Facile fabrication of hierarchical porous Co3O4 nanoarrays as a free-standing cathode for lithium–oxygen batteries

Abstract 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.