Confining Phosphoric Acid in Quaternized COF Channels for Ultra-Stable and Fast Anhydrous Proton Transport.

Phosphoric acid (HPO) doping is a widely employed strategy to facilitate anhydrous proton transport in high-temperature proton exchange membrane fuel cells (HT-PEMFCs). However, significant HPO leaching during long-term operation poses critical challenges to maintaining membrane stability and proton conductivity. Herein, HPO is incorporated into positively charged nanochannels of quaternized covalent organic framework membranes (QACOFMs), leveraging strong electrostatic interactions and confinement effects to achieve exceptional HPO retention under hydration conditions. Moreover, the shortened hydrogen bond length between HPO (O-H…O <2.7 Å) and the highly interconnected hydrogen bond network in the HPO@QACOFMs facilitate ultra-fast anhydrous proton transport. As a result, the HPO@QACOFMs exhibit superior anhydrous proton transport in a broader temperature range (60 °C-200 °C) and the highest proton conductivity reaches about 379.7 mS cm at 200 °C.