Naphthalene‐based polybenzimidazole cross‐linked with 3‐hexyl spacers N,N‐dimethylpiperidinium cations for alkaline anion exchange membrane water electrolysis

Abstract To enhance the hydroxide conductivity and alkaline stability of the polybenzimidazole as alkaline anion exchange membranes (AEM) to produce hydrogen via alkaline water electrolysis, a deprotonated poly[2,2′‐(1,4‐naphthalene)‐5,5′‐dibenzimidazole] (NPBI) was cross‐linked with 3‐hexyl spacers N , N ‐dimethylpiperidinium cations (QDMP) cationic groups, forming QDMP‐NPBI‐ x composite membrane. Some ‐NH‐ groups of NPBI are deprotonated, forming ammonium‐piperidine complexes with QDMP, which leads to ion cross‐linking in the AEM. The homogeneous cross‐linked structure within the QDMP‐NPBI membranes not only significantly augmented their thermal and chemical stability but also enhanced their longevity and ionic conductivity under alkaline conditions. Specifically, the hydroxide ion conductivity of the QDMP‐NPBI‐20 membrane reached a higher level of 139.7 mS/cm, in contrast to the 103 mS/cm exhibited by the pristine NPBI membrane at 363 K, and it showed a current density of 113.5 mA/cm 2 at 2.4 V in a 1 M KOH solution. All cross‐linked AEMs exhibited augmented thermal stability, and the ionically cross‐linked structure began to degrade at 420°C. The QDMP‐NPBI membranes maintained 93.1% of their initial hydroxide ion conductivity after a 500‐h alkaline stability test in the 1 M KOH at 80°C, with no discernible changes in morphology or mass. Characterization results affirm that these prepared QDMP‐NPBI membranes harbor superior physicochemical properties and elevated hydroxide ion conductivity, underscoring their substantial potential for deployment in alkaline AEM water electrolysis technologies. Highlights The introduction of QDMP increased the hydroxide OH ‐ exchange sites of the AEM. Three‐dimensional mesh structure provides a spatial site‐blocking effect. Cross‐linked structure enhances the thermal stability of the AEM. QDMP‐NPBI‐20 membrane achieves a conductivity of 139.7 mS/cm at 363 K.