Investigating the Influences of Polystyrene-Based Hydroxide Ion Conducting Ionomer on Electrode in Anion Exchange Membrane Fuel Cells

Alkaline anion exchange membrane fuel cells (AEMFCs) are an attractive alternative to proton exchange membrane fuel cells because they have the advantage of cost savings due to the use of non-noble metal catalysts. Since AEMFCs has a charge carrier of hydroxide ions, anion exchange membranes having various cationic groups substituted on the hydrocarbon polymer backbone have been actively studied for high hydroxide conductivity, mechanical properties and durability. In addition, the electrode ionomer of the core material of the membrane electrode assembly acts as a binder for uniformly dispersing the catalyst and fixing the catalyst layer and anion exchange membrane. It also serves as a transport pathway for hydroxide ions produced from the cathode to the anode. In particular, it is important that the electrode ionomer greatly affects the catalyst layer type and fuel cell performance. Herein, polystyrene-based copolymers with variable molecular weight are prepared by radical polymerization of styrene, grafted with bromo-alkyl chains of different length (C3 or C6) through Friedel-Crafts acylation, and quaternized to afford a series of hydroxide ion–conducting ionomers. The performance of anion-exchange membrane fuel cells (AEMFCs) constructed using the prepared electrode ionomers is affected by several ionomer properties, and a maximal power density of 407 mW cm−2 and a durability exceeding that of a reference cell with a commercially available ionomer are achieved under optimal conditions. Thus, the developed approach is concluded to be well suited for the fabrication of next-generation electrode ionomers for high-performance AEMFCs.