▎ 摘　　要

The bifunctional electrocatalytic activities of birnessite-type layered manganese oxide with lithium ion as an intercalated cation (Li-bir) and its composite with reduced graphene oxide (Li-bir/rGO) toward oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) were investigated. The enhanced catalytic activity of the Li-bir/rGO composite can be ascribed to the elevated electrical conductivity of the birnessite suggested via a lower charge transfer resistance obtained from the electrochemical impedance spectroscopy. Moreover, the local oxidation states of Mn in the Li-bir/rGO were investigated by in situ X-ray absorption spectroscopy during the ORR and OER processes. Interestingly, the generated oxygen gas from the OER process observed via the in situ gas chromatography of the Li-bir/rGO is 5.44 mmol g(-1) which is higher than that of the pristine Li-bir (4.98 mmol g(-1)). These results suggest that the Li-bir/rGO can be further utilized as a bifunctional electrocatalyst for high-performance metal-air batteries. (C) 2019 The Electrochemical Society.