Adsorption and Electro-Oxidation of CO at Pure Platinum Catalysts

Adsorption and Electro-Oxidation of CO at Pure Platinum Catalysts 

It has been suggested that the first step of reaction (6) may be the formation of a carboxylic species COOHads. Carboxyl radicals have indeed been observed by Zhu et al. for potentials lower than 0.65 V using Fourier Transform infrared Reflectance Absorption Spectroscopy with the Attenuated Total Reflection mode (ATR-FTtR). Moreover Anderson et al. made numerical simulation which indicated that the formation of an adsorbed carboxylic species was energetically more favorable. Here, it has to be noted that the electro-oxidation of CO being a stracture sensitive reaction (sensitive to the superficial stracture symmehy and to the presence of surface defects) this species can be used to study the activity of a catalyst but also as a molecular probe to characterize the catalytic surface.  

Figiwe 2. CO sh ipping voltammograms recorded at a Pt(40 wt%)/C catalyst with a mean size diameter of 2.5 nm, in a 0.5 M H2SO4 deaerated elech olyte. CO was adsorbed at 0.1 V vs. RHE from a CO-saturated electrolyte (v = 20 mV s, T = 20°C). 

The electric current response, in terms of peak position, multiplicity and intensity, of CO stripping voltammograms recorded on supported platinum nanoparticles is heavily discussed in the literature. The electro-oxidation of CO is a complex reaction, as it is evidenced by the multiplicity of the voltammetric oxidation peaks which are recorded in a relatively narrow potential range. This multiplicity of peak was also observed for continuous bulk CO oxidation and studied using electrochemical and UV-visible potential modulated reflectance spectroscopy, and was shown to be dependent on the CO admission potential. For example, the vol-tammogram of CO stripping presented in Fig. 2, recorded at a Pt (40 wt %) /C catalyst prepared via the water in oil method,displays at least three oxidation peaks a prepeak centered close to 0.6 V, a second peak well defined close to 0.755 V and a third one close to 0.820 V vs. RHE. Several models were proposed to explain the multiplicity of peak. 

In 1984, Bilmes et al. attempted to explain on the basis of electrochemical studies the multiplicity of CO oxidation peaks on polycrystalline platinum by a model involving the participation of two different CO adsorbed states. In 1990, Beden et al. studied 

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