New Insights on the Sodium Water-in-Salt Electrolyte and Carbon Electrode Interface from Electrochemistry and Operando Raman Studies

Rafael Vicentini; Raissa Venâncio; Willian Nunes; Leonardo Morais Da Silva; Hudson Zanin

doi:10.1021/acsami.1c18777

New Insights on the Sodium Water-in-Salt Electrolyte and Carbon Electrode Interface from Electrochemistry and Operando Raman Studies

ACS Appl Mater Interfaces. 2021 Dec 29;13(51):61139-61153. doi: 10.1021/acsami.1c18777. Epub 2021 Dec 17.

Authors

Rafael Vicentini¹, Raissa Venâncio¹, Willian Nunes¹, Leonardo Morais Da Silva², Hudson Zanin¹

Affiliations

¹ Advanced Energy Storage Division, Center for Innovation on New Energies, Carbon Sci-Tech Labs and Manufacturing Group, School of Electrical and Computer Engineering, University of Campinas, Av. Albert Einstein 400, Campinas, SP 13083-852, Brazil.
² Department of Chemistry, Laboratory of Fundamental and Applied Electrochemistry, Federal University of Jequitinhonha and Mucuri's Valley, Rodovia MGT 367, km 583, 5000, Alto da Jacuba, Diamantina, MG 39100-000, Brazil.

PMID: 34915700
DOI: 10.1021/acsami.1c18777

Abstract

Comprehensive electrochemical and operando Raman studies are performed to investigate the electrochemical stability window (ESW) of supercapacitors filled with normal (salt-in-water) and highly concentrated (water-in-salt, WiSE) electrolytes. Impedance and chronoamperometric experiments are employed and combined with cyclic voltammetry to correctly define the ESW for a WiSE-based device. The total absence of water-splitting resulted in phase angles close to -90° in the impedance data. It is verified that a 17 m NaClO₄ electrolyte avoids the water-splitting up to 1.8 V. Furthermore, Raman studies under dynamic and static polarization conditions corroborate the existence of a solvent blocking interface (SBI), which inhibits the occurrence of water-splitting. Also, the reversible nature of the charge-storage process is assessed as a function of the applied voltage. At extreme polarization, the SBI structure is disrupted, thus allowing the occurrence of water-splitting and anionic (ClO₄^-) intercalation between the graphene sheets.

Keywords: Raman probing the surface effects; WiSE; charge-storage process; impedance study of blocked interfaces; salt-in-water electrolytes; solvent blocking interface.