Studying Heterogeneous Catalysis by the Scanning Electrochemical Microscope (SECM): The Reduction of Protons by Methyl Viologen Catalyzed by a Platinum Surface

Abstract

The feedback mode of the scanning electrochemical microscope (SECM) was used for studying a surface-catalyzed electron-transfer reaction. As a model system we examined the reduction of protons by reduced N,N‘-dimethyl-4,4‘-bipyridinum, methyl viologen radical cation, MV+•, catalyzed by a platinum surface. The experimental configuration comprises a biased amalgamated Au ultramicroelectrode (UME) that approaches an unbiased Pt UME substrate of the same radius. MV+• that is electrochemically generated at the amalgamated UME is oxidized at the Pt surface as a result of reducing protons. This novel configuration permits the simultaneous measurement of the catalytic current and the mixed potential (open-circuit potential) attained at the Pt surface. The results are interpreted by an electrochemical model which was previously suggested; however, our approach makes it possible to measure, for the first time, the current−potential relation predicted by the theory. Our results indicate that methyl viologen behaves ...