Tin on platinum

Fig. 4.1. Current and mass signal during an on-line mass spectroscopic experiment showing the effect of adsorbed tin on platinum upon methanol electrooxidation. 1 M CH3OH/0.5 M H2S04 sweep rate 10 mV/s, 24 °C.

Fig. 4.3. Cyclic voltammogram for adsorbed tin on platinum, v = 10 mV/s. Experimental procedure 11 min. adsorption from a 4 x 10-4 M Sn(S04)2 solution in 0.5 M H2S04 at 0.5 V followed by electrolyte replacement with pure supporting electrolyte.

Ruthenium on platinum was found to promote the oxidation of AoCOad while tin on platinum was found effective for eoCOad. Enhancement of the methanol oxidation to CO2 was confirmed on platiniua with either rutheniiim or tin. Molybdates on platinum was also found to promote the oxidation of botheoCOad ai d methanol. 

In contrast to the above systems, where electronic support interactions were negligible, the work of Bowles and Cranshaw 198) points to the presence of such effects for tin on platinum. Tin was deposited on platinum electrodes at a potential high enough to ensure a fractional tin monolayer. Subsequent 119Sn Mossbauer spectroscopy showed a tin isomer shift characteristic of a Pt-Sn alloy, thereby evidencing the electronic interaction between these two metals. The possible modification by the support of the... 

Surface alloys obtained depositing tin on platinum surfaces... 

Bittins-Cattaneo B, Iwasita T (1987) Electrocatalysis of methanol oxidation by adsorbed tin on platinum. J Electroanal Chem Interfacial Electrochem 238 151-161... 

Nickel on nickel Gold on gold Platinum on platinum Copper on copper Indium on indium Lead on lead Aluminium on aluminium Silver on silver Iron on iron Tin on tin Steel on tin alloy Steel on steel Steel on Pb alloy Steel on Al. bronze Steel on cast iron Steel on brass Steel on bronze Steel on Pb. brass... 

In the presence of tin, the number of active platinum sites seems to be superior compared to catalyst B and thus an increase in the space velocity by a factor of ten does not seem to saturate all the sites. These results show the importance of the role played by tin since platinum loading was the same in both cases. It is reasonable to think that in the case of catalyst B, due to the method of deposition, some aggregates of platinum are formed on the surface of the catalyst. In the presence of tin, a part of the aggregates could disappear and some Pt/Sn alloy particles, better dispersed at the surface, could be formed. 

Adatoms produce a strong change in catalytic properties of the metal on which they are adsorbed. These catalytic effects are highly specific. They depend both on the nature of the metal and on the nature of the adatoms they also depend on the nature of the electrochemical reaction. For instance, tin adatoms on platinum strongly (by more than two orders of magnitude) enhance the rate of anodic methanol oxidation. 

Fig. 4.4. Potential dependence of (a) the coverage degree of platinum by tin and (b) charge transferred during tin adsorption on platinum (according to Eq. 4.1). Tin was adsorbed from Sn(S04)2 ( ) and from SnS04 (O).

The electrolysis of alkyl halides on platinum cathode and tin anode has been mentioned above. A completely different mechanism is associated with alkylation on tin cathodes. Electroreduction of allyl bromide on tin electrodes yields tetraallylstannane (Ca 90%). This is done in acetonitrile solutions with LiClC>4, Et4NBr or BujNBr as electrolyte and followed by CV with Ag/AgBr reference. Yields decrease to 78% in DMF. The proposed mechanism67 in this case is ... 

In this chapter, the effects and roles of secondary materials on platinum were investigated using electrochemically modified electrodes with ruthenimn, tin and molybdates. 

As stated before, the enhancement effects of ruthenium and tin on the catalytic activity for the methanol oxidation are different in their mechanisms, i. e. ruthenium facilitates the oxidation of hoCOad while tin has the same effect on eoCOad One may naturally ask what if both of them are present on platinum. To answer this question, the oxidation of COad and methanol on Pt-Ru-Sn electrode were investigated. 

Ruthenium was first deposited on platinum in the same condition as described in the section for Pt-Ru electrodes. For high area platinum, tin was deposited after washing the electrode with hydrogen-saturated water. For smooth platinum, before that, ruthenium was removed at 1100 mV for 30 s to obtain higher activities as described before. 

Ruthenium on platinum was found to facilitate the oxidation of oCOad but noteoCOad interacting water, appeared to play a role of the oxygen source, replacing Pt-OH. Contrarily, tin and molybdates on platinum showed promoting effects for the oxidation of eoCOad but not AoCOad Redox couples of tin or molybdenum oxides appeared to play a role of a mediator as well as the ox en source. The active potentials were the bwest for molybdates and the second for tin. 

The simultaneous presence of ruthenitun and tin on a platinum electrode was effective for the oxidation of both eoCOad EoCOad-... 

EXAFS experiments of Pt/Si02 and tin-modified platinum catalysts demonstrate that Sn addition has strong effects on Pt structures. The results obtained from the fit of EXAFS spectra gave us important information on the structures present in... 

On Pt-Sn, assuming that ethanol adsorbs only on platinum sites, the first step can be the same as for platinum alone. However, as was shown by SNIFTIRS experiments [37], the dissociative adsorption of ethanol on a PtSn catalyst to form adsorbed CO species takes place at lower potentials than on a Pt catalyst, between 0.1 and 0.3 V vs RHE, whereas on a Pt catalyst the dissociative adsorption of ethanol takes place at potentials between 0.3 and 0.4 V vs RHE. Hence it can be stated that the same reactions occur at lower potentials and with relatively rapid kinetics. Once intermediate species such as Pt-(COCH3)adsand Pt-(CO)ads are formed, they can be oxidized at potentials close to 0.3 V vs RHE, as confirmed by CO stripping experiments, because OH species are formed on tin at lower potentials [39, 40] ... 

Tin has been electrodeposited from basic and acidic chloroaluminate liquids on platinum, gold, and glassy carbon [53]. On Au the deposition starts in the UPD regime and, from the electrochemical data, one monolayer was reported. Furthermore there seems to be some evidence for alloying between Sn and Au. On glassy carbon three-dimensional growth of Sn occurs. 

To assess the electrochromic response of the bipyridinium dications embedded into multilayers of 7, we envisaged the possibility of assembling these films on optically transparent platinum electrodes.27d f Specifically, we deposited an ultrathin platinum him on an indium-tin oxide substrate and then immersed the resulting assembly into a chloroform/methanol (2 1, v/v) solution of 7. As observed with the gold electrodes (Fig. 7.5), the corresponding cyclic voltammograms show waves for the reversible reduction of the bipyridinium dications with a significant increase in 2p with the immersion time. In fact, is 0.8,1.5, and 3.1 nmol/cm2 after immersion times of 1, 6, and 72 h, respectively. Furthermore, the correlation between ip and v is linear after 1 h and deviates from linearity after 6 and 72 h. Thus, the bisthiol 7 can indeed form multiple electroactive layers also on platinum substrates. 

Rotating optically semii-transparent electrodes for spectroelectro-chemical or photoelectrochemical studies can be fabricated by vapour deposition techniques on a quartz substrate. In this way, tin oxide, platinum and gold electrodes, amongst others, can be made. Electrical contact is with silver paint. 

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