Enhanced CO₂ Electroreduction Selectivity toward Ethylene on Pyrazolate-Stabilized Asymmetric Ni–Cu Hybrid Sites

Abstract

Metal-organic frameworks (MOFs) possess well-defined, designable structures, holding great potential in enhancing product selectivity for electrochemical CO₂ reduction (CO₂R) through active site engineering. Here, we report a novel MOF catalyst featuring pyrazolate-stabilized asymmetric Ni/Cu sites, which not only maintains structural stability under harsh electrochemical conditions but also exhibits extraordinarily high ethylene (C₂H₄) selectivity during CO₂R. At a cathode potential of -1.3 V versus RHE, our MOF catalyst, denoted as Cu₁Ni-BDP, manifests a C₂H₄ Faradaic efficiency (FE) of 52.7% with an overall current density of 0.53 A cm^-2 in 1.0 M KOH electrolyte, surpassing that on prevailing Cu-based catalysts. More remarkably, the Cu₁Ni-BDP MOF exhibits a stable performance with only 4.5% reduction in C₂H₄ FE during 25 h of CO₂ electrolysis. A suite of characterization tools─such as high-resolution transmission electron microscopy, X-ray absorption spectroscopy, <i>operando</i> X-ray diffraction, and infrared spectroscopy─and density functional theory calculations collectively reveal that the cubic pyrazolate-metal coordination structure and the asymmetric Ni-Cu sites in the MOF catalyst synergistically facilitate the stable formation of C₂H₄ from CO₂.