CO stripping voltammetry

CO Stripping Voltammetry As discussed in the previous section, the chronoamperometric transients can be modeled using the LH mechanism. Using the... 

Figure 6.26. CO stripping voltammetry of UHV sputter-cleaned electrodes in 0.5 M H2S04 on (a) Pt and (b) Ru. Solid curves represent the stripping of CO in the first positive-going sweep dotted lines represent the voltammetric profiles in the absence of CO (adapted from Ref. [153]).

Figure 17 CO stripping voltammetry from Dynamic Monte Carlo simulations, for pure Pt ( Ru = 0), various Pt-Ru alloy surfaces, and pure Ru. Details of the kinetic rate constants can be found in the original publication. CO surface diffusion is very fast, hopping rate D from site to site of 1000s . (Adapted from Ref. [49].)...

Finally, dynamic Monte Carlo simulations are very useful in assessing the overall reactivity of a catalytic surface, which must include the effects of lateral interactions between adsorbates and the mobility of adsorbates on the surface in reaching the active sites. The importance of treating lateral interactions was demonstrated in detailed ab initio-based dynamic Monte Carlo simulations of ethylene hydrogenation on palladium and PdAu alloys. Surface diffusion of CO on PtRu alloy surfaces was shown to be essential to explain the qualititative features of the experimental CO stripping voltammetry. Without adsorbate mobility, these bifunctional surfaces do not show any catalytic enhancement with respect to the pure metals. 

CO oxidation was studied on Ru decorated Au(lll) electrodes in order to clarify the effect caused by the substrate and the electronic modification by nanosized Ru islands.12 l4,16 Since the Au( 111) surface is inactive for CO adsorption or oxidation at potentials lower than l.Oy15 55 56 the reaction on Ru/Au(lll) was limited to the Ru nanoislands themselves. CO stripping voltammetry curves of Ru/Au(l 11) surfaces prepared by electrochemical Ru deposition, obtained after 5-min CO adsorption at -0.25 V and subsequent purging of the solution with argon,12,16 are presented in Fig. 19. 

The CO stripping voltammetry for Ru/Au(l 11) prepared by 3-min spontaneous deposition from 1 mM RuC/3 in 0.1 M HCIO4 is depicted in Fig. 20. The CO stripping is shown as a solid line, whereas the second sweep, which is shown as a dotted line, indicates the complete removal of CO from the solution and represents CV of the Ru/Au(l 11) surface in 0.5 M H2SO4 (see also Fig. la). 

CO stripping voltammetry measurements were performed using Ru/Pt(lll), prepared by spontaneous Ru deposition. A typical CV curve for CO stripping on Ru/Pt(lll), showing a clear split in the... 

CO-stripping voltammetry is also used for the calculation of the true electrode surface area (Figure 21.5). CO adsorption on the electrode was carried out by bubbling CO gas for 2 min at 0.05 V versus RHE. Thereafter, CO was removed from the solution by bubbling nitrogen for 15 min. 

In this section, we discuss anion and OH coadsorption on Pt(l 11) surface to elucidate the effect of competitive adsorption on CO oxidation electrocatalysis. We first perform coadsorption simulations to understand base voltam-mograms, i.e., in the absence of CO oxidation. Next, we show the effect of anions on CO electrooxidation by performing simulations of CO stripping voltammetry, where a monolayer of CO is oxidized by a potential sweep. 

Koper and coworkers have performed KMC simulations to simulate CO stripping voltammetry on PtRu alloy electrodes in the absence of specific anion adsorption [55]. Their results show that for a randomly dispersed alloy of Pt and Ru, their model provides good agreement to experiments of Gas-teiger and coworkers [89]. 

This same procedure was performed for a Pd foil and 1 ML Pd/WC in a 0.05 M H2SO4 environment. The results of this CO stripping voltammetry are shown in Fig. 2.2. The two peaks on the Pd foil CO stripping scan show the CO being oxidized from the steps ( 0.55 V) and terraces ( 0.88 V) of the foil [46]. For the 1 ML PdAVC surface, the oxidation peak starts below the potential at which the Pd foil terrace sites start to oxidize CO. This figure also suggests that using WC as a substrate increases the CO tolerance of the precious metal. 

After 10 h of operation the presenee of Ru islands on Pt inereased the oxidation current density approximately 20-fold in the case of PtRu-53, followed closely by PtRu-35. Combining cyclic voltammetry with surface NMR two COad populations were identified COad close to (or possibly on) Ru sites undergoing fast thermally activated diffusion and COad on Pt characterized by slow diffusion [91]. These two types of COad are responsible for two separate peaks in CO stripping voltammetry, at low ( 0.3 V) and high (above 0.4 V) potentials, respectively. Ru decreases the activation barrier for COad surface diffusion by reducing electron back-donation. 

Figure 11.6. CO stripping voltaimnogram on Pt/C. T = 60 °C 0.5 M H2SO4 scan rate =10 mV [52], (Reprinted from Journal of Eleetroanalytieal Chemistry, 576(2), Sugimoto W, Aoyama K, Kawaguchi T, Murakami Y, Takasu Y, Kinetics of CH3OH oxidation on PtRu/C studied by impedance and CO stripping voltammetry, 215-21, 2005, with permission from...

Sugimoto W, Aoyama K, Kawaguchi T, Murakami Y, Takasu Y. Kinetics of CH3OH oxidation on PtRu/C studied by impedance and CO stripping voltammetry. J Electroanal Chem 2005 576 215-21. 

Effect of upper cycling potential on (a) percentage voltage loss measured at 1 A/cm, and (b) effective platinum surface area (EPSA) loss measured from CO stripping voltammetry, cycled from 0.6 V to varying upper potentials. (Source Jia etal., 2009.)... 

---