(Invited) Stable Catalysts, Functionalized Supports and Fluorocarbon Additives for Fuel Cell Electrodes
Authors: Ramaswamy Nagappan 
Published: December 2024

Proton Exchange Membrane (PEM) fuel cell operating on hydrogen is an alternative for the diesel-powered internal combustion engines for medium- and heavy-duty vehicle applications due to their higher efficiency and zero-local greenhouse gases emission. To achieve this prospect, PEM fuel cells need to demonstrate improved durability over a much longer operational lifetime of ~30,000 hours (or an equivalent of a million miles of driving distance) and lower total cost of ownership (sum of capital and operational expenses) compared to the diesel-based incumbent. In this regard, the United States Department of Energy (DOE) has set an end-of-test platinum specific power density target of 2.5 kW/gPGM at a rated voltage of 0.7 V after running a 25,000-hour equivalent accelerated stress test (AST). Japanese New Energy & Industrial Development Organization (NEDO) has set an even more aggressive 2030 ultimate target of 5.3 kW/gPGM (Figure 1).
Fuel cell cathode electrodes are composed of high surface area carbon black supported platinum or platinum-alloy nanoparticles for electrocatalytic Oxygen Reduction Reaction (ORR) dispersed along with perfluorosulfonic acid (PFSA) ionomer to serve both as proton conducting and binding agent. The continuous loss in power delivered by a fuel cell could be attributed to the i) loss in electrochemical surface area of Pt, ii) loss in kinetic activity of Pt/PtCo catalyst and iii) contamination effects of dissolved cobalt alloying element in the ionomer phase. Of this, the loss in electrochemical surface area is the single largest contributor to the fuel cell voltage degradation which is due to the coarsening of platinum nanoparticles either via migration-coalescence on the carbon support and/or via dissolution-reprecipitation (electrochemical Ostwald ripening).
In this context, recent developments in fuel cell cathode materials from General Motors focusing on improving durability by modifying the platinum/carbon support interface and re-designing platinum/ionomer-water interface will be presented. These include the development of i) durable Pt catalysts via surface protection with ZrO2-x nanoclusters,[1] ii) sulfate functionalized carbon supports for alternate electrode structures,[2] and iii) small molecule fluorocarbon modified catalysts interfaces for improved durability.

Acknowledgements: This work was partially supported by U.S Department of Energy (DOE), Hydrogen and Fuel Cell Technologies Office (HFTO) under grants DE-EE0008821 and DE-EE0010749.

References:

Ramaswamy, N., Z. Shi, B. Zulevi, G. McCool, N.P. Mellott, A. Kongkanand, S. Kumaraguru, M.L. Ostraat, D.A. Muller, N.N. Kariuki, D.J. Myers, and A.J. Kropf, Surface Decoration of Platinum Catalysts by ZrO2–x Nanoclusters for Durable Fuel Cell Applications. ACS Catalysis, 2024: p. 4441-4452.

Yarlagadda, V., N. Mellott, S. Kumaraguru, and N. Ramaswamy, Proton Transport Functionality-Enabled Carbon Support for Improved Fuel Cell Performance and Durability. ACS Applied Materials & Interfaces, 2023. 15(48): p. 55669-55678.

Figure 1