Inner electrocatalysis

Since 1976 until present time Toshima-t5q)e nanocolloids always had a major impact on catalysis and electrocatalysis at nanoparticle surfaces [47,210-213,398-407]. The main advantages of these products lie in the efficient control of the inner structure and morphology especially of bimetallic and even multimetallic catalyst systems. 

The concept of electrocatalysis and its relation to chemical surface bonding of reactive intermediates is closely related to that of heterogeneous catalysis. Following the previous section, simple Gibbs energy curves can illustrate the essential ideas of how adsorption of intermediates and their associated Gibbs energy affect the rate of an inner-sphere reaction. 

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. ... 

The rate constants for such outer-sphere reactions can therefore differ markedly from those corresponding to true weak-overlap pathways, even after correction for electrostatic double-layer effects. This can cause some difficulties with the operational definition of inner-sphere electrocatalysis considered above, whereby outer-sphere reactions are regarded as "non-catalytic processes. In addition, there is evidence that inner- rather than outer-sphere pathways can provide the normally preferred pathways at metal-aqueous interfaces for reactants containing hydrophobic functional groups [116]. 

A major application of eqn. (47) is to diagnose the presence of catalytic, presumably inner-sphere, electrochemical pathways. This utilizes the availability of a number of homogeneous redox couples, such as Ru(NH3)e+/2+ and Cr(bipyridine) +,2+ that must react via inner-sphere pathways since they lack the ability to coordinate to other species [5]. Provided that at least one of the electrochemical reactions also occurs via a well-defined outer-sphere pathway, the observation of markedly larger electrochemical rate constants for a reaction other than that expected from eqn. (47) indicates that the latter utilizes a more expeditious pathway. This procedure can be used not only to diagnose the presence of inner-sphere pathways, but also to evaluate the extent of inner-sphere electrocatalysis (Sect. 4.6) it enables reliable estimates to be made of the corresponding outer-sphere rate parameters [12a, 116, 120c]. 

In electrocatalysis, on the other hand, a high reactivity of Ti electrodes is required. This is realized by the deposition of conductive oxides that are not typical passive films [166]. Their lifetime, however, will be limited by passivation of the inner surface Ti/catalytic layer. Therefore, the passivation is avoided as far as possible. 

Zagal, J.H., M.A. Gulppi, C.A. Caro, and I.G. Cardenas-Jiron (1999). Paradoxical effect of the redox potential of adsorbed metaUophthalocyanines on their activity for the oxidation of 2-mercaptoethanol Inner versus outer sphere electrocatalysis. 

Ramaswamy N, Mukerjee S (2011) Influence of inner-and outer-sphere electron transfer mechanisms during electrocatalysis of oxygen reduction in alkaline media. J Phys Chem C 115 18015-18026... 

Bard, A. J. Inner-sphere heterogeneous electrode reactions. Electrocatalysis and photocatalysis The challenge. J Am Chem Soc 2010,132, 7559-7567. 

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