Chemically stable anion exchange membrane with 2,6-protected pendant pyridinium cation for alkaline fuel cell

Abstract

In alkaline environment, cationic membranes regularly experience degradation because of OH− attack on the cation in anion exchange membrane fuel cells (AEMFCs). Unlike quaternized amine (alicyclic and aliphatic) cations, aromatic cations are unaffected by Hofmann ß-elimination, however, because of planar geometry they are highly susceptible to nucleophilic substitution reaction. A series of polysulfone (PSU) based anion exchange membranes (AEMs) was fabricated carrying pendant pyridinium cation with different substituent groups to shield the cation against OH− ions attack. The pyridinium cations were C-2 substituted, C-4 substituted and simultaneously C-2 and C-6 substituted with either –NH2, –OH or –CH3. Chloromethylation, azidation and CuAAC reactions were employed to synthesize the copolymers. The collaborative analysis of 1H NMR and FT-IR spectroscopy was used to confirm the successful preparation of the desired product. All membranes exhibited adequate thermo-mechanical stabilities and sufficient hydration level without any serious swelling at all ranges of temperature (20–80 °C). The highest recorded ionic conductivity, peak power density and current density were 59.6 mS cm−1, 486.8 mW cm−2 and 1481.8 mA cm−2 respectively. The alkaline stability results suggest that simultaneous protection of pyridinium cation at C-2 and C-6 turns the membrane thoroughly resistant to OH− attack while the ones with exposed cations degrade at accelerated rate at elevated temperature. This study is aimed at providing a broader understanding of designing durable AEMs with promising performance by exploring the influence of changes in structural configuration of aromatic cations with different functional groups on the overall performance of AEMs and how the cations withstand the nucleophilic attack in AEMFCs.