To develop a long-lifetime metal-air battery, oxygen reduction electrodes with improved mass-transfer routes are designed by adjusting the mass ratio of the hydrophobic polytetrafluoroethylene (PTFE) to carbon nanotubes (CNTs) in nickel foam. The oxygen reduction catalyst MnO2 is grown on the nickel foam using a hydrothermal method. Scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and Brunauer-Emmett-Teller analysis are employed to characterize the morphology, crystal structure, chemical composition, and pore structure of the electrodes, respectively. The air electrodes are evaluated using constant-current tests and electrochemical impedance spectroscopy. A PTFE: CNT mass ratio of 1:4-2:1 with 3-mm-thick nickel foam yields the optimal performance due to the balance of hydrophilicity and hydrophobicity. When the electrodes are applied in primary zinc-air batteries, the electrode with a PTFE: CNT mass ratio of 1:4 achieves the maximum power density of 95.7 mW cm(-2) with a discharge voltage of 0.8 V at 100 mA cm(-2), and completes stable discharge for over 14400 s at 20 mA cm(-2). (C) The Author(s) 2018. Published by ECS.