Grafting a Rh–bipyridine complex on carbon nitride through coordination: ligand modification of single-atom Rh for enhanced CO2 reduction and inhibited H+ reduction

Abstract

Herein, we developed a coordination grafting strategy to prepare a Rh–bipyridine complex grafted carbon nitride (Rh₁–bpy/CN) homogeneous catalyst analog hybrid photocatalyst by post-coordination of bipyridine with single-atom Rh anchored on carbon nitride for enhanced photocatalytic CO₂ reduction. When 2,2′-bipyridine coordinates with a single atom Rh to form a single-site Rh–bipyridine molecular cocatalyst, the hydrogen production rate is effectively inhibited and the CO generation is significantly increased. Compared to single atom Rh anchored carbon nitride (Rh₁/CN), the CO production activity and selectivity of Rh₁–bpy/CN increased by 220 and 615 times under visible light and by 94 and 98 times under simulated sunlight, respectively. The modification of Rh with other substituted bipyridine and terpyridine can also promote CO₂ reduction. The experimental and theoretical calculations indicate that the modification of single atom Rh with pyridine promotes the separation and migration of photogenerated charges in carbon nitride and weakens the adsorption of reactants and intermediates on Rh due to the change in the coordination environment and electronic structure of the active site, overcoming the CO and other species poisoning of Rh during CO₂ reduction and increasing the adsorption energy of H, thus achieving the conversion from CO₂ to CO and inhibiting hydrogen production.