Three-Dimensional Graphene-Supported Ni ₃ Fe/Co ₉ S ₈ Composites: Rational Design and Active for Oxygen Reversible Electrocatalysis

The development of low-cost and efficient electrocatalysts with a bicomponent active surface for reversible oxygen electrode reactions is highly desirable and challenging. Herein, we develop an effective calcination-hydrothermal approach to fabricate graphene aerogel-anchored Ni ₃ Fe-Co ₉ S ₈ bifunctional electrocatalyst (Ni ₃ Fe-Co ₉ S ₈ /rGO). The mutually beneficial Ni ₃ Fe-Co ₉ S ₈ bifunctional active components efficiently balance the performance of oxygen reduction and oxygen evolution reactions (ORR/OER), in which Co ₉ S ₈ promotes the ORR and Ni ₃ Fe facilitates the OER. This balance behavior has an obvious advantage over that of monocomponent Ni ₃ Fe/rGO and Co ₉ S ₈ /rGO catalysts. Meanwhile, the additional synergy between porous rGO aerogels and Ni ₃ Fe-Co ₉ S ₈ endows the composite with more exposed active sites, faster electrons/ions transport rate, and better structural stability. Benefiting from the reasonable material selection and structural design, the Ni ₃ Fe-Co ₉ S ₈ /rGO exhibits not only outstanding ORR activity with the high onset- and half-wave potentials (E _onset = 0.91 V and E _1/2 = 0.80 V) but also satisfactory OER activity with a low overpotential at 10 mA cm ^-2 (0.39 V). Moreover, rechargeable Zn-air cells equipped with Ni ₃ Fe-Co ₉ S ₈ /rGO exhibit excellent rechargeability and a fast dynamic response.