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.