Effect of the Cu 2+/1+ Redox Potential of Non-Macrocyclic Cu Complexes on Electrochemical CO 2 Reduction.

Cu 2+/1+ complexes facilitate the reduction of CO 2 to valuable chemicals. The catalytic conversion likely involves the binding of CO 2 and/or reduction intermediates to Cu 2+/1+ , which in turn could be influenced by the electron density on the Cu 2+/1+ ion. Herein we investigated whether modulating the redox potential of Cu 2+/1+ complexes by changing their ligand structures influenced their CO 2 reduction performance significantly. We synthesised new heteroleptic Cu 2/1+ complexes, and for the first time, studied a (Cu-bis(8-quinolinolato) complex, covering a Cu 2+/1+ redox potential range of 1.3 V. We have found that the redox potential influenced the Faradaic efficiency of CO 2 reduction to CO. However, no correlation between the redox potential and the Faradaic efficiency for methane was found. The lack of correlation could be attributed to the presence of a Cu-complex-derived catalyst deposited on the electrodes leading to a heterogeneous catalytic mechanism, which is controlled by the structure of the in situ deposited catalyst and not the redox potential of the pre-cursor Cu 2+/1+ complexes.