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

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