Local spatial charge separation and proton activation induced by surface hydroxylation promoting photocatalytic hydrogen evolution of polymeric carbon nitride

Polymeric carbon nitride as an intriguing earth-abundant visible light photocatalyst for H-2 evolution has projected huge potentials. A high-performance polymeric carbon nitride photocatalyst system always requires fabrication of nanostructure or assistance of other semiconductors for ample reactive sites or rapid carrier migration/charge separation. Here, we disclose that hydroxylation as an efficient surface polarization decoration tactic without involving nanostructure or other semiconductors can substantially promote local spatial charge separation and proton activation of polymeric carbon nitride, thus achieving high photocatalytic H-2 evolution. The post-hydrothermal treatment allows polymeric carbon nitride surface controllable grafting of abundant hydroxyls (-OH) on the -C=N sites, which not only extends the 2D conjugate electron system of polymeric carbon nitride to 3D space to realize local spatial charge separation, but also polarizes the neighboring N atoms (C-N=C) to promote the proton adsorption and activation on them, further contributing to the high H-2 evolution performance. The deep hydroxylation offered by introduction of basic ammonium salts discloses a pH-dependent hydroxylation-level mechanism and renders a similar to 11-fold enhancement in H-2 generation rate with an AQY of 9.1% at 420 +/- 15 nm. The finding may bring a new opportunity for developing highly-efficient HER materials base on surface polarization of functional groups.