A Pseudocapacitor from Redox Active Covalent Organic Framework

Abstract

Small redox active organic molecules present the challenges of excessive dissolutions, interfacial crystallization, side reactions such as self-coupling and polymerizations. To address this, we have developed a quinone containing methylene bridged covalent organic framework (COF) as electrode material for aqueous zinc-based storage device. The capacity of the neat polymer was found to be 162.27 mAhg−1 at 0.1 A current density. Owing to the outstanding insolubility of the polymer, the excessive dissolution as well as the interfacial crystallization of the material were ruled out. We anticipated that the low capacity was due to the dendrite formation on Zinc anode surface during prolonged cycling experiment. The dendrite formation was controlled by performing the experiments in a silica dispersed electrolyte which was identified by analyzing the scanning electron microscopy images. Under this condition remarkable capacity retention was achieved with nearly 100% columbic efficiency. For further electrochemical enhancement, carbon nanotubes were loaded during the synthesis of the COF and the capacity was found to be 248 mAhg−1 and remained showing 241 mAhg−1 after 1000 continuous cycling and remained 218 mAhg−1 after 5000 cycles in the fumed silica dispersed electrolyte. Having specific structural robustness as well as their chemical inertness and extensive pi conjugation in addition to their good conductivity, carbon nano tubes (CNTs) impart very significant role to enhance the electrochemical characteristics of our material. A pouch cell was assembled to evaluate the applicability of the material and the open circuit potential (OCP) was found to be 1.196 V for 48 h which indicates the suitability of the material as pseudocapacitor.