Electronic Effects in Cobalt Phthalocyanine Catalysts Towards Noble-Metal-Free, Photocatalytic CO2-to-CO Reduction

Noble-metal-free CO2reduction systems based on cobalt phthalocyanine (CoPc) and its derivatives have demonstrated remarkable photocatalytic performances; however, their structure-activity relationship with electronic tuning remains unexplored. Herein, we now provide a systematic study to investigate the electron effects of substituents on theCoPcfamily in photocatalytic CO2reduction, where a Cu(I) heteroleptic photosensitizer is utilized. The highest performance can be achieved using cobalt tetracarboxylphthalocyanine in light-driven CO2-to-CO reduction, with a maximum turnover number of 2950 at 450 nm and an outstanding apparent quantum yield of 63.5% at 425 nm, over ten times the activity with the tetra-dimethylamino-substitutedCoPcderivative. The favorable electron-withdrawing effects have been further verified by DFT calculations and cyclic voltammetry, which reduces the overpotential required for CO2reduction and decreases the Gibbs free energy of the catalyst active intermediates, particularly the CO-desorption energetics.