Superprotonic Conductivity in Flexible Porous Covalent Organic Framework Membranes

Abstract

Poor mechanical stability of the polymer electrolyte membranes remains one of the bottlenecks towards improving the performance of the proton exchange membrane (PEM) fuel cells. The present work proposes a unique way to utilize crystalline covalent organic frameworks (COFs) as a self‐standing, highly flexible membrane to further boost the mechanical stability of the material without compromising its innate structural characteristics. The as‐synthesized p‐toluene sulfonic acid loaded COF membranes (COFMs) show the highest proton conductivity (as high as 7.8×10−2 S cm−1) amongst all crystalline porous organic polymeric materials reported to date, and were tested under real PEM operating conditions to ascertain their practical utilization as proton exchange membranes. Attainment of 24 mW cm−2 power density, which is the highest among COFs and MOFs, highlights the possibility of using a COF membrane over the other state‐of‐the‐art crystalline porous polymeric materials reported to date.

Combined Intrinsic and Extrinsic Proton Conduction in Robust Covalent Organic Frameworks for Hydrogen Fuel Cell Applications

“…When increasing the testing temperature, we found that the proton conductivity of H 3 PO 4 @NKCOFs increased (Figure b, Figures S43–S45 and Table S2) up to 1.13×10 −1 S cm −1 , 4.28×10 −2 S cm −1 , 1.12×10 −2 S cm −1 , and 7.71×10 −2 S cm −1 at 353 K under 98 % RH. Notably, H 3 PO 4 @NKCOF‐1 sets up a new record (1.13×10 −1 S cm −1 ) for all reported COF materials, which exceeds the current record (7.8×10 −2 S cm −1 for PTSA@TpAzo at 353 K under 95 % RH) and even comparable to the commercial Nafion (ca. 1×10 −1 S cm −1 at 353 K under 98 % RH) (Table S3).…”

A Dual Threat: Redox‐Activity and Electronic Structures of Well‐Defined Donor–Acceptor Fulleretic Covalent‐Organic Materials

“…The detailed procedure of iodine doping can be found in the Supporting Information. The values obtained herein are among some of the highest values reported in COFs to date . In addition, these conductivity studies are the first reports for COFs with covalently bound TCNQ moieties.…”

“…Herein, we demonstrate that the donor–acceptor alignment in well‐defined frameworks could drastically affect the electronic properties of the materials, resulting in circa 100 000 000‐fold conductivity enhancement, one of the largest increases reported for COFs . We probed charge transfer rates within the Marcus theory as a function of acceptor stacking.…”

Metal–Organic Frameworks and Other Crystalline Materials for Ultrahigh Superprotonic Conductivities of 10−2 S cm−1 or Higher

“…Very recently, Banerjee et al. presented a strategic method to synthesize a series of flexible and self‐standing porous COF membranes (COFMs) as efficient proton conductors . Among the three synthesized COFs, PTSA@TpAzo showed the best proton conductivity of 6.3×10 −2 S cm −1 at 30 °C and 95 % RH.…”