Recent Advances in Low and Pt-Free Loading in Anion Exchange Membrane Fuel Cells

Abstract

Anion exchange membrane (AEM) fuel cells have seen tremendous advances in recent years.[1] Power densities have now been obtained reaching over 3 W/cm2.[2] The advances in the field have been enabled by new AEM materials that have improved properties and durability as well as advances in electrode processing and performance. While the potential advantages of AEM fuel cells have been widely reported to be around the area of enabling non-precious electrocatalysis (and lower cost system materials), most of the results reported to date have focused on Pt containing electrocatalysts, often with high loadings to improve power density.[1] Now that exceptionally high-power densities have been achieved, it has become more important to focus on the performance and durability of AEM fuel cells at low loadings. At the National Renewable Energy Laboratory (NREL), we have investigated a number of different polymer systems and have demonstrated the ability to greatly improve performance through electrode processing techniques. We have also demonstrated durability greater than 500 hours with a wide range of different membrane compositions. We have found that electrodes play a much more critical role in determining performance and durability. Recently, we have demonstrated the ability to achieve high performance with a variety of different ionomeric electrode materials. Most of our initial work had focused on Pt at high loadings, but we have also explored low Pt and Pt-free catalysts. In this talk we will discuss the role of different polymers, different electrode fabrication techniques, and the impact of loading on observed fuel cell performance and durability. With the issue of power density largely demonstrated our efforts have focused on areas including increased robustness (operating under dynamic conditions particularly at different RH), low Pt group metal loading, impacts of carbon dioxide exposure, and durability.