Analysis of cooperative effects between activated carbons and acetylene black using electrochemical, rheological and textural characterizations to maximize supercapacitance

Abstract

The interactions arising in Electrochemical Double Layer Capacitors (EDLC) made up of commercial activated carbons (DLC 50 Norit, TF-B520 and Kuraray YP-80 F), acetylene carbon black (AB) and polytetrafluoroethylene (PTFE) are analyzed with the aim of maximizing their specific capacitances. AB is varied (0–10 wt%, 0–20 wt% only for further exploration of TF-B520) to minimize its content, while maintaining fixed the PTFE composition. The best rate capabilities are obtained at 5 wt% AB for TF-B520 and Kuraray YP-80 F, and 4 wt% AB for DLC 50 Norit on the basis of cyclic voltammetry, charge/discharge curves and electrochemical impedance spectroscopy. These results strongly depend on a minimum amount of AB in the composite determined through conductivity measurements (i.e. percolation threshold), which guarantees its electronic conductivity. According to N2 adsorption/desorption and textural studies, the critical property defining the electrode supercapacitance is its specific surface area (SSA), relying considerably on the surface area of the pristine AC (main component), regardless of its pore volume and size, or AB area. The specific capacitances present the following trend: TF-B520 (1711–1830 m2 g−1) > > (1356–1571 m2 g−1) > (1319–1504 m2 g−1). Viscoelasticity properties of the composites are less important than conductivity or SSA, since mechanical pressure alters the AC-AB interparticle network, generating better percolating media. In order to optimize specific capacitance, a balance is required between electronic conductivity (percolation in the porous media by AB) and ionic transference (specific surface area of AC) in the electrode composite.

Keywords

• Electrochemical double layer capacitors
• Activated carbon
• Acetylene carbon black
• Conductivity
• Rheology