Ultrafine Fe2C nanocrystals encapsulated in interconnected hollow carbon spheres as ORR electrocatalysts for Alkaline/Neutral Zn − Air batteries

Abstract

The development of high − performance non − noble metal electrocatalysts for oxygen reduction reaction (ORR) superior to commercial Pt/C in both alkaline and neutral medium is critical for renewable energy technology such as metal − air battery, but remains a great challenge. Herein, hollow spherical framework structure is introduced during the solid − state reaction, enabling the active sites to exist with smaller size and more uniform dispersion. Specifically, a grape − cluster − like ORR catalyst (Fc@Fe − NHCS) is synthesized in which Fe2C nanocrystals and Fe − Nx sites are embedded in carbon layers supported by nitrogen − doped hollow carbon spheres. The resultant Fc@Fe − NHCS exhibits an ORR half − wave potential of 0.85 V in alkaline medium compared to 0.86 V for Pt/C. For neutral ORR, the half − wave potential of Fc@Fe − NHCS is 0.76 V, which is equal to that of Pt/C. Furthermore, Fc@Fe − NHCS demonstrates satisfactory peak power density and open − circuit voltage comparable to Pt/C when utilized as air cathode in self − prepared alkaline and neutral zinc − air batteries (ZABs). The co − action of the spherical framework structure with active sites of Fe2C nanocrystals and Fe − Nx sites ensures excellent ORR electrocatalytic performance, which provides a favorable electrocatalyst for various energy devices including alkaline and neutral ZABs.