Potential of maximum adsorption

Figure 10.4. Adsorption isotherms for n-decylamine on Ni, Fe, Cu, Pb, and Pt at the potential of maximum adsorption. (From Ref. 5, with permission from the Electrochemical Society.)...

Adsorption of -hexanol on Ag(lOO) and Ag(llO) from aqueous 0.05 M KCIO4 solutions has been studied by Foresti et al. [59], who performed capacitive charge measurements and compared the results with those obtained for Ag(lll). The calculated adsorption free energy (at the potential of maximum adsorption) was = —17.7 kJ mol for Ag(lOO),... 

A simple equation results if we use the BDM isotherm for potentials far removed from the potential of maximum adsorption. In this case the high field aligns all water molecules in one orientation, leading to Z +. The term Za in the exponent of Eq. 27J will be nearly constant and small compared to pF, so that this equation can be simplified to ... 

The corresponding plots of the relative surface excess as a function of potential appear in Fig. 12H. We note that the potential of maximum adsorption (which is usually denoted for simp-... 

This is the BDM isotherm, not taking into account the small shift between the potential of zero charge and the potential of maximum adsorption, which arises from the different chemical energies of interaction of water with the surface in its two allowed orientations. 

In Fig. 49 the band center frequency is plotted against the potential for the 1220-1280 cm mode at both pH values. Potentials in this plot are referred to the normal hydrogen electrode. The wavenumbers for the band centers coincide at both pHs, giving a common slope of 112cm V. Other parameters, such as the halfwidths measured at the potential of maximum adsorption, are also similar (36.5 and 37.5 cm at pH 2.8 and 0.23, respectively). These properties, which are a... 

Figure 45. Coverage as a function of concentration for adsorption of cyclo-hexanol at zinc face curve 1, (0001), curve 2, (lOTO), and curve 3, (1120) at potential of maximum adsorption. " ...

For the (0001) face of zinc, a systematic change of the chain length of the adsorbate was analyzed. For n-propyl, n-butyl, and n-amyl alcohols (in 100 mM KCl + 0.1 mM H2SO4), the coverage varies with the concentration (at potential of maximum adsorption), as shown in Fig. 47. ... 

One of the problems in electrocatalysis is that electrochemical reactions are generally carried out in aqueous or nonaqueous solution. Thus, the solvent may intervene in the over-all reaction. In addition, it is necessary to carry out the reaction under highly purified conditions. Otherwise, impurities in the solution may affect the kinetics of the reaction concerned, so that mechanism studies become difficult. For gas phase reactions, though impurity concentrations are generally lower than in electrochemical reactions, one uses high-vacuum techniques for purification. Electrochemical purification techniques— pre-electrolysis or adsorption of impurities near the potential of maximum adsorption—are often simpler. The activation of a poissoned catalyst is often difficult or impossible. An electrocatalyst can often be reactivated in situ, by pulse techniques (cf. Section VII,D). 

We have studied the effect of bromine substituents on the two-dimensional condensation of C, U, and uridine. The potential of maximum adsorption, and thus the potential of the capacitance pit, depends on the mutual competition between the electrostatic and nonelectrostatic adsorption forces and the forces that repulse the adsorbed molecules from the electrode surface. In neutral bases and nucleosides, the nonelectrostatic adsorption usually prevails and the pit appears near the p.z.c. With C at pH 5.0, the electrostatic adsorption on the negatively charged electrode surface via the positive charge on AI-3... 

We studied the time dependence of the impedance of the electrode double layer around the potentials of the tensammet-ric peaks and around the potential of maximum adsorption of native and denatured calf thymus DNA (100 pg ml in 0.3 M NaCl with 0.05 M Na2HP04, pH 8.6). At potentials of maximum adsorption (around —0.7 V) the differential... 

In practice the potential of maximum adsorption does not coincide with the p.z.c. and a somewhat more complex model should be considered. 

The potential of maximum adsorption may be used as an alternative point of reference for comparison of the specific rate constants of a reaction on different metals. Thus it has been shown above (cf. p. 80) that at this point, equal numbers of water molecules are aligned in the two possible orientations and the net dipole potential contribution due to the aqueous solvent at the interface tends to zero. Theoretical calculationsshow that the potential of maximum adsorption should correspond approximately to the same charge on all metals. Hence the absolute potential drop across the interface is nearly the same for all metals at their respective potential of maximum adsorption, and fco, the chemical part of the electrochemical rate constant, can be conveniently compared using this potential as the point of reference. 

Thus the free energy of adsorption depends on the square of the difference between the electrode potential and the potential of maximum adsorption, 0. (j) is not identical with the potential of zero charge, but it is usually very near it. 

---