Fabrication of Ultrahigh-Loading Dual Copper Sites in Nitrogen-Doped Porous Carbons Boosting Electroreduction of CO₂ to C₂H₄ Under Neutral Conditions

Synthesis of high-loading atomic-level dispersed catalysts for highly efficient electrochemical CO₂ reduction reaction (eCO₂RR) to ethylene (C₂H₄) in neutral electrolyte remain challenging tasks. To address common aggregation issues, a host-guest strategy is employed, by using a metal-azolate framework (MAF-4) with nanocages as the host and a dinuclear Cu(I) complex as the guest, to form precursors for pyrolysis into a series of nitrogen-doped porous carbons (NPCs) with varying loadings of dual copper sites, namely NPC_MAF-4-Cu₂-21 (21.2 wt%), NPC_MAF-4-Cu₂-11 (10.6 wt%), and NPC_MAF-4-Cu₂-7 (6.9 wt%). Interestingly, as the loading of dual copper sites increased from 6.9 to 21.2 wt%, the partial current density for eCO₂RR to yield C₂H₄ also gradually increased from 38.7 to 93.6 mA cm^-2. In a 0.1 m KHCO₃ electrolyte, at -1.4 V versus reversible hydrogen electrode (vs. RHE), NPC_MAF-4-Cu₂-21 exhibits the excellent performance with a Faradaic efficiency of 52% and a current density of 180 mA cm^-2. Such performance can be attributed to the presence of ultrahigh-loading dual copper sites, which promotes C─C coupling and the formation of C₂ products. The findings demonstrate the confinement effect of MAF-4 with nanocages is conducive to the preparation of high-loading atomic-level catalysts.