Ternary alloy and metal oxides embedded in yolk-shell polyhedrons as bifunctional oxygen electrocatalyst

To improve the efficiency of oxygen electrolysis, exploiting bifunctional electrocatalysts with excellent activity and stability is extremely important due to the four-electron transfer dynamics of oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). Herein, a series of yolk-shell hollow polyhedrons (YHPs) embedded with NiCoFe ternary alloy and metal oxides, which are named YHP-x (x = 1, 2, 3, 4), were reported. By controlled etching multi-layered zeolitic imidazolate frameworks and following pyrolytic integration, YHPs are endowed with mass transfer tunnels, accessible inner active sites, and good electrical conductivity. Due to the synergetic effect of the alloy, metal oxides and the yolk-shell structure, YHP-1 exhibits excellent ORR performance with a half-wave potential of 0.79 V and YHP-2 displays superior OER performance with a low overpotential of 257 mV at 10 mA cm(-2). The strategy described in this work can be extended to a number of hollow/yolk-shell electrocatalysts for water splitting and metal-air batteries.