A strategy to design quaternized poly(2,6-dimethyl-1,4-phenylene oxide) anion exchange membranes by atom transfer radical coupling

Abstract

Sterically crowded organic cations are widely incorporated into aromatic polymers as anion exchange membranes (AEMs) materials to improve the chemical stability. However, due to the reduced entanglement between polymers, these AEMs suffer from poor mechanical properties, low conductivity, and insufficient water uptake, impeding their further application in alkaline fuel cells. To address these limitations, we demonstrate a strategy for designing a stable and conductive AEM material by atom transfer radical coupling reaction between bromomethylated poly (2,6-dimethyl-1,4-phenylene oxide) (BPPO) and quaternized 2,2,6,6-tetramethylpiperidinooxys (T-QA). These quaternized copolymers produced mechanical robust and transparent membranes with less water uptake and swelling ratio. The resulting TQPPO membrane possessing IEC value of 2.13 mmol/g had considerably higher OH − conductivity of 52.4 mS/cm (20 °C) and 103 mS/cm (80 °C) compared with AEMs containing BTMA cations or sterically-protected imidazoliums on PPO matrix, due to the well-developed microphase separation. Since these polymers were free of benzyl-containing quaternary ammoniums, higher alkaline stability over BTMA-based ones was observed when equilibrated in 1 M sodium hydroxide solution at 60 or 80 °C. In addition, a peak power density of 287.5 mW/cm 2 was observed at 80 °C for TQPPO membrane in the practical application of a single hydrogen/oxygen alkaline fuel cell. This work provided an effective strategy to synthesize conductive and stable AEMs from bromomethylated or chloromethylated polymers for alkaline fuel cell applications. • Conductive AEMs with improved alkaline stability were designed by ATRC reaction. • Pendant TEMPO-based cations induced the formation of hydrophilic-hydrophobic microphase separation in AEMs. • AEMs with TEMPO-based cations showed a PPD of 287.5 mW/cm 2 in fuel cells.