Organic carboxylate-assisted engineering for fabricating Fe, N co-doped porous carbon interlinked carbon nanotubes towards boosting the oxygen reduction reaction for Zn-air batteries

Abstract

Fe-Nx sites have been identified as core descriptors for Fe-N/C based oxygen reduction reaction catalysts. However, the low density and less utilization of Fe-Nx sites render these catalysts with inefficient catalytic performance. Herein, we develop an organic carboxylate-assisted engineering to construct Fe, N co-doped porous carbon interlinked carbon nanotubes (Fe/N-CCNTs) with high-density and sufficiently exposed Fe-Nx sites based on self-catalyzed effect. The existing forms of Fe include Fe-imidazole configuration and coordination with unsaturated Zn sites via organic carboxylate as linkers, leading to high-density Fe-Nx sites after pyrolysis. Besides, hexatomic carbon rings of organic carboxylate lower cyclization energy barrier for CNT formation, resulting in CNTs interlinked with separated active sites through “active point-conductive line-active point” connections. The optimal sample (Fe-BOAc-PNC) exhibits the onset potential of 0.93 V (vs. RHE) and half-wave potential of 0.84 V in alkaline solution. The liquid-state Zn-air battery (ZAB) employing Fe-BOAc-PNC generates large power density (160 mW/cm2) and stability over 160 h. Moreover, the assembled flexible ZAB displays superb power density of 93 mW/cm2 with robust flexibility. This work provides an insightful perspective for designing Fe-N/C catalysts with high-density and sufficiently exposed active sites for energy storage application.