Enhancing the Catalytic Activity of Co₃O₄ for Li–O₂ Batteries through the Synergy of Surface/Interface/Doping Engineering

Efficient bifunctional catalysts are highly desirable for Li–O2 batteries to accerlerate the oxygen reduction and oxygen evolution reactions. Surface/interface regulation or doping has been used to enhance the activity of the catalysts. Herein, we propose a facile synchronous reduction strategy to fabricate a yolk–shell Co3O4@Co3O4/Ag hybrid which integrates the advantages of surface, interface, and doping engineering as a highly active catalyst for Li-O2 batteries. The Co3O4@Co3O4/Ag-based cathode shows a high initial capacity (12000 mAh g–1@200 mA g–1), high rate capability (4700 mAh g–1@800 mA g–1), low overpotential, and long cycle life due to the synergetic interactions of surface, interface, and doping engineering. The underling synergetic mechanism has been uncovered by X-ray diffraction, X-ray photoelectron spectroscopy, X-ray absorption near-edge structure spectra, aberration-corrected scanning transmission electron microscopy, electrochemical impedance spectra, and ex situ scanning electron microscopy. For Co3O4@Co3O4/Ag, part of Ag has formed on the surface of Co3O4 shell as single atoms or clusters and a fraction of Ag has been doped into the crystal lattice of Co3O4 at the same time, which not only strengthens the Ag–Co3O4 interface binding but also tailors the valence electronic structure of Ag and Co species as well as improves the electronic conductivity. This particular architecture provides more active sites for the ORR/OER and also enhances the catalytic activity. In addition, flowerlike Li2O2 forms on the Co3O4@Co3O4/Ag cathode, which is more feasible to decompose in comparison to toroidal-like Li2O2. This study offers some insights into designing efficient cathode catalysts through a synergetic surface/interface/doping engineering strategy.