Phenazine-Based Covalent Organic Framework Cathode Materials with High Energy and Power Densities

TLDR

Redox‑active covalent organic frameworks (COFs) promise high‑capacity energy storage due to their dense redox sites, porosity, surface area, and tunable structures, yet their low electrochemical accessibility has confined devices to thin films or required conductive polymers. This study aims to create bulk microcrystalline COF‑based energy‑storage devices that avoid thin‑film fabrication and conductive‑polymer additives, thereby improving capacity and enabling scalable production. The authors synthesized a phenazine‑based 2D COF (DAPH‑TFP) and its PEDOT composite, and evaluated both as solution‑cast powder electrodes on bulk current collectors. The unmodified DAPH‑TFP COF achieved excellent redox‑site accessibility, outperformed the PEDOT composite of a prior anthraquinone system, and delivered high‑energy and high‑power densities, confirming the viability of unmodified redox‑active COFs for energy‑storage devices.

Abstract

Redox-active covalent organic frameworks (COFs) are promising materials for energy storage devices because of their high density of redox sites, permanent and controlled porosity, high surface areas, and tunable structures. However, the low electrochemical accessibility of their redox-active sites has limited COF-based devices either to thin films (<250 nm) grown on conductive substrates or to thicker films (1 μm) when a conductive polymer is introduced into the COF pores. Electrical energy storage devices constructed from bulk microcrystalline COF powders, eliminating the need for both thin-film formation and conductive polymer guests, would offer both improved capacity and potentially scalable fabrication processes. Here we report on the synthesis and electrochemical evaluation of a new phenazine-based 2D COF (DAPH-TFP COF), as well as its composite with poly(3,4-ethylenedioxythiophene) (PEDOT). Both the COF and its PEDOT composite were evaluated as powders that were solution-cast onto bulk electrodes serving as current collectors. The unmodified DAPH-TFP COF exhibited excellent electrical access to its redox sites, even without PEDOT functionalization, and outperformed the PEDOT composite of our previously reported anthraquinone-based system. Devices containing DAPH-TFP COF were able to deliver both high-energy and high-power densities, validating the promise of unmodified redox-active COFs that are easily incorporated into electrical energy storage devices.