Engineering CO₂ Pre-Activation in In-MOF for Enhancing its Electroreduction Activity

The efficiency of electrocatalytic CO₂ reduction (ECR) is largely governed by the adsorption of CO₂, a step often accompanied by pre-activation via molecular bending and electron redistribution before the first electron transfer occurs. However, the explicit correlation between the extent of CO₂ pre-activation and the resultant reaction performance remains elusive due to the lack of direct structural evidence. Herein, we employ two In-MOFs, FJU-350 and FJU-351, as crystalline model catalysts to visualize distinct CO₂ pre-activation configurations and unravel their critical role in ECR. FJU-350 exhibits superior ECR performance with FE_formate of 90.9% at -1.4 V (vs. RHE), outperforming FJU-351 (88.6% at -1.6 V). Single-crystal X-ray diffraction analyses indicate that this 200 mV efficiency gain is the consequence of their distinct structural microenvironments. FJU-350 features a polarized carboxyl-oxygen site, stabilizing a uniquely bent CO₂ species (127.2°) via single-site interaction, indicative of pronounced pre-activation. Theoretical calculations confirm that the highly distorted configuration facilitates charge transfer and lowers the energy barrier. In contrast, FJU-351 lacks such a directed site, accommodating near-linear CO₂ (≥153.3°) via delocalized π-interactions. This work reveals a correlation between the pre-activated CO₂ configuration and its electroreduction performance, providing a strategic foundation for designing efficient catalysts through precise micro-environment engineering.