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

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The feedback mode of the scanning electrochem. microscope (SECM) was used for studying a surface-catalyzed electron-transfer reaction. As a model system the authors examd. the redn. of protons by reduced N,N'-dimethyl-4,4'-bipyridinium, methylviologen radical cation, MV+•, catalyzed by a platinum surface. The exptl. configuration comprises a biased amalgamated Au ultramicroelectrode (UME) that approaches an unbiased Pt UME substrate of the same radius. MV+• that is electrochem. 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 electrochem. model which was previously suggested; however, the authors' approach makes it possible to measure, for the 1st time, the current-potential relation predicted by the theory. The authors' results indicate that methylviologen behaves reversibly under all the exptl. conditions, and that the rate const. of hydrogen evolution, that is calcd., is in perfect agreement with previous reports. The significant advantages of the authors' approach are discussed as well as its applicability for studying other electrochem. systems. [on SciFinder(R)]


CAPLUS AN 1999:100496(Journal)