Facile Fabrication of the Cu-N-C Catalyst with Atomically Dispersed Unsaturated Cu-N2 Active Sites for Highly Efficient and Selective Glaser-Hay Coupling

M-N-C catalysts have attracted considerable attention in the fields of energy storage and conversion as well as catalysis over the past decades. However, the current synthetic strategies for fabricating M-N-C catalysts via high-temperature pyrolysis unavoidably lead to a structural heterogeneity with the presence of a mixture of species including atomically dispersed M-N_x moieties and inorganic metal-containing particles, which not only decreases the atomic utilization but also clouds the accurate understanding of the nature of the catalytically active sites. Herein, we first report a straightforward and cost-effective preparation strategy for fabricating a Cu-N-C catalyst with atomically dispersed and coordinately unsaturated Cu-N₂ moieties on hierarchically N-doped porous carbon (Cu₁/NC-800) without formation of any metal-containing phases. Cu₁/NC-800 exhibits outstanding catalytic performance for Glaser-Hay coupling of terminal alkynes under mild and sustainable conditions, which surpass those of the state-of-the-art catalysts. A broad set of (un)symmetrical aryl-aryl, aryl-alkyl, and alkyl-alkyl 1,3-diynes were selectively synthesized in high yields with good tolerance of various functional groups. More importantly, the Cu₁/NC-800 could be easily reused with good maintenance of the activity and atomic dispersion of Cu in the structure. Experimental results and theoretical calculations reveal that the low N coordination number of single-atom Cu sites in Cu-N₂ exhibit a preferential adsorption to terminal alkyne; meanwhile, the adjacent pyridinic N sites on the carbon matrix facilitate the deprotonation of the adsorbed alkyne to generate the key intermediate Cu^δ-acetylide species, thus synergistically boosting the reaction. Therefore, this work not only provides an alternative facile synthetic strategy for fabricating atomically dispersed M-N-C catalysts but also represents a significant advance for accessing (un)symmetrical 1,3-diynes from Glaser-Hay coupling.

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 Cu^I -N₂ and Cu^II -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-N_x 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.