Active and Durable PGM-free Cathodic Electrocatalysts for Fuel Cell Application

Recipient Pajarito Powder Fuel Cell Catalysts (PI: Alexey Serov)

Subs Madeleine Odgaard (EWII Fuel Cells, LLC), Tatyana Reshetenko (University of Hawaii, Hawaii Natural Energy Institute/HNEI)

Abstract The performance and understanding of Platinum Group Metal(PGM)-free Oxygen Reduction Reaction(ORR) electrocatalysts have been improving steadily for the past decade. Currently the leading performance catalysts are embedded or grafted pyrollic or Heme-like active sites where single metal atoms, such as Fe or Co, are bound to nitrogen atoms which are in turn bound to a carbonaceous matrix forming the frame of the catalyst particle. These catalysts are often called M-N-C type catalysts. Several approaches to making these types of catalyst have been developed over the years, as have the complex analytical and characterization methods necessary to determine the nature of possible active sites, their structures, and relative activity and stability. The iterative combination of improved understanding and improved catalyst design yielded more active catalysts, but severe limitations exist. An emphasis on pure activity, as measured over time periods below an hour, have created catalysts and synthesis approaches which favor catalysts that cannot provide both high activity and continue to do so for relevant durations. We assembled a team that include the world leading PGM-free ORR catalysts developer and manufacturer Pajarito Powder (PP), world-class electrode developer and manufacturer with unprecedented experience in PGM-free electrode development EWII Fuel Cells, LLC (EWII), and fuel cell testing and diagnostics expert Hawaii Natural Energy Institute (HNEI) to address the needs for more active and durable PGM-free catalysts and electrodes. The proposed technology is based on three research thrusts which rationally selected as main factors determine M-N-C catalysts performance and durability 1) Materials design and synthesis of scale. Pajarito Powder will modify their existing synthesis platforms to make higher concentration M-N4-C type active sites catalysts, since these active sites are both the most stable and active catalysts sites. The higher active site densities will be achieved through careful selection of the organic and metallic precursors, where the PIs vast experience and Pajarito’s knowledge base including understanding of the necessary physical-chemical properties of precursors will be used to further develop the 3 existing PGM-free catalyst products practiced by Pajarito. While the initial focus will be on Fe-based catalysts, the potential for improved Fe-free formulations will be determined in the second year. These catalysts will then be 2) incorporated into advanced electrode designs by EWII, who will optimize electrodes for the thicker catalysts layers needed and enhanced transport requirements. EWII will use proprietary techniques, developed over several years, to integrate PGM-free catalysts into the CCM structure through optimization of several factors including: selection of solvent for ink formation, viscosity and parameters of catalyst deposition on membrane. The MEAs will then be 3) evaluated electrochemically by the team and HNEI, a critical need in deriving the fundamental understanding of the fine interplay between catalyst precursor chemistry, resulting physical structure and activity, and electrode performance. The knowledge gained will enable the team to further improve catalysts, electrodes, and understand the physical-chemical processes that ensure active and durable PGM-free catalysts development. We assembled a team with world class capability, complementary talents and diverse strengths to successfully develop and commercialize PGM-free PEMFC catalysts and electrodes with high performance and improved durability with EEREs support that will meet the 2025(0.044 A/cm2 at 0.9 V) and interim performance targets (0.025 A/cm2 at 0.90V). The proposed approach will also leverage the materials and electrode expertise from members of the ElectroCat consortium, including electron microscopy, electrode diagnostics, and multi-scale modeling of electrode transport.