Shell thickness controlled core–shell Fe3O4@CoO nanocrystals as efficient bifunctional catalysts for the oxygen reduction and evolution reactions

Abstract

Core–shell Fe₃O₄@CoO NCs have been demonstrated to be efficient bifunctional catalysts for the oxygen reduction (ORR) and evolution (OER) reactions. Their activities are strongly shell thickness dependent. Specifically, nanocrystals with ∼2 monolayers of CoO can exhibit a potential difference of 0.794 V at OER and ORR current densities of 10 and −3 mA cm⁻², respectively. This value is competitive to those of most active bifunctional catalysts reported. In addition, they are also used as the oxygen cathode for Zn–air batteries and can deliver a peak power density of 109 mW cm⁻², much higher than that of the Pt–RuO₂/C (88.1 mW cm⁻²).