posted on 2024-01-11, 15:08authored byXuan Liu, Yuhan Wang, Jiashun Liang, Shenzhou Li, Siyang Zhang, Dong Su, Zhao Cai, Yunhui Huang, Lior Elbaz, Qing Li
Surface
polarization under harsh electrochemical environments usually
puts catalysts in a thermodynamically unstable state, which strictly
hampers the thermodynamic stability of Pt-based catalysts in high-performance
fuel cells. Here, we report a strategy by introducing electron buffers
(variable-valence metals, M = Ti, V, Cr, and Nb) into intermetallic
Pt alloy nanoparticle catalysts to suppress the surface polarization
of Pt shells using the structurally ordered L10-M-PtFe
as a proof of concept. Operando X-ray absorption spectra analysis
suggests that with the potential increase, electron buffers, especially
Cr, could facilitate an electron flow to form a electron-enriched
Pt shell and thus weaken the surface polarization and tensile Pt strain.
The best-performing L10-Cr-PtFe/C catalyst delivers superb
oxygen reduction reaction (ORR) activity (mass activity = 1.41/1.02
A mgPt–1 at 0.9 V, rated power density
= 14.0/9.2 W mgPt–1 in H2-air
under a total Pt loading of 0.075/0.125 mgPt cm–2, respectively) and stability (20 mV voltage loss at 0.8 A cm–2 after 60,000 cycles of accelerated durability test)
in a fuel cell cathode, representing one of the best reported ORR
catalysts. Density functional theory calculations reveal that the
optimized surface strain by introducing Cr on L10-PtFe/C
accounts for the enhanced ORR activity, and the durability enhancement
stems from the charge transfer contribution of Cr to the Pt shells
and the increased kinetic energy barrier for Pt dissolution/Fe diffusion.