Cyclic Voltammetric Analysis of Ferrocene Alkanethiol Monolayer Electrode Kinetics Based on Marcus Theory

Abstract

Theory for electrode kinetics of surface-immobilized monolayers in cyclic voltammetry is developed based on the Marcus free energy-rate relation. Numerical calculations show that when the applied overpotential exceeds ~30% of the reorganizational energy of the electrode reaction, voltammetry predicted from Marcus theory differs from that based on classical Butler-Volmer kinetics with regard to wave shape, peak currents and their dependence on potential sweep rate, and variation of peak potential with potential sweep rate. Estimates of the standard rate constant, A®, can be made from Epak data without exact knowledge of reorganizational energies.Examples are given of evaluating A® for monolayers of ferrocene alkanethiols chemisorbed on Au(lll) electrodes, when the monolayers are highly ordered, and kinetically monodisperse, and when they are somewhat disordered, and kinetically disperse on bulk gold electrodes at room and 150 K temperatures.Theory enabling measurement of heterogeneous electrontransfer rates from cyclic voltammetric oxidation-reduction peak potential separations, AEpeak, was presented some time ago by Nicholson and Shain1 for diffusing and by Laviron2 for diffusionless (i.e., surface bound) electrochemical systems. This methodology is appealing by its ease of application; standard electron-transfer rate constants (A°) result from analysis of the dependence of AE^v alues on potential sweep rate using numerically generated working curves1 or explicit expressions.2 These theoretical formulations are based on the Butler-Volmer3 free energy-rate relation, which in the context of modern electron-transfer theory due to Marcus,4 assumes that the applied potential (free energy, overpotential, = E -E°') is much smaller than the electrode reaction's reorganizational energy barrier ( ). This paper will describe the theoretical and experimental behavior of cyclic voltammetry of nondiffusing (immobilized) electrode reactants when is not negligible in comparison to , i.e., in or approaching what is commonly referred to as the Marcus inverted region.4•5 This contribution is made in the context of recent potential step experiments6•7 with electroactive, self-assembled monolayers in which the ratio / is not small. Cochemisorption of a mixture of the alkanethiols CH3(CH2)i5SH and CpFeCpC02(CH2),6SH

Fundamental signatures of short- and long-range electron transfer for the blue copper protein azurin at Au/SAM junctions

“…S2 and S3. The method of Weber and Creager (59) and Tender et al (60), which is based on the Marcus relation (1) (see also ref. 61), was applied to obtain unimolecular standard rate constants and reorganization free energies through a fitting algorithm for values of the cathodic and anodic peak potentials as a function of the scan rate (see also refs.…”

Voltammetry of Adsorbed Molecules. Part 2: Irreversible Redox Systems

“…The development of self assembled monolayers in which an electroactive center could be positioned at fixed distances from the electrode has opened up the study of electrochemical reactions which can be used to test Marcus theory [11]. The initial use of Marcus theory in an experimental model was for chronoamperometry [12] but recently theories for LSV and CV have been published [8][9][10]. The rate constant for cathodic and anodic reaction in which there is weak electronic coupling between the reactants is [12] …”

Effect of the Interfacial Potential Distribution on the Measurement of the Rate Constant for Electron Transfer between Electrodes and Redox Adsorbates

“…Another recent development in the study of the linear sweep and cyclic voltammetry of adsorbates has been an attempt to include Marcus theory into models of the irreversible voltammetric response of redox adsorbates [15][16][17] . Nahir et al 15 used their model to explain the experimental CV for cytochrome c adsorbed on an carboxyalkanethiol monolayer.…”