Alkaline quaternary ammonium hydroxides and their polymer electrolytes for electrochemical capacitors

Aqueous quaternary ammonium hydroxides were investigated as electrolytes for electrochemical capacitors (ECs) in both liquid and polymer-gel forms. Alkaline polymer electrolytes, composed of tetraethylammonium hydroxide (TEAOH) and poly(vinyl alcohol) (PVA) in different ratios, were developed and characterized. An optimized TEAOH-PVA electrolyte was developed and compared to KOH-PVA under controlled and ambient conditions. The stability of the polymer electrolytes and the solid ECs were characterized using cyclic voltammetry and electrochemical impedance spectroscopy. While both polymer electrolyte-based ECs demonstrated high rate capability in pristine condition, the TEAOH-based solid EC device showed a much better shelf life than the KOH-based device. This is likely due to the water retention capability of TEAOH, which promoted the amphorous phase and ion mobility, contributing to higher ionic conductivity and better environmental stability.