High-density discrete Cu3N nanocrystals were deposited on XC-72 carbon black by plasma-enhanced atomic layer deposition (PEALD). This heterostructured noble-metal-free catalyst served as a high-performance electrocatalyst for enhanced oxygen reduction reaction (ORR). The electronic band structure of Cu3N was determined by ultraviolet photoelectron spectroscopy (UPS) and UV-vis spectrophotometry. The work function (φ) of the Cu3N nanocrystals was calculated to be 5.04 eV, which is lower than that of Pt (â5.60 eV). With lower energy barrier, Cu3N would exhibit stronger electron transfer to cause ORR than typical Pt catalyst. The UPS analysis also confirmed the synergistic coupling effect between the Cu3N nanocrystals and the carbon support. Coupled with the XC-72, the Cu3N200/C showed even smaller φ (=4.34 eV) than pure Cu3N nanocrystals. Thus, the Cu3N200/C electrocatalyst prepared with 200 ALD cycles exhibited similar ORR catalytic activity, significantly improved mass activity, and potentially greater durability than its Pt/C counterpart in alkaline solution. The fabrication of Cu3N by PEALD and its good performance in ORR suggest a promising alternative of non-noble-metal electrocatalyst for application in fuel cells.