Urea‐Modified Carbon Nitrides: Enhancing Photocatalytic Hydrogen Evolution by Rational Defect Engineering

Abstract

The primary amine groups on the heptazine‐based polymer melon, also known as graphitic carbon nitride (g‐C 3 N 4 ), can be replaced by urea groups using a two‐step postsynthetic functionalization. Under simulated sunlight and optimum Pt loading, this urea‐functionalized carbon nitride has one of the highest activities among organic and polymeric photocatalysts for hydrogen evolution with methanol as sacrificial donor, reaching an apparent quantum efficiency of 18% and nearly 30 times the hydrogen evolution rate compared to the nonfunctionalized counterpart. In the absence of Pt, the urea‐derivatized material evolves hydrogen at a rate over four times that of the nonfunctionalized one. Since “defects” are conventionally accepted to be the active sites in graphitic carbon nitride for photocatalysis, the work here is a demonstrated example of “defect engineering,” where the catalytically relevant defect is inserted rationally for improving the intrinsic, rather than extrinsic, photocatalytic performance. Furthermore, the work provides a retrodictive explanation for the general observation that g‐C 3 N 4 prepared from urea performs better than those prepared from dicyandiamide and melamine. In‐depth analyses of the spent photocatalysts and computational modeling suggest that inserting the urea group causes a metal‐support interaction with the Pt cocatalyst, thus facilitating interfacial charge transfer to the hydrogen evolving centers.