In operando imaging of self-catalyzed formaldehyde burst in methanol oxidation reactions under open circuit conditions.

We employ a surface plasmon resonance imaging (SPRi) technique to monitor the in operando process of formaldehyde (HCHO) production during methanol oxidation with high spatial and temporal resolutions. While common wisdom suggests HCHO is generated as an intermediate during continuous electron transfer towards CO2 , we find that the majority of HCHO is produced via self-catalyzed chemical and electrochemical reactions under open-circuit conditions, which lead to an unprecedented HCHO burst immediately after withdrawal of external potential. Because open-circuit conditions better represent the operating environments of practical direct methanol fuel cells (DMFCs), this work uncovers a hidden pathway of HCHO accumulation by adopting a quantitative and in operando SPRi technique for the first time. These theoretical and technical advances are anticipated to help the fundamental understanding of the comprehensive mechanism of methanol oxidation with implications for improving the performance of DMFCs.