Rapid and Efficient Redox Processes within 2D Covalent Organic Framework Thin Films

TLDR

Two‑dimensional covalent organic frameworks (2D COFs) are ideally suited for arranging redox‑active subunits into periodic, permanently porous polymer networks that are promising for pseudocapacitive energy storage. The study presents a method to synthesize crystalline, oriented thin films of a redox‑active 2D COF on gold electrodes. Crystalline, oriented thin films were fabricated on Au electrodes, with film thickness tuned by varying the initial monomer concentration. Thin films thinner than 200 nm exhibited 80–99 % electrochemical accessibility of anthraquinone groups and a 400 % increase in capacitance compared to randomly oriented powder, demonstrating that morphology control markedly enhances performance.

Abstract

Two-dimensional covalent organic frameworks (2D COFs) are ideally suited for organizing redox-active subunits into periodic, permanently porous polymer networks of interest for pseudocapacitive energy storage. Here we describe a method for synthesizing crystalline, oriented thin films of a redox-active 2D COF on Au working electrodes. The thickness of the COF film was controlled by varying the initial monomer concentration. A large percentage (80-99%) of the anthraquinone groups are electrochemically accessible in films thinner than 200 nm, an order of magnitude improvement over the same COF prepared as a randomly oriented microcrystalline powder. As a result, electrodes functionalized with oriented COF films exhibit a 400% increase in capacitance scaled to electrode area as compared to those functionalized with the randomly oriented COF powder. These results demonstrate the promise of redox-active COFs for electrical energy storage and highlight the importance of controlling morphology for optimal performance.