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.