taken into account (Frumkin-Melik-Gaikazyan model).     

General Synthesis of 3-Azabicyclo[3.1.1]heptanes and Evaluation of Their Properties as Saturated Isosteres**

A general approach to 3-azabicyclo[3.1.1]heptanes by reduction of spirocyclic oxetanyl nitriles was developed. The mechanism, scope, and scalability of this transformation were studied. The core was incorporated into the structure of the antihistamine drug Rupatidine instead of the pyridine ring, which led to a dramatic improvement in physicochemical properties.