▎ 摘　　要

An efficient oxygen reduction reaction (ORR) on the air cathode is a prerequisite for high-performance metal-air batteries (MABs), as it decreases the excessive charge-discharge overpotential to reduce side-reactions. Here, we develop a composite catalyst for MABs by loading ultrathin CeO2 nanoflakes (UCNFs) on a three-dimensional graphene (3DG) network to form the UCNFs@3DG. The UCNFs@3DG composite features a high activity approaching the commercial Pt/C catalyst in the ORR, probably due to synergic effects of the catalytically active UCNFs and the conductive 3DG network. The UCNFs@3DG can serve as an efficient air cathode in a series of MABs, delivering a capacity of 613 mAh h g(Zn)(-1) in the Zn-air battery (ZAB) and 839 mAh h g(Al)(-1) in the Al-air battery (AAB), respectively. Finally, the UCNFs@3DG cathode in lithium-oxygen batteries (LOBs) achieves a high discharge capacity of 21,166 mAh h g(c)(-1) at 0.2 A g(c)(-1) and over 15,000 mAh h g(c)(-1) under elevated current densities up to 2 A g(c)(-1), validating the UCNFs@3DG as a general air cathode in MABs. (c) 2017 Published by Elsevier Ltd.