Water content and ionic conductivity of thin films of different anionic forms of anion conducting ionomers

Typically, in polymer electrolyte-based electrochemical devices such as electrolyzers and fuel cells, ionomers in the catalyst layers are present as ultrathin films coating the electrochemically active component. Acidic ionomer thin films have been extensively characterized over the past decade, yet there are few reports on the alkaline ionomer thin films. Here, we present a study on anion-exchange ionomers; specifically, we investigate the water content and conductivity of fluoride, bromide, and carbonate forms of 50 nm thick FAA3 and PPO ionomer thin films at 30 °C and 0−90% RH. A thermodynamic analysis was performed to compute the Gibbs free energy of anionic interaction with water to discuss the impact of anion type on the anionic mobility. Structural analysis using GISAXS was performed on the anion-exchange ionomer thin films. Furthermore, conductivity and water content relationships between FAA3 thin films and membranes and between FAA3 and PPO thin films were compared and discussed in terms of structure and ion clustering.