Substrate Curvature‐Induced Regulation of Charge Distribution of Covalent Organic Frameworks Promotes Capacitive Deionization

Abstract Covalent organic frameworks (COFs) are promising high‐performance capacitive deionization (CDI) materials. Strategies to optimize CDI performance of COFs focus largely on hybridization with conductive substrates, to improve their their intrinsically poor conductivity. A new structure‐function relationship between COFs and their substrates is proposed here based on substrate‐induced surface curvature. Graphene (zero‐curvature) and carbon nanotubes (CNT, curved) are selected as COF growthsubstrates to assess the effect of curvature engineering effect on CDI performance of TpPa‐SO₃H‐COF. Ultrahigh ion (Na⁺) adsorption capacity (58.74 mg g⁻¹) is achieved by CNT‐COF hybrid (cf. compared to graphene‐COF hybrid 34.20 mg g⁻¹), demonstrating the significance of curvature engineering. Notably, the corresponding salt (NaCl) adsorption capacity of CNT‐COF hybrid reaches 149.25 mg g⁻¹ in 1000 ppm at 1.2 V, representing state‐of‐the‐art CDI performance, and the highest value among organic CDI electrodes. X‐ray photoelectron spectroscopy and theoretical calculations subsequently reveal that substrate curvature can induce local strain, which regulates charge distribution within the COF skeleton, causing a lower binding energy state for Na⁺ adsorption. Electrochemical quartz crystal microbalance measurements revealed faster Na⁺ adsorption kinetics of CNT‐COF due to regulated charge distribution within COF skeleton induced by substrate curvature. This work gives new insight into design of COF materials based on curvature engineering.