Electrochemical CO2 reduction to alcohols using flexible and rigid MOF electrocatalysts

Abstract

Metal–organic frameworks (MOFs) are a versatile class of materials with significant potential for electrochemical CO₂ reduction to multicarbon products. Most MOFs for electrocatalysis rely on benzene-ring-containing linkers, but their limited electrocatalytic activity hinders progress. Flexible MOFs, constructed from aliphatic-chain-containing linkers, offer an alternative due to their ability to respond to external stimuli such as electricity. Despite their potential, few studies have explored flexible MOFs for electrochemical CO₂ reduction to value-added liquid products. This work synthesized two MOFs using metal nuclei (Mg and Zn) and distinct organic linkers: oxalic acid and 2,5-dihydroxyterephthalic acid (H₄DOBDC, MOF-74). Electrochemical analysis revealed that the flexible MOF derived from oxalic acid exhibited superior charge transport properties, as confirmed by electrochemical impedance spectroscopy (EIS). Structural and chemical analyses, such as TEM, XRD, XPS, and acidity tests with pyridine, were performed using the synthesized MOFs. In situ ATR-FTIR during electrolysis and post-electrolysis using ¹H NMR revealed the production of diverse carbon products, including ethanol, isopropanol, and methanol. The oxalic acid MOF demonstrated superior selectivity over well-known MOF-74 at −0.19 V vs. RHE. This study highlights the advantages of flexible MOFs over conventional benzene-based frameworks and paves the way for their application in CO₂ electroreduction to liquid products.