Replacing scarce and expensive platinum (Pt) with metal-nitrogen-carbon (M-N-C) catalysts for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs) has largely been impeded by the low activity of M-N-C, in turn limited by low site density and low site utilization. Herein, we overcome these limits by implementing chemical vapor deposition (CVD) to synthesize Fe-N-C, an approach fundamentally different from previous routes. The Fe-N-C catalyst, prepared by flowing iron chloride vapor above a N-C substrate at 750 ℃, has a record Fe-N4 site density of 2×1020 sites·gram-1 with 100% site utilization. A combination of characterizations shows that the Fe-N4 sites formed via CVD are located exclusively on the outer-surface, accessible by air, and electrochemically active. This catalyst delivers an unprecedented current density of 33 mA·cm-2 at 0.90 ViR-free (iR-corrected) in an H2-O2 PEMFC at 1.0 bar and 80 ℃.