Covalent organic frameworks confining ultra-dense hydrated hydrogen-bond networks for efficient intrinsic proton conduction

Abstract

Confining hydrated hydrogen bonds to generate proton channels is a promising strategy for promoting intrinsic proton conductivity, while high water-harvesting capacity is key for proton-conducting materials. Herein, by preinstalling proton donor groups, two covalent organic frameworks (COFs) with exceptional water adsorption capacities (2,6-DHNA-TA and 2,3-DHNA-TA) were rationally designed. 2,6-DHNA-TA possesses hexa-leaf clover pores, and the hydroxyl groups are suspended anisotropically to the edges of adjacent pores, forming independent hydrophilic domains. 2,3-DHNA-TA exhibits hexagonal pores, and the hydrophilic diketone group in each compartment forms a wide hydrophilic band. The grand canonical Monte Carlo method was applied to verify that water molecules are preferentially adsorbed at the hydrophilic sites, and the water-filled process was initiated at predefined independent anchors and terminated in domain-limited mesopores. Free water is enriched in COF pores and is rearranged in short and dense hydrogen bonds, facilitating proton conduction at low energy barriers. The two COFs exhibit excellent proton conductivity, especially 2,6-DHNA-TA (1.27 × 10⁻³ S cm⁻¹), which surpasses most of the reported COFs. This study extends the application of the water confinement strategy to proton conduction.