Two-dimensional β-cobalt hydroxide phase transition exfoliated to atom layers as efficient catalyst for lithium-oxygen batteries

Highlights: • Atom-layered β-Co(OH)₂ nanosheets are prepared viaphase transition exfoliation of α-Co(OH)₂. • The overpotential is decreased through the exfoliation. • The atom-layered β-Co(OH)₂ nanosheets show significant improvement in the cyclic stability and specific capacity. • It gives a new way to improve ability for LOBs by exfoliation of 2D materials. Metal-oxygen batteries, especially Li-oxygen batteries (LOBs), have attracted tremendous research attentions in the past decades. It is necessary to design novel cost-effective catalysts in the development of high performance rechargeable LOBs. Herein, we prepare the atom-layered two-dimensional (2D) β-Co(OH)₂ nanosheets (AL-β-Co(OH)₂) via phase transition of layered α-Co(OH)₂ nanosheets (α-Co(OH)₂) in a mild wet chemical process. The thickness of AL-β-Co(OH)₂ is less than 1.5 nm. It is the first time of using atom-layered β-Co(OH)₂ in the system of LOBs and this material shows outstanding catalytic performance. The AL-β-Co(OH)₂ nanosheets as electrocatalysts in LOBs can better reduce the over-potential, enhance the specific capacity and improve cycling capability. It demonstrates a high initial capacity 11841 mAh g⁻¹ at a current density of 100 mA g⁻¹. It displays long cycle stability more than 70 cycles with a capacity restriction of 1000 mAh g⁻¹. These results suggest that this strategy for designing oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) catalysts via exfoliation of materials to atom-layered level could be a promising way to improve the performance of LOBs.