A comb-like ionomer based on poly(2,6-dimethyl-1,4-phenylene oxide) for the use as anodic binder in anion-exchange membrane direct methanol fuel cells

Ionomeric binders are crucial to a proper use of fuel cells. In anion-exchange membrane direct methanol fuel cells (AEM-DMFCs) the requirements for the ionomeric binders are anionic conductivity, chemical and thermal stability and facilitation of the reactant and product transport in the three-phase boundary. In this study, we present the synthesis of a poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) based comb-like ionomer and the physical and electrochemical characterization of this ionomer. The ionomer consists of a PPO backbone and a partially fluorinated cationic sidechain. In comparison to an imidazolium functionalized PPO ionomer, the comb-like ionomer showed higher stability regarding ionic conductivity and ion exchange capacity in alkaline media. Besides this, a low swelling ratio for 4 M methanol anodic fuel was found for the ionomer making it a suitable candidate for an application in the anodic catalyst layer in AEM-DMFCs. Thermogravimetric analysis coupled with a mass spectrometer proved the ionomer to be thermally stable in AEM-DMFC working conditions. Therefore, the comb-like ionomer was implemented in single cells as a catalyst binder. A single cell with an ionomer content of 25 wt% showed a 2.75 times higher power output compared to a single cell with PTFE as anode catalyst binder when run with KOH-free anodic fuel.