Template Synthesis of Ag@Fe-N-Doped Carbon Electrocatalyst for Oxygen Reduction Reaction in Alkaline Media

Abstract

With the development of fuel cells, it is critical to find suitable oxygen reduction reaction (ORR) catalyst materials to replace current commercial Pt/C catalysts. On the one hand, atomically dispersed Fe-N-C with highly active Fe-Nx centers has been proved to be one of the best ORR catalysts comparable to the Pt/C. In addition, structural effects and strong metal-carrier interactions greatly improve performance. Therefore, various templates have been used for controlling the structure of Fe-N-C catalysts. For instance, polypyrrole is widely utilized as a nitrogen-rich carbon precursor, and hollow porous Fe3O4 microspheres with polypyrrole (PPy) encapsulated on the surface were pyrolyzed to obtain Fe-N-doped double-shell hollow carbon microspheres. Also, silica balls were applied as templates to fabricate hollow Fe-N-C carbon using a nano-casting method. These hollow structural Fe-N-C materials showed efficient ORR catalytic activities. On the other hand, Ag-based catalysts are also considered as possible candidates for ORR in alkaline medium due to their comparatively low cost and good CO tolerance capability. For example, Janus nanostructured Ag@N-C synthesized by pyrolyzing core-shell Ag@PPy demonstrated comparable ORR activity to the Pt/C, which was largely attributed to the synergistic effect between Ag nanoparticles and carbonized PPy shell. Therefore, rational design of porous Fe-N-C structure with Ag nanoparticles would achieve excellent ORR electrocatalysts. Herein, Ag@Fe3O4 nanoparticles were synthesized by a solvothermal method and utilized as templates, and PPy enveloped on the template surface functioned as nitrogen and carbon sources. After pyrolysis, hollow porous Fe-N-C was decorated with Ag nanoparticles, which demonstrated excellent ORR catalytic activity and durability in alkaline medium. Therefore, this study provides a new simple method for preparing Ag@Fe-N-C hybrid catalysts.