1：Experimental Design and Method Selection:

The study involved the design and fabrication of solid state electrolyte type formaldehyde gas sensors using pyrochlore structure Gd2Zr2O7 solid electrolyte and rod-shaped ZnO sensing electrode. The methodology included hydrothermal synthesis followed by high temperature sintering for the preparation of electrolyte materials and sensing electrodes.

2：Sample Selection and Data Sources:

Gd2-xCaxZr2O7 (x = 0, 0.02, 0.05 and 0.1) solid electrolyte materials were prepared. Rod-shaped ZnO sensing material was synthesized via hydrothermal method.

3：02, 05 and 1) solid electrolyte materials were prepared. Rod-shaped ZnO sensing material was synthesized via hydrothermal method. List of Experimental Equipment and Materials:

3. List of Experimental Equipment and Materials: Equipment included X-ray diffractometer (XRD), Raman spectroscopy, impedance analyzer, Field-Emission Scanning Electron Microscopy (FE-SEM), Transmission Electron Microscopy (TEM), and Energy-Dispersive X-ray Spectroscopy (EDS). Materials included Gd(NO3)3·6H2O, Ca(NO3)2·2H2O, ZrOCl2·8H2O, ZnCl2·2H2O, and Na2CO

4：Experimental Procedures and Operational Workflow:

The synthesis of electrolyte materials involved hydrothermal synthesis followed by sintering. The ZnO sensing material was prepared via hydrothermal method and then sintered. Sensors were fabricated by printing Pt paste on electrolyte substrates, attaching ZnO sensing material, and sintering.

5：Data Analysis Methods:

The sensing performance was evaluated using a static test method. Polarization curves were measured to investigate the sensing mechanism.