Covalent organic frameworks with flexible side chains in hybrid PEMs enable highly efficient proton conductivity.

Electrochemical hydrogen compression (EHC) is an emerging energy conversion technology. Proton exchange membranes (PEMs) with high proton conductivity and high mechanical strength are highly required to meet the practical requirements of EHC. Herein, ionic covalent organic frameworks (iCOFs) with tunable side chains were synthesized and introduced into the sulfonated poly (ether ether ketone) (SPEEK) matrix to fabricate hybrid PEMs. In our membranes, the rigid iCOFs afford ordered proton conduction channels, whereas the flexible side chains on iCOFs afford abundant proton conduction sites, adaptive hydrogen bonding networks, and high local density short hydrogen bonds for highly efficient proton transport. Moreover, the hydrogen bond interactions between the side chains on iCOFs and the SPEEK matrix enhance the mechanical stability of membranes. As a result, the hybrid PEM acquires an enhanced proton conductivity of 540.4 mS cm-1 (80 °C, 100%RH), a high mechanical strength of 120.41 MPa, and a superior performance (2.3 MPa at 30 °C, 100%RH) in EHC applications.

Oil-Water-Oil Triphase Synthesis of Ionic Covalent Organic Framework Nanosheets.

Ionic covalent organic framework nanosheets (iCOFNs) with long-range ordered and mono-dispersed ionic groups hold great potential in many advanced applications. Considering the inherent drawbacks of oil-water biphase method, herein, we explore an oil-water-oil triphase method based on phase engineering strategy for the bottom-up synthesis of iCOFNs. The middle water phase serves as a confined reaction region, and the two oil phases are reservoirs for storing and supplying monomers to the water phase. A large aqueous space and low monomer concentration lead to the anisotropic gradual growth of iCOFNs into few-layer thickness, large lateral size, and high crystallinity. Notably, the resulting three cationic and anionic iCOFNs exhibit ultra-high aspect ratios of up to 20,000. We further demonstrate their application potential by processing into ultrathin defect-free COF membranes for efficient biogas separation. Our triphase method may offer an alternative platform technology for the synthesis and innovative applications of iCOFNs.