Investigation on Electroreduction of CO₂ to Formic Acid Using Cu₃(BTC)₂ Metal-Organic Framework (Cu-MOF) and Graphene...

A recent class of porous materials, viz., metal-organic frameworks (MOFs), finds applications in several areas. In this work, Cu-based MOFs (Cu-benzene-1,3,5-tricarboxylic acid) along with graphene oxide, viz., Cu-MOF/GO, are synthesized and used further for reducing CO₂ electrochemically. The reduction was accomplished in various supporting electrolytes, viz., KHCO₃/H₂O, tetrabutylammonium bromide (TBAB)/dimethylformamide (DMF), KBr/CH₃OH, CH₃COOK/CH₃OH, TBAB/CH₃OH, and tetrabutylammonium perchlorate (TBAP)/CH₃OH to know their effect on product formation. The electrode fabricated with the synthesized material was used for testing the electroreduction of CO₂ at various polarization potentials. The electrochemical reduction of CO₂ is carried out via the polarization technique within the experimented potential regime vs saturated calomel electrode (SCE). Ion chromatography was employed for the analysis of the produced products in the electrolyte, and the results showed that HCOOH was the main product formed through reduction. The highest concentrations of HCOOH formed for different electrolytes are 0.1404 mM (-0.1 V), 66.57 mM (-0.6 V), 0.2690 mM (-0.5 V), 0.2390 mM (-0.5 V), 0.7784 mM (-0.4 V), and 0.3050 mM (-0.45 V) in various supporting electrolyte systems, viz., KHCO₃/H₂O, TBAB/DMF, KBr/CH₃OH, CH₃COOK/CH₃OH, TBAB/CH₃OH, and TBAP/CH₃OH, respectively. The developed catalyst accomplished a significant efficiency in the conversion and reduction of CO₂. A high faradic efficiency of 58% was obtained with 0.1 M TBAB/DMF electrolyte, whereas for Cu-MOF alone, the efficiency was 38%. Thus, the work is carried out using a cost-effective catalyst for the conversion of CO₂ to formic acid than using the commercial electrodes. The synergistic effect of GO sheets at 3 wt % concentration and Cu⁺OH^- interaction leads to the formation of formic acid in various electrolytes.