Investigation of Electrochemical and Chemical Processes Occurring at Positive Potentials in "Water-in-Salt" Electrolytes
Journal article, 2021

Lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) based water-in-salt electrolytes (WiSEs) has recently emerged as a new promising class of electrolytes, primarily owing to their wide electrochemical stability windows (similar to 3-4 V), that by far exceed the thermodynamic stability window of water (1.23 V). Upon increasing the salt concentration towards superconcentration the onset of the oxygen evolution reaction (OER) shifts more significantly than the hydrogen evolution reaction (HER) does. The OER shift has been explained by the accumulation of hydrophobic anions blocking water access to the electrode surface, hence by double layer theory. Here we demonstrate that the processes during oxidation are much more complex, involving OER, carbon and salt decomposition by OER intermediates, and salt precipitation upon local oversaturation. The positive shift in the onset potential of oxidation currents was elucidated by combining several advanced analysis techniques: rotating ring-disk electrode voltammetry, online electrochemical mass spectrometry, and X-ray photoelectron spectroscopy, using both dilute and superconcentrated electrolytes. The results demonstrate the importance of reactive OER intermediates and surface films for electrolyte and electrode stability and motivate further studies of the nature of the electrode.

Author

Marion Maffre

Université du Québec

University of Montpellier

Roza Bouchal

Chalmers, Physics, Materials Physics

Stefan A. Freunberger

Institute of Science and Technology Austria

Niklas Lindahl

Chalmers, Physics, Materials Physics

Patrik Johansson

Chalmers, Physics, Materials Physics

Frederic Favier

University of Montpellier

Centre national de la recherche scientifique (CNRS)

Olivier Fontaine

Institut Universitaire de France

University of Montpellier

Vidyasirimedhi Institute of Science & Technology

Daniel Belanger

Université du Québec

Journal of the Electrochemical Society

0013-4651 (ISSN)

Vol. 168 5 050550

Subject Categories

Inorganic Chemistry

Materials Chemistry

Other Chemistry Topics

DOI

10.1149/1945-7111/ac0300

More information

Latest update

6/18/2021