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

Abstract Phosphoric acid (H 3 PO 4 ) doping is a widely employed strategy to facilitate anhydrous proton transport in high‐temperature proton exchange membrane fuel cells (HT‐PEMFCs). However, significant H 3 PO 4 leaching during long‐term operation poses critical challenges to maintaining membrane stability and proton conductivity. Herein, H 3 PO 4 is incorporated into positively charged nanochannels of quaternized covalent organic framework membranes (QACOFMs), leveraging strong electrostatic interactions and confinement effects to achieve exceptional H 3 PO 4 retention under hydration conditions. Moreover, the shortened hydrogen bond length between H 3 PO 4 (O−H…O <2.7 Å) and the highly interconnected hydrogen bond network in the H 3 PO 4 @QACOFMs facilitate ultra‐fast anhydrous proton transport. As a result, the H 3 PO 4 @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.