Oxygenation electrocatalytic

The influence of the oxide resistivity on oxygen electrocatalytic activity was studied in a series of oxides La. Sr MnOg and LaNi(1 I)MI03 (M = Fe, Co and V) of similar BET surface areas. It was found that ja increased with the degree of Sr substitution and decreased with nickel substitution. 

Oxygen Electrocatalytic Properties Oxygen Reduction. Figure 8 compares steady-state polarization curves for the electroreduction of Op on a typical pyrochlore catalyst, Pb2(Rui.42Pbo.53)06.5 15 w/o platinum on carbon. The latter was considered representative of conventional supported noble metal electrocatalysts. The activities of both catalysts are quite comparable. While the electrodes were not further optimized, their performance was close to the state of the art, considering that currents of 1000 ma/cm could be recorded, at a relatively moderate temperature (75 C) and alkali concentration (3M KOH). Also, the voltages were not corrected for electrolyte resistance. The particle size of the platinum on the carbon support was of the order of 2 nanometers, as measured by transmission electron microscopy. 

Complexities of the Oxygen Electrocatalytic Reaction in Both Directions... 

In acid electrolytes, carbon is a poor electrocatalyst for oxygen evolution at potentials where carbon corrosion occurs. However, in alkaline electrolytes carbon is sufficiently electrocatalytically active for oxygen evolution to occur simultaneously with carbon corrosion at potentials corresponding to charge conditions for a bifunctional air electrode in metal/air batteries. In this situation, oxygen evolution is the dominant anodic reaction, thus complicating the measurement of carbon corrosion. Ross and co-workers [30] developed experimental techniques to overcome this difficulty. Their results with acetylene black in 30 wt% KOH showed that substantial amounts of CO in addition to C02 (carbonate species) and 02, are... 

Carbon shows reasonable electrocatalytic activity for oxygen reduction in alkaline electrolytes, but it is a relatively poor oxygen electrocatalyst in acid electrolytes. A detailed discussion on the mechanism of... 

Beden, B. Electrocatalytic Oxidation of Oxygenated Aliphatic Organic Compounds at Noble Metal Electrodes 22... 

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... 

Electrocatalytic reactions, such as the transformation of O2 from the zirconia lattice to oxygen adsorbed on the film at or near the three-phase-boundaries, which we denote by 0(a), have been found to take place primarily at these three phase boundaries.5 8 This electrocatalytic reaction will be denoted by ... 

Alt H, Binder H, Sandstete G (1973) Mechanism of the electrocatalytic reduction of oxygen on metal chelates. J Catal 28 8-19... 

Behret H, Binder H, Sandstede G (1975) Electrocatalytic oxygen reduction with thiospinels and other sulphides of transition metals. Electrochim Acta 20 111-117... 

A third way to increase both the active surface area and the number of oxygenated species at the electrode surface is to prepare alloy particles or deposits and then to dissolve the non-noble metal component. This technique, which is similar to that used to prepare Raney-type catalysts, yields very high surface area electrodes and hence some improvements in the electrocatalytic activities compared with those of pure platinum. However, it is always difficult to be sure whether the mechanism of enhancment of the activities is due to this effect or the possible presence of remaining traces of the dissolved metal. Results with PtyCr and PtSFe were encouraging, although the effect of iron is still under discussion. From studies in a recent work on the behavior of R-Fe particles for methanol electrooxidation, it was concluded that the electrocatalytic effect is due to the Fe alloyed to platinum. ... 

Beden, C. Lamy, and J.-M. Leger, Electrocatalytic Oxidation of Oxygenated Aliphatic Organic Compounds at Noble Metal Electrodes, in Modem Aspects of Electrochemistry, Vol. 22, Ed. by J. O M. Bockris, B. E. Conway, and R. E. White, Plenum Press, New York, 1992, pp. 97-264. 

The YSZ reactor could be operated catal3rtically or electrocatalytically, depending on the mode of oxygen addition. Oxygen could be supplied either electrochemically by means of the solid electrolyte wall of the reactor (electrocatal3 ic operation) or in the gas phase (catalsdic operation) (Fig. 1). 

In the case of electrocatalytic operation, a galvanostat was used to apply constant currents I between the catalyst and a counter electrode deposited at the outer walls of the YSZ tube. In this way, oxygen is supplied to the Ag-based catalyst at a rate I/2F mol 0/s, where F is Faraday s constant. In this case the catalyst acts as an electrocatalyst [9,12,14]. 

The molecular sieve adsorbent traps ethylene quantitatively, thus practically freezing step 4. Ethane trapping is only partial, thus the desired step 3 is not decelerated significantly. Steps 1,3 and 4 are predominantly catalytic or electrocatalytic, depending on the mode of oxygen addition. 

In the present chapter we want to look at certain electrochemical redox reactions occurring at inert electrodes not involved in the reactions stoichiometrically. The reactions to be considered are the change of charge of ions in an electrolyte solution, the evolution and ionization of hydrogen, oxygen, and chlorine, the oxidation and reduction of organic compounds, and the like. The rates of these reactions, often also their direction, depend on the catalytic properties of the electrode employed (discussed in greater detail in Chapter 28). It is for this reason that these reactions are sometimes called electrocatalytic. For each of the examples, we point out its practical value at present and in the future and provide certain kinetic and mechanistic details. Some catalytic features are also discussed. 

In this section we treat some electrochemical reactions at interfaces with solid electrolytes that have been chosen for both their technological relevance and their scientific relevance. The understanding of the pecularities of these reactions is needed for the technological development of fuel cells and other devices. Investigation of hydrogen or oxygen evolution reactions in some systems is very important to understand deeply complex electrocatalytic reactions, on the one hand, and to develop promising electrocatalysts, on the other. 

The catalytic activity of the N4 complexes depends both on the nature of the central metal ion and on the nature of the ligand and aU substituents. It was found that the metal ion is the active site where the electrocatalytic process is accomplished. During its adsorption, an oxygen molecule forms a stable complex (adduct) with the... 

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