Integrating Single Atoms with Different Microenvironments into One Porous Organic Polymer for Efficient Photocatalytic CO Reduction.

The precise identification of single-atom catalysts (SACs) activity and boosting their efficiency toward CO conversion is imperative yet quite challenging. Herein, for the first time a series of porous organic polymers is designed and prepared simultaneously, containing well-defined M-N and M-N O single-atom sites. Such a strategy not only offers multiactive sites to promote the catalytic efficiency but also provides a more direct chance to identify the metal center activity. The CO photoreduction results indicate that the introduction of salphen unit with Ni-N O catalytic centers into pristine phthalocyanine-based Ni-N framework achieves remarkable CO generation ability (7.77 mmol g ) with a high selectivity of 96% over H . In combination with control experiments, as well as theoretical studies, the Ni-N O moiety is evidenced as a more active site for CO RR compared with the traditional Ni-N moiety, which can be ascribed to the M-N O active sites effectively reducing the energy barrier, facilitating the adsorption of reaction radicals *COOH, and improving the charge transportation. This work might shed some light on designing more efficient SACs toward CO reduction through modification of their coordination environments.