An electrode potential regulation strategy for supercapacitors

Abstract

Supercapacitors have garnered increasing attention due to their exceptional characteristics, including ultra-fast charge–discharge rates and excellent cycling stability. However, the inability of the device's operating voltage to reach the electrolyte's theoretical maximum voltage (electrochemical stability window) due to mismatched electrode potentials severely limits enhancement of energy density. To address this bottleneck, this study proposes using redox additives to drive the electrode potentials, aiming to enable the device's operating voltage to reach the electrolyte's theoretical maximum voltage. To validate the feasibility of this strategy, this study prepared an electrolyte with an NaClO₄, H₂O, and urea (UR) ratio of 1–7–3, in which the salt and UR replaced the solvated H₂O, thereby suppressing the activity of the solvated H₂O. Furthermore, UR formed stronger hydrogen bonds with H₂O molecules, effectively broadening the electrochemical window of the aqueous system to 2.45 V. In this electrolyte system, conventional double-layer supercapacitors operate at a voltage of only 2.1 V due to a mismatch in electrode potentials (with hydrogen evolution occurring preferentially at the anode), which is far below the upper limit of the electrolyte's theoretical voltage window. By introducing redox additives to dynamically modulate the electrode potentials, the device's operating voltage successfully reached the electrolyte's theoretical maximum voltage of 2.45 V, thereby resolving the bottleneck of electrode potential mismatch. This strategy offers new insights into resolving electrode potential mismatches.