Unique Single-Copper Metal-Organic Framework Enables Highly Selective Electrocatalytic CO₂ Reduction to Ethylene via...

The prevailing paradigm in electrocatalytic CO₂ reduction asserts that multinuclear copper are indispensable for facilitating C-C coupling, whereas isolated single-copper sites in MOFs are considered inefficient for C₂₊ production. Herein, we challenge this wisdom using two Cu-MOFs from the same ligand: CuTTB-1 featuring isolated single copper sites and CuTTB-2 possessing multinuclear copper. Counterintuitively, CuTTB-1 achieved a Faradaic efficiency (FE) of ethylene production comparable to that of CuTTB-2, along with a superior partial current density across both alkaline and acidic electrolytes. Remarkably, CuTTB-1 delivered an exceptional FE(C₂H₄) of 47.4% with a high partial current density of -142.2 mA cm^-2 at an applied potential of -1.3 V vs. RHE and the corresponding overpotential of 1.38 V in acidic medium, surpassing all reported MOFs-based catalysts and rivaling the performance of state-of-the-art catalysts. Density functional theory calculations combined with operando infrared spectra revealed that ^*CO intermediate generated on an isolated copper site in CuTTB-1 can desorb and migrate to a distant ^*CHO species, enabling asymmetric C-C coupling. This newly identified mechanism exhibits a substantially lower free energy compared to conventional symmetric coupling in CuTTB-2. This work redefines the design principles for single-site catalysts by demonstrating the viability of asymmetric coupling via reactant migration.