Abstract
Noble-metal-free CO(2) reduction 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 the CoPc family in photocatalytic CO(2) reduction, where a Cu(I) heteroleptic photosensitizer is utilized. The highest performance can be achieved using cobalt tetracarboxylphthalocyanine in light-driven CO(2)-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-substituted CoPc derivative. The favorable electron-withdrawing effects have been further verified by DFT calculations and cyclic voltammetry, which reduces the overpotential required for CO(2) reduction and decreases the Gibbs free energy of the catalyst active intermediates, particularly the CO-desorption energetics.