Thermodynamic and kinetic characteristics of intermediates of electrode reactions: Determination by direct and combined electrochemical methods

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.