Mechanically flexible bulky imidazolium-based anion exchange membranes by grafting PEG pendants for alkaline fuel cells

Abstract

Imidazoliums with bulky substitutes are promising alternative cations for anion exchange membranes due to their superior stability under alkaline conditions. However, bulky imidazolium-based AEMs suffer from low conductivity as well as poor film-forming ability, and thus unfavorable fuel cell performance. Herein, we presented a strategy to graft hydrophilic and flexible polyethylene glycol (PEG) chains on the imidazoliums to prepare imidazolium-type AEMs. The resulting AEMs showed excellent film-forming ability with reasonable tensile strengths of 18.7 MPã31.8 MPa and high elongation at break of 21.2%–133.3%. Owing to the well-developed microphase-separated morphology and increased water uptake, the AEMs with a low ion exchange capacity of 0.95 meq./g displayed the hydroxide conductivity of 32.3 mS/cm at 20 °C. After immersion in 1 M NaOH at 80 °C for 1248 h, the initial conductivity was maintained by 37.1%–47.9%, and the degradation mechanism was explored by model imidazolium cations investigation. In addition, the Im-PEG-PPO-70 membrane having the highest conductivity was fabricated into membrane electrode assembly, exhibiting a peak power density of 179 mW/cm2 at 60 °C in a single H2/O2 alkaline fuel cell. A short-term life test on this MEA under 200 mA/cm2 showed a performance decay rate of 2.3 mV/h over 100 h of operation.