Capacitive Charge Storage at the Glassy Carbon Electrode: Comparison Between Aqueous and Non-Aqueous Electrolytes

Herein the charge storage capabilities of a planar non-porous glassy carbon electrode (GCE) in electrolytes of aqueous 0.5 M Na2SO4 and 1 M tetraethylammonium tetrafluoroborate (TEABF(4)) in acetonitrile are compared using a combination of cyclic voltammetry (CV), step potential electrochemical spectroscopy (SPECS) and electrochemical impedance spectroscopy (EIS). In all techniques the resultant capacitance was substantially higher for the GCE in 1 M TEABF(4) compared to 0.5 M Na2SO4, with the differences due to solvation of the adsorbing electrolyte ions. Adsorbing Na+ cations in the aqueous system have a substantial solvation sheath that increases the resistance associated with capacitive charge storage, decreases the capacitance, as well as inhibits the packing of similar electrolyte ions in the vicinity of the GCE. Conversely, the adsorbing BF4- ions in the acetonitrile-based electrolyte exhibit a low resistance to charge storage, a greatly enhanced capacitance, as well as exhibit an improved ability to pack at the electrode-electrolyte interface. The impact of this behaviour on electrode performance has also been discussed.