Surface Molecular Encapsulation with Cyclodextrin in Promoting the Activity and Stability of Fe Single-Atom Catalyst for Oxygen Reduction Reaction

Fe single-atom catalysts (Fe-SACs) have been extensively studied as a highly efficient electrocatalyst toward the oxygen reduction reaction (ORR). Nonetheless, they suffer from stability issue induced by dissolution of Fe metal center and the OH⁻ blocking. Herein, a surface molecular engineering strategy is developed by using β-cyclodextrins (CDs) as a localized molecular encapsulation. The CD-modified Fe-SAC (Fe-SNC-β-CD) shows obviously improved activity toward the ORR with 0.90 V, 4.10 and 4.09 mA cm⁻² for E_1/2, J₀ and J_k0.9, respectively. Meanwhile, the Fe-SNC-β-CD shows the excellent long-term stability against aggressive stress and the poisoning. It is confirmed through electrochemical investigation that modification of β-CD can, on one hand, regulate the atomic Fe coordination chemistry through the interaction between the CD and FeN_x moiety, while on the other mitigate the strong adsorption of OH⁻ and function as protective barrier against the poisoning molecules leading to enhanced ORR activity and stability for the Fe-SACs. The molecular encapsulation strategy demonstrates the uniqueness of post-pyrolysis surface molecular engineering for the design of single-atom catalyst.