Rationally-Designed Sandwiched Nanostructures Boosting Fe-N Based Catalysts toward Efficient Oxygen Reduction Electrocatalysis in Acidic Medium

The development of acidic-available noble-metal-free oxygen reduction reaction (ORR) catalysts with high activity and good long-term durability is of significant importance for efficient proton exchange membrane fuel cells, but is still very challenging. Herein, we develop originally a facile wet-chemical-adsorption, pyrolysis and post-etching strategy to effectively intercalate Fe clusters among two nitrogen-doped carbon (NC) layers, forming unique hollow spherical nanostructures with sandwiched NC/Fe/NC shells as an active ORR catalyst. Thanks to the sandwiched nanostructure and the active Fe-N species, this as-prepared hollow sandwiched NC/Fe/NC catalyst could present superior ORR activity in an acidic medium, with a nice onset potential of 0.92 V and decent diffusion-limited current density of ~5.1 mA/cm². The NC/Fe/NC catalyst manifests strong methanol tolerance and outstanding durability during a long-term acidic ORR operation, being a promising alternative to Pt-based catalysts toward efficient proton exchange membrane fuel cells. Synchrotron radiation characterizations and X-ray photoemission spectroscopy reveal at the atomic-level that the abundant robust Fe−N bonds presented in the sandwiched shells of hollow NC/Fe/NC spherical catalyst contribute substantially to high electrochemical activity and superior corrosion-resistance for efficient 4e⁻ ORR in acidic electrolyte.