Unraveling the catalytic mechanism of transition-metal oxides (TMOs) for the charging reaction in a Li−O 2 battery and characterizing their surface structures and electronic structure properties of active sites are of great importance for the development of an effective catalyst to improve low round-trip efficiency and power density. In the current study, an interfacial model is first constructed to study the decomposition reaction mechanism of Li 2 O 2 supported on Co 3 O 4 surfaces. The computational results indicate that the O-rich Co 3 O 4 (111)C with a relatively low surface energy in high O 2 concentration has a high catalytic activity in reducing overpotential and O 2 desorption barrier due to the electron transfer from the Li 2 O 2 layer to the underlying surface. Meanwhile, the basic sites of Co 3 O 4 (110)B surface induce Li 2 O 2 decomposition into Li 2 O and a dangling Co− O bond, which further leads to a high charging voltage in the subsequent cycles. The calculations for transition-metal (TM)-doped Co 3 O 4 (111) indicate that P-type doping of Co 3 O 4 (111) exhibits significant catalysis in decreasing both charging overpotential and O 2 desorption barrier. The ionization potential of doped TM is determined as an important parameter to regulate the catalytic activity of metal oxides.

The facet-dependent performance has aroused great interest in the fields of catalyst, lithium ion battery and electrochemical sensor. In this study, the well-defined Co 3 O 4 cubes with exposed (001) plane and octahedrons with exposed (111) plane have been successfully synthesized and the facet-dependent electrocatalytic performance of Co 3 O 4 for rechargeable Li−O 2 battery has been comprehensively investigated by the combination of experiments and theoretical calculations. The Li−O 2 battery cathode catalyzed by Co 3 O 4 octahedron with exposed (111) plane shows much higher specific capacity, cycling performance, and rate capability than Co 3 O 4 cube with exposed (001) plane, which may be largely attributed to the richer Co 2+ and more active sites on (111) plane of Co 3 O 4 octahedrons. The DFT-based first-principles calculations further indicate that Co 3 O 4 (111) has a lower activation barrier of O 2 desorption in oxygen evolution reaction (OER) than Co 3 O 4 (001), which is very important to refresh active sites of catalyst and generate a better cyclic performance. Also, our calculations indicate that Co 3 O 4 (111) surface has a stronger absorption ability for Li 2 O 2 than Co 3 O 4 (001), which may be an explanation for a larger initial capacity in Co 3 O 4 (111) plane by experimental observation.

Unraveling the descriptor of catalytic activity, which is related to physical properties of catalysts, is a major objective of catalysis research. In the present study, the first-principles calculations based on interfacial model were performed to study the oxygen evolution reaction mechanism of Li2O2 supported on active surfaces of transition-metal compounds (TMC: oxides, carbides, and nitrides). Our studies indicate that the O2 evolution and Li(+) desorption energies show linear and volcano relationships with surface acidity of catalysts, respectively. Therefore, the charging voltage and desorption energies of Li(+) and O2 over TMC could correlate with their corresponding surface acidity. It is found that certain materials with an appropriate surface acidity can achieve the high catalytic activity in reducing charging voltage and activation barrier of rate-determinant step. According to this correlation, CoO should have as active catalysis as Co3O4 in reducing charging overpotential, which is further confirmed by our comparative experimental studies. Co3O4, Mo2C, TiC, and TiN are predicted to have a relatively high catalytic activity, which is consistent with the previous experiments. The present study enables the rational design of catalysts with greater activity for charging reactions of Li-O2 battery.