Concave Structural Carbon Co-Doped with Iron Atom Pairs and Nitrogen as Ultra-High Performance Catalyst Toward Oxygen Reduction.

It is crucial to rationally design and synthesize atomic-scale transition metal-doped carbon catalysts with high electrocatalytic activity to achieve a high-efficient oxygen reduction reaction (ORR). Herein, an electrocatalyst comprised of Fe-Fe dual atom pairs and N-doped concave carbon are reported (N-CC@Fe DA) that achieves ultrahigh electrocatalytic ORR activity. The catalyst is prepared by a gaseous doping approach, with zeolitic imidazolate framework-8 (ZIF-8) as the carbon framework precursor and cyclopentadienyliron dicarbonyl dimer as the Fe-Fe atom pair precursor. The catalyst exhibits high cathodic ORR catalytic performance in an alkaline Zn/air battery and proton exchange membrane fuel cell (PEMFC), yielding peak power densities of 241 mW cm-2 and 724 mW cm-2, respectively, compared to 127 mW cm-2 and 1.20 W cm-2 with conventional Pt/C catalysts as cathodes. The presence of Fe atom pairs coordinate with N atoms is revealed by X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) analysis, and Density Functional Theory (DFT) calculation results show that the Fe-Fe pair structure is beneficial for adsorbing oxygen molecules, activating the O─O bond, and desorbing OH* intermediates formed during oxygen reduction, resulting in a more efficient oxygen reaction. The findings may provide a new pathway for preparing ultra-high-performance doped carbon catalysts with Fe-Fe atom pair structures.