Accounting for species’ thermodynamic activities changes mechanistic interpretations of electrochemical kinetic data

17 February 2022, Version 1
This content is a preprint and has not undergone peer review at the time of posting.


The thermodynamic activity of a reacting species, rather than the concentration of that species, generally determines the rate of a kinetically-limited reaction. In this work we demonstrate the need for the explicit accounting of reacting species’ thermodynamic activities in solution, especially when conducting electrochemical kinetic tests. In hydrogen evolution in an alkaline acetonitrile-water blended electrolyte as well as previously-reported oxygen-atom transfer reactions (cyclooctene epoxidation and cyclohexanone lactonization), we demonstrate that accounting for species thermodynamic activity causes water-dependence measurements to yield different mechanistic interpretations than data which treats concentration as a proxy for activity. We hypothesize many ways in which water contributes to the reaction rate beyond direct participation in the reaction, offer initial molecular interpretations of the water activity-concentration relationship in the blended electrolyte, and discuss implications of these findings for better understanding solvent effects.


hydrogen evolution
nonideal thermodynamics
thermodynamic activity
blended electrolytes
electrochemical kinetics
mechanistic analysis
solvent effects
oxygen-atom transfer

Supplementary materials

Supplementary information - Accounting for species’ thermodynamic activities changes mechanistic interpretations of electrochemical kinetic data
Materials, detailed methods, raw data for main-text figures, and in-depth discussions of topics related to the main text.
Graphical Abstract
TOC figure for the article


Comments are not moderated before they are posted, but they can be removed by the site moderators if they are found to be in contravention of our Commenting Policy [opens in a new tab] - please read this policy before you post. Comments should be used for scholarly discussion of the content in question. You can find more information about how to use the commenting feature here [opens in a new tab] .
This site is protected by reCAPTCHA and the Google Privacy Policy [opens in a new tab] and Terms of Service [opens in a new tab] apply.