Performance evaluation of electrochemical capacitors with activated carbon spheres as electrode material and aqueous electrolyte

Abstract

The model activated carbon spheres (ACSs) were optimized to be used as negative electrode in asymmetric electrochemical capacitors (ECs). A microporous commercial activated carbon was used as positive electrode.Carbon spheres (CSs) were synthesized by precipitation polymerization at room temperature followed by pyrolysis and activation. By enhancing the carbon:KOH ratio from 1:2 to 1:4, an increase in the specific surface area from 380 m2 g−1 to 2835 m2 g−1 (1:4) was achieved along with an increase in pore volume/size. Consequently, the electrochemical performance in the aqueous electrolyte was improved. After activation, low-temperature-pyrolyzed polymer spheres (400 °C) result in random-like particles with macroporous structure, while intermediate- and high-temperature-pyrolyzed materials (550 °C and 700 °C) lead to partially and totally conserved spheres.The interaction between the electrode material and electrolyte is important and is related to the texture, morphology, and surface chemistry of ACS. In 1 mol L−1 H2SO4, capacitance and rate handling are mostly affected by electrode morphology and wettability with the electrolyte. In 1 mol L−1 Li2SO4 electrolyte solution, texture and surface chemistry of the electrode material are crucial to obtain high-performance EC. Regardless of morphology, poor wetting properties of synthesized materials were found in Li2SO4, compared to the H2SO4 solution.