Dual-Acid-Tailored Ionic Covalent Organic Frameworks for High-Temperature Proton Conduction under Anhydrous Conditions and the Practical Opportunities

An organic salt (DMAP/Pa-SO3H) composed of
2,5-diaminiobenzenesulfonic
acid (Pa-SO3H) and dimethylaminopyridine (DMAP) was demonstrated
as a linker to construct ionic covalent organic frameworks (iCOFs).
The iCOF denoted as TpDMAP/Pa-SO3H was prepared by the
condensation reaction of the triformylphloroglucinol (Tp) building
block and DMAP/Pa-SO3H and offers the potential to accommodate
an external proton source (H3PO4; PA), enabling
the immobilization of PA moieties within the pore structure through
a strong ionic hydrogen bonding interaction evidenced by DFT calculations.
Furthermore, H3PO4-doped iCOF denoted as PA@TpDMAP/Pa-SO3H proclaimed the advantage of engineering at the linker position,
which in turn promotes proton conductivity to 1.56 × 10–2 S cm–1 (increased 100-fold as related to PA@TpPa-SO3H) at 140 °C under anhydrous conditions. Finally, we
investigated the adaptability of a dual-acid system in sulfonated
poly(ether ether ketone) (SPEEK) membranes, a common acid-modified
polymeric material. PA-doped DMAP-modified SPEEK (PA@SPEEK/DMAP) evidenced
a 100-fold appreciation of proton conductivity at 120 °C, as
compared to bare SPEEK membranes under anhydrous conditions.