Chemical degradation of ionomer in the electrodes of proton exchange membrane fuel cells
Eugene Jeong, Jisu Park, Sang Ha Lee, Shawn Litster
Abstract
Chemical degradation of ionomer in proton exchange membrane fuel cell (PEMFC) electrodes can impact durability and cost. However, it is less well understood than membrane degradation due to the small amount of ionomer used in electrodes and the difficulty in separating its contribution from the membrane's. Here, we used a pellet of PEMFC electrode catalyst-ionomer composite and subjected it to treatments with Fenton's reagent to evaluate the chemical degradation. Fluoride measurements revealed that catalyst-layer-like structures degrade much more slowly than membranes, possibly due to a combination of reduced ionomer accessibility and radical scavenging by the platinum. We also fabricated membrane electrode assemblies (MEAs) with catalyst layers selectively degraded by a Fenton treatment. Electrochemical characterization revealed that low-current performance is not affected by treatments corresponding to 1 % fluorine loss in the membrane. However, some parameters, such as oxygen transport resistance, are systematically changed by the Fenton test. Our results show that the ionomer chemical degradation may be less impactful than other forms of electrode degradation; however, extended and more aggressive experiments could reveal additional details. We suggest using model systems, such as the bulk pellet in this work, to streamline performing Fenton's reagent-based experiments and preparing samples for analytical chemical characterizations.