Mn atomic clusters and Fe nanoparticles in-situ confined nitrogen carbon nanotubes for efficient and durable ORR electrocatalysts in both alkaline and acidic media

Developing robust and durable nonprecious metal ORR electrocatalysts for use in both alkaline and acidic media is still challenging. Herein, highly dispersed Mn atomic clusters and standalone Fe nanoparticles dual-sites in-situ confined nitrogen doped carbon nanotubes (Mn-Fe@NCNTs) were fabricated via a facile one-step process of high-temperature calcination and simultaneous chemical vapor deposition. The resultant Mn-Fe@NCNTs catalysts exhibited excellent ORR catalytic activity and durability in both alkaline and acidic media due to the special constitute and structure, which not only provided abundant active sites and defects, good electronic conductivity and effective electron transfer, but also enhanced the corrosion resistance and decreased the Fenton reactivity of the catalyst. In 0.1 M KOH solution, the half-wave potential of Mn-Fe@NCNTs is 0.872 V, more positive than that of the commercial Pt/C catalyst (E1/2 = 0.835 V) and many other previously reported NCNTs based non-precious metal ORR electrocatalysts. While in 0.1 M HClO4 solution, Mn-Fe@NCNTs exhibits a half-wave potential of 0.760 V, only 60 mV negative shift compared to the Pt/C catalyst. Furthermore, the as-prepared catalysts exhibit much higher stability, with much lower current attenuation and smaller shift of the ORR polarization curves after continuous chronoamperometric testing for 29,000 s and continuous CV test for 5,000 cycles, than those of Pt/C in both alkaline and acidic solutions. When applied in Zn-air batteries for testing, the Mn-Fe@NCNTs electrocatalysts are obviously outperforming the commercial Pt/C with higher specific capacity of 774.0 mAh g−1Zn and power density of 139.2 mW cm−2. This study offers a facile and instructive protocol for developing low-cost and high-efficiency electrocatalysts to be applied in fuel cells, metal-air cells and many other clean electrochemical storage devices.