Atomically dispersed Co2+ in a redox-active COF for electrochemical CO2 reduction to ethanol: unravelling mechanistic insight through operando studies

Abstract

Designing cheap, stable, and efficient electrocatalysts for selective CO₂ reduction to ethanol is a green and sustainable approach for converting the greenhouse gas into value-added products. In this context, developing single-atom-based electrocatalysts (SAEs) could be advantageous because of their maximum atom utilization. Here, we report the design and synthesis of a donor–acceptor-based redox-active covalent organic framework (COF), TAPA-OPE, obtained by condensation between tris-(4-aminophenyl) amine (TAPA) and oligo-(p-phenyleneethynylenes) (OPE) based dialdehyde. Owing to the presence of suitable metal chelating sites, TAPA-OPE was utilized for covalent grafting of atomic Co²⁺ (Co-TAPA-OPE), which has been confirmed by EXAFS, HAADF-STEM, and XPS studies. Co-TAPA-OPE acts as a stable SAE for selective reduction of CO₂ to ethanol at −0.67 V vs. RHE. Faradaic efficiency (FE) for the ethanol formation is calculated to be 66.8%. The in situ XAS study discloses that the single Co-site transiently changes its oxidation state and coordination environment during the electrocatalytic reduction process. Furthermore, an in situ FTIR study is performed to track the intermediates during the CO₂ reduction reaction (CO₂RR), which eventually assists in elucidating a plausible reaction mechanism through density functional theory (DFT).