Enhanced OH− conductivity and stability of polybenzimidazole membranes for electrocatalytic CO2 reduction via grafting and crosslinking strategies

A set of crosslinked quaternized polybenzimidazole (cQAPBI-nC) membranes with varying carbon chain lengths of crosslinking agents are designed and prepared through grafting and crosslinking reactions for their applications in electrocatalytic CO2 reduction reaction (CO2RR). The cQAPBI-6C membrane stands out among all the cQAPBI-nC membranes due to its ingenious construction of a hydrophilic/hydrophobic micro-phase separation structure. As a result, this membrane exhibits exceptional OH− conductivity and selectivity of 79.40 mS cm−1 and 54.73%, respectively, surpassing those of the commercially available FAA-3-PK-130 membrane (OH− conductivity: 33.38 mS cm−1, selectivity: 39.00%). Moreover, the cQAPBI-6C membrane has excellent mechanical and alkaline stabilities. In the self-made membrane electrode assembly reactor, the cQAPBI-6C membrane demonstrates higher CO Faraday efficiency (FE) compared with FAA-3-PK-130 membrane at −100 ∼ −160 mA cm−2. Furthermore, the cQAPBI-6C membrane can operate continuously and stably for over 32 h at −150 mA cm−2, and the CO FE and voltage maintain at around 95% and −3.7 V. These findings provide strong evidence to support the practical significance of the proposed modification strategy in the development of polybenzimidazole-based anion exchange membranes for CO2RR applications.