Arrays of 1 mu m long C nanorods were grown by glancing angle deposition on flat and patterned Si wafers, coated with 0.1 mg/cm(2) Pt catalyst by magnetron sputtering, removed from the substrates, and tested as cathode electrodes in proton exchange membrane (PEM) fuel cells. Deposition on flat substrates yields a nearly fully dense nucleation layer with < 5 nm wide pores, followed by the formation of separated rods with an average width that strongly increases with rod height, from < 30 to 190 nm. In contrast, deposition on a patterned surface results in regularly spaced 50 nm wide pores and a rod width that only moderately increases with height, from 95 to 155 nm. Polarization curves on pure H-2 and O-2 for the two sample types are identical at high potential E>0.55 V. However, the cathodes deposited on the patterned substrates yield considerably higher currents at low potential, with a 2 times higher limiting current density i(L)=0.73 A/cm(2) than those grown on flat substrates. The higher current in the mass-transport-limited regime is attributed to the 10 times wider engineered pores that facilitate O-2 transport to the active catalyst sites, resulting in a 5 times lower mass transport resistance R-MT=1.5 cm(2) at E=0.50 V, as quantified by electrochemical impedance spectroscopy.