Voltammetric Detection of Singlet Oxygen Enabled by Nanogap Scanning Electrochemical Microscopy

Despite the significance of singlet oxygen (¹O₂) in several biological, chemical, and energy storage systems, its voltammetric reduction at an electrode remains unreported. We address this issue using nanogap scanning electrochemical microscopy (SECM) in substrate-generation/tip-collection mode. Our investigation reveals a reductive process on the SECM tip at -1.0 V (vs Fc⁺/Fc) during the breakdown of the Li₂CO₃ substrate in deuterated acetonitrile. Notably, this value is approximately 0.9 V more positive than the reduction potential of triplet oxygen (³O₂), consistent with thermodynamic estimates for the energy of the formation of ¹O₂. This finding holds significant implications for understanding the reaction mechanisms involving ¹O₂ in nonaqueous media.