Enhancing the Catalytic Activity of CoO Nanosheets for Li-O Batteries by the Incoporation of Oxygen Vacancy with Hydrazine Hydrate Reduction.

Li-O battery attracts great interest because of the high energy density. But the poor kinetics of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) have blocked the practical application. Designing the efficient bifunctional cathode catalysts is of great importance for the Li-O battery. Tuning the electronic and surface structure of the catalysts plays an important role. Herein, we propose to enhance the catalytic performance of CoO nanosheets for rechargable Li-O batteries by hydrazine hydrate-induced oxygen vacancy formation. The hydrazine hydrate reduction not only introduces oxygen vacancies into CoO nanosheets and modulates the electronic structure but also roughens the surface, which all contribute to the enhancement of ORR and OER activity, especially the activity and stability for OER. Li-O cells catalyzed by the oxygen defects-enriched CoO ultrathin nanosheets exhibit much better electrochemical performances in terms of the high initial capacity (∼11 000 mAh g), the lower overpotential (∼1.1 V), and the longer cycle life (150 cycles@200 mA g). This can be largely attributed to the synergy of the enriched oxygen vacancies and the roughened surface of CoO nanosheets, which not only improves the electron and Li conductivity but also provides more active sites and reaction spots. The proposed facile strategy may also be applied to modify other oxides based catalysts for Li-O batteries or other fields.