Finite element modelling of surface-bound quinone proton coupled electron transfer voltammetry

Area of Science:

• Electrochemistry
• Computational Chemistry
• Surface Science

Background:

• Proton coupled electron transfer (PCET) is crucial in biological and chemical systems.
• Surface-bound quinones are important electroactive species.
• Accurate modeling of PCET is needed to understand electrochemical reactions and develop sensors.

Purpose of the Study:

• To develop a numerical (finite element) model for simulating PCET reactions of surface-bound quinones.
• To investigate the impact of various parameters on simulated voltammograms.
• To assess the applicability of Laviron analysis for determining electron transfer (ET) rate constants in PCET systems and to provide solutions for voltammetric pH sensing.

Main Methods:

• Development of a user-friendly finite element numerical model.
• Simulation of voltammograms under varying conditions (scan rate, pH, buffer capacity, pKa, surface coverage, rate constants).
• Comparison of ET rate constants derived from simulated data using Laviron plots versus analytical expressions.

Main Results:

• The model accurately simulates PCET reactions and shows factors influencing voltammograms.
• For 1e-1H+ PCET with fast proton transfer, Laviron analysis agrees well with analytical methods.
• For 2e-2H+ PCET, Laviron analysis is unreliable due to complex protonation/deprotonation kinetics; model suggests reducing surface coverage by two orders of magnitude for effective pH sensing.

Conclusions:

• The developed model is a versatile tool for studying PCET reactions.
• Laviron analysis is not quantitatively applicable to 2e-2H+ PCET systems.
• Model provides practical guidelines for using quinone electrodes in voltammetric pH sensing by managing surface coverage to avoid proton depletion/accumulation effects.