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

ABSTRACT

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 fsc 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.