Electrocatalytic and Photocatalytic Reduction of CO2 to CO by Cobalt(II) Tripodal Complexes: Low Overpotentials, High Efficiency and Selectivity

The reduction of carbon dioxide (CO₂ ) has been considered as an approach to mitigate global warming and to provide renewable carbon-based fuels. Rational design of efficient, selective, and inexpensive catalysts with low overpotentials is urgently desired. In this study, four cobalt(II) tripodal complexes are tested as catalysts for CO₂ reduction to CO in a MeCN/H₂ O (4:1 v/v) solution. The replacement of pyridyl groups in the ligands with less basic quinolinyl groups greatly reduces the required overpotential for CO₂ -to-CO conversion down to 200-380 mV. Benefitting from the low overpotentials, a photocatalyst system for CO₂ -to-CO conversion is successfully constructed, with an maximum turnover number (TON) of 10 650±750, a turnover frequency (TOF) of 1150±80 h^-1 , and almost 100 % selectivity to CO. These outstanding catalytic performances are further elucidated by DFT calculations.