Molecular engineering of benzimidazolium anion exchange membranes via 2-position carbon phenylation for enhanced...

The development of high-performance anion exchange membranes (AEMs) is a critical bottleneck for the advancement of anion exchange membrane water electrolysis (AEMWE). Benzimidazolium groups are known for their exceptional chemical stability, attributed to their resistance to Hofmann elimination reactions. This study introduced a phenyl substituent at the 2-position carbon site of benzimidazole, leveraging its steric hindrance to significantly elevate the energy barrier against ring-opening degradation of the polymer main chain. A series of poly(dimethyl piperidinium-terphenyl-benzimidazole) (DMPT-P-x) AEMs with multiple ion sites were successfully synthesized. This was achieved via the Friedel-Crafts reaction catalyzed by superacid, which incorporated 2-phenylbenzimidazole (2-PBI) into a polymer backbone composed of p-terphenyl and 1-methyl-4-piperidone. This research integrates surface electrostatic potential theory calculations with experimental characterization to elucidate the charge distribution characteristics of the 2-PBI active sites, which underpins the unique chemical stability mechanism of DMPT-P-x. Notably, the hydroxide ion (OH^-) conductivity of these membranes at 80 °C reaches 208.0 mS·cm^-1. After immersing in a 1 M NaOH solution for 2000 h, the OH^- conductivity decreases by only 7.9 %, demonstrating their outstanding long-term stability. Moreover, when employing a NiFe-layered double hydroxide catalyst with DMPT-P-4 in AEMWE, a current density of 2.6 A·cm^-2 was achieved at 2 V, outperforming most reported AEMs. This work not only provides innovative and effective molecular design strategies for constructing high-performance, alkali-resistant AEMs but also accelerates the practical application of AEMWE.