The Oxidation of Adsorbed CO on Pt(100) Electrodes in the Pre-peak Region

Abstract

The oxidation of CO adsorbed on Pt(100) electrodes in the pre-peak region (between 0.30 and 0.60 V) was studied using cyclic voltammetry, currenttime transients and Fourier transform infrared spectroscopy. According to our results, the pre-peak corresponds to the oxidation of a small fraction (<15%) of the CO adlayer, adsorbed on the terraces and adjacent to the step sites, the rate of CO oxidation being limited, within this potential region and at these high CO coverages, by the diffusion of CO to the reactive sites. The picture emerging from the results reported is as follows: the reaction is initiated by a one-dimensional nucleation-and-growth oxidation of CO ads along the steps, immediately followed by surface diffusioncontrolled oxidation of CO ads diffusing from the terraces to the steps and by a two-dimensional nucleation-and-growth process. The analysis of the Tafel slopes, as obtained from cyclic voltammograms at different scan rates and from plots of the logarithm of the current at the maximum, the time at the current maximum and the current at the minimum vs. the potential, suggests that the two-dimensional nucleationand-growth process occurs more slowly than the other two processes. Only the process responsible for the twodimensional nucleation and growth has not been clearly identified, although two possibilities are given.

CO oxidation over supported Pt clusters at different CO coverage

“…The reaction mechanism is always affected by the fluxionality of metal clusters. In the CO oxidation reaction, the reconstruction of catalysts induced by reactant gases (CO on (Pt110) or oxygen on Pt(100) or Pd(110)) and the different adsorbates structures have a strong influence on CO oxidation reaction mechanism . In order to investigate the catalysts structure and CO oxidation reaction mechanism under realistic/industrial conditions, a lot of studies have been performed at the low and high reactant gases coverage .…”

“…In the CO oxidation reaction, the reconstruction of catalysts induced by reactant gases (CO on (Pt110) or oxygen on Pt(100) or Pd(110)) and the different adsorbates structures have a strong influence on CO oxidation reaction mechanism. [19][20][21][22][23][24][25] In order to investigate the catalysts structure and CO oxidation reaction mechanism under realistic/industrial conditions, a lot of studies have been performed at the low and high reactant gases coverage. [19,[26][27][28][29][30] Under high O 2 pressure, for late-transition and noble metal elements such as Rh, Pd, Ag, and PtRh alloy, surface oxides have been proposed as the active phases.…”

Dynamics of Oxidation of Reduced Forms of CO2 under Electrochemical and Open-Сircuit Conditions on Polycrystalline Pt in H2CO3

“…Two oxidation regions are usually considered: the regions of 0.35-0.6 V (R.H.E.) before the oxidation peak [50][51][52][53] and from 0.6 V to higher potentials [54][55][56][57][58]. The authors [57] suggested, on the basis of differential electrochemical mass spectrometry data, that the changes of the Tafel slope at the variation of the scan speed are caused by the changes in the degree of the Pt surface coverage by OH particles and not by different CO oxidation mechanisms.…”

Role of dissolved CO in the solution on the origin of CO pre-oxidation on Pt(1 1 1)-Type electrodes

“…Now we are going to make some considerations about the diffusion of CO on surface during the electro-oxidation of the COads layer. Another way to interpret the influence of potential scan rate on the charge of CO pre-oxidation is to consider the limited surface diffusion of COads from any site on which this species is adsorbed to the reactive sites, as suggested for the electro-oxidation of COads on Pt(100) electrode (in principle with the COfree solution) [18]. For the Pt(111) surface in CO saturated solution at potentials in the preoxidation zone, by in situ high-speed scanning tunneling microscopy technique, diffusion of CO on surface (from any site to the reactive sites) is assigned to dynamics of defects in the COads compressed layer [22].…”

“…Due to its importance in terms of catalysis, many publications address the issue of CO pre-oxidation, in particular on Pt and Pt-based electrodes [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23]. Generally, the divergences that exist on the topic concern the mechanism underlying the CO pre-oxidation phenomenon.…”