Yolk-Shell-Structured Cu/Fe@γ-Fe2O3 Nanoparticles Loaded Graphitic Porous Carbon for the Oxygen Reduction Reaction

Core-shell Cu/gamma-Fe2O3@C and yolk-shell-structured Cu/Fe@gamma-Fe2O3@C particles are prepared by a facile synthesis method using copper oxide as template particles, resorcinol-formaldehyde as the carbon precursor, and iron nitrate solution as the iron source via pyrolysis. With increasing carbonization temperature and time, solid gamma-Fe2O3 cores are formed and then transformed into Fe@gamma-Fe2O3 yolk-shell-structured particles via Ostwald ripening under nitrogen gas flow. The composition variations are studied, and the formation mechanism is proposed for the generation of the hollow and yolk-shell-structured metal and metal oxides. Moreover, highly graphitic carbons can be obtained by etching the metal and metal oxide nanoparticles through an acid treatment. The electrocatalytic activity for oxygen reduction reaction is investigated on Cu/gamma-Fe2O3@C, Cu/Fe@gamma-Fe2O3@C, and graphitic carbons, indicating comparable or even superior performance to other Fe-based nanocatalysts.