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.