1：Experimental Design and Method Selection:

The study uses cyclic voltammetry, potentiostatic and galvanostatic deposition experiments to investigate selenium deposition from selenide and polyselenide solutions at pH 9.2 and temperatures of 25°C and 70°C. Theoretical models include Pourbaix diagrams and formal potentials for redox reactions.

2：2 and temperatures of 25°C and 70°C. Theoretical models include Pourbaix diagrams and formal potentials for redox reactions. Sample Selection and Data Sources:

2. Sample Selection and Data Sources: Solutions were prepared using potassium selenide (K2Se) and polyselenides in carbonate buffer (pH 9.2). Fresh solutions were used for each measurement under oxygen-free conditions.

3：2). Fresh solutions were used for each measurement under oxygen-free conditions. List of Experimental Equipment and Materials:

3. List of Experimental Equipment and Materials: Glassy carbon working electrode (diameter 3 mm), graphite rod counter electrode, saturated calomel reference electrode, Autolab PGSTAT12 potentiostat, PANalytical Empyrean X-ray diffractometer, Zeiss EVO MA10 SEM, Oxford Instruments X-act EDX system, polishing materials (aluminum oxide slurries), chemicals (selenium, KCl, K2CO3, KHCO3), deionized water.

4：Experimental Procedures and Operational Workflow:

Electrodes were polished and sonicated. Cyclic voltammetry was performed with potential sweeps. Deposition experiments were conducted potentiostatically at 0.2 V and galvanostatically with varying current densities. Samples were analyzed using PXRD, SEM, and EDX.

5：2 V and galvanostatically with varying current densities. Samples were analyzed using PXRD, SEM, and EDX. Data Analysis Methods:

5. Data Analysis Methods: Data were analyzed using GPES or NOVA software, WinXPow for PXRD, AzTec for EDX, and OriginLab2017 for figure preparation. Diffusion coefficients were estimated using the Randles-?ev?ík equation.