A hierarchically porous Fe-N-C synthesized by dual melt-salt-mediated template as advanced electrocatalyst for efficient oxygen reduction in zinc-air battery

The reasonable design of porous structures is important but usually overlooked for nonprecious metal ORR catalysts. In this study, a facile dual melt-salt-mediated templating method is developed to prepare a Fe-N-C catalyst with tailored porous framework. The ZnCl2 and NaCl are employed to construct abundant micropores and promote the transformation of partial micropores to mesopores, respectively, reasonably forming a 3D hierarchically porous framework. The catalyst demonstrates a satisfactory surface area (1605 m2/g), promoting mass transport and exposure of FeN4 sites. Interestingly, the dual melt-salt templates avoid rapid loss of nitrogen during pyrolysis, thus enhancing Fe-N4 active center density. Therefore, the obtained Fe-N-C material presents outstanding ORR performance in both alkaline and acid media, as well as good stability. The advances of this catalyst are further proved in liquid and solid-state Zn-air battery, with nice discharge stability and high peak power densities.