Single zero charge, potential

The first attempt to determine zero charge potential for single-crystal sp metal was described for zinc [3, 6] from C-E capacitance curves in dilute solutions. Epzc for the face of Zn(OOOl) was about 80 mV more positive than that for Zn(lOlO). Later, it was pointed out [6, 10] that the determination of Epzc directly from C-E dependencies was not possible for zinc because the potential is close to the reversible standard potential of zinc in aqueous solution. 

In recent years, similar studies have been carried out for Cd single crystal electrode. Korotkov et al. [3] showed that the zero charge potential ( pzc) of a Cd(1120) in surface inactive electrolytes, NaF and Na2S04, was shifted slightly in the negative direction in comparison with Epzc of pc-Cd. 

Naneva and Popov et al. [4, 5] have studied Cd(OOOl) grown electrolytically in a Teflon capillary in NaF aqueous solution. A value of fpzc equal to —0.99 V (versus saturated calomel electrode (SCE)) was evaluated from minimum potential (Amin) on the differential capacity C-E curves obtained in dilute electrolyte. The zero charge potential was found to be practically independent of the crystallographic orientation. The Apzc and the irmer layer capacity of Cd(OOOl) single crystals were determined in KF solution as a function of temperature [5]. The positive values of AApzc/AT indicated that the water dipoles in the inner part of the double layer were orientated with their negative part to the electrode surface. It was found that the hydrophilicity of the electrodes was increasing in the order Cd(OOOl) < Ag(100)[Pg.768]

The influence of the single crystal face of the Pb electrode on zero charge potential has been analyzed. The difference between these potentials is within the range of 60 mV [8] and the potential value increases with lowering atomic density [11]. The increase of the inner layer capacitance at zero charge in the sequence Pb(lOO) < Pb(llO) < Pb(112) < polycrystalline Pb < Pb(lll) has been explained by increasing hydrophilicity of the surface [6,11]. 

Fig. 11 The dependence of zero-charge potential (PZTC values for Pt metals) on the atomic density for various single-crystal electrodes (metals noted in figure) (updated from Ref [5]).

General trends of zero charge potential behavior for electro-deposited platinum metals were formulated 20 years prior to the period of active thermodynamical studies of single crystalhne surfaces. In what follows we try to catch similarities and disagreements missed or scarcely discussed earlier. 

A possibility to consider polyciystalline platinum surface as some combination of low index surfaces or as some disordered single crystalline surface surely caimot be immediately concluded from the values of zero charge potentials exclusively. Experiments with some intermediate model systems more or less reduceable to simple additive combinations of several planes, or of terraces and steps, are of increasing interest. Microfacetted electrodes, various types of nanoparticles prepared by precise non-electrochemical techniques, non-coalesced electrodeposited particles, " and single platinum microspheres deposited on micro-electrodes, as well as highly ordered templated electrdeposits can be considered as most ordered real platinum materials helpful to discover stractural effects at atomic level. However they all are still too simple to compare with, to say, platinized platinum, and attempts to electrodeposit the dispersed metallic multilayers of more and more ordered type ° are also relevant. 

Reference electrodes of mercury have been used by several investigators in an attempt to measure single electrode potentials. Stastny and Strafelda (5 ) concluded that the zero charge potential of such an electrode in contact with an infinitely dilute aqueous solution is -0.1901V referred to the standard hydrogen electrode. Hall ( ) states that the potential drop across the double layer under these conditions is independent of solution composition when specific adsorption is absent. Daghetti and Trasatti (7, ) have used mercury reference electrodes to study the absolute potential of the fluoride ion-selective electrode and have compared their estimates of ion activities in NaF solutions with those provided by other methods. Their method is based on the assumption that the potential drop across the mercury I solution interface is independent of the electrolyte concentration once the diffuse layer effects are accounted for by the Gouy-Chapman theory. 

Potentials of Zero Charge of Au Single-Crystal Faces in Aqueous... 

Figure 12. (a) Dependence of the potential of zero charge, Eaw0, on the crystallographic orientation for the metals Cu, Ag, and Au, which crystallize in the fee system. From Ref. 32, updated, (b) (pg. 155) Correlation between Eam0 of single-crystal faces of Cu, Ag, and Au, and the density of broken bonds on the surface of fee metals. From Ref. 32, updated. 

CO adsorption on electrochemically facetted (Clavilier), 135 Hamm etal, 134 surfaces (Hamm etal), 134 Platinum group metals in aqueous solutions, 132 and Frumkin s work on the potential of zero charge thereon, 129 Iwasita and Xia, 133 and non-aqueous solutions, 137 potentials of zero charge, 132, 137 preparation of platinum single crystals (Iwasita and Xia), 133 Platinum-DMSO interfaces, double layer structure, 141 Polarization time, 328 Polarons, 310... 

Many studies at single-crystal electrodes of xp-metals were directed at the special features of double-layer stracture and the potential of zero charge at the various single-crystal faces. It was shown that rather large differences could exist between the potentials of zero charge of different faces (see Table 10.1). 

Capacitance as a function of charge was calculated.79 The capacitance curves showed a single hump, near qM = 0, and leveled off for qM about 10 /xC/cm2 on either side of the potential of zero charge, due to the dielectric saturation of the dipole system. The limiting values of the capacitance increased with increasing electron density of the metal. The nonideality of the metal was shown to... 

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