One electron oxygen reduction in room temperature ionic liquids: A comparative study of Butler-Volmer and Symmetric Marcus-Hush theories using microdisc electrodes

TL;DR

This study compares Butler-Volmer and Symmetric Marcus-Hush theories in modeling oxygen reduction at microdisc electrodes in ionic liquids, finding Butler-Volmer more certain and estimating solvent reorganization energy at 0.4-0.5 eV.

Contribution

It introduces a comparative analysis of two electrochemical theories in ionic liquids and estimates the solvent reorganization energy for oxygen reduction.

Findings

Butler-Volmer theory yields more certain parameters than SMH.

Solvent reorganization energy for oxygen reduction is 0.4-0.5 eV.

Theoretical models establish relationships between microdisc and spherical electrodes.

Abstract

The voltammetry for the reduction of oxygen at a microdisc electrode is reported in two room temperature ionic liquids: 1-butyl-1-methylpyyrolidinium bis(trifluoromethylsulfonyl) imide ([Bmpyrr][NTf2]) and trihexyltetradecylphosphonium bis9trifluoromethylsulfonyl) imide ([P14,6,6,6][NTf2]) at 298 K. Simulated voltammograms using Butler-Volmer theory and Symmetric Marcus-Hush (SMH) theory were compared with experimental data. Butler-Volmer theory consistently provided experimental parameters with a higher level of certainty than SMH theory. A value of solvent reorganisation energy for oxygen reduction in ionic liquids was inferred for the first time as 0.4-0.5 eV, which is attributable to inner-sphere reorganisation with a negligible contribution from solvent reorganisation. The developed Butler-Volmer and Symmetric Marcus-Hush programs are also used to theoretically study the possibility of kinetically limited steady state currents, and to establish an approximate equivalence relationship between microdisc electrodes and spherical electrodes resting on a surface for steady state voltammetry for both Butler-Volmer and Symmetric Marcus-Hush theory.