Water-alcohol dispersible and self-cross-linkable sulfonated poly(ether ether ketone): Application as ionomer for direct methanol fuel cell catalyst layer

Abstract A sulfonated poly(ether ether ketone) containing hydroxyl groups (HO-SPEEK) has been synthesized for investigation as the ionomer in cathode of direct methanol fuel cells. Na salt-formed HO-SPEEK shows excellent solubility in some aqueous solutions of monohydric alcohol and can be successfully self-cross-linked in-situ during the hot-pressing process of membrane-electrode assembly (MEA) fabrication. The resulted cross-linked HO-SPEEK displays improved stability and mechanical strength. MEA incorporating the HO-SPEEK as both membrane and ionomer shows excellent peak power density of 29.0 mW cm−2 at 25 °C with 4 M methanol, which is comparable to the Nafion reference MEA (31.8 mW cm−2) and 2.9-fold higher than that of the MEA prepared from catalyst ink that contained dimethyl sulfoxide (10.3 mW cm−2). Thanks to the avoidance of high-boiling point solvent, the resulted HO-SPEEK-based cathode is loosened with many large pores for reactant gas and product transportation. These results demonstrate that water-alcohol dispersible and cross-linkable sulfonated hydrocarbons hold technological promise as ionomer for electrode.