Self-Standing combined covalent-organic-framework membranes for subzero conductivity assisted by ionic liquids

The development of proton-conducting materials in cold regions is still at the initial stage due to the challenge in breaking the subzero temperature limit, especially in covalent organic frameworks (COFs). Herein, we fabricated a series of proton-conductive COFs as self-standing, highly flexible combined membranes (ssc-COFMs) composed of a processable TpBD-Me2 and a conductive Tp-TGCl, in-situ encapsulated proton-conducting ionic liquids (PCILs) as additional proton sources into backbones. Compositions and microstructures of ssc-COFMs are monitored by XRD, FTIR, nitrogen adsorption and elemental analysis. Comparison to other porous organic conductors, a great advance propelled renders the combined COF membranes to have a high protonic conductivities at medium and subzero temperatures (243 to 353 K), owing to the resultant multifaceted synergistic effect of multiple proton units. Specifically, the proton conductivities of the ssc-COFMs loaded with –SO4H functionalized PCILs reaches 2.87 × 10-4 S cm−1 (~58% RH) and 9.93 × 10−4 S cm−1 (~98% RH) at 243 K, together with 6.84 × 10−2 S·cm−1 under 353 K and ~ 98% RH.