Radiochemical Labeling of Methanol Adsorption

Simultaneous measurements of the surface signal and voltammetric current were also conducted in methanol containing solutions (Figs. 25 and 26). In such experiments, C-labeled methanol was added at -0.05 V vs. RHE, when the electrode surface was covered with adsorbed hydrogen. With clean Pt, it is seen that the CO adsorption rate is significantly reduced when the surface is 

Dynamic radiometry results on a Pt/Ru electrode are shown in Fig. 26. There is a clear similarity between the data shown in Figs. 25 and 26, highlighting hysteresis on both the HE and TIE profiles. However, the drop in CO surface coverage and the maximum current on the positive-going scan on Pt/Ru occur at a potential c.a. 0.2 V less positive than on Pt, and the maximum CO coverage at the Pt/Ru electrode is about half of that at the Pt electrode. 

The difference in the potential dependence of CO adsorption on the Pt and Pt/Ru catalysts are caused by either or both of the following two effects  

The values of the rate constants are given in Table 3. Since methanol adsorbs dissociatively only on the Pt atoms present on the alloy surface the difference in the adsorption rates indicates that surface properties of platinum became modified by mthenium. Thus the significant difference in methanol adsorption rates on Pt and Pt/Ru is a clear manifestation of the electronic effect, that is either activation energy for adsorption, and/or the pre-exponential factor became affected by the mthenium modification. 

The increase in the bulk concentration of methanol from 0.01 to 0.1 M (Fig. 30) has a clearly measurable effect on adsorption rates at short times up to 30 min at 0.2 V and 90 min at 0.1 V. Above these time values, adsorption tails at a similar rate, showing a surface state limitation rather than kinetic limitation. 

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