We demonstrate the solvent-free synthesis of a covalent organic framework (COF) containing 5,10,15,20-tetra-(4-aminophenyl)porphyrin Fe(III) chloride (FeTAPPCl) and 2,5-dihydroxyterephthalaldehyde (Dha) for the reduction of CO 2 to CO with good turnover frequency (>600 h −1 mol −1 of electroactive Fe sites) and reasonable Faradaic efficiency for CO (an average of 80%) at −2.2 V (vs Ag/AgCl) over 3 h in MeCN with 0.5 M trifluoroethanol. Characterization and stability of the COFs were probed by chemical and electrochemical methods. X-ray photoelectron spectroscopy analysis of the COF showed the formation of imine bonds and hemiaminal groups. Cyclic voltammetry of FeDhaTph-COF electrodes revealed three redox couples in MeCN or N,Ndimethylformamide (DMF) systems. The Fe(II/I) and Fe(I/0) redox couples were observed at comparable potentials as FeTAPPCl in solution. Inductively coupled plasma optical emission spectroscopy results suggested that the COF network has retained FeTAPPCl molecules substantially better than simple adsorption in either MeCN or DMF solvent.

Visible-light-driven catalytic reduction of CO2 is at the heart of artificial photosynthesis. Here, we demonstrate the first example of a Ru complex that can function both as a photosensitizer and catalyst for CO2 reduction. The catalyst exhibited excellent activity for CO evolution with a high turnover number (TON, 353 for 24 h), reaction rate (TOF, 14.7 h–1), and product selectivity (97%) under visible-light irradiation. We also succeeded in selective product formation (CO or HCOOH) by changing the basicity of the reaction media. This finding will open new avenues for visible-light-driven photoredox catalysis using Ru-based function-integrated photocatalysts.

A Ru polypyridyl complex containing a phosphine donor promoted electrocatalytic CO2 reduction at a low overpotential. Mechanistic investigations revealed that the introduction of a phosphine donor at the trans position to the labile ligand is the key to reduce the overpotential for CO2 reduction.

A pentanuclear cobalt complex that consists of five cobalt ions and six bpp− ligands (Co5, Hbpp = 3,5-bis(2-pyridyl)pyrazole) was newly developed. The obtained complex can catalyze CO2 reduction under electrochemical and photochemical conditions.