Two shapes of Co3O4 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–O2 batteries. Particularly, the single crystalline feature of Co3O4 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–O2 battery with Co3O4 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 Co3O4 nanosheets cathode is ascribed to the enlarging specific area and increasing the exposed Co3+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.