Long-spacer-chain imidazolium functionalized poly(ether ether ketone) as hydroxide exchange membrane for fuel cell

• A spacer-modified imidazolium-functionalized PEEK (PEEK-AeImOH) was synthesized.
• The PEEK-AeImOH membrane shows the conductivity as high as 48 mS cm−1.
• The PEEK-AeImOH membrane has good stability in 1 M KOH at 60 °C.
• High open circuit voltage of 1.02 V and power density of 120 mW cm−2 were achieved.

An imidazolium-functionalized poly(ether ether ketone) containing a long spacer chain between imidazolium group and polymer main-chain (PEEK-AeImBr) was synthesized by the reaction of chloromethylated PEEK and self-synthesized 1-Aminoethyl-2,3-dimethylimidazolium bromide. 1H NMR spectra confirmed the successful synthesis of PEEK-AeImBr. The corresponding PEEK-AeImOH HEM was prepared by casting the PEEK-AeImBr solution and subsequent ion-exchange process. Ion exchange capacity (IEC) of PEEK-AeImOH membranes ranges from 1.50 to 2.07 mmol g−1 with the degree of chloromethylation from 58% to 92%. Hydroxide conductivity of PEEK-AeImOH membranes increases with increasing IEC. PEEK-AeImOH membrane with IEC of 2.07 mmol g−1 has the highest conductivity of 48 mS cm−1. The spacer-modified PEEK-AeImOH membrane maintained good alkali stability at 60 °C. The H2/O2 single cell with the PEEK-AeImOH membrane exhibits high open circuit voltage of 1.02 V and peak power density of 120 mW cm−2 at room temperature.