A stable MIL-100(In) metal–organic framework for multifunctional CO₂ capture and electrochemical conversion to formic acid

Abstract

The electroreduction of carbon dioxide (CO₂) into valuable chemicals, along with its effective storage, constitutes a crucial approach for reducing greenhouse gas emissions and combating climate change. Most of the research so far has focused on gas capture, with limited methods available for the combined capture and conversion of CO₂ within a single material. The metal–organic framework (MOF) utilized in this study consists of 1,3,5-benzenetricarboxylic acid and indium ions, designated as MIL-100(In), and was synthesized via a solvothermal method. The obtained MIL-100(In) was studied as a dual function CO₂ capture agent and electroreduction catalyst. Nitrogen (N₂) physisorption measurements revealed a high Brunauer–Emmett–Teller (BET) specific surface area of 1694.3 m² g⁻¹. The temperature-programmed desorption (TPD) of CO₂ at various temperatures allowed the estimation of the activation energy for CO₂ desorption. Stability evaluations of MIL-100(In), performed by CO₂ adsorption–desorption cycling studies, demonstrated that the MOF maintains exceptional structural integrity, preserving its adsorption efficacy across 48 successive cycles. The MIL-100(In) adsorbed 1.91 mmol g⁻¹ of CO₂ at 0 °C and 1.41 mmol g⁻¹ at 25 °C under 1 0.1 MPa. Moreover, MIL-100(In) was also explored as a catalyst in CO₂ electroreduction studies. To alleviate the limited solubility of CO₂ in water, electroreduction was performed under moderate pressures (below 1.5 MPa). The MOF predominantly produced formic acid during the electroreduction process, making it the major reaction product and an important compound for energy storage and industrial applications. A maximum formic acid (FA) concentration of 1.72 mmol L⁻¹ was obtained after 2 h of electrolysis at −1.102 V vs. RHE. The electroreduction mechanisms were further clarified by density-functional theory (DFT) simulations, which highlighted the pivotal role of In-MOF in the production of formic acid over carbon monoxide.