A Durable Platinum Group Metal-Free Oxygen Reduction Catalyst for Polymer Electrolyte Fuel Cells

Abstract

A Durable Platinum Group Metal-free Oxygen Reduction Catalyst for Polymer Electrolyte Fuel Cells Hanguang Zhang, Hoon T. Chung, Ulises Martinez, Edward F. Holby, and Piotr Zelenay Materials Physics and Applications Division, Los Alamos National Laboratory, Los Alamos, NM 87545, USA Performance of platinum group metal-free (PGM-free) catalysts for oxygen reduction reaction (ORR) in polymer electrolyte fuel cells (PEFCs), especially high-temperature metal-nitrogen-carbon (M-N-C) materials, has improved a lot in the last two decades,1, 2 however, their durability continues to present a big challenge. PGM-free catalysts typically suffer a 40-80% activity loss during the first 100 hours of operation in the low-temperature fuel cell cathode, which is way short of the 8,000-hour lifetime target for PEFCs.3, 4 Significant improvements to PGM-free catalyst performance durability are thus required before they can be considered for practical PEFCs.In this presentation, we will introduce a ‘dual-zone’ approach to high-temperature synthesis of PGM-free catalysts, which results in modifications to the catalyst surface and, ultimately, in very significant improvements to their durability. In H2-air fuel cell testing, the ‘dual-zone’ fuel cell catalyst has shown a minimal performance loss during up to 80,000 voltage cycles using standardized PGM-free durability test protocol developed in ElectroCat consortium and approved by DOE. The catalyst has also retained 70% of its initial activity in a 600-hour constant-voltage fuel cell test at 0.70 V.We will report fuel cell performance data in the first part of this presentation, followed by discussion of possible origins of the much improved performance durability imparted by the ‘dual-zone’ approach. Acknowledgement This research was supported by the U.S. DOE, Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office under the auspices of the Electrocatalysis Consortium (ElectroCat). References Wu, G.; More, K. L.; Johnston, C. M.; Zelenay, P., High-performance electrocatalysts for oxygen reduction derived from polyaniline, iron, and cobalt. Science 2011, 332, 443-447.Chung, H. T.; Cullen, D. A.; Higgins, D.; Sneed, B. T.; Holby, E. F.; More, K. L.; Zelenay, P., Direct atomic-level insight into the active sites of a high-performance PGM-free ORR catalyst. Science 2017, 357, 479-484.Shao, Y.; Dodelet, J.-P.; Wu, G.; Zelenay, P., PGM-Free Cathode Catalysts for PEM Fuel Cells: A Mini-Review on Stability Challenges. Mater. 2019, 31, 1807615.U.S. DRIVE Fuel Cell Technical Team Roadmap; Department of Energy, US, 2017.