In the U.S., medium and heavy-duty vehicle (HDV) account for about 25% of the transportation sector greenhouse gas emissions.¹ Compared with polymer electrolyte membrane fuel cell (PEMFC) powered light-duty vehicle (LDV), HDV has predictable routes and require less infrastructure investment, which is beneficial for its wide commercialization. However,, PEMFC-powered HDV do require longer lifetimes and mileage compared to LDV.² Improving the PEMFC system durability, especially that of the cathode catalyst layer is of critical importance to obtaining higher efficiency and reducing the total cost of ownership.³ In this work, we investigated the durability of high surface area carbon supported well dispersed Pt (Pt/HSC), annealed Pt (a-Pt/HSC) and de-alloyed PtCo (d-PtCo/HSC) alloy catalysts. A H₂/N₂ catalyst specific accelerated stress test (AST) was used where the electrode was cycled between 0.6 to 0.95V for 90K cycles. To probe the catalyst layer degradation, mass activity, O₂ transport resistance, electrochemical active surface area (ECSA), catalyst surface utilization, CO displacement and ionomer coverages^4,5 were measured at different stages of the durability test.

Compared to the d-Pt/HSC catalyst, the d-PtCo/HSC catalyst show much higher BOT mass activity. The mass activity enhancement becomes less significant beyond 30K cycles due to Co leaching, as supported by the WAXS, TEM-EDS analysis. The well-dispersed Pt/HSC also show higher initial mass activity but also suffers from faster degradation due to catalyst dissolution and redeposition. From the ECSA measurement, the a-Pt/HSC and d-PtCo/HSC sample show similar tread of ECSA loss from 30K to 90K AST cycles, while the well dispersed Pt/HSC show more significant ECSA loss. From the H₂/Air polarization curves, the d-PtCo/HSC sample has BOT mass transport resistance compared with a- Pt/HSC and well-dispersed Pt/HSC sample. The d-PtCo/HSC sample’s mass transport loss becomes more significant after AST cycles. The catalyst utilization measurement at different RH conditions using CO stripping method revealed that all three catalysts show less RH sensitivity after AST cycles, suggesting more Pt gets redeposited to the outside of the carbon support and potentially small amount of carbon support corrosion.

Acknowledgement

This work was authored in part by Alliance for Sustainable Energy, LLC, the manager and operator of the National Renewable Energy Laboratory for the U.S. Department of Energy (DOE) under Contract No. DE-AC36-08GO28308. This material is based on work performed by the Million Mile Fuel Cell Truck (M2FCT) Consortium, technology manager Greg Kleen. Funding was provided by the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office (HFTO). The views expressed in the article do not necessarily represent the views of the DOE or the U.S. Government. The U.S. Government retains and the publisher, by accepting the article for publication, acknowledges that the U.S. Government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others to do so, for U.S. Government purposes.

References

1. U. S. E. P. Agency, Fast Facts on Transportation Greenhouse Emissions https://www.epa.gov/greenvehicles/fast-facts-transportation-greenhouse-gas-emissions.
2. D. A. Cullen et al., Nat. energy, 1–13 (2021).
3. J. Marcinkoski et al., Hydrogen Class 8 Long Haul Truck Targets (US Department of Energy, 2019 https://www.hydrogen.energy.gov/pdfs/19006_hydrogen_class8_long_haul_truck_targets.pdf.
4. T. Van Cleve et al., J. Power Sources, 482, 228889 (2021).
5. T. Van Cleve et al., ACS Appl. Mater. Interfaces, 11, 46953–46964 (2019).