Single Ni Atoms Anchored on Porous Few-Layer g-C3 N4 for Photocatalytic CO2 Reduction: The Role of Edge Confinement.

It is greatly intriguing yet remains challenging to construct single-atomic photocatalysts with stable surface free energy, favorable for well-defined atomic coordination and photocatalytic carrier mobility during the photoredox process. Herein, an unsaturated edge confinement strategy is defined by coordinating single-atomic-site Ni on the bottom-up synthesized porous few-layer g-C3 N4 (namely, Ni5 -CN) via a self-limiting method. This Ni5 -CN system with a few isolated Ni clusters distributed on the edge of g-C3 N4 is beneficial to immobilize the nonedged single-atomic-site Ni species, thus achieving a high single-atomic active site density. Remarkably, the Ni5 -CN system exhibits comparably high photocatalytic activity for CO2 reduction, giving the CO generation rate of 8.6 µmol g-1 h-1 under visible-light illumination, which is 7.8 times that of pure porous few-layer g-C3 N4 (namely, CN, 1.1 µmol g-1 h-1 ). X-ray absorption spectrometric analysis unveils that the cationic coordination environment of single-atomic-site Ni center, which is formed by Ni-N doping-intercalation the first coordination shell, motivates the superiority in synergistic N-Ni-N connection and interfacial carrier transfer. The photocatalytic mechanistic prediction confirms that the introduced unsaturated Ni-N coordination favorably binds with CO2 , and enhances the rate-determining step of intermediates for CO generation.