Stable Immobilization of Nickel Ions on Covalent Organic Frameworks for Panchromatic Photocatalytic Hydrogen Evolution.

Post-coordination design on covalent organic frameworks (COFs) is an efficient strategy for elevating the photocatalytic activity of organic moiety. However, the rigid skeletons and densely layered stacking of two-dimensional (2D) COFs cannot be flexibly adapted for specific conformations of metal complexes, thereby impairing the metal-COF cooperation. Here, we adopt a solvothermal method to immobilize nickel(II) ions into a 2,2'-bipyridine-containing 2D COF, forming a stable coordination motif. Such the complex remarkably enhances the photocatalytic performance, giving an optimized H evolution rate of as high as 51 300 μmol h  g , 2.5 times higher than the pristine COF. The evolved hydrogen gas can also be detected upon 700-nm light irradiation, while its analog synthesized by the traditional coordination method is photo-catalytically inert. This work provides a strategy for optimizing the metal-COF coordination system and strengthening a synergy for electronic regulation in photocatalysis.