Space-charge layers chemisorption

This form of an isotherm is characteristic for a chemisorption process on an n-type catalyst forming a boundary layer with a space charge. It is evident that this mechanism is quite different from the mechanism of physical or van der Waals adsorption, which is represented by the Langmuir equation. 

Space Charge Boundary Layers In Electrochemical Equilibrium with the Gas Phase Chemisorption... 

The first stage in chemisorption probably consists in the transfer of electrons either to or from the cations of the lattice, leading to the formation of a charge transfer bond. This bond will be more stable at low than at high temperatures. Secondary effects occur at higher temperatures, such as reaction with the oxygen ions of the lattice or the creation or destruction of lattice vacancies. When the adsorbed gas is an ion, there will be a space charge or barrier layer which will affect the character of the adsorption isotherm, modify the rates of adsorption, and create lattice vacancies. 

The relationship of this type of space charge to that arising in the purely electronic boundary-layer theory of chemisorption is discussed elsewhere (8). 

Figure 4b shows a surface after chemisorption. Chemisorbed atoms or molecules will in general (1) introduce new surface states, (2) change the total chaise of the surface — Q and of the space charge + Q, and (3) add a dipiole layer to the surface. The electron affinity x at the surface and the work function , will be reduced by... 

In this section, we will consider the properties of perhaps the second most well developed of the electrochemical capacitor systems those based on the oxides of the transition and noble metals. In general, a distinction is made between the metal oxide systems and the carbon systems on the basis that the former are redox active materials, i.e., charge is stored by means of changes in the oxidation state of the metal when an ionic species (e.g., a proton) reacts with the surface (or bulk) of the oxide, and the chemisorption is accompanied by the simultaneous injection of an electron into the oxide. The carbon capacitors are supposed to be more purely of the double-layer or space-charge variety. In fact, as was pointed out earlier, the distinction is less clear. In the case of carbon, surface functional groups may be oxidized and reduced in very much the... 

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