Chemisorption effects

While it is related to and sometimes dependent upon chemisorption effects, one pathway for electrode decomposition can be looked upon as a separate type of charge transfer phenomenon. Here, charge transfer generally occurs between species in the semiconductor near the surface and not across the interface to species in the electrolyte. This charge transfer can be highly... 

System 2. The presence of polyvalent lattice ions in the system containing minerals with PDIH+ and OH- leads to their specific adsorption in the EDL and is often accompanied with a change in IP and PZC provided the surface charge has the opposite sign of that of the adsorbing lattice ion. This leads to an inhibition or activation of the mineral surface as shown in Fig. 16179). The same is true for a hydrolytic product of lattice ions exhibiting a stronger surface activity than non-hydrolyzed ions, as a result of a combined electrostatic and chemisorptive effect. 

Electrode potential influences organic adsorption at Pt surfaces from aqueous solutions primarily by bringing to the surface competing adsorbates such as OH or H [61] (Fig. 30) and by oxidation or reduction of the adsorbate. Based upon the limited reliable data available, it appears that these redox and chemisorption effects greatly outweigh the electrostatic effects. 

In the last decade an abundant literature has focused more and more on the properties of low-symmetry systems having large unit cells which render unwieldy the traditional description in terms of the Bloch theorem. Low-symmetry systems include compUcated ternary or quaternary compounds, man-made superlattices, intercalated materials, etc. The k-space picture becomes totally useless for higher degrees of disorder as exhibited by amorphous materials, microcrystallites, random alloys, phonon-induced disorder, surfaces, adsorbed atoms, chemisorption effects, and so on. 

Related to these matters has been the question whether two-component electrode metals (dual-site model) could lead to an electrocatalyst surface that exhibited catalytic properties better than either of its components. Qualitative ideas about electron spillover between one component and another at microcrystal grain boundaries, or transfer of the chemisorbed intermediate from one site to another, could suggest the possibility of such an effect. However, a quantitative theoretical analysis of this question by Parsons (149), based on his treatment of chemisorption effects at single metals (23) having various AG ,, h values, showed that, for practical applications, almost no... 

Oxygen Chemisorption Effects on Graphite Thermoelectric Power, P. L Walker, Jr., L G. Austin, and J. J. Tietjen... 

Reproduced from Chemisorption, D. O. Hayward and B. M. W. Trapnbll, Butterworths, London, 1964. Metals which show slow chemisorption effects after an initial rapid chemisorption are indicated in brackets in the second column. ... 

The aim of mechanistic studies of chemical reactions is to determine reaction pathway(s), identifying if possible the rate-determining step (rds) and the species involved in it. This involves (1) evaluation of the reaction orders of the various participating reactants, taking into account any chemisorption effects when the process is heterogeneous (2) characterization of reaction intermediates and their adsorption behavior, and in addition in the case of electrochemical reactions, double-layer effects ... 

Although as yet there is no direct evidence to support the contention that partial encapsulation of the metal may occur after high temperature reduction, this offers a possible explanation of the observed chemisorption effects. It is perhaps significant that even in the case of Si02-supported Ni there is evidence that OH ions can migrate from the support to the metal and inhibit the adsorption of H2... 

In the case of this concept, too, empirical findings are of greater interest than exact theoretical predictions of catalytic activity. It is particularly useful for explaining many chemisorption effects and for oxidation reactions. 

A strong immobilization of the indicator was observed. It can be attributed to the chemical interactions of functional groups of the dyes with the hydroxy groups of cellulosic support, which govern the chemisorption effect. Calibration curves of two pH optrodes are shown in figure 8. 

In addition to the double layer electrochemical reactions and diffusion effects, specific adsorption (or chemisorption) effects can be present in some systems. Adsorption is a process where species are chemically boimd to the metal surface of an electrode due to their chemical affinity and not to coulom-bic forces based on charge difference or polarity. Adsorption and electrochemical reactions take place on the electrode surface as a Unction of applied DC electrochemical potential and are determined by specific electrochemical properties of participating species. For the overall analyzed system, the voltage difference between two electrodes and the resulting current can be measured with an ordinary voltmeter and amperemeter (Figure 1-5). 

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