Potential-charge curve

Fig. 9. Discharge and charging curves for a sintered iron electrode at a constant current of 0.2 A where the apparent geometrical surface area is 36 cm and porosity is 65%. A and B represent the discharging and charging regions, respectively. Overall electrode reactions, midpoint potentials, and, in parentheses, theoretical potentials at pH 15 ate Al, n-Fe + 2 OH Fe(OH)2 + 2, 0.88 V (1.03 V) B, Fe(OH)2 FeOOH + H+ +, 0.63 V (0.72 V) C,...

Prepare 250 mL of 0.02 M potassium dichromate solution and an equal volume of ca 0.1 M ammonium iron(II) sulphate solution the latter must contain sufficient dilute sulphuric acid to produce a clear solution, and the exact weight of ammonium iron(II) sulphate employed should be noted. Place 25 mL of the ammonium iron(II) sulphate solution in the beaker, add 25 mL of ca 2.5M sulphuric acid and 50 mL of water. Charge the burette with the 0.02 M potassium dichromate solution, and add a capillary extension tube. Use a bright platinum electrode as indicator electrode and an S.C.E. reference electrode. Set the stirrer in motion. Proceed with the titration as directed in Experiment 1. After each addition of the dichromate solution measure the e.m.f. of the cell. Determine the end point (1) from the potential-volume curve and (2) by the derivative method. Calculate the molarity of the ammonium iron(II) sulphate solution, and compare this with the value calculated from the actual weight of solid employed in preparing the solution. 

Figure 6.3. Schematic potential energy curve describing the interactions between colloidal particles. The overall potential is a sum of an electrostatic repulsive term which arises due to any charged groups on the surface of the particle and the attractive van der Waals term.

Figure 5. Effects of an highly polar solvent (e=40) on the potential energy curves describing trans-cis isomerizations at the 2-3 and 3-4 C-C bonds of BMPC when using charge distributions obtained by...

The galvanostatic and potentiodynamic charging curves of platinum electrodes shift approximately 60 mV in the negative direction when the solution pH is raised by 1 unit. This implies that when potentials which refer to the equilibrium potential of a hydrogen electrode in the same solution (RHE) are used, these curves remain practically at the same place within a wide range of solution pH. Hence, we shall use this scale while analyzing these curves. 

As mentioned above, the distribution of the various species in the two adjacent phases changes during a potential sweep which induces the transfer of an ion I across the interface when the potential approaches its standard transfer potential. This flux of charges across the interface leads to a measurable current which is recorded as a function of the applied potential. Such curves are called voltammograms and a typical example for the transfer of pilocarpine [229] is shown in Fig. 6, illustrating that cyclic voltammograms produced by reversible ion transfer reactions are similar to those obtained for electron transfer reactions at a metal-electrolyte solution interface. 

Fig. 1 Illustration of the DLVO theory interaction of two charged particles as a function of the interparticle distance (attractive energy curve, VA, repulsive energy curve, VR and net or total potential energy curve, Vj).

In their work [58], GY demonstrated that a standard Lennard-Jones model grossly over-predicted the well-depth of rare gas-halide ion dimer potential energy curves when they were parametrized to reproduce the neutral rare gas-halide dimer curves. They further showed that the OPNQ model performed just as badly when the charge dependence of the expressions were ignored, but the potential energy curves for both the neutral and ionic dimers could be simultaneously be reproduced if the charge dependence is considered. 

Recent studies of the processes of activation and deactivation111 have shown, as seen in Fig. 20, that the time dependences of the potential, upon the application of current steps, resemble those characteristic of porous film formation and that the differences are of a quantitative nature. The initial part, representing a typical galvanostatic charging curve (with the initial jump due to the... 

The capacitance determined from the initial slopes of the charging curve is about 10/a F/cm2. Taking the dielectric permittivity as 9.0, one could calculate that initially (at the OCP) an oxide layer of the barrier type existed, which was about 0.6 nm thick. A Tafelian dependence of the extrapolated initial potential on current density, with slopes of the order of 700-1000 mV/decade, indicates transport control in the oxide film. The subsequent rise of potential resembles that of barrier-layer formation. Indeed, the inverse field, calculated as the ratio between the change of oxide film thickness (calculated from Faraday s law) and the change of potential, was found to be about 1.3 nm/V, which is in the usual range. The maximum and the subsequent decay to a steady state resemble the behavior associated with pore nucleation and growth. Hence, one could conclude that the same inhomogeneity which leads to pore formation results in the localized attack in halide solutions. 

Fig. 7-7. Potential energy curves for an elementary step of reaction in equilibrium (solid curve) and in nonequilibrium (dashed curve) 4glq = activation energy in equilibrium 4gj s forward activation energy in nonequilibrium p>. , -electrochemical potential of activated partide in equilibrium p = symmetry factor Zi = charge number of reacting partide.

Figure 10.9. Anodic charging curves from 0.4 V during the galvanostatic transients anodic potential sweep at 91 mA/cm in 1N HCIO4 (curve a) and in 1N HCIO4 + HCOOH (curve b). (From Ref. 3, with permission from the Electrochemical Society.)...

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