Pure Ruthenium Electrodes

Figure 4-1 is a voitammogram of ruthenium deposited chemically on a platinum wire, in 3 M sulfuric add. It seems that the deposition was thick enough to cover the surface totally because there are no features of platinTun. Therefore, the voitammogram provides for a pure ruthenium electrode. 

To investigate the electrochemical properties of pure ruthenium also, ruthenium was chemically reduced and deposited as a thick layer on a platinum wire becaiise ruthenixim metal is not commercially available as a wire nor a plate due to its brittleness. A platinum wire (0.1 mm in diameter) was placed in an alkaline 0.05 M ruthenium (IQ) nitrosylnitrate solution containing 1 M hydrazine as a reducing agent and heated up to 60°C. The deposition did not start imtil the heat was applied. After the deposition, the electrode was washed with water and used for the electrochemical measurements. 

One of the drawbacks of DMFCs is the relatively slow rate of the anodic oxidation of methanol even on highly active platinum electrodes. It was shown that the Pt-Ru system is much more catalytically active than pure platinum (pure ruthenium is inert towards this reaction) (-> platinum-ruthenium -> electrocatalysis). The so-called bifunctional mechanism is broadly accepted to describe this synergistic effect, according to which organic species are chemisorbed predominantly on platinum centers while ruthenium centers more readily adsorb species OH, required for the oxidation of the organic intermediates. Usually the composition of such alloys is Pto.sRuo.s and the metal loading is 2-4 mg cm-2. 

It is noteworthy that for both surface coverages twith Ru, Pt(lll)/Ru exhibits features corresponding to CO frequencies near those of pure ruthenium and pure Pt as well. This is not the case for the PtRu (50 50) alloy, which exhibits only one band at frequencies close to those for pure Pt (Figs. 18 and 23). It can be thus stated that opposite to the Pt(lll)/Ru electrode, the behavior of the alloy surface is that of a more homogeneous surface, with respect to the distribution of individual Pt and Ru atoms. 

Figure 3-6 shows that performance equivalent to that obtained on pure hydrogen can be achieved using this approach. It is assumed that this approach would also apply to reformed natural gas that incorporate water gas shift to obtain CO levels of 1% entering the fuel cell. This approach results in a loss of fuel, that should not exceed 4 percent provided the reformed fuel gas can be limited to 1 percent CO(l). Another approach is to develop a CO-tolerant anode catalyst such as the platinum/ruthenium electrodes currently under consideration. Platinum/ruthenium anodes have allowed cells to operate, with a low-level air bleed, for over 3,000 continuous hours on reformate fuel containing 10 ppm CO (27). 

Ion implantation has also been used for the creation of novel catalyticaHy active materials. Ruthenium oxide is used as an electrode for chlorine production because of its superior corrosion resistance. Platinum was implanted in mthenium oxide and the performance of the catalyst tested with respect to the oxidation of formic acid and methanol (fuel ceU reactions) (131). The implantation of platinum produced of which a catalyticaHy active electrode, the performance of which is superior to both pure and smooth platinum. It also has good long-term stabiHty. The most interesting finding, however, is the complete inactivity of the electrode for the methanol oxidation. 

Ruthenium was electrochemically deposited on platinum foil at a potential of 50 mV for 10 s. The cyclic voitammogram of this Pt—Ru electrode in 3 M H2SO4 is shown in Fig. 4—2. The voitammogram shows the hydrogen adsorption-desorption features from 50 mV to 200 mV and the oxidation and reduction current over 300 mV. The voltanunogram seemed stable when the upper limit potential was 800 mV. When the upper limit was higher than 800 mV, the voitammogram became slowly like pure... 

Potential holding measurements were conducted to examine the sustained current. The surface cleaning steps used for pure platinum were not applied on Pt-Ru electrode because the high potential causes the removal of ruthenium. Instead, the potential was stepped to 800 mV for 5 s for cleaning and stepped to the potential to examine the oxidation current... 

The chronoamperometry curves at 500 mV in 3 M sulfuric acid with 1M methanol are shown in Fig. 4-9 and Fig. 4-10 for smooth and high area Pt-Ru electrodes, respectively. Although Pt-Ru electrodes showed less current than the pure platinum at first, they showed much less decay and higher sustained current. Even the electrode with higer coverage of ruthenium (I.IV for 15 s), which showed more than ten fold smaller current than pure platinum at first, gave higher ciirrent after 40s. In the case of... 

Figure 4-11 shows the infiiared spectra for Pt- Ru electrode after Ru was stripped at 1100 mV for 30s. Unlike for pure platinum (See Fig. 3—30), no clear COad was found at any potential except a very blunt peaks around 2070 cm at 400 to 450 mV. CO2 starts to appear at 375 mV. which is not very different from the 400 mV for pure platinum. This suggests that the direct oxidation of methanol to CO2 is not enhanced much. The activity enhancement effect of ruthenium is, therefore, considered mainly as the result of a high COad removal rate. 

The first example addresses ruthenium-modified platinum electrodes, vsdiich show an enhanced electrochemical activity for the oxidation of H2/CO gas mixtures as compared with pure platinum [4, 5]. This makes them interesting electrocatalysts for low-temperature fuel cell applications. Here we discuss the mesoscopic structure of... 

Min et al. [35] experimented on high-catalyst loading with 60% carbon and 40% Teflon backing claimed to be the most efficient electrode for direct methanol/proton exchange membrane fuel cell (PEMFC). The catalysts used were platinum and ruthenium which formed an alloy at an atomic ratio 1 1. The formation of the alloy was seen in XRD as there were no pure metal peaks found. The alloy formation of Pt and Ru promotes oxidation of methanol at lower temperatures. The 60% carbon backing makes it evident that the lower the percentage of carbon increases the efficiency. 

For reasons that are discussed in Section 19.4, the catalyst for the hydrogen electrode in polymer electrolyte membrane fuel cells is a mixed platinum-ruthenium catalyst applied to carbon black, rather than pure platinum. The overall thickness of modern MEA is about 0.5-0.6mm (of which 0.1 mm for the membrane, for each of the two GDLs, and for each of the two active layers). The bipolar plates have a thickness of about 1.5 mm, the channels on both sides having a depth of about 0.5 mm. 

Purely inorganic films on electrode surfaces for electrocatalytic and ion-sensing applications have been produced by the electrochemical precipitation of Prussian Blue (PB) and its ruthenium analog on electrode surfaces. " The nickel analog of PB can be prepared by dissolution of a nickel electrode in the presence of ferricyanide/ ... 

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