Pyrophosphoric Acid-Mediated Hydrogen-Bond Crosslinking: Design and Performance Breakthrough in High-Selectivity H2 Separation Membranes.

Current H2-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 H2 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 PI2-PPA1-60°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 PI2-PPA1-60°C membrane with extremely high H2 permeability (167.24 Barrer), while achieving efficient molecular sieving, elevating H2/CH4 and H2/N2 selectivity to 708.51 and 443.56 respectively (PI-H2/CH4: 95.34; H2/N2: 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.