Low-carbon CeOx/Ru@RuO2 nanosheets as bifunctional catalysts for lithium-oxygen batteries

Abstract

Lithium-oxygen (Li-O2) batteries are facing challenges in capacity, cycling stability, and kinetics for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Advanced catalysts should have a high and bifunctional catalytic activity for ORR and OER. Moreover, the trade-off carbon in catalysts should have good oxidation resistance and high electronic conductivity and be used in a tiny amount. Up to now, it is still a challenge. Therefore, this work introduces a low-carbon CeOx/Ru@RuO2 nanosheet as efficient cathode catalysts for Li-O2 batteries and studies the preparation and working mechanisms using a variety of characterization and electrochemical techniques. The air oxidation treatment oxidizes Ru into Ru@RuO2 and simultaneously removes unstable C into CO2, leaving a tiny amount of stable carbon. CeOx/Ru@RuO2 has enormous mesopores, well-distributed sub-5 nm CeOx and Ru@RuO2 nanocrystals, a tiny amount of anti-oxidation carbon (1.2 %), and a high specific surface area of 159.3 m² g−1. These aspects optimize the Li-O reaction and regulate the Li2O2 nucleation to form uniform and ultrathin Li2O2 nanoflakes. As a result, the ORR and OER overpotentials are only 0.17 V and 0.45 V, respectively. This work provides a novel material combination and structure design for developing bifunctional catalyst materials in Li-O2 batteries.