Photoderived Bi⁰ nanobridge enabling an S-scheme Bi₂O₂CO₃-Bi⁰-TiO₂ heterojunction for efficient photocatalytic water...

Constructing strongly coupled S-scheme heterojunctions without sacrificing redox capability remains a central challenge in photocatalytic water splitting. Herein, we report the in situ photogeneration of metallic Bi (Bi⁰) nanobridges from layered Bi₂O₂CO₃ (BOC) under UV irradiation, which effectively wire BOC with TiO₂ (P25) to form a ternary BOC-Bi⁰-TiO₂ S-scheme heterojunction. Under ultraviolet-visible light or simulated sunlight, the optimized BOC-0.5P25 catalyst achieves a high H₂ evolution rate of ∼5.8 mmol·g^-1·h^-1, which further increases by ∼24 % (to ∼7.2 mmol·g^-1·h^-1) after light-activated cycling. The apparent quantum efficiency (AQE) reaches 2.45 % at 380 nm. Structural characterizations confirm the light-induced formation of Bi⁰, accompanied by a slight chemical shift in Ti 2p and Bi 4f spectra, consistent with interfacial band bending. Band structure and kinetics analyses elucidate an S-scheme charge transfer mechanism where electrons preferentially flow via Bi⁰ into TiO₂ while holes stay on Bi₂O₂CO₃, driven by the built-in field. Isotopic labeling experiments via Gas Chromatography-Mass Spectrometry (GC-MS) isotopologues (CH_xD_4-x in D₂O/MeOH) together with online Differential Electrochemical Mass Spectrometry (DEMS) signals confirm that water contributes to both H₂ production and methanol oxidative reforming (partially to CH₄). The concept of light-triggered, in-situ mediator activation provides a practical route for photocatalytic water reduction coupled with methanol oxidative reforming under unbiased and noble-metal-free conditions through engineering tightly coupled S-scheme interfaces.