Regulating Catalytic Properties and Thermal Stability of Pt and PtCo Intermetallic Fuel-Cell Catalysts via Strong Coupling Effects between Single-Metal Site-Rich Carbon and Pt

Abstract

Developing low platinum-group-metal (PGM) catalysts for the oxygen reduction reaction (ORR) in proton-exchange membrane fuel cells (PEMFCs) for heavy-duty vehicles (HDVs) remains a great challenge due to the highly demanded power density and long-term durability. This work explores the possible synergistic effect between single Mn site-rich carbon (Mn_SA-NC) and Pt nanoparticles, aiming to improve intrinsic activity and stability of PGM catalysts. Density functional theory (DFT) calculations predicted a strong coupling effect between Pt and MnN₄ sites in the carbon support, strengthening their interactions to immobilize Pt nanoparticles during the ORR. The adjacent MnN₄ sites weaken oxygen adsorption at Pt to enhance intrinsic activity. Well-dispersed Pt (2.1 nm) and ordered L1₂-Pt₃Co nanoparticles (3.3 nm) were retained on the Mn_SA-NC support after indispensable high-temperature annealing up to 800 °C, suggesting enhanced thermal stability. Both PGM catalysts were thoroughly studied in membrane electrode assemblies (MEAs), showing compelling performance and durability. The Pt@Mn_SA-NC catalyst achieved a mass activity (MA) of 0.63 A mg_Pt^-1 at 0.9 V_{<i>iR</i>-free} and maintained 78% of its initial performance after a 30,000-cycle accelerated stress test (AST). The L1₂-Pt₃Co@Mn_SA-NC catalyst accomplished a much higher MA of 0.91 A mg_Pt^-1 and a current density of 1.63 A cm^-2 at 0.7 V under traditional light-duty vehicle (LDV) H₂-air conditions (150 kPa_abs and 0.10 mg_Pt cm^-2). Furthermore, the same catalyst in an HDV MEA (250 kPa_abs and 0.20 mg_Pt cm^-2) delivered 1.75 A cm^-2 at 0.7 V, only losing 18% performance after 90,000 cycles of the AST, demonstrating great potential to meet the DOE targets.