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.