Enhanced Electrocatalytic Carbon Dioxide Reduction Activity via Local Charge Environment Regulation of Active Sites with Rational Functionalization.

Covalent organic frameworks (COFs) are a new emerging class of electrochemical catalysts for the CO2 reduction reaction (CO2RR) with fascinating structural tunability. In this work, to dig more detailed information about the effect of local charge environment regulation of active sites via structure modification on the catalytic performance of COFs for CO2RR, the Gibbs free-energy change (ΔG) of each elementary reaction step involved in the CO2RR and competitive hydrogen evolution reaction (HER) on COF366-Co and its derivatives were examined theoretically. It is observed that the valence band maximum (VBM) energy level of the COFs is increased by incorporation of electron-donating groups, and then the charge distribution on the Co center of COF366-Co is increased due to the increased charge-transfer amount from the electron-occupied N sp2 hybrid orbitals to the empty Co3d orbitals. For incorporating electron-withdrawing groups, the VBM energy level and the d-band center (ξd) of the Co atom are downshifted, and the d-band center gets closer to the occupied VBM energy level as the VBM is decreased to a larger extent than the ξd. As a result, electrosorption of the intermediate is facilitated and the CO2RR performance is enhanced by such a linker functionalization strategy, especially for electron-withdrawing groups. Our study highlights the key role that controlled local electrical environment via chemical structure modification of COFs can play in regulating the catalytic activity for its CO2RR applications.