Toward a Comprehensive Understanding of Cation Effects in Proton Exchange Membrane Fuel Cells

Metal alloy catalysts (e.g., Pt-Co) are widely used in fuel cells for improving the oxygen reduction reaction kinetics. Despite the promise, the leaching of the alloying element contaminates the ionomer/membrane, leading to poor durability. However, the underlying mechanisms by which cation contamination affects fuel cell performance remain poorly understood. Here, we provide a comprehensive understanding of cation contamination effects through the controlled doping of electrodes. We couple electrochemical testing results with membrane conductivity/water uptake measurements and impedance modeling to pinpoint where and how the losses in performance occur. We identify that (1) similar to 44% of Co2+ exchange of the ionomer can be tolerated in the electrode, (2) loss in performance is predominantly induced by O-2 and proton transport losses, and (3) Co2+ preferentially resides in the electrode under wet operating conditions. Our results provide a first-of-its-kind mechanistic explanation for cation effects and inform strategies for mitigating these undesired effects when using alloy catalysts.

Automated summary

In this study, the effects of cation contamination on fuel cell performance were comprehensively understood through controlled doping of electrodes. The research identified that around 44% of Co2+ exchange in the ionomer can be tolerated in the electrode, with performance losses mainly induced by oxygen and proton transport losses. It was also found that Co2+ preferentially resides in the electrode under wet operating conditions, providing insights for strategies to mitigate undesired effects when using alloy catalysts.