Directing Quasiparticle Movement in Graphitic Carbon Nitride through Spatial Engineering for Enhanced Photocatalytic Hydrogen Evolution

The inherently low dielectric properties of polymeric semiconductors lead to high exciton binding energy, impeding the photogenerated electron and hole separation. The aim of this work is to regulate the spacing of charge through spatial engineering in graphitic carbon nitride (CN), which performs photocatalysis through dual routes, where ruthenium phosphide (Ru_xP) and hydroxide ions (OH⁻) serve as the electron acceptor and hole extractor, respectively. The unique heterojunction of Ru_xP incorporated in the bulk CN (B-Ru_xP-CN) shows a lower exciton binding energy (61 meV) than bare CN and CN surface-deposited Ru_xP (S-Ru_xP-CN). This favors high carrier density and rapid escape of active electrons from bound excitons. The photocatalytic hydrogen (H₂) evolution rate of B-Ru_xP-CN increases with increasing pH. However, S-Ru_xP-CN maintains an almost invariable H₂ production rate even with similar increases in pH. We reasonably ascribe the different H₂ evolution performances of both photocatalysts to their contrasting structures and discrepancy in quasiparticle relaxation dynamics. The wrapped structure of B-Ru_xP-CN endows it with a prolonged charge separation lifetime (189 ns) and an enhanced H₂ evolution rate (32.0 μmol/h) in an alkaline scavenger solution. This work provides a controllable procedure for quasiparticles' directional movement in polymeric photocatalysts.