Electrocatalysis theory

J. M. Orts, R. G6mez, J. M. Feliii, A. Aldaz, J. Clavilier, International Conference on Progress in Electrocatalysis Theory and Practice, Ferrara (1993), Extended Abstract A8. 

Some pessimism in assessing the situation in the field of electrocatalysis may also derive from the fact that one of the final aims of work in this held, setting up a full theory of electrocatalysis at a quantum-mechanical level while accounhng for all interactions of the reacting species with each other and with the catalyst surface, is still very far from being reahzed. So far we do not even have a semiempirical— if sufficiently general—theory with which we could predict the catalytic activity of various catalysts. 

Electrocatalysis of Oxygen Reduction in Polymer Electrolyte Fuel Cells A Brief History and a Critical Examination of Present Theory and Diagnostics... 

Electrochemical Electron Transfer From Marcus Theory to Electrocatalysis... 

In the electron transfer theories discussed so far, the metal has been treated as a structureless donor or acceptor of electrons—its electronic structure has not been considered. Mathematically, this view is expressed in the wide band approximation, in which A is considered as independent of the electronic energy e. For the. sp-metals, which near the Fermi level have just a wide, stmctureless band composed of. s- and p-states, this approximation is justified. However, these metals are generally bad catalysts for example, the hydrogen oxidation reaction proceeds very slowly on all. sp-metals, but rapidly on transition metals such as platinum and palladium [Trasatti, 1977]. Therefore, a theory of electrocatalysis must abandon the wide band approximation, and take account of the details of the electronic structure of the metal near the Fermi level [Santos and Schmickler, 2007a, b, c Santos and Schmickler, 2006]. 

Electrocatalysis and Catalyst Screening from Density Functional Theory Calculations... 

Koper MTM. 2005. Combining experiment and theory for understanding electrocatalysis. J Electroanal Chem 574 375-386. 

Medvedev IG. 2004. To a theory of electrocatalysis for the hydrogen evolution reaction The hydrogen chemisorption energy on the transition metal alloys within the Anderson-Newns model. Russ J Electrochem 40 1123-1131. 

Koper MTM, van Santen RA, Neurock M. 2003. Theory and modeling of catalytic and electro-catalytic reactions. In Savinova ER, Vayenas CG, Wieckowski A, eds. Catalysis and Electrocatalysis at Nanoparticle Surfaces. New York Marcel Dekker. pp. 1-34. 

This series covers recent advances in electrocatalysis and electrochemistry and depicts prospects for their contribution into the present and future of the industrial world. It illustrates the transition of electrochemical sciences from a solid chapter of physical electrochemistry (covering mainly electron transfer reactions, concepts of electrode potentials and stmcture of the electrical double layer) to the field in which electrochemical reactivity is shown as a unique chapter of heterogeneous catalysis, is supported by high-level theory, connects to other areas of science, and includes focus on electrode surface structure, reaction environment, and interfacial spectroscopy. 

Trasatti, S. (ed.) (2003) Electrocatalysis from theory to industrial applications. Electrochim. Acta, 48, 3727-3974. 

This may be explained by the bifunctional theory of electrocatalysis developed by Watanabe and Motoo [14], according to which Pt activates the dissociative chemisorption of methanol to CO, whereas Ru activates and dissociates water molecules, leading to adsorbed hydroxyl species, OH. A surface oxidation reaction between adsorbed CO and adsorbed OH becomes the rate-determining step. The reaction mechanism can be written as follows [15] ... 

The theory of electrocatalysis is still in its infancy. It was developed first for the hydrogen evolution reaction in the second half of the 1900s. The grounds can be traced back in a seminal paper by Floriuti and Polanyi [25]. Accordingly, for a simple one-electron electrode reaction ... 

A complete theory of electrocatalysis leading to volcano curves has been developed only for the process of hydrogen evolution and can be found in a seminal paper by Parsons in 1958 [26]. The approach has shown that a volcano curve results irrespective of the nature of the rate-determining step, although the slope of the branches of the volcano may depend on the details of the reaction mechanism. 

Trasatti, S. (1999) Interfacial electrochemistry of conductive metal oxides for electrocatalysis, in Interfacial Electrochemistry Theory, Practice, Applications (ed. A. Wieckowski), Marcel Dekker, New York. 

In this paper we report the application of bimetallic catalysts which were prepared by consecutive reduction of a submonolayer of bismuth promoter onto the surface of platinum. The technique of modifying metal surfaces at controlled electrode potential with a monolayer or sub-monolayer of foreign metal ("underpotential" deposition) is widely used in electrocatalysis (77,72). Here we apply the theory of underpotential metal deposition without the use of a potentiostat. The catalyst potential during promotion was controlled by proper selection of the reducing agent (hydrogen), pH and metal ion concentration. 

The development of a consistent theory for a dissociative electron transfer is a recent challenge in the field of theoretical electrocatalysis. Progress in this field of electrochemistry has involved the use of an harmonic Morse curves [25] instead of harmonic approximations. Applying the principles of the theory of the activated complex to adiabatic dissociative electron transfer reactions, the work of Saveant resulted in the following expressions [24] for the Gibbs energy of activation... 

J. Horiuti and M. Polanyi, Acta Physicochem. URSS 2 505 (1935). Fust theory of electrocatalysis. 

The approach to P given above is a simplification, although it does show why the effect of the change in the electrode potential on the charge-transfer rate is less titan that expected if the full potential were applied, an important realization. Another virtue of the early theory is the basis it gives to a theory of electrocatalysis. 

In the case of hydrogen evolution, the theory of electrocatalysis on single individual metals was established about thirty years ago [32, 33]. However, no decisive advances have been made since then from the point of view of the theory of composite materials. It is probably for this reason that a great deal of applied research has been conducted thus far following the always convenient approach of try and see . In one case [34], it has been explicitly reported that more than 400 different materials have been tested in a few years with the purpose of finding the best one. 

Hydrogen evolution is the only reaction for which a complete theory of electrocatalysis has been developed [33]. The reason is that the reaction proceeds through a limited number of steps with possibly only one type of intermediate. The theory predicts that the electrocatalytic activity depends on the heat of adsorption of the intermediate on the electrode surface in a way giving rise to the well known volcano curve. The prediction has been verified experimentally [54] (Fig. 2) and the volcano curve remains the main predictive basis on which the catalytic activity is discussed [41, 55],... 

Some predictions beyond the theory of electrocatalysis for pure metals seem indeed possible. It is, however, necessary to stress again that the applicability of a cathode depends on the impact of many factors, the most outstanding ones being the intrinsic stability and the resistance to poisoning. This is probably still the weak point of cathodes. Their life-time appears to be lower than for anodes, although the deactivation process for cathodes is slower and less abrupt than for anodes. 

Rossmeisl J, Greeley J, Karlberg GS. Electrocatalysis and Catalyst Screening from Density Functional Theory Calculations. In Koper M, editor. Fuel cell catalysis a surface science approach. Hoboken, NJ Wiley-VCH 2009. Chapter 3. 

Koper MTM. Thermodynamic theory of multi-electron transfer reactions Implications for electrocatalysis. J Electroanal Chem 2011 660 254-60. 

Fundamentals of ab initio calculations, including density functional theory (DFT) methods, help to understand several key aspects of fuel cell electrocatalysis at the molecular level. 

In onr gronp we have developed a new approach for electrochemical system, using DFT calcnlations as inpnt in the SKS Hamiltonian developed by Santos, Koper and Schmickler. In the framework of this model electronic interactions with the electrode and with the solvent can be inclnded in a natmal way. Before giving the details of this theory, we review the different phenomena involved in electrochemical reactions in order to nnderstand the mechanism of electrocatalysis and the differences with catalysis in snrface science. Next, a brief snmmary of previous models will be given, and finally the SKS Hamiltonian model will be dis-cnssed. We will show how the different particular approaches can be obtained on the basis of the generalized model. As a first step, idealized semielhptical bands shapes will be considered in order to understand the effect of different parameters on the electrocatalytic properties. Then, real systems will be characterized by means of DFT (Density Fimctional Theory). These calculations will be inserted as input in the SKS Hamiltonian. Applications to cases of practical interest will be examined including the effect not only of the nature of the material but also structural aspects, especially the electrocatalysis with different nanostructures. 

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