Pyrophosphoric Acid‐Mediated Hydrogen‐Bond Crosslinking: Design and Performance Breakthrough in High‐Selectivity H ₂ Separation Membranes

ABSTRACT Current H 2 ‐selective polymer membranes face an inescapable permeability‐selectivity trade‐off. We report a hydrogen‐bond crosslinking strategy mediated by pyrophosphoric acid (PPA) to engineer chain packing in unprotonatable 6FDA‐TFMB polyimides (PI) for ultra‐selective H 2 separation. Through molecular design, rigid non‐coplanar 6FDA‐TFMB PI featuring trifluoromethyl side groups was subsequently incorporated with hydroxyl‐rich PPA. Collaborative simulation‐experimental validation confirmed that the hydrogen‐bond (C═O···H−O) crosslinking between PI and PPA in the PI 2 ‐PPA 1 ‐60°C membrane achieved 4% compression of polymer chain spacing (d‐spacing from 3.95 to 3.69 Å) compared to pristine PI, constructing a hierarchically graded chain‐spacing architecture with 2.18–5.17 Å gradient distribution. This engineering structure endowed the PI 2 ‐PPA 1 ‐60°C membrane with extremely high H 2 permeability (167.24 Barrer), while achieving efficient molecular sieving, elevating H 2 /CH 4 and H 2 /N 2 selectivity to 708.51 and 443.56 respectively (PI–H 2 /CH 4 : 95.34; H 2 /N 2 : 40.59). The breakthrough separation performance surpassed the 2015 Robeson upper bound, providing an engineerable supramolecular solution to decouple the permeability‐selectivity conflict in membrane technology.