In this work, two shapes of mesoporous Co3O4 nanoarrays (i.e., nanosheets, nanowires) were synthesized through a facile hydrothermal method on nickel foam (Ni foam) substrates and tested as the Li-O-2 cathodes. The comparison of these two shapes of Co3O4 nanoarrays revealed that the single crystalline feature of Co3O4 nanosheets with a predominant high reactivity {112} exposed crystal plane, favorable nanostructure and high specific area displayed better catalytic performance. Furthermore, a new binder/carbon-free Pd nanoparticles (PdNPs) decorated Co3O4 nanosheets cathode was also fabricated through the chemical reduction method. The presence of PdNPs effectively promotes the uniform growth of a fluffy, porous discharge product Li2O2 layer on the surface of Pd/Co3O4 electrode. The Pd/Co3O4 electrode catalyzed Li-O-2 battery exhibited a higher specific capacity (1551 mAh g(-1) at 50 mA g(-1)), lower over-potential and longer cycle life over 72 cycles at 100 mA g(-1) with the capacity limited at 300 mAh g(-1). The superior catalytic performance for Li-O-2 batteries is ascribed to the unique design in both component and architecture of Pd/Co3O4 electrode. (C) 2017 Published by Elsevier B.V.