Abstract

Rechargeable Zn-air batteries are promising energy storage systems. Nevertheless, it is necessary to develop efficient bifunctional OER/ORR catalysts based on non-precious metals. In this work, different M-N-C@FeNPs catalysts were synthesized using Fe3O4 nanoparticles as a template and Fe source. Aniline and different metallic salts (Fe, Co, and Ni) were used as carbon, nitrogen, and metallic precursors. The catalysts were characterized by HRTEM, EDX, XPS, XRD, 57Fe Mossbauer spectroscopy, and electrochemical techniques, evidencing the presence of M-Nx units and Fe-based nanoparticles in the N-doped carbon material, where the M-Nx units act as the primary ORR/OER active sites. The electrocatalytic activities, studied using a rotating ring-disk electrode in alkaline media, showed that the Ni-based material presents the best performance, achieving a Delta E value of 0.82 V. The Ni-N-C@FeNPs catalyst was tested as a positive electrode in a Zn-air battery and compared with a commercial PtRuC 20 %. Notably, it displayed a remarkable performance and cyclability, surpassing the commercial catalyst with a round-trip voltage of 1.30 V after 50 h. The improved performance may be associated with the catalytic activity of the Ni-Nx active sites acting in synergy with the Fe-based nanoparticles embedded within the graphitized carbon matrix.