Water on platinum

Drop spread from distilled water on platinum sheet and air dried in grease free container at 20°C. 

The following Sections will summarize some recent results on the application of the laser-induced temperature jump method to characterize the net orientation of interfacial water on platinum single-crystal electrodes, under electrochemical conditions. 

H. Yoshida, K. Hirao, J. Nishimoto, K. Shimura, S. Kato, H. Itoh and T. Hattori, 2008, Hydrogen production from methane and water on platinum loaded titanium oxide photocatalysts, J. Phys. Chem. C, 112, 5542-5551. 

Plot the shape of the contact line pinned to a defect using Eq. X-30 for water on polyethylene, stearic acid, and platinum. Assume that the upper cutoff length is 2 mm. How does the shape of the pinned contact line compare with your observations of raindrops on dirty windows ... 

If an appreciable amount of residue remains, note its colour. Add a few drops of water and test the solution (or suspension) with htmus or with Universal indicator paper. Then add a httle dilute hydrochloric acid and observe whether efiervesceiice occurs and the residue dissolves. Apply a flame test with a platinum wire on the hydrochloric acid solution to determine the metal present. (In rare cases, it may be necessary to subject a solution of the residue to the methods of qualitative inorganic analysis to identify the metal or metals present.) If the flame test indicates sodium, repeat the ignition of the substance on platinum foil. 

The electrolytic processes for commercial production of hydrogen peroxide are based on (/) the oxidation of sulfuric acid or sulfates to peroxydisulfuric acid [13445-49-3] (peroxydisulfates) with the formation of hydrogen and (2) the double hydrolysis of the peroxydisulfuric acid (peroxydisulfates) to Caro s acid and then hydrogen peroxide. To avoid electrolysis of water, smooth platinum electrodes are used because of the high oxygen overvoltage. The overall reaction is... 

Electrolysis of acidified water using platinum electrodes is a convenient source of hydrogen (and oxygen) and, on a larger scale, very pure hydrogen (>99.95%) can be obtained from the electrolysis of warm aqueous solutions of barium hydroxide between nickel electrodes. The method is expensive but becomes economical... 

V) is actually required to electrolyze water when platinum electrodes are used. Much contemporary research on electrochemical cells involves attempts to reduce the overpotential and hence to increase the efficiency of electrolytic processes. 

Glassy carbon electrodes polished with alumina and sonicated under clean conditions show activation for the ferrl-/ ferro-cyanlde couple and the oxidation of ascorbic acid. Heterogeneous rate constants for the ferrl-/ ferro-cyanlde couple are dependent on the quality of the water used to prepare the electrolyte solutions. For the highest purity solutions, the rate constants approach those measured on platinum. The linear scan voltammetrlc peak potential for ascorbic acid shifts 390 mV when electrodes are activated. 

Figure 2.20 Nucleate pool boiling of water on a platinum wire at different pressures, data of Addoms, (1948) (a) wire diameter = 0.0241 in. (0.061 cm) (b) wire diameter = 0.048 in. (0.122 cm). (From Mikic and Rohsenow, 1969. Copyright 1969 by American Society of Mechanical Engineers, New York. Reprinted with permission.)...

The mother liquor is evaporated to dryness on the water bath, and the powdered residue is extracted with alcohol in an extraction apparatus. Semicarbazone crystallises out in the flask of the apparatus. If a sample of the main portion of the material leaves a considerable amount of ash when ignited on platinum foil, this portion also should be extracted in the same way. 

Secondly, fp is the probability that the adsorbed methanol follows the CO path. The COad formation reaction does not need an oxygen source in prindple. FTER studies by Weaver however, found no COad on platinum surface in nonaqueous media. Therefore, it is quite reasonable to think that water also plays some roles in the poison formation reaction. Nevertheless since water is one of the two reactants for the complete oxidation path, the importance of water would be probably greater for the complete oxidation path than for the CO path. Therefore, the lack of water would result in depressing the complete oxidation path more than the CO path in concentrated media. Consequently, fp would be larger in concentrated adds. 

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 situation is quite different in the case of an acetic acid-water system. The energy of acetic acid adsorption on platinum is low and therefore the voltammetric curves taken in the absence and in the presence of acetic acid in the supporting electrolyte are nearly the same. However, radiometric data show that C-labeled acetic acid is adsorbed on the electrode surface. Most likely the acetic acid molecules are adsorbed on the top of the water molecules populating the electrode surface. Simultaneously recorded voltammetric and counting rate data are shown in Fig. 8. 

These examples show that adsorption of water molecules on platinum electrodes depends on the solution components. If the energy of the solute adsorption is higher than that of water molecules, water tends to adsorb on the top of the primary solute layer, which is directly bound to the platinum adsorption sites. If the interaction of organic molecules with platinum is weak, water adsorbs directly onto the electrode surface. In the... 

Figure 14. Infrared data summarizing the decomposition of formic acid, methyl formate, ethyl formate, and ethyl acetate on platinum [64]. Panel A in independent experiments, the platinum disk was exposed to formic acid solutions with different concentrations (0.005-20 wt%). For the last experiment (20 wt% formic acid), the CO-adsorbed platinum disk was further flushed by water. Panel B the platinum disk was exposed to methyl formate, ethyl formate, and ethyl acetate, respectively, and the CO-adsorbed platinum disk was rinsed by water to remove the spectroscopic interference from the organics. The positions of CO peaks are in the range of 1950-2100 cm-1. [Reproduced by permission of Springer fromMa, Z. Zaera, F. Catal. Lett. 2004, 96, 5-12.]...

Williams and coworkers preliminarily reported that CO oxidation on Pt/Al203 is faster in the presence of water solvent than in the presence of ethanol [141]. We then studied CO oxidation on platinum surface in the presence of different solvents, and identified obvious solvent effects, namely, CO oxidation takes place the most easily with water solvent, the least easily with carbon tetrachloride solvent, and follows the overall trend of water > ethanol > methanol > cyclohexane > benzene carbon tetrachloride [67]. We subsequently took advantage of the solvent effect to design a diagnosing tool to pin down low-coverage CO at the liquid-solid interface, by flushing the liquid-solid interface with water and carbon tetrachloride individually [67]. 

At potentials higher than 0.6 V vs RHE, the dissociative adsorption of water occurs on platinum, providing -OH adsorbed species, able to oxidize further the adsorption residues of ethanol. Then, oxidation of adsorbed CO species occurs as was shown by FTIR reflectance spectroscopy and CO stripping experiments [36] ... 

The wetting of water on a platinum plate is achieved very satisfactorily by using commercially available plates that are roughened. This property produces almost complete wetting that is, 0 = 0. 

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