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).