NiCoFe-Layered Double Hydroxides/N-Doped Graphene Oxide Array Colloid Composite as an Efficient Bifunctional Catalyst for Oxygen Electrocatalytic Reactions

Ternary NiCoFe-layered double hydroxide ((NiCoFe)-Fe-III-LDH) with Co3+ is grafted on nitrogen-doped graphene oxide (N-GO) by an in situ growth route. The array-like colloid composite of (NiCoFe)-Fe-III-LDH/N-GO is used as a bifunctional catalyst for both oxygen evolution/reduction reactions (OER/ORR). The (NiCoFe)-Fe-III-LDH/N-GO array has a 3D open structure with less stacking of LDHs and an enlarged specific surface area. The hierarchical structure design and novel material chemistry endow high activity propelling O-2 redox. By exposing more amounts of Ni and Fe active sites, the (NiCoFe)-Fe-III-LDH/N-GO illustrates a relatively low onset potential (1.41 V vs reversible hydrogen electrode) in 0.1 mol L-1 KOH solution under the OER process. Furthermore, by introducing high valence Co3+, the onset potential of this material in ORR is 0.88 V. The overvoltage difference is 0.769 V between OER and ORR. The key factors for the excellent bifunctional catalytic performance are believed to be the Co with a high valence, the N-doping of graphene materials, and the highly exposed Ni and Fe active sites in the array-like colloid composite. This work further demonstrates the possibility to exploit the application potential of LDHs as OER and ORR bifunctional electrochemical catalysts.