Asymmetric Marcus–Hush model of electron transfer kinetics: Application to the voltammetry of surface-bound redox systems

The asymmetric Marcus–Hush model (MH) is applied to the study of the voltammetric response of electroactive monolayers. While the well-documented symmetric MH model has been successful in modelling many aspects of surface-bound redox systems, it cannot account for the asymmetry evident in the Tafel plots for many experimental systems. ymmetric model has previously been used to explain deviations from the symmetric MH model observed for solution-phase redox systems [E. Laborda, M.C. Henstridge, R.G. Compton, J. Electroanal. Chem. 667 (2012) 48–53] by taking into account inner-shell differences between the oxidised and reduced species. We extend the theory to the description of electron transfer reactions of surface-bound species and examine several experimental features for both cyclic and square wave voltammetry, as well as Tafel plots, using both symmetric and asymmetric Marcus–Hush models and the phenomenological Butler–Volmer model. ymmetric MH model is seen to outperform the other models in terms of the quantitative description of the full voltammetric waveshape and is able to reproduce all of the experimental trends examined, as such its use for the analysis of surface-bound redox couples is highly recommended.