Monovalent silicotungstate salts as electrolytes for electrochemical supercapacitors

Highlights: • Li-, Na-, and K- silicotungstate salts were investigated as electrolytes for EDLC. • All salts are neutral and retained the Keggin structure. • All salt solutions showed high ionic conductivity and wide potential windows. • Carbon EDLCs utilizing these salt electrolytes can achieve a 1.5 V cell voltage. - Abstract: Lithium, sodium, and potassium salts of silicotungstic acid were synthesized and characterized as aqueous neutral electrolytes for electrochemical supercapacitors. The acidity of the aqueous solution and the structure of the solid-state anion were examined to confirm the presence of SiW salts. Ionic conductivity and the electrochemical stability potential window were characterized and compared to a silicotungstic acid solution using metallic blocking electrodes. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to investigate the performance of carbon EDLC cells enabled by the neutral electrolytes and revealed a 1.5 V cell voltage and good cycle life. The similarities and differences among the three salts are explained based on the properties of cations in these neutral electrolytes