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The precise identification of single-atom catalysts (SACs) activity and boosting their efficiency toward CO2 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-N4 and M-N2 O2 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 CO2 photoreduction results indicate that the introduction of salphen unit with Ni-N2 O2 catalytic centers into pristine phthalocyanine-based Ni-N4 framework achieves remarkable CO generation ability (7.77 mmol g-1 ) with a high selectivity of 96% over H2 . In combination with control experiments, as well as theoretical studies, the Ni-N2 O2 moiety is evidenced as a more active site for CO2 RR compared with the traditional Ni-N4 moiety, which can be ascribed to the M-N2 O2 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 CO2 reduction through modification of their coordination environments.
Dong et al. (Thu,) studied this question.