A secondary template strategy for synthesis of hierarchical porous carbon-hosted single-atomic FeNx and CoO towards bifunctional oxygen reduction reaction and oxygen evolution reaction

The intrinsic activity and full exposure of active sites play important roles in high performance electrocatalytic reactions . Herein, a novel "secondary template strategy" is reported, for first time, to synthesize a hierarchical porous carbon-based catalyst loaded by single-atomic FeN x and CoO nanoparticles (CoO@Fe-NC ZnO ) from well-defined ZnO-Fe-PPY precursor, in which the PPY (polypyrrole) in-situ grown on the surface of the ZnO templates followed by the outer coating of FeCl 3 . The utilization of ZnO templates involve their decomposition during the pyrolysis process , leading to the porous structures of the resulted Fe-NC ZnO . Simultaneously, the pyrolysis products of FeCl 3 (Fe/Fe 3 O 4 ) can gradually formed in the remaining parts of the decomposed ZnO, effectively preventing the collapse of the porous structures (so-called secondary template strategy). Subsequently, the introduction of CoO further enhances the intrinsic activity of the as-prepared CoO@Fe-NC ZnO for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), respectively, with an excellent half-wave potential (E 1/2 ) of 0.917 V (vs. RHE) and a low potential of 1.556 V (vs. RHE) at a current density of 10 mA cm −2 (E 10 ). Meanwhile, zinc-air batteries assembled with CoO@Fe-NC ZnO catalyst have great application potential. This work provides a pathway for the preparation of bifunctional electrocatalysts with a hierarchical porous structure.