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

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.