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

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.