Mamo, Tadios TesfayeTadios TesfayeMamoQorbani, MohammadMohammadQorbaniHailemariam, Adane GebresilassieAdane GebresilassieHailemariamRaghunath, PutikamPutikamRaghunathChu, Che‐MenChe‐MenChuYuan, Wen‐HsinWen‐HsinYuanSabbah, AmrAmrSabbahWang, Yen‐YuYen‐YuWangChang, Shuo‐YunShuo‐YunChangLin, Ming‐ChangMing‐ChangLinWoon, Wei‐YenWei‐YenWoonLu, Yu‐JungYu‐JungLuWu, Heng‐LiangHeng‐LiangWuWong, Ken‐TsungKen‐TsungWongChen, Kuei‐HsienKuei‐HsienChenChen, Li‐ChyongLi‐ChyongChen2026-02-102026-02-102026-01-20https://scholars.lib.ntu.edu.tw/handle/123456789/735902Photocatalytic conversion of CO2 into value-added fuels offers a viable approach to combat climate change and address global energy demands. Here, we present a fluorine-doped SnS2 thin film with sulfur vacancy (i.e., SV-SnS2:F), prepared via thermal evaporation, post-sulfurization, and fluorine ion-implantation. Substitution of sulfur with fluorine and sulfur vacancy formation changes the product selectivity from CH4 to CO with about 40-fold enhanced yield and boosted internal quantum efficiency (IQE) of 0.52%. Transient absorption, in situ near-ambient pressure X-ray photoelectron, and in situ Fourier transform infrared spectroscopies, along with first-principles density functional theory calculations, suggest that nearest-neighbor Sn to F serves as an active site and stabilizes the *COOH intermediate. Our findings shed light on how F doping activates the nearby elements and its crucial role in intermediate stabilization toward selectivity change in a heterogeneous photocatalysis process.enin situ FTIRin situ NAP-XPSion implantationphotocatalysisreaction pathwaythin filmjournal article10.1002/advs.202522924