We have redesigned the air cathode for metal–air batteries by adapting fiber-paper-supported carbon nanofoams as the base electrode architecture. Electrocatalytic functionality for the oxygen reduction reaction (ORR) is added into the conductive, ultraporous nanofoam paper by electroless deposition at the carbon walls of conformal nanoscopic coatings of birnessite-like manganese oxide (10–20-nm thick MnO x ) via redox reaction with aqueous permanganate (MnO4 −). We report the ORR activity measured using an air-breathing electroanalytical cell for a series of native and MnO x -functionalized carbon nanofoams in which the size of the pore network is varied from tens to hundreds of nanometers, the thickness of the air cathode is varied, and the degree of hydrophilicity/hydrophobicity of the electrode structure is altered. Technologically relevant ORR activity is obtained at 0.9V vs. Zn for MnOx-functionalized carbon nanofoams that are ≥180-μm thick, have pores on the order of 100–200nm, and are modified with hydrophobic poly(vinylidene difluoride).