Potential of zero charge, PZC

The second terms on the right-hand side of Eqs. (4)-(6), however, are not always negligible. The negative adsorption, i.e., the depletion, of nonsurface active ions is associated with the contribution of the second term, making the value on the left-hand side negative [31]. In this case, the interfacial tension at the potential of zero charge, pzc. 

The other is AG g, at the potential of zero charge (PZC), where no direct electrostatic effect is expected. The former reflects the affinity to the interfacial region when the driving forces toward the interface from W and from O are balanced, notwithstanding that the surface activity at Aq phase-boundary potential as Aq 4>f is usually different from the PZC. AG g, values at the PZC are, however, useful in comparing the intrinsic or chemical surface activities of ionic compounds. 

This is not a useful form since the potential 0(0) cannot be measured. The electrode potential 0 differs from 0(0) by a constant when 0(0) = 0 the electrode carries no charge, and the corresponding electrode potential 0pzc is the potential of zero charge (pzc). So we rewrite Eq. (3.11) in the form ... 

The potential of zero charge (pzc) is a characteristic potential for a given interface, and hence is of obvious interest. In the absence of specific adsorption, it can be measured as the potential at which the Gouy-Chapman capacity obtains its minimum this value must be independent of the electrolyte concentration, otherwise there is specific adsorption. For liquid metals the pzc coincides with the maximum of the surface tension (see Section 3.5). 

The problem of influence of the electric field intensity on the permittivity of solvents has been discussed in many papers. The high permittivity of water results from the intermolecular forces and is a cumulative property. The electric field intensity is the lowest at the potential of zero charge (pzc), thus allowing water molecules to adsorb in clusters. When the electrode is polarized, the associated molecules, linked with hydrogen bonds, can dissociate due to a change in the energy of their interaction with the electrode. Moreover, the orientation of water molecules may also change when the potential is switched from one side of the pzc to the otha. 

For any combination of metal and electrolyte, there is a potential called the potential of zero charge (pzc) where there is no excess charge on the metal. At this potential the nanotubule membranes should show neither cation nor anion permselectivity, and should approach 0 mV. for the tubule-containing membrane does, indeed, go from the ideal cation-... 

Tab. 2 Potentials of zero charge ( pzc) for pc-Au electrode in contact with selected nonaqueous solvent-electrolyte systems. The pzc for pc-Au IH2O is equal to 0.20 V versus aqueous standard hydrogen electrode (SHE) and 0.85 V versus bis(biphenyl)chromium(l)/(0) redox couple (BBCr) [4]...

Tab. 1 Surface density of atonns (<7at) measured at the potentials of zero charge (PZC), and double-layer capacitances of the inner part of the double layer (Q) for different crystal planes of Ag (lattice constant d = 0.2889 nm)...

Tab. 2 Maximum Br coverage and potentials of zero charge (PZC) values of Ag in alcohols with 0.4 M LiBr [67]...

In the absence of specific adsorption and dipolar contributions, there is no excess charge in the whole double layer when positive and negative ions are equally distributed at the plane of closest approach qM and A02 will be both zero. The corresponding electrode potential is the potential of zero charge (pzc) which can be evaluated from the minimum in the differential capacity—potential curve for a metal electrode in contact with a dilute electrolyte [6]... 

The extrapolation from high over potentials to the reversible potential may also be open to question if the potential distribution across the interface strongly depends on the actual electrode potential. This is particularly important close to the potential of zero charge (pzc) and leads to non-linear log j plots as discussed in Sect. 3.5. 

Adsorption of uncharged organic molecules without clear indication of chemical bond formation occurs by replacement of solvent (water) at the interface at potentials close to the potential of zero charge (pzc) because the surface energy of the adsorbate is less than that of the polar solvent (water). At very negative and positive electrode potentials with respect to the pzc, highly polar water molecules are more stable at the interface in the presence of high electric fields. 

This is not unexpected since the potential of zero charge (pzc) correlates almost linearly with the work function [18, 100] which changes for the different crystal faces, leading to different ionic adsorption behaviours for the same metal. 

Taylor et al. conducted DFT simulations using a periodic model of the interface between water and various metal surfaces with an index of (1 1 l).102 The chemistry of water at these charged interfaces was investigated and the parameters relevant to the macroscopic behavior of the interface, such as the capacitance and the potential of zero charge (PZC), were evaluated. They also examined the influence of co-adsorbed CO upon the equilibrium potential for the activation of water on Pt(l 1 1). They found that for copper and platinum there was a potential window over which water is inert. However, on Ni(l 1 1) surface water was always found in some dissociated form (i.e., adsorbed OH or H ). The relaxation of water... 

For ideally polarizable electrodes - since as a whole, the double layer is electrically neutral - the absolute value of the -> surface charge on the metal (opposite charge accumulated at the solution phase near the metal (surface charge density and for the ideally polarizable electrode it is equal to the surface charge density (Q), i.e., electrocapillary measurements. When oM = os = 0, i.e., at the -> potential of zero charge (pzc, Ea = Eq = 0) the - Galvani potential difference between the two phases is due to the orientation of dipoles (e.g., water molecules) [i.v]. 

The concept of the potential of zero charge (PZC or E, has already been discussed in the context of electrocapillary thermodynamics, where we showed that, for an ideally polarizable interphase, the PZC coincides with the electrocapillary maximum. In view of the very high accuracy attainable with the electrocapillary electrometer, it is possible to measure E for liquid metals near room temperature to within about 1 mV. This accuracy is limited, however, to mercury, some dilute amalgams, and gallium. 

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