Proton and Metal Cage-Based Anion-Conductive Fluoropolymers for AMFCs

Abstract

Alkaline membrane fuel cells (AMFCs) have attracted a great deal of attention due to its use of non-precious metal catalysts. However, the lack of chemically stable and highly ion-conductive anion-exchange polymer membrane has impeded the development and adoption of AMFCs by our society. Under strong alkaline conditions, hydroxide anions can be both a nucleophile and a strong base that degrade the hydrocarbon polymer backbones as well as the anion-exchange groups attached to the side chains of the polymer. Typically, positively charged quaternary amine or guanidinium groups are used for hydroxide transportation. Unfortunately, these functional groups are subjected to nucleophilic and elimination attacks by hydroxide anions. In this presentation, we will disclose a new class of chemically stable anion-exchange fluoropolymers that can be casted into AMFC membranes. The structure of a proton trap-based fluoropolymer is shown in the attached figure. This polymer was chemically synthesized from a perfluorosulfonic acid (PFSA) via a novel C-C coupling reaction. The highly fluorinated polymer backbone and side chains were known to tolerate chemical degradation while its proton cage group is robust against caustic conditions. In our polymer, a proton is encapsulated inside a three-dimensional cage and it is protected from hydroxide attacks. Such a polymer demonstrated remarkable stability in strong alkali media with good ion conductivity. In our talk, we will also discuss several other types of anion-exchange fluoropolymers including zirconium-based membranes and lithium cage-based electrolytes. Figure 1