Atomic dispersed Fe-based catalysts (Fe-N-C) are a promising class of non-noble metal oxygen reduction reaction (ORR) materials. However, their practical application is severely limited by slow mass transfer and insufficient oxygen supply at device level, like the fuel cells. Herein, we report a rational design of a unique yolk-shell nanostructured catalyst (Fe-N-C_T) with triple-layer actives site distribution, exhibiting competitive ORR performance. Comprehensive characterization confirms its unique yolk-shell nanostructure, showing that the Fe-Nx moieties are atomically dispersed in the core, inner shell, and outer surface, significantly improving the active site density. Fe-N-C_T exhibits excellent ORR activity and stability in acidic media. Integration into an H₂-air fuel cell achieves a peak power density of 496 mW·cm⁻² and maintained stable operation with minimal voltage drop during 30,000 accelerated durability cycles. In-situ Raman spectroscopy and COMSOL simulations show that the unique yolk-shell structure acts as an oxygen reservoir, enriching O₂ molecules and reducing mass transfer polarization, thereby achieving excellent ORR performance at the device level.

Development of robust electrocatalyst for oxygen reduction reaction (ORR) in a seawater electrolyte is the key to realize seawater electrolyte-based zinc-air batteries (SZABs). Herein, constructing a local electric field coupled with chloride ions (Cl^—) fixation strategy in dual single-atom catalysts (DSACs) was proposed, and the resultant catalyst delivered considerable ORR performance in a seawater electrolyte, with a high half-wave potential (E_1/2) of 0.868 V and a good maximum power density (Pmax) of 182 mW·cm⁻² in the assembled SZABs, much higher than those of the Pt/C catalyst (E_1/2: 0.846 V; Pmax: 150 mW·cm⁻²). The in-situ characterization and theoretical calculations revealed that the Fe sites have a higher Cl⁻ adsorption affinity than the Co sites, and preferentially adsorbs Cl⁻ in a seawater electrolyte during the ORR process, and thus constructs a low-concentration Cl⁻ local microenvironment through the common-ion exclusion effect, which prevents Cl⁻ adsorption and corrosion in the Co active centers, achieving impressive catalytic stability. In addition, the directional charge movement between Fe and Co atomic pairs establishes a local electric field, optimizing the adsorption energy of Co sites for oxygen-containing intermediates, and further improving the ORR activity.