Cycling characteristics of high energy density, electrochemically activated porous-carbon supercapacitor electrodes in aqueous electrolytes

Abstract

Carbon-based supercapacitors typically have low energy density but high cycle lifetime relative to batteries. Surface functionalization can significantly increase charge storage through reversible faradaic reactions at the electrode/electrolyte interface, a phenomenon known as pseudocapacitance. However, pseudocapacitive reactions, if not completely reversible, can contribute to reduced cycling performance. In this letter, we describe an electrochemical activation procedure on porous carbon synthesized via pyrolysis of photoresist which yields high specific capacitance and energy density of ∼250 F cm⁻³ and 35 mW h cm⁻³. We also demonstrate that the choice of aqueous electrolyte has a significant effect on both overall capacitance and cycle lifetime, through a comparison of KCl and H₂SO₄ electrolytes. Cycling in acid electrolyte yields excellent capacitance retention of 97% after 10 000 cycles.