Post-formation Copper-Nitrogen Species on Carbon Black: Their Chemical Structures and Active Sites for Oxygen Reduction Reaction.

The 3d transition metal and nitrogen co-doped carbon materials (TM-N-C) are considered as the most promising next-generation electrocatalysts, as alternatives to precious Pt, for the oxygen reduction reaction (ORR). Herein, we have fabricated a Cu-N-C catalyst through directly grafting copper-nitrogen complexes, composed by cuprous chloride and ammonia water, onto the surface of carbon black at 500 °C. In an alkaline environment, the synthesized catalyst exhibits excellent ORR catalytic activity, which is comparable to the state-of-the-art Pt/C catalyst, but far exceeding that obtained by the original carbon. Moreover, the catalyst displays much better stability than Pt/C. The enhanced ORR performance is proven to originate from the post-formation CuI -N2 and CuII -N4 sites at the carbon surface, as evidenced by X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS). The possible ORR process catalyzed by these Cu-Nx species is discussed at the atomic level. This work provides a simple and fast synthesis strategy for efficient TM-N-C catalysts on a large scale for energy storage and conversion systems.