Ultra-thin quaternized polybenzimidazole anion exchange membranes with throughout OH− conducive highway networks for high-performance fuel cells

Abstract

A hydrophilic–hydrophobic microphase separation structure is essential for anion exchange membranes (AEMs) to balance ion conduction and mechanical strength. However, continuous hydrophobic microphase will inevitably become a barrier for ion conduction between dispersed hydrophilic ionic clusters. In this study, throughout ion conductive highway networks are constructed in quaternized polybenzimidazole (PBI) AEMs, in which OH⁻ could break through the hydrophobic polymer backbone by forming dense hydrogen bond networks with pyridine nitrogen (–N) in PBI repeating units, and a tri-cationic/non-cationic ether pendant side chain is proposed to greatly improve ionic aggregation that was still difficult to achieve in reported quaternized PBI membranes. The molecular dynamics simulation indicates comparable OH⁻ coordination through ionic bonds in hydrophilic microphase and hydrogen bonds in the hydrophobic microphase. The as-prepared membranes exhibit excellent toughness to fabricate ultrathin self-supporting AEMs (10 μm) with low ohmic resistance. H₂/O₂ fuel cells achieves a high peak power density of about 1162.3 mW cm⁻² at a large current density of 2749.5 mA cm⁻², which is the highest value among recently reported PBI-based AEMs and multi-cation side-chain type AEMs. The design of throughout conductive highway network makes the highly stable commercial PBI material one of the best candidates for AEMFCs.