Systematic Analysis of False‐Positive CH₄ Production in Photocatalytic CO₂ Reduction: The Role of Solvent and Reagent Decomposition

Photocatalytic carbon dioxide (CO₂) reduction has emerged as a promising strategy for achieving carbon neutrality under mild reaction conditions. While methane (CH₄) is widely regarded as a valuable target product in CO₂ reduction studies, the reliability of such measurements can be compromised by unintended CH₄ generation from solvent or sacrificial reagent decomposition during photoreactions. Herein, we systematically evaluate the stability of seven common solvents and five sacrificial reagents under visible-light irradiation (λ >420 nm) in CO₂-, air-, and N₂-saturated atmosphere, employing three distinct photosensitizers. Notably, acetone, dimethyl sulfoxide (DMSO), and triethylamine (TEA) were identified as high-risk reagents prone to photodecomposition, generating substantial CH₄ yields of up to 2770 μmol ⋅ h^-1 ⋅ L^-1. Isotopic labeling experiments conclusively demonstrated that the source of CH₄ originated from the solvents or sacrificial reagents rather than CO₂. These findings highlight critical pitfalls in experimental design for photocatalytic CO₂ reduction and emphasize the necessity of rigorous reagent screening to avoid artifactual methane production.