Polycrystalline Platinum

The activity and selectivity of a Cs unsaturated aldehyde (prenal) has been investigated in gaseous phase on a platinum polycrystalline sample. The aim of this work was the study of the respective effects of the pretreatment of the sample by oxygen and of the presence of a small partial pressure of H2S in the gas phase. The results gave us a better understanding of the surface mechanism and proved the importance of the chemisorption mode of the molecule. 

Figure 11. Infrared reflectance spectra (EMIRS) of the adsorbed species resulting from the chemisorption of methanol on a platinum polycrystalline electrode in acid medium (10 M CH3OH in 0.5 M HCIO4, room temperature).

A study to compare these simulation results [40] with experimentally acquired data has been reported, where the monolayer model A discussed above was applied to the (under potential deposition and) stripping of a monolayer of lithium at platinum polycrystalline and monocrystalline [(100), (110), and (111)] electrodes in tetrahydrofuran [54]. 

Poly crystalline silver layer electrodeposited on a polycrystalline platinum electrode. 

Santos MC, Machado SAS (2004) Microgravimetric, rotating ring-disc and voltammetric studies of the underpotential deposition of selenium on polycrystalline platinum electrodes. J Electroanal Chem 567 203-210... 

It was quickly seen from studies on platinum single crystals that voltammograms for hydrogen adsorption and desorption differ somewhat among the different faces and between the single-crystal faces and polycrystalline platinum. Despite these differences, though, they have common traits as weU. The areas under these curves,... 

Chronoamperometric transients for CO stripping on polycrystalline platinum were measured by McCallum and Fletcher [1977], Love and Lipkowski [1988] were the hrst to present chronoamperometric data for CO stripping on single-crystalline platinum. However, they interpreted their data on the basis of a different model than the one discussed above. Love and Lipkowski considered that the oxidation of the CO adlayer starts at holes or defects in the CO adlayer, where OH adsorbs. These holes act as nucleation centers for the oxidation reaction, and the holes grow as the CO at the perimeter of these holes is oxidized away by OHads- This nucleation and growth (N G) mechanism is fundamentally different from the mean held model presented above, because it does not presume any kind of mixing of CO and OH [Koper et ah, 1998]. Basically, it assumes complete surface immobility of the chemisorbed CO. 

Clavilier J, Parsons R, Durand R, Lamy C, Leger JM. 1981. Formic acid oxidation on single crystal platinum electrodes. Comparison with polycrystalline platinum. J Electroanal... 

Cohen JL, Volpe DJ, Abmna HD. 2007. Electrochemical determination of activation energies for methanol oxidation on polycrystalline platinum in acidic and alkaline electrolytes. Phys Chem Chem Phys 9 49-77. 

Iwasita T, Pastor E. 1994. A DEMS and FTIR spectroscopic investigation of adsorbed ethanol on polycrystalline platinum. Electrochim Acta 39 531 -537. 

Lamy C, Leger JM, Clavilier J. 1982. Structural effects in the electrooxidation of methanol in alkahne medium. Comparison of platinum single crystal and polycrystalline electrodes. J Electroanal Chem 135 321-328. 

Beden B, Juanto S, Leger JM, Lamy C. 1987. Infrared spectroscopy of the methanol adsorbates at a platinum electrode Part III. Structural effects and behaviour of the polycrystalline surface. J Electroanal Chem 238 323-331. 

Lu G-Q, Crown A, Wieckowski A. 1999. Formic acid decomposition on polycrystalline platinum and palladium electrodes. J Phys Chem B 103 9700-9711. 

Okamoto H, Kon W, Mukouyama Y. 2004. Stationary voltammogram for oxidation of formic acid on polycrystalline platinum. J Phys Chem B 108 4432-4438. 

Xia XH, Iwasita T, Ge E, Vielstich W. 1997. Structural effects and reactivity in methanol solution on polycrystalline and single-crystal platinum. Electrochim Acta 41 711-718. 

We used polycrystalline films of ZnO and Sn02 as adsorbents. The films were deposited from the water suspension of respective oxides on quartz substrates. These substrates contained initially sintered contacts made of platinum paste. The gap between contacts was of about lO" cm. All samples were initially heated in air during one hour at T 500 C. We used purified molecular oxygen an acceptor particle gas. H and Zn atoms as well as molecules of CO were used as donor particles. We monitored both the kinetics of the change of ohmic electric conductivity and the tangent of inclination angle of pre-relaxation VAC caused by adsorption of above gases and the dependence of stationary values of characteristics in question as functions of concentrations of active particles. 

More than a decade ago, Hamond and Winograd used XPS for the study of UPD Ag and Cu on polycrystalline platinum electrodes [11,12]. This study revealed a clear correlation between the amount of UPD metal on the electrode surface after emersion and in the electrolyte under controlled potential before emersion. Thereby, it was demonstrated that ex situ measurements on electrode surfaces provide relevant information about the electrochemical interface, (see Section 2.7). In view of the importance of UPD for electrocatalysis and metal deposition [132,133], knowledge of the oxidation state of the adatom in terms of chemical shifts, of the influence of the adatom on local work functions and knowledge of the distribution of electronic states in the valence band is highly desirable. The results of XPS and UPS studies on UPD metal layers will be discussed in the following chapter. Finally the poisoning effect of UPD on the H2 evolution reaction will be briefly mentioned. 

Thermal desorption spectra of carbon monoxide on polycrystalline and on single crystal platinum are well known from experiments in the gas phase [48,49], The system is therefore appropriate to test the experimental setup. 

Muller (ISO) has recently shown that the dehydrocyclization of 2,2,4,4-tetramethylpentane to 1,1,3,3-tetramethylcyclopentane occurs on thick polycrystalline platinum film catalysts with a rate that is comparable to the formation of 1,1,3-trimethylcyclopentane from 1,2,2-trimethyl-pentane. As Muller points out, reactions (10)—(12) cannot occur from 2,2,4,4-tetramethypentane, and it is clear that either these mechanisms are inadequate, or at least there must be an alternative mechanism available. Muller suggests mechanism (14) which requires two adjacent platinum sites. 

Methanol Oxidation at a Smooth Polished Polycrystalline Platinum Electrode d 3.3—The Electrochemical Reduction of CO[sub(2)]... 

Methanol oxidation at a smooth polished polycrystalline platinum electrode... 

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