Electrochemical conversion of CO2 to syngas with a stable H2/CO ratio in a wide potential range over ligand-engineered metal–organic frameworks

Abstract

The efficient electrochemical conversion of CO₂ to value-added chemicals is a promising approach to mitigate the current energy and environmental challenges. In this work, a ligand-engineering strategy was reported to be applied to stabilize CO₂ adsorption in metal–organic frameworks (MOFs). Zn-based MOFs (Zn-MOFs) related to two different carboxyl functional ligands, i.e., 1,3,5-benzenetricarboxylic acid (Zn-BTC) and 1,4-benzenedicarboxylate (Zn-BDC), were investigated for the CO₂ reduction reaction (CO₂RR) in a flow cell electrolyzer. Zn-BTC exhibits a stable H₂/CO ratio (≈1 : 2) up to a high current density (−300 mA cm⁻²) in a wide potential range (−0.96 to −1.96 V vs. RHE) in 1 M KOH. The molar H₂/CO ratio is steady in both neutral and alkaline electrolytes. Ex situ experimental results indicate that the carboxyl groups in Zn-BTC are more durable than those in Zn-BDC, which also enhances the absorption of CO₂. In situ attenuated total reflection surface-enhanced infrared absorption spectroscopy elucidates that carboxyl groups can stabilize CO₂RR intermediates. This work not only verifies the significance of the carboxyl groups in sustaining molecular structures but also offers valuable understandings in electrocatalyst design.