Imidazolium-functionalized poly(ether ether ketone) as membrane and electrode ionomer for low-temperature alkaline membrane direct methanol fuel cell

A series of imidazolium-functionalized poly(ether ether ketone)s (PEEK-ImOHs) were successfully synthesized by a two-step chloromethylation–Menshutkin reaction followed by hydroxide exchange. PEEK-ImOH membranes with ion exchange capacity (IEC) ranging from 1.56 to 2.24 mmol g−1 were prepared by solution casting. PEEK-ImOHs show selective solubility in aqueous solutions of acetone and tetrahydrofuran, but are insoluble in lower alcohols. PEEK-ImOH membranes with IEC of 2.03 mmol g−1 have high hydroxide conductivity (52 mS cm−1 at 20 °C), acceptable water swelling ratio (51% at 60 °C), and great tensile strength (78 MPa), and surprising flexibility (elongation-to-break of 168%), and high thermal stability (Decomposition temperature: 193 °C). In addition, PEEK-ImOH membranes show low methanol permeability (1.3–6.9 × 10−7 cm2 s−1). PEEK-ImOH membrane was tested in methanol/O2 fuel cell as both the HEM and the ionomer impregnated into the catalyst layer; the open circuit voltage is 0.84 V and the peak power density is 31 mW cm−2.