Free-Standing Polymer Covalent Organic Framework Membrane with High Proton Conductivity and Structure Stability

The two-dimensional covalent organic framework (COF)with continuousand stable pores as well as tunable functional groups is consideredas promising proton exchange membrane (PEM) material. However, dueto the strong rigidity and inferior processability of COFs, it stillremains challenging to prepare a self-standing and robust membrane.Herein, self-standing and robust thin COF membranes (20 & mu;m inthickness) were fabricated through the in situ involvement of hyperbranchedpolyethylenimine (HPEI). The HPEI cross-links the adjacent COF particlesand enhances the interactions among them. The involvement of HPEIenables polyCOM to have excellent structure ability, mechanical property,and proton conduction ability. As a result, poly(0.2)COMobtains a high water uptake of 72.3% at 80 & DEG;C (vs 49.11% forNafion) with a negligible swelling ratio of 1.5%. In addition, thetensile strength of poly(0.2)COM reaches 45.4 MPa, 2.4 timeshigher than that of the TpPa-SO3H membrane (13.26 MPa).Importantly, polyCOM shows high proton conductivities of 223 and 35mS cm(-1) under saturated humidity and a low relativehumidity (RH) of 30%, respectively, far exceeding those of the commercialNafion membrane (80 and 5.5 mS cm(-1)). Moreover,poly(0.02)COM acquires a remarkable power density of 111.1mW cm(-2) and a current density of 664 mA cm(-2) at 80 & DEG;C and 40% RH.