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.