Electrical-field-driven electron self-exchange in a mixed-valent osmium(II/III) bipyridine polymer: solid-state reactions of low exothermicity

Abstract

The dynamics of electrical-field-driven solid-state electron transfers between Os(II) and Os(III) sites in the 1:1 mixed-valent redox polymer poly [Os(III/II)(bpy)2(vpy)2] (C104)2 3 (bpy = bipyridine; vpy = vinylpyridine) are described. The nonlinear molecular conductivity of the polymer is modeled as an experimentally controllable intersite free energy gradient imposed by the electrical field. Electron self-exchange rates are analyzed as a function of free energy and temperature from 83 to 295 K with both classical and semiclassical electron-transfer theories. The analysis shows that room-temperature electron transfers lie near the high-temperature limit of classical behavior with a thermal barrier of 7-8 kcal/mol, but those at lowered temperature exhibit non-Arrhenius behavior and involve a nuclear tunneling mechanism. A single-frequency vibronic model gives 250 cm"1 as the vibrational energy and ca. 7 cm"1 as the electronic coupling term HAB. We derive an apparent intersite reaction free energy that is 3-8 times larger than those estimated from the applied voltage bias £ divided by the number of monolayers of osmium complex sites in the film. This effect may arise from imperfections in contacting electrodes to discussions with Professor R. P. Buck (UNC), Professor E. A. Irene (UNC), S. Feldberg (Brookhaven), and C. E. D. Chidsey (Bell Labs) are gratefully acknowledged.Registry No. Poly[Os(III/II)(bpy)2(vpy)2] (C104)2 5, 106762-37-2; Pt,

Redox and electrochemical water splitting catalytic properties of hydrated metal oxide modified electrodes

“…Similar quasi-diffusive effects have been discussed for a number of electroactive polymer systems. 205,[242][243][244][245][246] In light of the above discussion, the rate of charge percolation in the oxide layers may be quantified in terms of a charge transport diffusion coefficient D CT , reflecting either the rate of electron 'hopping' or the diffusion of protons/hydroxide ions via a rapid Grotthus type mechanism. 17 In this sense, Laviron [247][248][249][250][251][252] and Aoki 253,254 have developed useful models allowing the voltammetric response to be analysed quantitatively as a function of sweep rate.…”

Redox switching and oxygen evolution electrocatalysis in polymeric iron oxyhydroxide films

“…The variation of the hydrous oxide charge capacity, Q (which is proportional to the redox charge capacity, C, defined for electroactive polymer films in the work of Chidsey and Murray, [28][29][30][31] ) with analytical sweep rate is outlined in Fig. 6.…”

Solid-State Voltammetry — Analytical Prospects

“…In this situation, the mass transport (hopping) of electrons cannot be supported with ionic motion and the development of electrolytically generated concentration gradients is precluded [36,44]. The current developed with such mixed-valence materials is exponentially related to the applied voltage; however, for small voltage gradients it can be linearized [48,49]. Within this linear regime, the electrical (molecular) conductivity, j, can be related to the electron-self exchange dynamics [13] and expressed in terms of the electron diffusion as…”