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Hierarchal Porous Graphene-Structured Electrocatalysts with Fe-N5 Active Sites Modified with Fe Clusters for Enhanced Performance Toward Oxygen Reduction Reaction.

The local coordination environment around the active centers has a major impact on tuning the intrinsic activity of M-N-C catalysts. Herein, a porous graphene with Fe-N5 active sites modified with Fe clusters is successfully fabricated by using Fe3+-SCN- and NaHCO3 as the metal precursor and pore-forming agent, respectively. The unique Fe-N5 configuration accompanying Fe clusters and the improved ORR activity are confirmed by various characterization techniques and theoretical calculations. Benefiting from the pores, mass and electron transfer channels are successfully constructed, making more active sites accessible and facilitating the ORR process. As a consequence, the as-prepared catalyst has an excellent ORR activity with a half-wave potential of 0.89 V, comparable selectivity, and superior stability. In addition, a homemade primary zinc-air battery using this material as the cathode catalyst has a maximum power density of 0.205 W/cm2, revealing the potential of the as-constructed CSA-Fe-N-C catalyst to replace precious Pt catalysts.