Selective electroreduction of CO2 to value-added C1 and C2 products using MOF and COF-based catalysts

Abstract

Carbon dioxide (CO2) capture and conversion to value-added chemicals such as hydrocarbons or other energetic fuels is a potential alternate to carbon capture and sequestration in order to control the atmospheric CO2 concentration. In this regard, electrochemical CO2 reduction is one of the most important techniques to convert CO2 into valuable chemicals. For this process, abundant and cost-effective catalysts are required to ensure sustainable scale-up of the process. Metal Organic Frameworks (MOFs) and Covalent Organic Frameworks (COFs), two different classes of porous crystalline solids having a lot of similarities in terms of ordered porosity, tunable pore size, thermal & chemical stability and modular tailor-ability are currently being explored for developing potential electrocatalysts for CO2 reduction reaction. However, in most of the cases, the end product is CO, a potentially toxic gas molecule that has less energetic value compared to other hydrocarbons including methanol (CH3OH), methane (CH4), ethanol (C2H5OH), ethylene (C2H4), and formic acid (HCOOH) etc. Also, in most of the cases, the electrochemical CO2 reduction processes suffer from low current densities and low faradaic efficiency, limiting the scale-up of the technology. However, this has been overcome in some cases via composite formation with conducting materials including nanoparticle-based systems, conducting polymers etc. Herein we highlight the MOFs and COFs-based electrocatalysts capable of reducing CO2 to some value-added C1 and C2 products. It will also address the challenges in the field in terms of catalyst design and the future perspective of this field. Moreover, a structure-property relationship of MOFs and COFs-based electrocatalysts for CO2 reduction has been realized which is crucial to understanding their catalytic performances. It has been comprehended that catalysts' efficiency is mainly dominated by three factors including high porosity/surface area, availability of active sites & nature of coordination environment and electronic structure and conductivity of the catalysts. However, the possibility of functionalization and structural stability under harsh electrochemical conditions also plays an important role in their catalytic efficiency.