Nanostructured Electrodes and Optical Considerations

In early in-situ infrared spectroscopy studies of catalyst supported on reflective Au substrates, it was recognized that spectral bands develop distortions due to anomalous optical effects as the catalyst coverage becomes greater than a few monolayers [17, 18, 158]. Different procedures were adopted to ensure that catalyst coverages on Au remained low [15, 17, 18, 157, 158]. Related to these efforts are experiments that examine the electrochemical and optical properties of nanostructured metal electrodes prepared by chemical, vapor, or electrochemical deposition methods (cf. Refs. [79, 137, 141, 170-179] and references therein). Much of the work in this area has targeted SEIRAS measurements. 

The understanding of factors that lead to enhanced band intensities and dispersive band shapes is of central interest in studies with nanostructured electrodes. Effective medium theory has often been employed to identify mechanisms for enhanced infrared absorption [28, 128, 172, 174, 175]. Osawa and coworkers applied Maxwell-Garnett and Bruggeman effective medium models in early SEIRAS work [28, 128]. Recently, Ross and Aroca overviewed effective medium theory and discussed the advantages and disadvantages of different models for predicting characteristics of SEIRAS spectra [174]. When infrared measurements on nanostructured electrodes are performed by ATR sampling, as is typically the case in SEIRAS experiments, band intensity enhancements occur, but the band shapes are usually not obviously distorted. In contrast, external 

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