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

Abstract

While extensive research has been conducted on the conversion of CO 2 to C 1 products, the synthesis of C 2 products still strongly depends on the Cu electrode. One main issue hindering the C 2 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 CO 2 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 NH 2 to electron-withdrawing NO 2, the Cu–Cu distance and charge of Cu can be significantly tuned, thus modulating the adsorption strength of CO 2 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 CO 2 to CH 3 CH 2 OH 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 C 2 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.

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