Charge electrocatalysis

Electrocatalysis Again by definition, an electrocatalyst is a solid, in fact an electrode, which can accelerate a process involving a net charge transfer, such as e.g. the anodic oxidation of H2 or the cathodic reduction of 02 in solid electrolyte cells utilizing YSZ ... 

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. 

Temperature programmed desorption, TPD detection of backspillover species, 228 of oxygen, 228 Thermodynamics of adsorption, 306 of spillover, 104, 499 Three phase boundaries charge transfer at, 114 electrocatalysis at, 115 length, measurement of, 243 normalized length, 243 Time constants ofNEMCA analysis of, 198 and backspillover, 198 prediction of, 200... 

Potentials of Zero Charge of Electrodes Nonequilibrium Fluctuations in the Corrosion Process Electrocatalysis... 

So far, uncatalysed electrochemical processes have had to compete with catalytic organic processes. There is considerable scope for a specific catalyst to be developed for specific organic electrochemical reactions. This implies reduced overpotential and acceleration of slow chemical rather than relatively fast charge-transfer steps (Jansson, 1984). Electrocatalysis... 

Anson FC, Ni CL, Saveant JM. 1985. Electrocatalysis at redox polymer electrodes with separation of the catalytic and charge propagation roles. Reduction of dioxygen to hydrogen peroxide as catalyzed by cobalt(II) tetrakis(4-A-methylpyridyl)porphyrin. J Am Chem Soc 107 3442. 

In recent years, electrochemical charge transfer processes have received considerable theoretical attention at the quantum mechanical level. These quantal treatments are pivotal in understanding underlying processes of technological importance, such as electrode kinetics, electrocatalysis, corrosion, energy transduction, solar energy conversion, and electron transfer in biological systems. 

The lure of new physical phenomena and new patterns of chemical reactivity has driven a tremendous surge in the study of nanoscale materials. This activity spans many areas of chemistry. In the specific field of electrochemistry, much of the activity has focused on several areas (a) electrocatalysis with nanoparticles (NPs) of metals supported on various substrates, for example, fuel-cell catalysts comprising Pt or Ag NPs supported on carbon [1,2], (b) the fundamental electrochemical behavior of NPs of noble metals, for example, quantized double-layer charging of thiol-capped Au NPs [3-5], (c) the electrochemical and photoelectrochemical behavior of semiconductor NPs [4, 6-8], and (d) biosensor applications of nanoparticles [9, 10]. These topics have received much attention, and relatively recent reviews of these areas are cited. Considerably less has been reported on the fundamental electrochemical behavior of electroactive NPs that do not fall within these categories. In particular, work is only beginning in the area of the electrochemistry of discrete, electroactive NPs. That is the topic of this review, which discusses the synthesis, interfacial immobilization and electrochemical behavior of electroactive NPs. The review is not intended to be an exhaustive treatment of the area, but rather to give a flavor of the types of systems that have been examined and the types of phenomena that can influence the electrochemical behavior of electroactive NPs. 

ELASTICITY COEFFICIENT ELECTRIC CHARGE ELECTRIC POTENTIAL ELECTROMOTIVE EORCE ELECTROACTIVE SPECIES ELECTROCATALYSIS Electrocyclic reaction,... 

Several important energy-related applications, including hydrogen production, fuel cells, and CO2 reduction, have thrust electrocatalysis into the forefront of catalysis research recently. Electrocatalysis involves several physiochemical environmental dfects, which poses substantial challenges for the theoreticians. First, there is the electric potential which can aifect the thermodynamics of the system and the kinetics of the electron transfer reactions. The electrolyte, which is usually aqueous, contains water and ions that can interact directly with a surface and charged/polar adsorbates, and indirectly with the charge in the electrode to form the electrochemical double layer, which sets up an electric field at the interface that further affects interfacial reactivity. 

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. 

The chemistry of electrochemical reaction mechanisms is the most hampered and therefore most in need of catalytic acceleration. Therefore, we understand that electrochemical catalysis does not, in principle, differ much fundamentally and mechanistically from chemical catalysis. In addition, apart from the fact that charge-transfer rates and electrosorption equilibria do depend exponentially on electrode potential—a fact that has no comparable counterpart in chemical heterogeneous catalysis—in many cases electrocatalysis and catalysis of electrochemical and chemical oxidation or reduction processes follow very similar if not the same pathways. For instance as electrochemical hydrogen oxidation and generation is coupled to the chemical splitting of the H2 molecule or its formation from adsorbed hydrogen atoms, respectively, electrocatalysts for cathodic hydrogen evolution—... 

Electrocatalysis is, in the majority of cases, due to the chemical catalysis of the chemical steps in an electrochemical multi-electron reaction composed of a sequence of charge transfers and chemical reactions. Two factors determine the effective catalytic activity of a technical electrocatalysts its chemical nature, which decisively determines its absorptive and fundamental catalytic properties and its morphology, which determines mainly its utilization. A third issue of practical importance is long-term stability, for which catalytic properties and utilization must occasionally be sacrificed. 

Amino acid residue models such as a tyrosine residue model (p-cresol) lengthen remarkably the charge hopping distance, a phenomenon which can solve i he problem in the electrocatalysis mentioned in the above item 5) and enhance remarkably the catalytic activity. 

Regarding item 6) above on electrocatalysis, the coexistence of tyrosine residue model, p-cresol (p-Crej, enhanced remarkably the catalytic activity of Ru-red confined in a Nafion membrane coated on an electrode (Fig. 19.3).20) This was attributed to the nearly twofold lengthening of the charge hopping distance by p-cresol from 1.28 nm to 2.25nm). 

The selective facilitation of the charge transfer of the species of interest is called electrocatalysis. In such a case, the species of interest are transformed at energies substantially lower than those of the interferants. The higher selectivity therefore implies a lower applied potential at the modified working electrode, which exhibits such selective electrocatalytic properties. In such a situation, the choice of the... 

Mediated electrocatalysis at a polymer-modified electrode charge and mass transport processes. 

The changes in the potential profile of the interfacial region because specific adsorption do indeed affect the electrode kinetics of charge transfer processes, particularly when these have an inner sphere character [13, 26] (see Fig. 1.12). When this influence leads to an improvement of the current response of these processes, the global effect is called electrocatalysis. ... 

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