Electrocatalysis temperature effects

A period of high research activity in electrocatalysis began after it had been shown in 1963 that fundamentally, an electrochemical oxidation of hydrocarbon fuel can be realized at temperatures below 150°C. This work produced a number of important advances. They include the discovery of synergistic effects in platinum-ruthenium catalysts used for the electrochemical oxidation of methanol. 

The bond strength measured or estimated at a constant temperature or at a specified facet of single-crystal planes are, of cause, important factors in the discussion of electrocatalysis. But, if they are obtained under different conditions from the practical ones, the conclusion might not be correct. The author believes that the general understanding on the size effect still needs further experimental and theoretical studies. Particularly careful attention should be paid to the operation temperature, the coagulation of nanoparticles during the experiment, or the territory. Of course, evaluation on the stability of such small particles is essential in the practical application. 

Perhaps the most important advancements in electrocatalysis that contributed mostly to the development of low-temperature fuel-cell technology belong to the domain of practical electrocatalysis and include maximized catalyst dispersion and effective packaging of the required... 

Interesting supports are the polymeric materials, notwithstanding their thermal instability at high temperatures. In the electrocatalysis field, the use of polypyrrole, polythiophene and polyaniline as heteropolyanion supports was reported [2]. The catalytically active species were introduced, in this case, via electrochemical polymerization. Hasik et al. [3] studied the behavior of polyaniline supported tungstophosphoric acid in the isopropanol decomposition reaction. The authors established that a HPA molecular dispersion can be attained via a protonation reaction. The different behavior of the supported catalysts with respect to bulk acid, namely, predominantly redox activity versus acid-base activity, was attributed to that effect. 

Starting point for the emergence of electrocatalysis was the discovery that hydrocarbons could be oxidized at low temperatures (this fact had not been a part of the Ostwald scenario). Then it was discovered that synergistic effects were operative in the use of ruthenium-platinum catalysts for methanol oxidation, and that compounds such as platinum-free metalloporphyrins were useful catalysts for certain electrochemical reactions in fuel cells. Hopes were expressed that in the future expensive platinum catalyst could be replaced. Again, in the attempts of commercial realization of these discoveries considerable difficulties were encountered, which led to a period of disenchantment and pessimism in 1970s and 1980s. It had been demonstrated beyond doubt that, fundamentally, hydrocarbons could be oxidized at low temperatures, but practical rates that could be achieved were unrealistically low. It had also been demonstrated that fuel cells could be made to work without... 

Understanding the nature of the electric field (electrode potential) effects on the electronic structure at the sohd-hquid interface is an outstanding issue in electrocatalysis and in the theory of the electrical double layer. To illustrate such effects via NMR, we show in Fig. 14, the electrode potential-induced C fine shifts for CO (circles) [8] and CN (squares) [6] on polycrystalline Pt. These results were obtained under active external potentiostatic control, and at room temperature, and the inset shows typical C NMR spectra of CN, recorded at... 

Hamta M, Tsubota S Catalysis and electrocatalysis at nanoparticle surfeces. In Andrzej W, Savinova ER, Vayenas Constantino G, editors Effects of size and contact structure of supported noble metal catalysts in low temperature CO oxidation. New York, 2009, Taylor Francis, pp 645-666. 

These preliminary results are a first demonstration that the shape-selected particles concept may work in a realistic fuel cell environment. Future research will focus on degradation and stability tests of the novel materials as well as their application in other fuel cell types, as for instance direct methanol fuel cells and high-temperature pol)uner electrolyte membrane fuel cells. Moreover, the effect of the surfactant requires special attention, as the surfactant molecules may also influence the electrocatalysis by a ligand effect or an ensemble effect directing the adsorption of reactants to specific surface sites. 

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