Regulating Activity and Selectivity of Photocatalytic CO 2 Reduction on Cobalt by Rare Earth Compounds.

Cobalt-based catalysts are ideal for CO 2 reduction reaction (CO 2 RR) due to the strong binding and efficient activation of CO 2 molecules on cobalt. However, cobalt-based catalysts also show low free energy of hydrogen evolution reaction (HER), making HER competitive with CO 2 RR. Therefore, how to improve the product selectivity of CO 2 RR while maintaining the catalytic efficiency is a great challenge. Here, this work demonstrates the critical roles of the rare earth (RE) compounds (Er 2 O 3 and ErF 3 ) in regulating the activity and selectivity of CO 2 RR on cobalt. It is found that the RE compounds not only promote charge transfer but also mediate the reaction paths of CO 2 RR 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 (Er 2 O 3 and ErF 3 ) 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.