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

Abstract

Phosphoric acid (H₃PO₄) doping is a widely employed strategy to facilitate anhydrous proton transport in high-temperature proton exchange membrane fuel cells (HT-PEMFCs). However, significant H₃PO₄ leaching during long-term operation poses critical challenges to maintaining membrane stability and proton conductivity. Herein, H₃PO₄ is incorporated into positively charged nanochannels of quaternized covalent organic framework membranes (QACOFMs), leveraging strong electrostatic interactions and confinement effects to achieve exceptional H₃PO₄ retention under hydration conditions. Moreover, the shortened hydrogen bond length between H₃PO₄ (O-H…O <2.7 Å) and the highly interconnected hydrogen bond network in the H₃PO₄@QACOFMs facilitate ultra-fast anhydrous proton transport. As a result, the H₃PO₄@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^-1 at 200 °C.