1：Experimental Design and Method Selection:

The study used DC resistance measurements and Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) to investigate the sensing mechanism. Sensors were operated at 300 °C in a background of 50 ppm oxygen in N2, with exposure to different CO concentrations (25, 50, 100, 200, 400 ppm). The approach was inspired by prior work to clarify reception/transduction functions in loaded SMOX.

2：Sample Selection and Data Sources:

Samples included unloaded In2O3 (pure-In2O3), 0.5 at% Rh2O3 loaded In2O3 (0.5Rh-In2O3), and 1.0 at% Rh2O3 loaded In2O3 (1.0Rh-In2O3). The unloaded In2O3 was purchased from Sigma Aldrich, and loaded samples were prepared by stirring In2O3 with RhCl3xH2O in deionized water at pH 1 and 80°C for two hours, followed by drying at 70°C.

3：5 at% Rh2O3 loaded In2O3 (5Rh-In2O3), and 0 at% Rh2O3 loaded In2O3 (0Rh-In2O3). The unloaded In2O3 was purchased from Sigma Aldrich, and loaded samples were prepared by stirring In2O3 with RhCl3xH2O in deionized water at pH 1 and 80°C for two hours, followed by drying at 70°C. List of Experimental Equipment and Materials:

3. List of Experimental Equipment and Materials: Equipment included a Bruker Vertex 80v spectrometer for DRIFTS measurements, alumina substrates for sensor deposition, and materials such as In2O3 powder, RhCl3xH2O, deionized water. Gases used were CO, oxygen, and nitrogen.

4：Experimental Procedures and Operational Workflow:

Powders were deposited onto alumina substrates. DRIFTS and DC resistance measurements were performed simultaneously at 300°C under exposure to CO in nitrogen with 50 ppm oxygen background. Absorbance spectra were calculated as -log(sample spectrum/reference spectrum).

5：Data Analysis Methods:

Data from DC resistance and DRIFTS were analyzed to observe changes in resistance and infrared absorbance bands, with interpretations based on literature for band assignments and mechanisms like Fermi-level pinning.