Constructing Interfacial B–P Bonding Bridge to Promote S-Scheme Charge Migration within Heteroatom-Doped Carbon Nitride Homojunction for Efficient H₂O₂ Photosynthesis

The emerging step (S)-scheme heterojunction systems became a powerful strategy in promoting photogenerated charge separation while maintaining their high redox potentials. However, the weak interfacial interaction limits the charge migration rate in S-scheme heterojunctions. Herein, we construct a unique S-scheme carbon nitride (CN) homojunction with boron (B)-doped CN and phosphorus (P)-doped CN (B-CN/P-CN) for hydrogen peroxide (H₂O₂) photosynthesis. The B-CN/P-CN nanosheet composites revealed extensively tight interfacial contact, improved visible-light harvesting, and reduced carrier lifetime. The structural investigation results also indicate that the interfacial chemical B-P bonding is formed between B-CN and P-CN nanosheets, inducing an accelerated interfacial S-scheme charge migration. Density functional theory calculations further clarify the S-scheme charge transfer mechanism. Consequently, the 2e^- oxygen reduction reaction was the predominant pathway of H₂O₂ production, facilitated by the B-CN/P-CN homojunction. The optimal H₂O₂ yield rate reached 2199.5 μmol L^-1 h^-1 over the B-CN/P-CN homojunction (S3) photocatalyst under monochromatic LED irradiation, increasing 2-8 times as against most of the C₃N₄ photocatalysts. This study highlights the crucial role of interfacial charge transfer between heterojunction/homojunction materials, accompanied by an unveiling reaction mechanism for solar-energy conversions.