Facile fabrication of hierarchical porous Co ₃ O ₄ nanoarrays as a free-standing cathode for lithium–oxygen batteries

Two shapes of Co ₃ O ₄ nanoarrays (i.e., nanosheets, nanowires) with different densities of exposed catalytic active sites were synthesized through a facile hydrothermal method on Ni foam substrates and tested as the binder/carbon free and free-standing cathodes for Li–O ₂ batteries. Particularly, the single crystalline feature of Co ₃ O ₄ nanosheets with a predominant high reactivity {112} exposed crystal plane and hierarchical porous nanostructure displayed better catalytic performance for both oxygen reduction reaction (during discharge process) and oxygen evolution reaction (during charge process). Li–O ₂ battery with Co ₃ O ₄ nanosheets cathode exhibited a higher discharge specific capacity (965 mAh g ⁻¹ ), lower discharge/charge over-potential and better cycling performance over 63 cycles at 100 mA g ⁻¹ with the specific capacity limited at 300 mAh g ⁻¹ . The superior catalytic performance of Co ₃ O ₄ nanosheets cathode is ascribed to the enlarging specific area and increasing the exposed Co ³⁺ catalytic active sites within predominant {112} crystal plane which plays the key role in determining the adsorption energy for the reactants, enabling high round-trip efficiency and cyclic life.