In Situ Raman Spectroscopy Correlates *OOH Intermediates with Oxygen Reduction Activity on Pt-Based Nanocatalysts.

Understanding the molecular origins of oxygen reduction reaction (ORR) activity on Pt-based catalysts is essential for the rational design of high-performance electrocatalysts. Herein, by combining electrochemical measurements with in situ shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS), we systematically investigate the ORR pathway on Pt-based alloy nanocatalysts incorporating different transition metals to elucidate how surface oxygenated intermediates dictate ORR activity. Among the catalysts examined, PtNi exhibited higher activity than PtFe, PtCo, and commercial Pt/C, underscoring the pronounced sensitivity of intrinsic ORR activity to alloy composition. Potential-dependent in situ Raman spectra, corroborated by isotopic labeling, directly identified *OOH as a key ORR intermediate and established a clear correlation between its vibrational frequency and catalytic activity. The results suggest that Ni alloying may modify the electronic environment of Pt, thereby weakening the Pt-O interaction, optimizing the adsorption state of the kinetically relevant *OOH intermediate, and consequently promoting ORR kinetics. This study establishes an effective spectroscopic platform for probing ORR intermediates on realistic electrocatalyst surfaces and offers molecular-level understanding of the activity enhancement in Pt-based alloy catalysts.