Ligand-Engineered Metal–Organic Frameworks for Electrochemical Reduction of Carbon Dioxide to Carbon Monoxide

Abstract

The economic feasibility of electrocatalytic carbon dioxide reduction reaction (CO2RR) relies on developing highly selective and efficient catalysts operating at a high current density. Herein, we explore a ligand-engineering strategy involving the use of metal–organic frameworks (MOFs) and combining the desirable features of homogeneous and heterogeneous catalysts for boosting the activity of CO2RR. Zn-based MOFs involving two different azolate functional ligands, i.e., 1,2,4-triazole (Calgary Framework 20, CALF20) and 2-methylimidazole (zeolitic imidazolate framework-8, ZIF-8), were investigated for CO2RR in an alkaline flow cell electrolyzer. The highest CO partial current density of −53.2 mA/cm2 was observed for a Zn-based MOF (CALF20). CALF20 showed the highest reported Faradaic efficiency of Zn-based MOFs for CO production (∼94% at −0.97 V versus reversible hydrogen electrode, RHE), with a turnover frequency (TOF) of 1360.8 h–1 and a partial current density of −32.8 mA/cm2. Experimental and density functional theory (DFT) results indicate that the sp2 carbon atoms in azole ligands coordinated with the metal center in MOFs are the active sites for CO2RR due to the fully occupied 3d orbital of Zn­(II) centers. Ab initio investigation shows that both azolate frameworks in CALF20 and ZIF-8 have the most favorable adsorption sites at the N–sp2 C. Adopting the triazole ligand in CALF20 enhances the charge transfer (as compared with the diazole group in ZIF-8), which induces more electrons in the adjacent active sites at the azole ligand and facilitates *COOH formation, boosting current density and Faradaic efficiency toward CO production. This study suggests that ligand engineering in MOFs could be a viable approach to design a highly efficient CO2RR catalyst.

Three-dimensional porphyrinic covalent organic frameworks for highly efficient electroreduction of carbon dioxide

“…Recently, porous crystalline covalent organic frameworks (COFs) have attracted extensive attention in many fields including gas storage, catalysis, and photoelectric areas because of their well-defined tailorable chemical and pore structures and large specific surface areas. 32–44 Moreover, the associated unique features such as strong CO 2 adsorption capacity and single active sites make COFs to be a good choice for CO 2 RR. 45–57 Since Yaghi and co-workers first reported that the cobalt porphyrin-based COF-366-Co can catalyze the CO 2 RR to produce CO, 58 several other metal porphyrin- and phthalocyanine-based COFs have been reported as electrodes to promote the CO 2 RR in aqueous medium.…”

Metallocavitins as Promising Industrial Catalysts: Recent Advances

“…A desired electrocatalyst should have a high TON, a high TOF, and low overpotential (Zhang H. et al, 2021). The Zn-based MOF CALF20 demonstrates the highest CO Faradaic efficiency of 94.5% at −0.97 V vs. RHE with a TOF of 1360.8 h −1 and a partial current density of −32.8 mA/cm 2 for electrochemical CO 2 R to CO (Al-Attas et al, 2021). The redox-active In-MOF shows the first example of an Ni-based MOF catalyst in electrocatalytic CO 2 R, which suggests new prospects for designing novel and efficient non-noble, metal-based, redox-active, biomimetic MOFs (Zhou et al, 2021).…”

Toward High‐Performance CO2‐to‐C2 Electroreduction via Linker Tuning on MOF‐Derived Catalysts

“…Adjusting organic linkers to regulate the selectivity of eCO 2 RR is a novel strategy in catalyst design. [ 12,16,17 ] Al‐Attas et al. have introduced the 1,2,4‐triazolate group into zeolitic imidazolate framework‐8 (ZIF‐8) to replace the 2‐methylimidazolate group, increasing CO selectivity from 61% to 94%.…”