Nitrogen doped porous carbon polyhedral supported Fe and Ni dual-metal single-atomic catalysts: template-free and metal ligand-free sysnthesis with microwave-assistance and d-band center modulating for boosted ORR catalysis in zinc-air batteries

Constructing dual-metal single-atom catalysts (DSAs) now stands for a unique and worthwhile strategy for developing high-efficiency electrocatalysts for oxygen reduction reaction (ORR). However, the facile synthesis of DSAs uniformly located on nitrogen porous carbon materials is still challenging. Herein, Fe and Ni dual-metal single-atomic active sites uniformly located on nitrogen doped porous carbon polyhedrals (FeNi-DSAs-PNCH) are successfully prepared by a facile and rapid microwave-assisted adsorption and subsequent pyrolysis process with free template and free metal ligand. The FeNi-DSAs-PNCH catalyst exhibits boosted ORR activity and long time stability. Experimental investigations and density functional theory calculation results verify that, besides the hierarchical porous structure, large specific surface area and abundant catalytic active sites, the adjacent Ni-Nx atomic sites can modulate the d-band center of Fe-Nx single atomic active centers and balance the adsorption–desorption affinities to O2 molecules and oxygen-containing intermediates on Fe-Nx, thus leading to an superior ORR activity with a more positive half-wave potential (0.89 V vs. RHE) than the single Fe or Ni atomic catalyst and the commercial Pt/C catalyst. Moreover, with FeNi-DSAs-PNCH as the air cathode and zinc foil as the anode, an assembled Zn-air battery exhibits a higher open-circuit voltage of 1.48 V and a larger specific capacity of 802.18 mAh g−1 than that of the Pt/C-based Zn-air battery (1.37 V and 664.78 mAh g−1, respectively). This work develops a convenient strategy for preparing dual-metal single-atomic cataysts as promising substitutes for the commercial Pt/C catalysts in the practical energy conversion applications, and also offers experimental and theoretical guidance for rational designing and improvement of ORR and other catalysts by tailoring the d-band center of the active sites.