Jacob S. Spendelow

Polymer electrolyte fuel cell performance is limited mainly by the cathode, where poor oxy- gen reduction reaction (ORR) kinetics and slow transport of O2 to active sites lead to large overpotentials. State-of-the-art high surface area Pt alloy catalysts also suffer from poor du- rability due to loss of surface area (particle growth) and leaching of base metals. We have recently demonstrated that the use of intermetallic nanoparticle catalysts such as L10-PtCo can enable significant improvements in long-term performance due to improved stabiliza- tion of base metal in the ordered lattice. New catalysts based on the L10 structure have shown excellent durability in fuel cell membrane electrode assemblies (MEAs), meeting DOE targets for accelerated stress tests (30K voltage cycles in MEA) with minimal perfor- mance degradation. Recent results and future directions for this catalyst research will be discussed. While kinetic performance and durability of these catalysts is promising, perfor- mance at high power densities continues to be limited by slow O2 transport. Several fac- tors, including slow diffusion through ionomer films, Knudsen diffusion through mi- cropores, and pore blockage by liquid H2O contribute to these transport limitations. Design of unconventional electrode structures that can minimize these limitations is needed to en- able full utilization of cathode catalysts. New hierarchical electrode structures capable of re- ducing these transport losses will be presented.