Cobalt coordinated two-dimensional covalent organic framework a sustainable and robust electrocatalyst for selective CO2 electrochemical conversion to formic acid

Designing covalent organic frameworks (COFs) with suitable characteristics could meet the distinctive requirements of various applications, such as catalysis, energy conversion, and molecular-sensing devices. It is indispensable to realize the apt functionalization and modification of COFs, mainly by introducing the heteroatoms to their copious pores and distinct structures. Herein, we designed nitrogenated COFs (N-COFs) with well-ordered nanopores and nitrogen-atoms, using density functional theory (DFT) and experiments. The N-COFs provided a uniquely coordinated environment for a single cobalt atom anchored between two nitrogen-atoms, which enables efficient CO2-reduction to formic-acid. In N-COFs catalyst, the N-atoms network is covalently linked to the carbonic-framework, providing the structure a crystalline nature. Moreover, N-COFs material is stable even at 1000 °C. DFT analysis revealed that the bandgap of Co-N-COF decreases to 0.67 eV owing to the synergistic effect of structural features and Co-coordination, while the bandgap of N-COF was 1.80 eV. The excellent catalytic-activity with formate partial current-densities ~446 mA cm−2, selectivity with highest Faradaic efficiency ~97.4%, and stability of 100 h was delivered by the synthesized catalyst. Moreover, Co-N-COF electrocatalyst showed high purification of formic-acid solutions (~100 wt%) and lower selectivity for CO2 conversion to CO, which was ~3%, and for HER it was ~4%.