Redox potential regulated by electrolyte concentration: A case study of electrochemical oxidation of 2,2,6,6-tetramethyl piperidine-1-oxyl

•The redox potential of TEMPO can be regulated by electrolyte concentration.•The diffusion coefficients of TEMPO decrease as the concentration of LiTFSI increases.•The redox potential of TEMPO shifts negatively with an increase in LiTFSI concentration.•Solvation energy changes and ion pairing are the main contributors to these effects. The redox potential is a fundamental parameter in electrochemistry and is essential in understanding energy-related applications. A typical redox-active molecule, 2,2,6,6-tetramethyl piperidine-1-oxyl (TEMPO), which has an electrocatalytic effect on organic molecules and functions as a mediator in battery technologies, was selected as a model to investigate the dependence of redox potential on the concentration of the supporting electrolyte LiTFSI. Unusual results from cyclic voltammetry have been obtained, showing that the redox potential of TEMPO shifts negatively upon increasing the concentration of LiTFSI. Solvation energy changes from the tunability of dielectric constants and ion pairing are proposed to explain the phenomenon. This work provides insights into tuning the redox potential through simple methods, with applications in the fields of electrocatalysis and battery technology.