1：Experimental Design and Method Selection:

The study involved fabricating Si nanoconed arrays using electron beam drawing and depositing metallic nanoparticles (Au and Cu) via electrochemical deposition (E.D.) and photodeposition (P.D.) methods. Photoelectrochemical (PEC) measurements were conducted in a three-electrode cell to evaluate CO2 reduction performance.

2：Sample Selection and Data Sources:

p-type Si wafers with single-crystalline direction <100> and 10 Ω?cm-1 conductivity were used. Metallic nanoparticles were deposited from HAuCl4?H2O and CuSO4?H2O solutions. Gaseous products (H2, CO, CH4) were analyzed using gas chromatography.

3：List of Experimental Equipment and Materials:

Equipment included ELS-7500EX (Elionix Inc.) for e-beam drawing, UEP-3000-2C (ULVAC, Inc.) for Cr deposition, FE-SEM (JEOL 6701F), TEM (FEI Tecnai G2 F30), UV-visible spectrophotometer (UV-2500, Shimadzu), XPS (Escalab Mark II), electrochemical workstation (ALS/CH model 660A), gas chromatographs (GC-8A and GC-14B, Shimadzu), and a 300W Xenon lamp. Materials included ZEP-520 A, Espacer 300Z, HAuCl4?H2O, CuSO4?H2O, KHCO3, Nafion 117 membrane, and ultrapure Millipore water.

4：Experimental Procedures and Operational Workflow:

Si nanoconed arrays were fabricated via resist coating, e-beam drawing, development, Cr deposition, and liftoff. Metallic nanoparticles were deposited by E.D. or P.D. PEC measurements were performed in CO2-saturated 0.5 M KHCO3 electrolyte under Xenon lamp irradiation, with product analysis by GC.

5：5 M KHCO3 electrolyte under Xenon lamp irradiation, with product analysis by GC. Data Analysis Methods:

5. Data Analysis Methods: Faradaic efficiency was calculated from charge amounts for H2 and CO production. Photocurrent-potential curves were analyzed, and product distributions were quantified using GC data.