Product selectivity switching in photocatalytic H₂ and H₂O₂ production via carbonized polymer dots loading on carbon nitride hybrids

Selective regulation of competing photoreduction pathways remains a key challenge in photocatalysis. Most materials that promote one target product often unintentionally accelerate competing side reactions. Here, we demonstrated that carbonized polymer dots (CPDs) served as dual function in graphitic carbon nitride hybrids. By varying the CPDs loading, the continuous increase in hydrogen (H₂) evolution rate was achieved, while hydrogen peroxide (H₂O₂) production was suppressed. The optimal CPDs loading enhanced the H₂ evolution rate by 5.4 times and reduced the H₂O₂ yield by 72%. Mechanistic studies demonstrated that CPDs introduction narrowed the bandgap, promoted charge separation and transfer, and induced a downward shift of the conduction band minimum along with a lowered Fermi level. These energetic modifications weakened the thermodynamic driving force for the two-electron oxygen reduction pathway and steered the reaction toward a four-electron process. This work established CPDs as a versatile platform for reaction pathway regulation and provided a generalizable strategy for product-selective photocatalysis through precise band structure engineering.