Understanding the Effects of Edge Planes in Porous Carbon: Quantum Capacitance and Electrolyte Behavior in Supercapacitor.

Abstract

Electric double layer capacitors (EDLC) require large specific surface area to provide high power density. The generation of pores increases the electrochemical capacitance with more graphitic edge planes exposed to the electrolyte. Conventional theory believes this increasing in capacitance is owed to the increased specific surface area, but our work uncovers another mechanism. DFT calculations discover the commonly seen defect-free zigzag and armchair edges can increase the quantum capacitance (C_Q) due to their high chemical activity. Meanwhile, high chemical activity makes defect-free edges interact with electrolyte molecules more easily, leading to the potential reduce of electrolyte stabilization and the change on the origin mechanism of double layer capacitance (C_D). Additionally, edges with non-hexagonal defects show a better balance between high C_Q and electrolyte stability. Therefore, our discovery proves the preservation of non-hexagonal defects in edge planes through possible temperature controlling in heat treatment is important in reaching high electrochemical properties for EDLC.