Electrodes, bismuth platinum

Anodic stripping voltammetry was in use already in 1972 to determine Bi in plasma [120]. Bismuth is one of the elements most easily determined with this method. It can be deposited on electrodes at potentials at which most other elements ate in solution. Glassy carbon electrodes coated with films of mercury [100,121-124], but also of gold [101,125], are used. As reference served calomel or silver/silver chloride electrodes [121]. Platinum foils or wires were used as counterelectrodes. At -0.7 V carbon electrodes are precoated with mercury from acid Hg(II) or gold from acid Au(III) solutions. To deposit Bi on the electrode -0.2 to -0.3 V is a sufficient potential for preelectrolysis, but mostly higher voltages are chosen to determine other metals as well. Bi is stripped fiom the electrode at potentials of about -0.10 to -0.16 V. Only some elements interfere with Bi, such as arsenic, mercury, copper, and antimony. Copper interferes at high concentrations and is separated by extraction [101]. Arsenic or antimony in urine are oxidized to their pentavalent states [125]. 

Tetrabutylammonium [bismuth(III) bis(phthalocyanine)] undergoes a one-electron oxidation (dichloromethane, U = IV, platinum electrode, several days) to give bismuth bis(phthalocyanine).167... 

Henero E, Femandez-Vega A, Feliu JM, Aldaz A. 1993. Poison formation reaction from formic acid and methanol on platinum (111) electrodes modified by irreversibly adsorbed bismuth and arsenic. J Electroanal Chem 350 73-88. 

Smith PE, Ben-Dor KF, Abruna HD. 2000. Poison formation upon the dissociative adsorption of formic acid on bismuth-modified stepped platinum electrodes. Langmuir 16 787-794. 

Clavilier J, Feliu JM, Aldaz A. 1988. An irreversible structure sensitive adsorption step in bismuth underpotential deposition at platinum electrodes. J Electroanal Chem 243 419-433. 

Polonium may be purified by various processes. Such purification methods include precipitation of polonium as sulfide and then decomposing the sulfide at elevated temperatures spontaneous decomposition of polonium onto a nickel or copper surface and electrolysis of nitric acid solutions of polonium-bismuth mixture. In electrolytic purification polonium is electrodeposited onto a platinum, gold, nickel, or carbon electrode. 

In this paper we report the application of bimetallic catalysts which were prepared by consecutive reduction of a submonolayer of bismuth promoter onto the surface of platinum. The technique of modifying metal surfaces at controlled electrode potential with a monolayer or sub-monolayer of foreign metal ("underpotential" deposition) is widely used in electrocatalysis (77,72). Here we apply the theory of underpotential metal deposition without the use of a potentiostat. The catalyst potential during promotion was controlled by proper selection of the reducing agent (hydrogen), pH and metal ion concentration. 

The three electrodes GECE as working electrode, the Ag/AgCl as reference electrode and the platinum as auxiliary electrode, are immersed in a 25 ml electrochemical cell containing 0.1 M acetate buffer (pH 4.5) and 400 pg/1 of bismuth. During the stripping step, the current is recorded in quiescent solution. 

In our investigation we have used BiOHal electrodes obtained by the exhaustive anodic oxidation of a bismuth layer with a thickness of about 200 nm on a platinum substrate in aqueous solutions of potassium halides (KHal) using the method previously reported in full details [93]. The resulted BiOHal films exhibited porous structure (according to the BET data, the surface area was 47, 25, and 6 m2/g for BiOCl, BiOBr, and... 

Other metals, such as copper, nickel, or silver, have been used as electrode materials in connection with specific applications, such as the detection of amino acids or carbohydrates in alkaline media (copper and nickel) and cyanide or sulfur compounds (silver). Unlike platinum or gold electrodes, these electrodes offer a stable response for carbohydrates at constant potentials, through the formation of high-valence oxyhydroxide species formed in situ on the surface and believed to act as redox mediators (40,41). Bismuth film electrodes (preplated or in situ plated ones) have been shown to be an attractive alternative to mercury films used for stripping voltammetry of trace metals (42,43). Alloy electrodes (e.g., platinum-ruthenium, nickel-titanium) are also being used for addressing adsorption or corrosion effects of one of their components. The bifunctional catalytic mechanism of alloy electrodes (such as Pt-Ru or Pt-Sn ones) has been particularly useful for fuel cell applications (44). 

Although the Bonnemann method is very interesting by allowing to vary and to control easily the composition and the nanostructure of the catalyst and is adapted to the preparation of real fuel cell electrodes, it displays also some limitations. For example, bismuth-containing colloids could not be prepared with the Bonnemann method, and even in presence of platinum salts. Moreover, the presence of bismuth hinders the reduction of platinum salts [59], However, platinum-bismuth is a good catalyst for ethylene glycol electro-oxidation in alkaline medium [59-62], Moreover, colloid of tin alone could not be obtained, and the reaction was only possible by coreduction in the presence of a platinum salt. Then, other colloidal methods should be developed keeping in mind the necessity of a similar flexibility as that of the Bonnemann method. 

This potential, adjusted as a function of the pH of the solution and of the hydrogen pressure, is easily fixed between +0 1 V and — 0.9V/NHE (Normal Hydrogen Electrode). The H2/H+ couple was used to prepare supported catalysts with platinum, palladium, ruthenium, and rhodium modified with deposits of tin, lead, iron, germanium, and bismuth [50-54]. These catalysts were proposed for their good selectivities for different reactions in specialize organic chemistry. 

What, if any, relevance do such results have when predicting the influence of adsorbed bismuth on the CO of supported platinum nanoparticle catalysts In order to test the transferrability of results obtained on single crystals to practical fuel-cell anode catalysts, a series of experiments was performed [77] on a gas diffusion electrode of carbon-supported platinum (0.22 mg cm ) catalyst (Johnson Matthey). Figure 10 shows the results of polarization measurements for hydrogen oxidation at clean and bismuth-modified (0.65-ML) catalysts. In order to establish the CO tolerance of the electrodes, in addition to experiments involving pure H2,... 

This result is consistent with the observed effective poisoning of the CO oxidation reaction as reflected in the increased potential induced by bismuth in the cyclic voltammetry on the supported platinum electrodes (Figure 10a). The voltammetry of CO stripping on the supported catalysts indicates a similar behavior to that found on Pt(llO) in that bismuth results in a higher overpotential for CO oxidation. One must conclude that the morphology of the supported platinum catalyst results in facets more akin to the more open-packed Pt(l 10) surface than the Pt(lll) surface, a conclusion supported by comparison of the bismuth redox chemistry on the supported catalyst and the single-crystal surfaces [77]. 

A mixture of acryrlonitrile (24.8 g) and aqueous solution of 2N K2HPO4 (145 ml) was electrolyzed (0.5 A, 7 h) at 22°C in a divided cell with a bismuth cathode and a platinum anode. During electrolysis, 4.81 g of the anode was consumed. The organic layer of the solution in the anode compartment was separated and cooled to — 10°C, giving tris(2-cyanoethyl)bismuthine as white needles (8.22 g). The yields based on the current and electrode were 50 and 97%, respectively [74EL(10)1424],... 

Lead perchlorate and bismuth nitrate were added to the electrolytic solution at 5 x 10-5 and 10 5 M, respectively, to modify a platinum electrode, which has a real surface area of 40 cm2. The electrolysis cell has two identical compartments separated by an ion-exchange membrane (Nation 423). A Ptgolrio sheet and the Hg/Hg2S04, SOf s i, electrode served as counter and reference electrodes, respectively. 

Different voltammograms were recorded at various concentrations of metal adatoms (lead, bismuth, and thallium) in the presence of 10 mM lactose in 0.1 M Na2C03-NaHC03- Their optimized concentrations gave evidences of the electrocatalytic effect by the ratio / t rvi//pt for the current densities, with and without adatoms, versus electrode potential (Figure 21.22). In fact, the presence of metal adatoms at the platinum surface induces a shift of the lactose oxidation peaks toward lower potential and an increase in the current densities. 

With a different approach, the influence of bismuth on the electrocatalysis of glycerol was also investigated by Koper and co-workers [67]. They observed that a carbon supported platinum electrode in a bismuth-saturated solution is highly selective to the electro-oxidation of the secondary alcohol of the glycerol, leading to 100 % of dihydroxyacetone at a carefully chosen potential. Using a combinatiOTi of online HPLC and in situ FTIR, the authors have shown that bismuth not only blocks the pathway towards the primary alcohol oxidation but also provides a... 

Ding, Y., Liu, J.S., Qin, H.X., Zhu, J.S., and Wang, Y.N. (2001) Why lanthanum-substituted bismuth-titanate becomes fatigue free in a ferroelectric capacitor with platinum electrodes. Appl. Phys. Lett., 78, 4175-4177. 

Precipitation of lead dioxide by anodic deposition on a platinum gauze electrode Is a standard method of separation and determination for lead (H3) In the standard procedure the presence of chloride Ion, mercury, arsenic, tellurium, selenium and phosphorus prevent the complete deposition of lead, while bismuth, tin, antimony, and manganese co-deposit. The use of controlled potential deposition and com-plexlng agents make this separation method much more selective (l4). The eleotroanalytical method has been Important for lead analysis and is discussed In detail In section IV-10,... 

Differences in the reduction potentials for copper, bismuth, lead and cadmium with a dropping mercury electrode has been seen In Figure 12.. Similar differences exist If a platinum electrode Is used providing a suitable depolarizing agent Is employed to prevent excess polarization at the anode. Hydrazine hydrochloride or hydroxylamlne hydrochloride are the usual depolarizers (l4). 

Separation of bismuth and polonium from lead can also be achieved by Immersing a hydrogen soaked platinum electrode In a 0.1 M hydrochloric acid solution of the tracer lead, bismuth and polonium (E6). Nitric acid, bromine or other substances which might poison the platinum electrode for adsorption, of hydrogen must be absent. This has been used for separation of RaD from RaE and RaF (E6)(H5)- This method does not introduce nickel or silver contamination Into the RaD solution or In the RaE or RaP when these are dissolved from the electrode. 

Prom an "old sample" of thorium nitrate (one in which the thorlxim daughters are in equlllbrlxom), 1 gram la weighed out and dissolved in 20 to 25 ml 0-5 N hydrochloric acid. The requisite amount of standard bismuth solution (> 0.2 mg) is pipetted into the electrolysis solution which is heated in a water bath to 80-90°C. Clean platinum electrodes and a calomel half-cell are inserted and the electrolyzing current and a mechanical stirrer are switched on. The current is increased until a potential of 0.25-0.30 volte relative to the saturated calomel electrode is attained and the plating is continued for 25 minutes. 

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