Optimization of alkaline water electrolysis performance with binaphthyl-derived polybenzimidazole ion-solvating gel membrane.

Polybenzimidazole-based ion-solvating membranes (ISMs) are regarded as a promising contender for alkaline water electrolysis separators due to their mechanical stability, excellent thermal stability, and gas tightness. However, the trade-off between hydroxide conductivity and alkaline stability restricts the application. In this paper, poly(2, 2'-(4, 4′-1, 1′-binaphthyl)-5, 5′-benzimidazole) (BN-PBI) was synthesized from a molecular design perspective, followed by the in-situ scrapping of a BN-PBI membrane and subsequent immersion in a KOH solution to yield a KOH-doped ion-solvating BN-PBI gel membrane. m -PBI and N-PBI gel membranes were also fabricated under the same conditions for comparison. The incorporation of the bulky and rigid binaphthyl groups increased the free volume of the polymer, which effectively regulated the absorption of alkali and water. Consequently, the BN-PBI gel membrane exhibited an impressive hydroxide conductivity of up to 274.48 mS cm−1 in a 6 M KOH solution at 80 °C. Moreover, the ionic conductivity retention was still above 62.43 % after a 3400 h ex-situ alkaline stability test. During the AWE test, the cell with the BN-PBI gel membrane achieved the highest current density of 750 mA cm−2 at a voltage of 2 V and 80 °C. Additionally, under a constant current density of 500 mA cm−2 in a 6 M KOH solution at 80 °C, the cell demonstrated stable performance over 180 h with a voltage fluctuation of only 39 μV. Therefore, this work proposes a new perspective on addressing the trade-off between hydroxide conductivity and alkaline stability, facilitating the development of new separator materials for alkaline water electrolysis. [Display omitted] • Binaphthyl-derived polybenzimidazole ion-solvating gel membrane with OH− conductivity of up to 274.48 mS cm−1 was fabricated in-situ. • The BN-PBI gel membrane exhibited an excellent alkaline water electrolysis performance and extended durability. • A new approach has been proposed to address the trade-off between hydroxide conductivity and alkaline stability in ion-solvating membranes. [ABSTRACT FROM AUTHOR]