Computational Design and Experimental Validation of Enzyme Mimicking Cu-Based Metal–Organic Frameworks for the Reduction of CO2 into C2 Products: C–C Coupling Promoted by Ligand Modulation and the Optimal Cu–Cu Distance

While extensive research has been conducted on the conversion of CO₂ to C₁ products, the synthesis of C₂ products still strongly depends on the Cu electrode. One main issue hindering the C₂ production on Cu-based catalysts is the lack of an appropriate Cu-Cu distance to provide the ideal platform for the C-C coupling process. Herein, we identify a lab-synthesized artificial enzyme with an optimal Cu-Cu distance, named MIL-53 (Cu) (MIL= Materials of Institute Lavoisier), for CO₂ conversion by using a density functional theory method. By substituting the ligands in the porous MIL-53 (Cu) nanozyme with functional groups from electron-donating NH₂ to electron-withdrawing NO₂, the Cu-Cu distance and charge of Cu can be significantly tuned, thus modulating the adsorption strength of CO₂ that impacts the catalytic activity. MIL-53 (Cu) decorated with a COOH-ligand is found to be located at the top of a volcano-shaped plot and exhibits the highest activity and selectivity to reduce CO₂ to CH₃CH₂OH with a limiting potential of only 0.47 eV. In addition, experiments were carried out to successfully synthesize COOH-decorated MIL-53(Cu) to prove its high catalytic performance for C₂ production, which resulted in a -55.5% faradic efficiency at -1.19 V vs RHE, which is much higher than the faradic efficiency of the benchmark Cu electrode of 35.7% at -1.05 V vs RHE. Our results demonstrate that the biologically inspired enzyme engineering approach can redefine the structure-activity relationships of nanozyme catalysts and can also provide a new understanding of the catalytic mechanisms in natural enzymes toward the development of highly active and selective artificial nanozymes.