A nitrogen-rich porous carbon electrocatalyst derived from supramolecular polymer-encapsulated iron precursors for the oxygen reduction reaction

Abstract

The simultaneous optimization of activity and high atomic dispersion of metal moieties in metal embedded nitrogen-doped carbon (M–N–C) catalysts remains a significant challenge in the field of electrocatalysis. In this work, we created an innovative synthetic method by utilizing cucurbit[7]uril-bridged acrylic acid polymer (CB7&PAA) as a support matrix to simultaneously encapsulate metal precursors within its cavities and anchor them on its exterior surface. By strategically incorporating two distinct iron sources—ferrocene (Fc) confined within the cucurbit[7]uril (CB7) cavity and ferrous ions anchored on the CB7 exterior—we leveraged the abundant nitrogen sites in the CB7 supramolecule to facilitate efficient coordination. This design enabled the integration of Fe–N₄ sites and self-assembled iron complexes. Assisted by molten salts such as CsBr and ZnCl₂, we successfully synthesized Fe_1,2–N–C, an atomically dispersed electrocatalyst with a high metal loading of 2.33 wt%. The Fe_1,2–N–C catalyst demonstrated excellent oxygen reduction reaction (ORR) performance, achieving a half-wave potential (E_1/2) of 0.91 V. Additionally, we applied the Fe_1,2–N–C catalyst in zinc–air batteries (ZABs) across both aqueous and quasi-solid-state configurations. The aqueous ZAB exhibited an outstanding specific capacity of 816.0 mA h g_Zn⁻¹ and a maximum power density of 211.2 mW cm⁻². The quasi-solid-state ZAB achieved a specific capacity of 745.0 mA h g_Zn⁻¹, showcasing the versatility and effectiveness of the catalyst. This work not only establishes a direct connection between supramolecular polymer-derived iron complexes and carbon-based single-atom electrocatalysts but also shields light on the structure–activity relationship in supramolecular polymer-assisted ORR catalysis.