1：Experimental Design and Method Selection:

The study used a hydrothermal method to synthesize SnO2/NaNbO3 nanocomposites with varying Sn/Nb ratios. The rationale was to explore how different ratios affect humidity-sensing properties. Theoretical models included density functional theory (DFT) for computational analysis of adsorption energies and Nyquist diagrams for sensing mechanisms.

2：Sample Selection and Data Sources:

Samples were prepared with Sn/Nb molar ratios of 1:

3：2,

4：4,

5：6,

6：8, and

1. All reagents were analytical grade from Sinopharm Chemical Reagent Co., Ltd. Data on humidity responses were collected using saturated salt solutions to create different relative humidity levels.

7：All reagents were analytical grade from Sinopharm Chemical Reagent Co., Ltd. Data on humidity responses were collected using saturated salt solutions to create different relative humidity levels. List of Experimental Equipment and Materials:

3. List of Experimental Equipment and Materials: Equipment included a Teflon-lined stainless steel autoclave for hydrothermal synthesis, a muffle furnace for calcination, an X-ray diffractometer (Dandong DX-2700), field-emission scanning electron microscope (Hitachi S-4800) with EDS, and a digital electrical bridge instrument (Mydream Electronic, Model LCR-TH2828). Materials included SnCl4·5H2O, Nb2O5, NaOH, absolute ethanol, deionized water, and various salts for humidity generation.

8：8). Materials included SnCl4·5H2O, Nb2O5, NaOH, absolute ethanol, deionized water, and various salts for humidity generation. Experimental Procedures and Operational Workflow:

4. Experimental Procedures and Operational Workflow: Synthesis involved dissolving reagents, mixing under stirring and sonication, hydrothermal treatment at 180°C for 6h, washing, drying, and calcining at 450°C. Characterization used XRD, SEM, and EDS. Sensors were made by drop-coating slurry onto interdigitated electrodes, drying, and testing impedance at different humidities and frequencies.

9：Data Analysis Methods:

Data were analyzed using impedance measurements, response calculations (S = |ZRH11|/|ZRHy|), and computational methods like DFT with CASTEP code for adsorption energies. Statistical analysis included linear fitting for frequency selection and comparison of sensing properties.