Regulating Activity and Selectivity of Photocatalytic CO₂ Reduction on Cobalt by Rare Earth Compounds

Cobalt-based catalysts are ideal for CO₂ reduction reaction (CO₂RR) due to the strong binding and efficient activation of CO₂ molecules on cobalt. However, cobalt-based catalysts also show low free energy of hydrogen evolution reaction (HER), making HER competitive with CO₂RR. Therefore, how to improve the product selectivity of CO₂RR while maintaining the catalytic efficiency is a great challenge. Here, this work demonstrates the critical roles of the rare earth (RE) compounds (Er₂O₃ and ErF₃) in regulating the activity and selectivity of CO₂RR on cobalt. It is found that the RE compounds not only promote charge transfer but also mediate the reaction paths of CO₂RR and HER. Density functional theory calculations verify that the RE compounds lower the energy barrier of *CO → CO conversion. On the other hand, the RE compounds increase the free energy of HER, which leads to the suppression of HER. As a result, the RE compounds (Er₂O₃ and ErF₃) improve the CO selectivity of cobalt from 48.8 to 69.6%, as well as significantly increase the turnover number by a factor of over 10.