Effect of humidity on the interaction of CO₂ with alkaline anion exchange membranes probed using the quartz crystal microbalance

The alkaline anion exchange membrane fuel cell (AAEM-FC) is able to deliver a comparable performance to the traditional proton exchange membrane fuel cell (PEM-FC) without the use of precious metal electrocatalysts, making it a more cost-competitive alternative for low-temperature fuel cell applications. However, issues relating to degradation and specifically interaction with CO₂ still hinder the technology's commercialisation prospects. With hydration playing a key role in solid polymer electrolyte fuel cell operation, this study examines how membrane hydration affects the AAEM interaction with CO₂. The change of membrane conductivity upon exposure to atmospheric CO₂ has been compared with the change in viscoelastic properties of a cast thin-film ionomer, both as a function of humidity. The effect of CO₂ on the membrane as a function of hydration suggests a link to its solvation and swelling regimes and thus the access of CO₂ to the ionic channels within the membrane. The thin-film QCM composite resonator study has suggested that during the solvation (pore opening) regime, there is a linear increase in CO₂ uptake as water can further permeate the pore system and the cationic headgroups become increasingly accessible. During the transition to the pore swelling regime, there is a step increase in CO₂ uptake as the network is thought to be fully open; as such, subsequent increases in RH do not lead to any significant increase in CO₂ uptake.