Perovskite La0.5Ca0.5CoO3-δ nanocrystals on graphene as a synergistic catalyst for rechargeable zinc-air batteries

A novel structural hybrid material consisting of La0.5Ca0.5CoO3-δ nanocrystals anchored on reduced graphene oxide is developed as highly efficient bifunctional catalyst for oxygen reduction and evolution reaction in alkaline electrolyte. Nanostructural La0.5Ca0.5CoO3-δ particles, which are synthesized by a modified amorphous citrate precursor method in advance, are anchored homogeneously on the surface of reduced graphene oxide sheets through a simple chemical reduction process at ambient temperature. Although reduced graphene oxide or La0.5Ca0.5CoO3-δ alone possesses some catalytic activity, their hybrid presents a remarkable oxygen reduction catalytic activity, which is on a par with that of the commercial 20 wt% Pt/C. This La0.5Ca0.5CoO3-δ/ reduced graphene oxide hybrid also exhibits outstanding activity for oxygen evolution reaction which surpassed that of IrO2, allowing it to become a highly active non-noble metal bi-catalyst for both oxygen reduction and evolution reaction. More importantly, the same hybrid displays extremely excellent catalytic durability and superior cycling stability to the commercial Pt/C + IrO2 catalyst in the rechargeable zinc-air batteries, becoming one of the most promising bi-catalysts with low-cost. The unexpected bifunctional catalytic activities and surprisingly cycling life arise from synergetic effects between La0.5Ca0.5CoO3-δ and graphene. The rechargeable Zn-air battery with the hybrid as catalyst delivered a large peak power density of 223.6 mW cm−2 along with ultrastbale cyclability over 10,100 min at 5 mA cm−2.