Multi-function core-shell nanoparticles outperform single-phase counterparts for efficient single-atom catalysis

Nanoparticles (NPs) have been shown to enhance single-atom catalysis (SAC). However, current NPs are limited to single-phase and only display limited function and efficiency. Employing operando spectra, kinetic isotope effect, local pH measurement, and density functional theory calculations, we reveal that the core-shell Fe@Fe₃O₄ NPs, as a whole, realize weakening *OH adsorption, promoting water dissociation, and tandem proton transfer. This enables Fe_SAs-Fe@Fe₃O_4-NPs to achieve an ORR half-wave potential (E_1/2) of 0.952 V vs. reversible hydrogen electrode (V_RHE), outperforming commercial Pt/C (E_1/2 = 0.844 V_RHE) and the Fe_SAs-Fe_NPs (E_1/2 = 0.919 V_RHE). More importantly, the Fe₃O₄ shell protecting the Fe core provides robust durability with negligible loss after 50,000 potential cycles between 0.6 and 1.0 V_RHE, distinct from partial oxidation of Fe NPs under the oxygen reduction reaction conditions. At a device level, zinc-air batteries with Fe_SAs-Fe@Fe₃O_4-NPs as cathodic catalysts realize a peak power density of 250.2 mW cm^-2 and stable operation > 10,000 charge-discharge cycles with RuO₂ at 10 mA cm^-2. This work implies a new room to enhance the SAC and offers comprehensive insights into understanding NPs in steering reaction kinetics.