1：Experimental Design and Method Selection:

The study used an in-situ electrochemical reduction method to introduce oxygen vacancies into BiOI nanosheets, with characterization techniques including SEM, TEM, XRD, XPS, EPR, Mott-Schottky plots, PEIS, LSV, and UV-vis absorption. A tandem PEC system with BiVO4 photoanode and R-BiOI photocathode was designed for N2 reduction.

2：Sample Selection and Data Sources:

Samples included intrinsic BiOI (I-BiOI) and reduced BiOI (R-BiOI) fabricated on FTO substrates, using chemicals from Sinopharm Chemical Reagent Co., Ltd. and Aladdin Reagent Co. Data were collected from experimental measurements under controlled conditions.

3：List of Experimental Equipment and Materials:

Equipment included SEM (Hitachi S-4800), TEM (Tecnai G2 F20 S-Twin), XRD (Bruker D8 ADVANCE), EPR (Bruker EPR alpha 300~10/12), XPS (Thermos Fisher Scientific Escalab 250Xi), electrochemical instrumentation (Princeton VersaSTAT 3), UV-vis (Shimadzu UV-2550), and ammonia electrode (Rex PNH3-1). Materials included Bi(NO3)3·5H2O, KI, ethanol, nitric acid, dimethyl sulfoxide, NaOH, p-benzoquinone, vanadyl acetylacetonate, and FTO glass.

4：1). Materials included Bi(NO3)3·5H2O, KI, ethanol, nitric acid, dimethyl sulfoxide, NaOH, p-benzoquinone, vanadyl acetylacetonate, and FTO glass. Experimental Procedures and Operational Workflow:

4. Experimental Procedures and Operational Workflow: I-BiOI was synthesized by electrodeposition, R-BiOI by in-situ reduction in a three-electrode cell, and BiVO4 by calcination. N2 reduction was performed in a three-electrode system with N2-saturated electrolyte, bias voltage, and irradiation. Ammonia production was detected by IR and ammonia electrode.

5：Data Analysis Methods:

Data were analyzed using equations for Mott-Schottky plots, IPCE calculation, and band gap determination. Statistical comparisons were made for ammonia production rates.