Ultrauniformly Dispersed Cu Nanoparticles Embedded in N-Doped Carbon as a Robust Oxygen Electrocatalyst

Developing high-efficiency and low-cost nonprecious catalysts for the oxygen reduction reaction (ORR) is important but still challenging. Herein, a N-doped carbon catalyst embedded with uniformly dispersed Cu nanoparticles (∼30 nm) is fabricated by the spatial confinement effect of a nitrogen-rich Salen-based covalent organic framework (Salen-COF), in which Cu(II) ions are anchored onto open chelate sites of Salen-COF and isolated by aromatic rings to form uniformly dispersed Cu nanoparticles embedded in N-doped carbon (Cu NPs/N-C) during pyrolysis. The optimized Cu NPs/N-C-800 exhibits high ORR catalytic activity in both alkaline and acidic electrolytes, especially with an onset potential (Eonset) of 1.02 V and a half-wave potential (E1/2) of 0.88 V in an alkaline electrolyte. Attractively, the Cu NPs/N-C-800-derived Zn–air battery demonstrates a higher peak-power density (163.5 mW cm–2) and long-term cycling stability (118 h). The electronic interaction between the highly concentrated homogeneously dispersed Cu NPs and carbon shell results in an appropriate d-band center, and the porous graphitized carbon shell leads to faster electron transfer and mass transport, which are responsible for the high ORR performance of Cu NPs/N-C-800. This strategy provides a new prospect to synthesize uniformly dispersed metal nanoparticle electrocatalysts with more exposed active sites and efficient catalytic activities for renewable energy conversion devices.