Tailored hydrogen-bond engineering blend ion-solvating membranes enable efficient alkaline water electrolysis

Poly(oxindole biphenylene) ion-solvating membranes (POBP ISMs) exhibit exceptional chemical stability, yet their limited hydrophilicity and sparse oxindole groups result in restricted electrolyte uptake and suboptimal ion conductivity, thereby constraining their performance in alkaline water electrolysis (AWE). To overcome this, we blended high-functional-density poly(2,2′-(1,4-naphthalene)-5,5′-bibenzimidazole) (NPBI) with POBP and engineered a tailored internal hydrogen-bond between the indole of POBP and the imidazole of NPBI. This strategy enhances ion transport while preserving chemical stability. The optimized POBP-50 blend membrane, confirmed by multi-scale characterization, features a homogeneous microstructure, high mechanical strength (99 MPa tensile stress and 17.3% strain at break), and elevated ion conductivity (62 mS cm −1 ). It also exhibits over 8000 h of alkaline stability and a 6-fold improvement in antioxidant stability compared with pure NPBI. In a 6 M KOH AWE system, the hydrogen-bond-optimized membrane achieves a current density of 8 A cm −2 at 2.8 V, outperforming commercial Zirfon (1.6 A cm −2 ) and pure POBP (2.4 A cm −2 ). Moreover, it maintains stable operation for over 600 h under dynamic current cycling (0.5–1.5 A cm −2 ) without degradation. This work underscores the critical role of molecular-level hydrogen-bond engineering in designing blend membranes, offering a viable pathway toward high-performance membranes for efficient and durable AWE.