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.