NO electrocatalytic

Fe-polyphthalocyanine [sample No] Electrocatalytic activity y>20 [mV] Dark conductivity ctd [ohm-tcm-1]... 

Other results point to no electrocatalytic increment with amorphous metals. Heusler and Huerta [591] have investigated amorphous Co75B25 and Ni67B33 with respect to corrosion. For the reaction of hydrogen evolution, in the case of the Co alloy, Tafel slopes of 120 mV, along with lower exchange currents for the amorphous material have been reported. Thus, the mechanism is the same as for the crystalline metal. In the case of the Ni alloy, some decrease in the Tafel slope has been observed with heat treatment (which promotes crystallization). Similarly, the same Tafel slope of 120 mV and the same exchange current as for pure Fe have been measured with... 

Wagner was first to propose the use of solid electrolytes to measure in situ the thermodynamic activity of oxygen on metal catalysts.17 This led to the technique of solid electrolyte potentiometry.18 Huggins, Mason and Giir were the first to use solid electrolyte cells to carry out electrocatalytic reactions such as NO decomposition.19,20 The use of solid electrolyte cells for chemical cogeneration , that is, for the simultaneous production of electrical power and industrial chemicals, was first demonstrated in 1980.21 The first non-Faradaic enhancement in heterogeneous catalysis was reported in 1981 for the case of ethylene epoxidation on Ag electrodes,2 3 but it was only... 

Table 3.1 lists some of the anodic reactions which have been studied so far in small cogenerative solid oxide fuel cells. A more detailed recent review has been written by Stoukides46 One simple and interesting rule which has emerged from these studies is that the selection of the anodic electrocatalyst for a selective electrocatalytic oxidation can be based on the heterogeneous catalytic literature for the corresponding selective catalytic oxidation. Thus the selectivity of Pt and Pt-Rh alloy electrocatalysts for the anodic NH3 oxidation to NO turns out to be comparable (>95%) with the... 

Strictly speaking I0 is a measure of the electrocatalytic activity of the tpb for a given electrocatalytic reaction. It expresses the rates of the forward (anodic) and reverse (cathodic) electrocatalytic reaction under consideration, e.g. reaction (4.1), when there is no net current crossing the metal-solid electrolyte or, equivalently, the tpb. In this case the rates of the forward and the reverse reactions are obviously equal. It has been recently shown that, in most cases, as one would intuitively expect, I0 is proportional to the length, tpb, of the tpb.8... 

As shown in Figure 9.31, butane is formed electrocatalytically (Ab t < 1) since no gaseous H2 is supplied, thus Abutis restricted to its electrocatalysis limits (tA negative potential region of electrocatalysis, electrochemically promoted formation of isomerization products continues with large A and p values (Fig. 9.31). 

Electrocatalysis refers to acceleration of a charge transfer reaction and is thus restricted to Faradaic efficiency, A, values between -1 and 1. Electrochemical promotion (NEMCA) refers to electrocatalytically assisted acceleration of a catalytic (no net charge-transfer) reaction, so that the apparent Faradaic efficiency A is not limited between -1 and 1. 

In addition to these different types of alloys, some studies were also devoted to alternatives to platinum as electrocatalysts. Unfortunately, it is clear that even if some catalytic activities were observed, they are far from those obtained with platinum. Nickel tungsten carbides were investigated, but the electrocatalytic activity recorded for methanol oxidation was very low. Tungsten carbide was also considered as a possible alternative owing to its ability to catalyze the electrooxidation of hydrogen. However, it had no activity for the oxidation of methanol and recently some groups showed that a codeposit of Pt and WO3 led to an enhancement of the activity of platinum. ... 

In electrocatalysis, the major subject are redox reactions occurring on inert, nonconsumable electrodes and involving substances dissolved in the electrolyte while there is no stoichiometric involvement of the electrode material. Electrocatalytic processes and phenomena are basically studied in aqueous solutions at temperatures not exceeding 120 to 150°C. Yet electrocatalytic problems sometimes emerge as well in high-temperature systems at interfaces with solid or molten electrolytes. 

Figure 17.6 Redox hydrogel approach to immobilizing multiple layers of a redox enzyme on an electrode, (a) Structure of the polymer, (b) Voltammograms for electrocatalytic O2 reduction by a carbon fiber electrode modified with laccase in the redox hydrogel shown in (a) (long tether) or a version with no spacer atoms in the tether between the backbone and the Os center (short tether). Reprinted with permission fi om Soukharev et al., 2004. Copyright (2004) American Chemical Society.

As the generality of equations of type (5.2.3) should not be exaggerated (e.g. in the presence of strong adsorption, such as in electrocatalytic processes, they are no longer valid), the basic features of electrochemical kinetics will be explained by using the simple electrode reaction... 

Interpreting these results on a detailed molecular basis is difficult because we have at present no direct structural data proving the nature of the split Co(IIl/lI) voltammetry (which seems critical to the electrocatalytic efficacy). Experiments on the dissolved monomeric porphyrin, in CH-C solvent, reveal a strong tendency for association, especially for the tetra(o-aminophenyl)porphyrin. From this observation, we have speculated (3) that the split Co(III/II) wave may represent reactivity of non-associated (dimer ) and associated forms of the cobalt tetra(o-aminophenyl)porphyrins, and that these states play different roles in the dioxygen reduction chemistry. That dimeric cobalt porphyrins in particular can yield more efficient four electron dioxygen reduction pathways is well known (24). Our results suggest that efforts to incorporate more structurally well defined dimeric porphyrins into polymer films may be a worthwhile line of future research. 

There are reports of polymerisation of pyrrole [161, 162] and aniline [163] onto polyacetylene, to give oxygen and water stability [161], although there is some evidence for the polyacetylene acting electrocatalytically, oxidizing the pyrrole with no concomitant polymerisation. 

Re(bpy)(CO)3Cl-modified electrodes has not yet been explained. However, from the cyclic voltammograms of fac-Re(bpy)(CO)3Cl (Fig. 14) and from the intermediate complexes formed by electrolysis in acetonitrile in the presence and absence of C02, two different electrocatalytic pathways (Fig. 15) were suggested144 initial one-electron reduction of the catalyst at ca. -1.5 V versus SCE followed by the reduction of C02 to give CO and C03, and initial two-electron reduction of the catalyst at ca. -1.8 V to give CO with no C03. The electrochemistry of [Re(CO)3(dmbpy)Cl] (dmbpy = 4,4 -dimethyl-2,2 -bipyridine) was investigated145 to obtain mechanistic information on C02 reduction, and the catalytic reac-... 

In view of the conductive and electrocatalytic features of carbon nanotubes (CNTs), AChE and choline oxidases (COx) have been covalently coimmobilized on multiwall carbon nanotubes (MWNTs) for the preparation of an organophosphorus pesticide (OP) biosensor [40, 41], Another OP biosensor has also been constructed by adsorption of AChE on MWNTs modified thick film [8], More recently AChE has been covalently linked with MWNTs doped glutaraldehyde cross-linked chitosan composite film [11], in which biopolymer chitosan provides biocompatible nature to the enzyme and MWNTs improve the conductive nature of chitosan. Even though these enzyme immobilization techniques have been reported in the last three decades, no method can be commonly used for all the enzymes by retaining their complete activity. 

Different results were reported by Sasaki et al. [67], They studied the electrical conductivity and polarization performance of Ln, xSrxMn03 (Ln = Pr, Nd, Sm, and Gd) and found that the influence of the lanthanide ions at the A-site on the electrical conductivity and electrocatalytic activity is not significant. For example, the electrical conductivity was -200 Scm-1 at 1000°C for all Ln07Sr03MnO3 and the polarization performance showed no significant dependence on the kind of lanthanide elements. 

These results therefore indicate that a significant portion (ca. two-thirds) of the C02 formed during the positive-going sweep arises from electrooxidation of benzaldehyde (or possibly other interfacial species) rather than from adsorbed CO. In addition, the SFAIR spectra indicate that the formation of C02 commences only upon CO electrooxidation, and essentially no C02 from a source other than previously adsorbed CO appears until the CO coverage becomes very small (6 < 0.1). Although these results do not rule out the possible role of adsorbed CO as an intermediate in the electrooxidation of solution benzaldehyde to C02, they suggest that the majority of the adsorbate acts as a poison for this process, removal of which is required for initiation of the electrocatalytic pathway. 

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