Analytical Chemistry

Finite Element Modelling of the Combined Faradaic and Electrostatic Contributions to the Voltammetric Response of Monolayer Redox Films

Authors

Abstract

The voltammetric response of electrodes coated with a redox-active monolayer is computed by finite element simulations based on a generalized model that couples the Butler-Volmer, Nernst-Planck and Poisson equations. The model yields a full description of the electric potential and charge distributions across the monolayer and into the bulk solution, including the potential distribution associated with ohmic resistance in the bulk solution. In this way, it is possible to properly account for electrostatic effects at the molecular film/electrolyte interface, which are present due to the changing charge states of the redox head groups as they undergo electron transfer, under both equilibrium and non-equilibrium conditions. Our numerical simulations also significantly extend previous theoretical predictions by simultaneously including both the effects of finite electron-transfer rates and electrolyte conductivity. Distortion of the voltammetric wave due to ohmic potential drop in the solution is shown to be a function of the supporting electrolyte concentration and scan rate, in agreement with experimental observations. The electric potential and charge distributions across an electrochemically inactive monolayer and into the solution are also simulated as a function of applied potential and are found to agree with the Gouy-Chapman-Stern theory, allowing numerical predictions of the capacitive background currents in voltammetric experiments.

Content

Thumbnail image of 2. Modelling Redox SAM film paper_SHORT FINAL.pdf

Supplementary material

Thumbnail image of 3. Redox SAM modelling Supporting Information_SHORT FINAL.pdf
Supporting Information
SI 1. Details of the finite element model implemented in COMSOL Multiphysics SI 2. Voltammetric response of electrochemically inactive molecular films SI 3. Quantification of experimental errors caused by incorrect assumptions on the behaviour of the non-faradaic current SI 4. Simulated voltammetry of electrochemically active molecular films with low surface coverages of redox-active groups SI 5. Calculating the uncompensated resistance of the electrochemical cell SI 6: The RC transient response at the switching potential SI 7. Influence of supporting electrolyte and scan rate on the voltammetric response SI 8. Details of simulating a 2-electron redox system SI 9. References