Unveiling Atomic-Level Synergy of Pt3Fe Alloy Nanoparticles and Fe Single Atoms for Enhanced Electrochemical Stability.

The hybridization of single atom sites (SASs) and nanoparticles (NPs) demonstrates enhanced stability under acidic electrochemical environments when compared to their individual components; however, the underlying synergistic mechanisms remain elusive. Here we synthesize a hybrid catalyst featuring electron transfer from Pt3Fe NPs to high-spin D1-type FeN4 SASs. The online inductively coupled plasma mass spectrometry technique confirms a mutual suppression of electrochemical dissolution between Pt3Fe and D1-FeN4. In situ spectroscopy and theoretical calculations elucidate the mechanisms at play: electron enrichment at the D1-FeN4 site strengthens the Fe-N bond, thereby elevating the N-hydrogenation energy barrier. Conversely, electron withdrawal reduces the d-band center of Pt, consequently weakening the oxygen adsorption strength and inhibiting the formation of Pt oxides. Owing to mutual dissolution inhibition, the hybrid catalyst retains 99.6% of its oxygen reduction reaction (ORR) mass activity at 0.85 V (versus RHE) following 30,000 accelerated stress test cycles between 0.6 and 1.0 V in an inert atmosphere, markedly surpassing those of single-component counterparts. This work offers critical insights into the intricate synergistic interactions between SASs and NPs, paving the way for the rational design of SASs-NPs hybrid catalysts for ORR or beyond.