Pd electrode

T.I. Politova, G.G. Gal vita, V.D. Belyaev, and V.A. Sobyanin, Non-Faradaic catalysis the case of CO oxidation over Ag-Pd electrode in a solid oxide electrolyte cell, Catal. Lett. 44, 75-81 (1997). 

Figure 8.17 Activities of Pt(l 1 l)-wML Pd electrodes from rotating disk electrode measurements, with corresponding ball models (a) electro-oxidation of formic acid in 0.1 M HCIO4 ...

When a negative potential (-0.4V) was applied to the PDl-coated Pd electrode, the 1987 cm" band moved to 1983 cm" , while the application of a positive potential (-1-0.4V) shifted the band position to 1991cm" . The v(N=C) of the uncoordinated NC group remained at 2122 cm" as the applied potential was changed. 

In any 3D system the key problem is electroding. Morrison et al. use Pd-acetate to yield metallic Pd electrodes (Fig. 6) [9,10]. Probably the ideal combination at present is to use Pd as the outer electrode (which becomes the bottom electrode on the planar FET) and Ru as the inner (top) electrode. The Ru has better wetting characteristics but decomposes for temperatures much above 400 °C hence it cannot be used as the bottom (outer) electrode for SET, which requires a much higher temperature anneal. Ru can be used as the top electrode on either PZT or SET because the device is not subjected to very high temperatures after the top electrode is put down. 

In a survey dealing with palladium electrode, it is not possible to avoid mentioning the cold fusion controversy, started in 1989, where Pd electrode played and plays a central role. Hundreds of papers relating to palladium electrode are dealing exclusively with cold fusion and related subjects. The status of cold fusion was summarized in [104], recently. 

In [119], the hydrogen adsorption and desorption reactions in thin palladium electrodes were studied using the potential step method in order to analyze the mechanism of phase transformation. Transient current responses were recorded at the onset of the potential step for 47 pm thick Pd electrodes in 1 mol dm H2SO4 at ambient temperature. A model based on a moving boundary mechanism was proposed to account for the experimental i-t curves. It was found that the hydrogen adsorption reaction shows interfacial kinetic limitations and only numerical solutions can be obtained. Such kinetic limitations were not found for the desorption reaction and a semianalytical solution that satisfactorily fits the experimental data was proposed. 

The first systematic study on the oxide growth at Pd electrodes under well-defined potentiostatic conditions was reported in [135]. The impact of temperature variation on the development of Pd surface oxides was investigated in aqueous H2SO4. Various theoretical models were applied in order to elucidate the growth kinetics and mechanism in relation to the experimental conditions. 

For instance, the electrocatalytic reduction of nitrate ions on Pt, Pd, and Pt + Pd electrodes activated with Ge was studied in [142,143]. 

Recently, the electrochemical behavior saturated alcohols, that is, propargyl alcohol (HCSCCH2OH, PA) [145], benzyl alcohol (C6H5CH2OH, BA) [146] andallylalcohol [147], has been studied at Pd electrodes in an acid medium by cyclic voltammetry, chronoamperometry, and on-line mass spectrometry. For BA, it was observed that the fragmentation of the molecules occurs at potentials in the hydrogen ad-sorption/absorption region of palladium, whereas for PA the adsorbates maintain the C3-chain. On the other hand, the yields of the electroreduction and electrooxidation products for both PA and BA differ from those obtained at Pt [146,148,149]. 

The investigation of adsorption phenomena occurring on Pt and Pd electrodes is an important task for the clarification of their behavior in electrocatalytic processes. A characteristic feature for these systems is the hydrogen adsorption reflected by the shape of voltammetric curves taken under suitable conditions. This experimental approach constitutes the intersection point where the problem of perchlorate... 

There was significant interest in zinc UPD, since zinc plays a major role in plating technology. Underpotential deposition of zinc in acidic solutions on polycrystaUine Pt electrode was shown by using cyclic voltammetry [190]. Later, Zn UPD was also demonstrated on Au and Pd electrodes in acidic and alkaline solutions [191, 192]. 

To further investigate the role of palladium nanoparticles in this system, we switched the current between the two electrodes, so that now the Pd electrode was the cathode (Figure 2, right). The rationale behind this experiment was that in theory. 

Similarly, in electrochemical studies of TCE, the reduction on pure Pd electrodes was slower than that on Pd/Fe this was attributed to strong sorption of TCE to Fe, which then allowed reduction by atomic H in the Pd matrix. (Li and Farrell 2000)... 

The catalyst support impacts the rate of a catalyzed reaction, the reaction pathway (quantities and species of intermediates and products) and the resistance of the catalyst to deactivation. In DBCP reactions, powders had higher rate constants than beads, presumably due to reduced mass transfer limitations alumina yielded a faster rate than C, which had a faster rate than PEI/silica. Sorptive capabilities of the supports may also play an important role Kovenklioglu found that supports which sorbed 1,1,2-TCA more strongly had higher reaction rates, and Farrell concluded that TCE sorption to Fe cause higher reaction rates on Pd/Fe electrodes than on pure Pd electrodes. It is also clear that supports influence reaction products, but the correlation between a given support and pathways/products it promotes is not yet understood. The choice of support can also affect its resistance to deactivation this implies that catalyst supports may be tailored to maximize activity over the long term. 

Transverse IEF was also conducted in a pressure-driven flow for BSA and soybean lectin separation on-chip [1040], Here, Pd electrodes were used (in preference to Au) because of the non-gassing character of Pd. In addition, the protein sample was sandwiched between two buffer streams and was prevented from direct contact with the channel wall (and hence the electrode), a process akin to hydrodynamic focusing [1040],... 

Molecular hydrogen (H2 AHDBE, 435 kJ mol-1) is resistant to electrochemical oxidation at inert electrodes (glassy carbon or passivated metals Ni, Au, Hg, Cu). At passivated Pt and Pd dissolved H2 exhibits only broad, diffuse, anodic voltammetric peaks with irreproducible peak currents that are not proportional to the partial pressure of dissolved H2 (PH2). However, with freshly preanodized Pt and Pd electrodes well-defined oxidation peaks for H2 are obtained, which have peak currents that are proportional to P (Figure 8.3).14 The surface... 

The sintered chips are next terminated which involves coating the ends with a paint, in the case of Ag-Pd electroding consisting of a mixture of powdered silver and glass frit, and a suitable organic vehicle, which is fired on at about 800 °C. 

Fig. 12.88. SEM micrograph of Pd electrode electrolyzed for 30 min at overpotential of tj = -0.35 V and temperature of T = 20 °C. Magnification x2500. (Reprinted from Z. Minevski, dissertation, Texas A M University, 1995.)...

A considerable amount of work has been done on the deposition of H2 gas at cathodes and on O2 gas at anodes. The reduction of H+ ions at a metal cathode to form H2 gas is no less complex than the process of catalytic hydrogenation. The current-voltage relation is very sensitive to trace impurities in the solution and also to the metal used and its conditioning. The data obtained with smooth Pt and Pd electrodes has been interpreted as due to a slow recombination of sorbed H atoms, while on Hg the mechanism has been presented as a slow H atom transfer from HaO near the surface to the metal electrode. 

Palladium nanoparticles (nm-Pd) were synthesized by ship-in-a-bottle technique in supercages of NaA zeolite. The behaviors of electrodes of thin film of nm-Pd accommodated in NaA zeolite were characterized by cyclic voltammetry. The results illustrated that the nm-Pd possess particular properties for hydrogen reaction, i.e. in contrast to hydrogen absorption on massive palladium electrode, the surface processes of hydrogen adsorption-desorption become the dominant reaction on electrodes of thin film of nm-Pd. The processes of adsorption and desorption of carbon monoxide on the electrodes were studied using in situ electrochemical FTIR reflection spectroscopy. It has been revealed that in comparison with CO adsorbed on a massive Pd electrode, the IR absorption of CO adsorbed on nm-Pd particles accommodated in NaA zeolite has been enhanced to about 36 times. 

A value of 36 has been calculated using equation (2). The variation of the center of the COb band (vb) versus E for massive Pd electrode and Pd Ec-NaA/GC is plotted in Figure 3a and 3b. Two straight lines can be observed in the case of Pd°Ec-NaA/GC. One is for E below -0.6 V, which yields a Stark shift rate (dva / dE) of 52 cm v. The second linear part is observed in the potential range between -0.6 V to -0.2 V, from which a Stark shift rate of 16 cm v has been evaluated. In comparison with the value of Stark shift rate of 47 cm v on massive Pd electrode, the small values of Stark shift rate in Figure 3 a may be attributed to the structure of Pd nanoparticles and geology in NaA zeolite. 

Figure 13. CV and MSCV plots for benzene chemisorbed on Au(332)-0.14ML-Pd electrodes in 0.1 M H2SO4. Experimental conditions were as in Fig. 12.

Although the data are not shown here, it will be mentioned that the CV and MSCV plots for benzene at Au(l 11)-0.6ML-Pd are not too different from those for Au(332)-0.82ML-Pd. In other words, reactions that occur at terrace sites are similar even if the structures of the underlying substrates are different [i.e., (Ill) vs. (332)]. Any noticeable divergence most likely arises from topographic differences as the smoother Au(lll)-Pd contains more contiguous uniform sites than the more corragated Au(332)-Pd electrode surface. 

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