Capture-Intensified Electrocatalytic Reduction of Postcombustion CO2 in Transporting and Catalytic Channels of Covalent Organic Frameworks

Abstract

Covalent organic frameworks (COFs) have been employed for electrochemical carbon dioxide reduction (CO₂RR) due to the high degree of molecular controllability. However, catalysis of the CO₂RR in dilute CO₂ conditions is hardly achieved because of the lacking ability of trapping and then transporting CO₂ to catalytic sites in low-concentration CO₂. In this work, we have achieved catalysis of the CO₂RR under simulated flue gas (CO₂/N₂ = 15/85, at 298 K) by constructing CO₂-trapping and -transporting channels to the catalytic centers of COFs. With decorating phytic acid (PA) along the pores, the selective capture and transport ability of CO₂ along the pore channels was significantly improved, and the superficial molecular H₂O close to the catalytic sites was also efficient bound. The optimized catalyst (PA-Co-COF) achieved a Faradaic efficiency for CO of 86.97% at −0.7 V and a maximum turnover frequency of 1208.8 h^–1 at −1.0 V in simulated flue gas, which were 152 and 710% of those from a catalyst with bare channels. The molecular dynamics simulations and theoretical calculation revealed that PA not only promoted CO₂ diffusion across the porous channels but also accelerated the formation of the intermediate COOH* and simulated the suppression of the competing hydrogen evolution reaction in the catalytic process, which contributed to higher activity and selectivity.