Impact of polymer additives on crack mitigation of rod-coated fuel cell cathode catalyst layers

Abstract

Cracks in catalyst layers (CLs) are a potential source of long-term failure in a fuel cell membrane electrode assembly (MEA). While modifications to the CL ink formulation can affect the degree of cracking, these changes may lead to lower initial performance than their cracked analogues due to the established link between formulation and performance. In this work, we explored the use of polymeric additives to mitigate CL cracks. Small quantities of poly (acrylic acid), poly (ethylene oxide), poly (methyl methacrylate), or poly (vinyl alcohol) – 5 wt% relative to ionomer mass – were added to the ink prior to its final mixing. Poly (vinyl alcohol) resulted in crack–free CLs, whereas the other polymers resulted in CLs with similar crack percentages as the control CL. Through a combination of transmission electron microscopy, X-ray computed tomography, and infrared spectroscopy, we ascribed the crack–mitigating mechanism of poly (vinyl alcohol) to its ability to hydrogen–bond with Nafion, the ion conducting polymer binder in the catalyst ink. Initial performance of this non–cracked electrode exhibited nearly identical electrochemical behavior to its cracked counterpart, demonstrating that PVA additives successfully reduce cracks while maintaining cell initial performance.