Candied Haws-Like Fe–N–C Catalysts with Broadened Carbon Interlayer Spacing for Efficient Zinc–Air Battery

As efficient nonprecious metal catalysts for oxygen reduction reaction (ORR), Fe–N–C materials are one of the most promising alternatives to Pt-based catalysts for fuel cells and metal–air batteries. However, the intrinsically low density of key active sites like FeN4 moieties hampers their commercial applications. Herein, we provide a smart strategy to construct a candied haws-like Fe–N–C catalyst (CH-FeNC) with broadened carbon interplanar spacing (>4 Å), starting with trehalose as a structure-built brick coupled with a zinc-zeolite imidazole framework (ZIF-8) and polyaniline (PANI) and then followed by copyrolysis carbonization of them. The obtained CH-FeNC exhibits half-wave potentials of 0.92 and 0.90 V (vs RHE) before and after 10,000 cycles in 0.1 M KOH, which are superior to the 0.90 and 0.85 V obtained by commercial Pt/C for ORR. The power density of a homemade zinc–air battery equipped with the catalyst is up to 131 mW cm–2, greater than that of Pt/C (124 mW cm–2). The extended X-ray absorption fine structure (EXAFS) results and density functional theory (DFT) theoretical calculations reveal that there exists enriched zigzag or armchair edge-hosted FeN4 active sites, located at the abundant interface between carbon components in this composite. Furthermore, the unique broadened carbon interlayer spacing plays a key role in deciding the ORR rate in alkaline but not in acidic environments because there exists a fifth ligand of active Fe in the form of FeN4 centers coupled with SO42– and ClO4– from acids