1：Experimental Design and Method Selection:

The study focuses on synthesizing dual-halide perovskites MAPb(I1?xBrx)3 via one-pot crystallization and evaluating their photocatalytic hydrogen evolution performance. Methods include material synthesis, stability mapping, characterization (XRD, XPS, SEM, HRTEM, UV-vis, PL), photocatalytic H2 evolution tests, photoelectrochemical measurements, and computational DFT analysis.

2：Sample Selection and Data Sources:

Samples are MAPb(I1?xBrx)3 powders with x = 0, 0.05, 0.10, 0.15, 0.20, synthesized from precursor solutions of PbI2, PbBr2, and MAI in GBL. Data sources include experimental measurements and computational simulations.

3：05, 10, 15, 20, synthesized from precursor solutions of PbI2, PbBr2, and MAI in GBL. Data sources include experimental measurements and computational simulations. List of Experimental Equipment and Materials:

3. List of Experimental Equipment and Materials: Equipment includes Rigaku D/max-2500 VB2+/PC XRD, Thermo ESCALAB250 XPS, Hitachi S-4700 SEM, Hitachi H-9500 HRTEM, Perkin Elmer Lambda 950 UV-vis spectrophotometer, Edinburgh Instruments FS5 spectrofluorometer, CEL-HXF300 Xe lamp, Agilent 7890B GC, ILT 1400-A thermopile sensor, and VASP for DFT. Materials include PbI2, PbBr2, MAI, GBL, diethyl ether, ethyl acetate, HI, HBr, H3PO2, FTO substrates.

4：Experimental Procedures and Operational Workflow:

Synthesis involves dissolving precursors in GBL, heating to 100°C for crystal growth, centrifugation with diethyl ether, and vacuum drying. Photocatalytic tests involve dispersing powder in HI/HBr solution, degassing with N2, irradiating with Xe lamp (λ ≥ 420 nm), and analyzing H2 with GC. Stability tests involve dipping powders in mixed solutions and characterizing with XRD. Photoelectrochemical measurements use a three-electrode system with Pt counter, SCE reference, and FTO working electrode.

5：Data Analysis Methods:

Data analysis includes XRD peak shifting for composition, UV-vis for bandgap (Kubelka-Munk method), PL for charge carrier dynamics, EIS for charge transfer resistance, and DFT for mechanistic insights.