Constructing novel cross-linked polybenzimidazole network for high-performance high-temperature proton exchange membrane

Abstract

Compared with linear polybenzimidazole (PBI) membranes, cross-linked phosphoric acid (PA)-PBI membranes with superior mechanical strength have greater potential for application in high-temperature proton exchange membrane fuel cells (HT-PEMFCs). However, performances of conventional cross-linked membranes are usually limited by densely cross-linked network, and reduced concentration of proton-conductive imidazole units. Therefore, it still remains a big challenge to fabricate high-performance cross-linked PA-PBI membranes. Herein, we build covalently cross-linked PBI network using commercially available 2,6-bis(hydroxymethyl)-4-methylphenol (BHMP) as cross-linking agent through a well-established film-forming process. The optimized covalently cross-linked network can combine high mechanical properties, desired proton conductivity as well as excellent fuel cell performance, owing to a loose but tough cross-linked molecular structure and existence of favorable additional hydroxyl for proton transport. Especially, the covalently cross-linked membrane with BHMP content of 1% display a high proton conductivity of 168.4 mS cm−1 and a good power density of 597.5 mW cm−2 at 160 °C without humidification, outperforming the pristine OPBI membrane. Additionally, in long-term durability test, the voltage decay of cross-linked membrane is low (0.0212 mV h−1) at current density of 200 mA cm−2, suggesting an excellent membrane stability.