A Covalent Organic Framework Bearing Single Ni Sites as a Synergistic Photocatalyst for Selective Photoreduction of CO 2 to CO.

Photocatalytic reduction of CO ₂ into energy-rich carbon compounds has attracted increasing attention. However, it is still a challenge to selectively and effectively convert CO ₂ to a desirable reaction product. Herein, we report a design of a synergistic photocatalyst for selective reduction of CO ₂ to CO by using a covalent organic framework bearing single Ni sites (Ni-TpBpy), in which electrons transfer from photosensitizer to Ni sites for CO production by the activated CO ₂ reduction under visible-light irradiation. Ni-TpBpy exhibits an excellent activity, giving a 4057 μmol g ^-1 of CO in a 5 h reaction with a 96% selectivity over H ₂ evolution. More importantly, when the CO ₂ partial pressure was reduced to 0.1 atm, 76% selectivity for CO production is still obtained. Theoretical calculations and experimental results suggest that the promising catalytic activity and selectivity are ascribed to synergistic effects of single Ni catalytic sites and TpBpy, in which the TpBpy not only serves as a host for CO ₂ molecules and Ni catalytic sites but also facilitates the activation of CO ₂ and inhibits the competitive H ₂ evolution.