Interfacial Bond Dipole Engineering for Accelerated Photogenerated Charge Migration in a Red Phosphorus Based Heterojunction

Gaining in-depth insights into the interfacial dipole is crucial for optimizing the transfer kinetics of photogenerated electrons at heterojunction interfaces. Herein, we establish interfacial bond polarity as a universal descriptor governing electron transfer kinetics, demonstrated via two model heterojunctions (RP/S₈ and RP/CdS) with identical P-O-S bonds. Density functional theory (DFT) calculation revealed a stronger interfacial dipole in RP/CdS (2.75 D) than in RP/S₈ (1.83 D). Femtosecond transient absorption spectroscopy (fs-TAS) demonstrates a pronounced acceleration of interfacial electron transfer, with RP/CdS exhibiting a rate constant of 5.5 × 10⁹ s^-1, significantly exceeding that of RP/S₈ (2.5 × 10⁸ s^-1). The stronger interface dipole is the key to facilitating the efficient migration of charges. Consistently, the photocatalytic hydrogen evolution (PHE) activities of RP/S₈ and RP/CdS were 1.5-fold and 4.5-fold enhanced compared with their corresponding mechanical mixtures, respectively. This study highlights interfacial dipole engineering as a powerful strategy for the rational design of high-efficiency heterojunction photocatalysts.