Effect of the Cu^2+/1+ Redox Potential of Non-Macrocyclic Cu Complexes on Electrochemical CO₂ Reduction

Cu^2+/1+ complexes facilitate the reduction of CO₂ to valuable chemicals. The catalytic conversion likely involves the binding of CO₂ 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 CO₂ 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 CO₂ 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.