Using “rigid - flexible” collaborative strategy to construct high performance alkyl - piperidinium grafted polybenzimidazole membranes for efficient CO2 reduction

Abstract

Polybenzimidazole (PBI) membrane demonstrates considerable potential for application in electrochemical CO₂ reduction (ECR), owing to its exceptional physicochemical properties. However, the PBI is limited by its intrinsic low ionic conductivity. Grafting is an effective method for enhancing microphase separation and ionic conductivity for PBI membrane. Here, a series of piperidinium-functional OPBI membranes (OPBI-n-Pip, n = 2, 6, 10) were designed and prepared using the “rigid-flexible” collaborative strategy. The backbone of OPBI-n-Pip polymer effectively suppress membrane swelling, while flexible piperidinium cations side chains offer dimensional stability and ionic conductivity. Furthermore, the ion transport and stability mechanism of OPBI-n-Pip membranes are revealed by molecular dynamics (MD) simulations and density functional theory (DFT) calculations. Notably, OPBI-6-Pip membrane exhibited best performance such as low area resistance (0.16 Ω cm², at 20 °C), limited swelling ratio (25.0 %) and robust alkaline stability in 1 M KOH (91.6 % retention after 1440 h, at 30 °C). In ECR systems, the OPBI-6-Pip membrane demonstrated high CO faraday efficiency (FEco) of 93.6 % at 100 mA cm⁻². This work provides good guidance for the practical implementation of PBI in electrochemical energy systems.