Enhancing the Catalytic Activity of Co₃O₄ Nanosheets for Li-O₂ Batteries by the Incoporation of Oxygen Vacancy with Hydrazine Hydrate Reduction

Abstract

Li-O2 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-O2 battery. Tuning the electronic and surface structure of the catalysts plays an important role. Herein, we propose to enhance the catalytic performance of Co3O4 nanosheets for rechargable Li-O2 batteries by hydrazine hydrate-induced oxygen vacancy formation. The hydrazine hydrate reduction not only introduces oxygen vacancies into Co3O4 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-O2 cells catalyzed by the oxygen defects-enriched Co3O4 ultrathin nanosheets exhibit much better electrochemical performances in terms of the high initial capacity (∼11 000 mAh g–1), the lower overpotential (∼1.1 V), and the longer cycle life (150 cycles­@­200 mA g–1). This can be largely attributed to the synergy of the enriched oxygen vacancies and the roughened surface of Co3O4 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-O2 batteries or other fields.

Tunable Cationic Vacancies of Cobalt Oxides for Efficient Electrocatalysis in Li–O2 Batteries

“…Notably, the area ratio of Co 3+ and Co 2+ peaks for Co‐300 is 2.75, obviously larger than that of Co 3 O 4 without vacancies (≈2), which confirms the presence of cationic vacancies in Co‐300 . [ 27,37,41 ] Although the high‐resolution spectra of Co 2p for Co‐400–Co‐700 samples in Figure S9 (Supporting Information) are similar with that of the Co‐300 sample, the calculated area ratios between Co 3+ and Co 2+ peaks gradually decrease within the 2.75–2.05 range with increasing calcination temperatures up to 700 °C. The result is in good agreement with the ICP results.…”

“…[ 3,24,26 ] To further improve catalytic activity of cobalt oxides, surface engineering (e.g., doping, vacancy, strain effect) is usually applied to modulate the atom arrangement and electronic properties for boosting the performance of Li–O 2 batteries. [ 27–31 ] Notably, the existence of vacancies can change the surface charge distribution to affect electrical conductivity and band structure. The newly generated catalytic sites would be created due to the lower coordination number.…”

“…Such oxygen vacancies can be generated via in situ reduction methods with various reducing agents (e.g., hydrazine hydrate, hydrogen). [ 27,28,37 ] Similarly, cobalt oxide with defected nanostructures have a great potential to work as an electrocatalysts for Li–O 2 batteries. The feasible method to prepare such cobalt oxide is essential for investigating on its catalytic effect.…”

Flower-like NiCo2O4–CN as efficient bifunctional electrocatalyst for Zn-Air battery

“…Oxygen species. The ORR/OER is the process involving oxygen oxidation and reduction, and oxygen species especially oxygen defects/vacancies of metal oxides have a vital influence on the activities [40][41][42][43][44]. The role of oxygen vacancies for metal oxides includes: being active sites for ORR/OER and being shallow donors to enhance electrical conductivity [40].…”

Defect Engineering on Electrode Materials for Rechargeable Batteries

“…Zheng and co‐workers synthesized the mesoporous Co 3 O 4 with abundant oxygen vacancy defects by sodium borohydride . Liu and co‐workers used hydrazine hydrate reduction strategy to synthesize the porous Co 3 O 4 ultrathin nanosheet with enriched oxygen vacancies for rechargeable Li–O 2 batteries . For transition metal disulfide, layered oxide, and other 2D semiconductor materials, defects can be easily made on a 2D material surface by solvent‐thermal method.…”