Enhancing the ORR durability of single atomic Fe-N₄ active sites with implanted SiO₂ nanoparticles as radical and H₂O₂ inhibitors.

Abstract

Highly efficient and durable single-atom catalysts (SACs) hold great promise for improving oxygen reduction reaction (ORR) in metal-air batteries and fuel cells. However, their long-term stability is challenged by the byproducts such as H₂O₂ and undesirable radicals. Herein, we report a Fe-N₄ active center-based SAC decorated with SiO₂ nanoparticles (NPs) as a radical scavenger, which was prepared using coffee grounds and industrial spent acid residue. The presence of SiO₂ NPs effectively suppresses the electrochemical H₂O₂ production, significantly improving durability with only a 5 mV half-wave potential loss after 30,000 voltage cycles in alkaline media. Electrochemical evaluations, in-situ characterizations, and density functional theory calculations reveal that the Fe-O-Si binding at the SiO₂-Fe-N₄ interface strengthens the binding of OOH* species, facilitating the 4-electron selectivity in ORR while inhibiting the formation of H₂O₂ and reactive oxygen species. Additionally, the SiO₂ NPs prevent the aggregation of Fe single atomic sites, thereby stabilizing the SAC active sites. Therefore, the incorporation of SiO₂ NP into Fe-based SAC offers a straightforward and effective strategy for enhancing ORR performance.