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

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 approximate to 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)).