β-Ketoenamine-Linked Covalent Organic Frameworks Capable of Pseudocapacitive Energy Storage

Two-dimensional covalent organic frameworks (2D COFs) are candidate materials for charge storage devices because of their micro- or mesoporosity, high surface area, and ability to predictably organize redox-active groups. The limited chemical and oxidative stability of established COF linkages, such as boroxines and boronate esters, precludes these applications, and no 2D COF has demonstrated reversible redox behavior. Here we describe a β-ketoenamine-linked 2D COF that exhibits reversible electrochemical processes of its anthraquinone subunits, excellent chemical stability to a strongly acidic electrolyte, and one of the highest surface areas of the imine- or enamine-linked 2D COFs. Electrodes modified with the redox-active COF show higher capacitance than those modified with a similar non-redox-active COF, even after 5000 charge-discharge cycles. These findings demonstrate the promise of using 2D COFs for capacitive storage.