Molybdenum-Pocket Driven Low-Platinum Oxygen Reduction Catalysts for 100-Watt-Scale Fuel Cell Stacks

Area of Science:

• Electrochemistry
• Materials Science
• Catalysis

Background:

• Commercialization of proton exchange membrane fuel cells (PEMFCs) requires highly efficient and low-platinum (Pt) loading stacks.
• Ultralow-loading Pt catalysts (<0.10 mg cm^-2) exhibit reduced activity and stability due to high oxygen resistance under operational conditions.

Purpose of the Study:

• To develop an advanced catalyst overcoming the limitations of ultralow-loading Pt catalysts for PEMFCs.
• To enhance oxygen reduction reaction (ORR) activity and catalyst stability in low-Pt catalysts.

Main Methods:

• Synthesis of a molybdenum oxide-pocket-driven Pt₂Co (MoO₃-Pt₂Co) alloy catalyst supported on carbon (C).
• Fabrication of membrane electrode assemblies (MEAs) using the MoO₃-Pt₂Co/C catalyst.
• Performance and durability testing of MEAs and a fuel cell stack under various conditions (H₂-O₂, H₂-air).

Main Results:

• The MoO₃-Pt₂Co/C catalyst exhibits enhanced ORR activity and minimized cobalt leaching due to molybdenum oxide's oxygen vacancy 'pocket'.
• MEAs achieved peak power densities of 3.20 W cm^-2 (H₂-O₂) and 1.73 W cm^-2 (H₂-air) at 0.10 mg cm^-2 Pt loading.
• The catalyst retained high mass activity (1.68 A mg^-1) after 30k cycles, operated stably at 0.65 V for over 550 hours, and a 123 W fuel cell stack projected Pt utilization below the DOE target.

Conclusions:

• The MoO₃-Pt₂Co/C catalyst significantly improves the performance and durability of low-Pt PEMFCs.
• This catalyst design offers a viable pathway towards cost-effective and commercially competitive fuel cell technology.
• The developed fuel cell stack demonstrates potential for meeting or exceeding US Department of Energy targets for Pt utilization in vehicles.