Hydrogen Adsorption and Evolution on Pt

Hupd were observed in the spectral range above 1000 cm , probably because of the adsorption at hoUow sites on Pt [106, 107] the Pt-H vibrational frequency for hydrogen atoms adsorbed at hoUow sites is known to be located around 550 cm [110]. 

A further conclusive support of the Vohner-Tafel mechanism is given by the log-log plot of the current density of HER (i) versus the band intensity shown in Fig. 8.22 B. The slope of 2 indicates iccff, which is the well-known rate equation of the Tafel step at limiting low 0 (i.e., in the framework of the Langmuir isotherm of adsorption) [103-105]. 

The Tafel plot suggests that the Volmer-Tafel mechanism holds over the potential range examined however, the slope in the semi-log plot of the band intensity deviates from 60 mV/decade at 0.02 V, where the intensity is proportional to (Fig. 8.21 B). The reason for the inconsistency between the SEIRAS 

Because of the great potential of methanol as a fuel for low-temperature fuel cells, the electro-oxidation of methanol on Pt or Pt-based alloy electrodes has been studied extensively in the past decades [112-115]. It is generally accepted that methanol is oxidized to CO2 by the so-called dual-path mechanism [112] via adsorbed CO (poison) and non-CO reactive intermediates. The formation of CO by dehydrogenation of methanol has been well confirmed, but no consensus has been reached so far on the nature of the reactive intermediates in the non-CO pathway. Various adsorbates such as CHxOH [116], -COH [116], formyl (-HCO), [117] carboxy (-COOH) [117], a dimer of formic acid [35], and COO [38] have been claimed to be the reactive intermediates from IRAS and other physicochemical measurements. However, the spectra of the reaction intermediates are not well reproduced by other groups. 

It is well known that formic acid and formaldehyde are formed and dissolved into the solution as by-products in the methanol electro-oxidation [119-121]. SEIRAS studies revealed that both formaldehyde and formic add also provide adsorbed formate on Pt electrodes in their oxidation [32, 33, 122, 123]. To identify the route of formate adsorption, the same experiment was carried out under flow conditions aiming to wash away produced formaldehyde and formic acid from the electrode surface, but no spectral changes were observed. The result suggests that formate is formed directly from methanol on the Pt surface. 

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Gomez R, Femandez-Vega A, Feliu JM, Aldaz A. 1993. Hydrogen evolution on Pt singlecrystal surfaces—Effects of Irreversibly adsorbed bismuth and antimony on hydrogen adsorption and evolution on Pt(lOO). J Phys Chem 97 4769-4776. 

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