Multi-electron redox asymmetric supercapacitors based on quinone-coupled viologen derivatives and Ti3C2Tx MXene

Organic materials are emerging for the pseudocapacitors as they offer high theoretical redox capacitance and can be derived from the renewable sources. They are composed of non-metals, resulting in light weight, flexible, and potentially low-cost devices. While there are hundreds of commercial organic molecules available and nearly unlimited can be synthesized, only a handful of them are suitable for the pseudocapacitive applications. Therefore, the discovery of innovative organic materials beyond conventional pseudocapacitive organic materials (e.g. quinones, conducting polymers, etc.) is much needed for the sustainable pseudocapacitors. Here, for the first time, we report quinone-functionalized viologen molecules as a high capacitance/rate pseudocapacitive organic electrode material on hybridization with reduced graphene oxide sheets. Given the reliable pseudocapacitance of quinone-functionalized viologen-based hybrids under positive potentials, optimized electrodes were paired with two-dimensional titanium carbide (Ti3C2Tx) MXene as negative electrodes to manufacture multi-electron redox asymmetric supercapacitors. The resulting full devices were capable to store charge within enlarged voltage window up to 1.5 V in 3 M H2SO4. In addition, these devices exhibited ultrahigh rate performance (-77% capacitance retention from 10 to 1,000 mV/s), energy density (-20 Wh/kg), and capacitance retention of 80% after 10,000 charge/discharge cycles. (C) 2020 Elsevier Ltd. All rights reserved.