Volumes of activation for electrode processes of various charge-types in nonaqueous solvents

Homogeneous versus Heterogeneous Self-Exchange Electron Transfer Reactions of Metal Complexes: Insights from Pressure Effects

“…This is critically important because, as Weaver has stressed, , inadequately corrected R u effects can masquerade as electrochemical kinetics. An attractive feature of the ACV method is its ability to separate kinetic information from resistive effects even in solvents of very low permittivity such as benzene, and consequently it has become the method of choice in the author's laboratory for high-pressure electrode kinetics in both aqueous and nonaqueous solutions, − ,− since the pressurizable cell design leads to fairly high R u . The in-phase and quadrature background currents, I b x and I b y , are measured to obtain the total cell impedance, from which R u is subtracted to give the double-layer charging impedance, Z dl .…”

“…Such deposits can usually be removed by potential cycling . The ferricenium−ferrocene (FeCp 2 + /FeCp 2 ; Cp = η 5 -C 5 H 5 ) couple in incompletely degassed acetonitrile deposits an organic polymeric film containing hydrous Fe(III) oxide on electrodes through reaction of FeCp 2 + with residual O 2 , leading to irreproducible electron transfer kinetics. ,− Thus, in 1994, Fawcett and Opałło 96 listed nine reported values of k el for the FeCp 2 + /FeCp 2 electrode reaction at Pt electrodes in acetonitrile at room temperature ranging from 0.0194 to 220 cm s -1 , though several values clustered near the presently accepted value of about 2 cm s -1 (a little too fast for techniques using conventional electrodes). Ironically, the Fe(CN) 6 3-/4- and FeCp 2 +/0 couples have traditionally been used as reference couples for aqueous and nonaqueous electrochemistry, respectively;2a currently, the recommended alternatives are Ru(NH 3 ) 6 3+/2+ 97 and decamethylferrocene(+/0), , which ordinarily do not form films on electrodes.…”

“…It would seem, then, that the idiosyncrasies of electrode rate processes make for bleak prospects for a successful correlation of k el with k ex and that the rather loose correlation in Figure may be to some degree fortuitous. It has been found, however, that pressure effects on k el and k ex are informative in this context (section 4), − ,− and a brief background on electrochemical measurements at elevated pressures is given next.…”

Research Into Kinetics of Electron Exchange Reactions in the System Sym. Octamethylferrocene/Sym. Octamethylferricinium Hexafluorophosphate

“…Over the past 10-15 years an emphasis of a great number of research works has been laid on the study into kinetics and mechanism of electron exchange in the system of ferrocene-ferricinium and their alkyl derivatives [1][2][3]. The main reason of an emphasis on these objects is due to the necessity of replacement of unstable in a number of solvents ferrocene-ferricinium reference electrode (Fс +/0 ) by more promising, from the point of IUPAC standards, systemshighly substituted alkyl derivatives of ferrocene [2,3].…”

“…The main reason of an emphasis on these objects is due to the necessity of replacement of unstable in a number of solvents ferrocene-ferricinium reference electrode (Fс +/0 ) by more promising, from the point of IUPAC standards, systemshighly substituted alkyl derivatives of ferrocene [2,3]. In spite of numerous experimental and theoretical studies of electron exchange in the homogeneous and electrochemical heterogeneous systems [1][2][3][4][5][6][7][8], no mechanism of its proceeding has completely been clarified [3,7]. This work is a continuation of our previous researches [7,8] revealing that the electron exchange process in the system of Ме 6 Fс +/0 is determined not by the electron conjugation of the reactants in the transition state and the dynamics of the solvent molecules but by the energy of the reorganization of the solvent molecules around reactants.…”