Pillar-Layered Porous Metal-Organic Frameworks with Co₂N₂O₈ Clusters and Tetragonal Ligands for CO₂ Conversion

Converting CO₂ to valuable chemicals and fuels is a viable method to establish a carbon-neutral energy cycle in the environment. Metal-organic frameworks (MOFs), characterized by dispersed active sites, high porosity, etc., have displayed a great application prospect in the electrochemical/chemical CO₂ reduction reaction (CO₂RR) process. Herein, we proposed a one-step production to establish a series of pillar-layered porous MOFs, [Co₂(L)(bimb)]_n (MOF 1) and [Co₄(L)₂(bidpe)₂]_n (MOF 2) [H₄L = 5'-(4-carboxyphenyl)-(1,1':2',1″-terphenyl)-4,4',4″-tricarboxylic, bimb = 1,4-bis(imidazol-1-yl)-butane, bidpe = 4'-bis(imidazolyl) diphenyl ether], for preferential conversion of CO₂ via ligand adjustment and increase of active sites' density. According to single-crystal X-ray diffraction studies, [Co₂(L)(bimb)]_n exhibits pillar-layered binuclear 3D frameworks with a 2,4,6-linked 3-nodes new topology structure, while [Co₄(L)₂(bidpe)₂]_n displays pillar-layered tetranuclear interspersed networks with a 4,6-linked 2-nodes topology structure through a ligand adjustment strategy. Meanwhile, the pillar-layered structure of the MOFs with abundant active sites is conducive to mass diffusion and benefits the conversion of CO₂. MOFs 1-2 exhibit good electrocatalytic activity for CO₂RR in 0.5 M KHCO₃ solution. Especially, the current density of MOF 2 generated at -0.90 V (vs. RHE) reaches -81.6 mA·cm^-2, which is 3.1 times higher than that under an Ar atmosphere. In addition, MOFs 1-2 can be used as a heterogeneous catalyst for chemical conversion of CO₂. The results are expected to provide inspiration for rational design to develop stable and high-efficiency MOF-based electrocatalysts for CO₂RR.