Modifying Surfactants Within Divergent Pores of Cluster-Based Metal-Organic Frameworks for Syngas Electrosynthesis

The electrochemical reduction of CO₂ to syngas (CO and H₂) provides a potential pathway for synthesizing fuels, but the ability to modulate the syngas composition across a wide range using a catalyst of invariant composition faces considerable difficulties. Herein, we report a new strategy to incorporate ammonium (R₄N⁺) surfactants into the divergent pores of cluster-based metal-organic frameworks (MOFs) to regulate the electrocatalytic CO₂ and H₂O reduction for efficient syngas production. Two divergent clusters, including a symmetric Cu₆S₆ cluster and an asymmetric Cu₈S₆ cluster on MOFs, allow the formation of two types of well-defined pores that selectively accommodate cationic quaternary ammonium surfactants and their anionic counterions, respectively, for modifying the interface of the cluster. The surfactants with longer alky chains sufficiently occupy the inner pore of MOFs, and suppress proton reduction and enhance CO₂ reduction, resulting in tunable syngas compositions, with CO/H₂ ratios ranging from 0.01 to 4.31. Through careful validation of host-guest interactions between the surfactants and the pores of coordination polymer via co-crystallization results, the structure-activity relationship between the surfactants and the catalytic sites was elucidated in depth, providing new insights into the rational regulation of electro-catalytic pathways via a supramolecular approach.