Aqueous Electrolytes, MXene-Based Supercapacitors and Their Self-Discharge

Abstract

Significant efforts have been dedicated to developing Ti3C2Tz-based MXene aqueous supercapacitors (SCs) with improved energy and power densities. Notably less research has been devoted to an equally important characteristic of aqueous SCs, viz. self-discharge (SD). The SD rates are rarely reported despite their crucial importance from a practical point of view. Herein, the SD rates in four different aqueous electrolytes: H2SO4, KOH, LiCl, and LiBr in Ti3C2Tz-based aqueous SCs are compared. For the latter two, the SD rates vary as a function of salt concentration in the electrolytes with higher LiCl or LiBr concentrations having the lowest SD rates, viz. 78.3% and 81.5% in 14 m LiCl and LiBr, respectively, after 10 h. Further, the influence of dissolved oxygen and the purities of the starting powders are examined, and it is concluded that parasitic reactions, including oxygen, are responsible for the SD.