ORR Activity and Voltage-Cycling Stability of a Carbon-Supported Pt_xY Alloy Catalyst Evaluated in a PEM Fuel Cell

Platinum-yttrium alloys (Pt_xY) are suggested to have superior oxygen reduction reaction (ORR) activity and long-term stability in proton exchange membrane fuel cells (PEMFCs). However, the actual ORR activity and stability of a Pt_xY catalyst with a high electrochemically active surface area (ECSA) in a PEMFC remains uncertain. Here, a Ketjen black (KB) carbon supported Pt_xY/KB catalyst with a high ECSA (∼60 m²/g) was synthesized using a carbon nitride precursor. Based on elemental analysis, XRD, electron microscopy, and a mass-balance based model, it was shown that the acid-leached Pt_xY nanoparticles of the catalyst consist of a ∼0.7 nm thick Pt-shell and a Pt₃Y core. Rotating disk electrode (RDE) and 5 cm² single-cell PEMFC measurements indicated that the ORR activity of the acid-leached Pt_xY/KB catalyst is similar to an analogously synthesized Pt/KB reference catalyst with the same ECSA. Voltage-cycling accelerated stress tests (ASTs) between 0.6−1.0 V (in H₂/N₂ at 80 °C/95% RH) in 5 cm² single-cells showed that the ORR activity and durability of the Pt_xY/KB catalyst is similar to that of the Pt/KB reference catalyst. Thus, the high durability of Pt-rare Earth alloys that has been claimed on the basis of RDE measurements is not observed in actual PEMFCs.