Defect-Engineered Continuous 3D Single-Atom Catalysts for Enhanced Oxygen Reduction Performance

In the presence of carbon-based substrates, the mobility of metal atoms is thermodynamically enhanced, leading to the aggregation of single atoms into clusters. To address this challenge, the coordination between isolated metal atoms and nitrogen (Nx) has been utilized to anchor single atoms and prevent aggregation. Among these structures, Fe─N₄-C moieties, with atomic-level dispersion, demonstrate promising oxygen reduction reaction (ORR) catalytic activity. However, the strong adsorption of oxygen intermediates on the Fe active sites limits their intrinsic activity. To overcome this, a novel strategy utilizing nitrogen-coordinated Fe single atoms (Fe─N₄) is developed to stabilize the metal atoms. Among these structures, the defect-engineered Fe─N₄O configuration, Fe single-atom catalyst (Fe SAs/NPGN), is synthesized via ammonia-thermal etching, significantly boosting oxygen reduction reaction (ORR) catalytic performance by providing abundant active sites and a high specific surface area of 2054.39 m² g^-1. The defect-synergistic structure further tunes the electronic properties of the Fe sites, facilitating more efficient ORR activity, as validated by experimental results and theoretical calculations. This approach offers a promising pathway for advancing defect-engineered single-atom catalysts for energy applications.