Electrochemical potential, analogy

Determining the cell potential requites knowledge of the thermodynamic and transport properties of the system. The analysis of the thermodynamics of electrochemical systems is analogous to that of neutral systems. Eor ionic species, however, the electrochemical potential replaces the chemical potential (1). 

When the electrochemical potential of the electrons in the metal is counted from the point of reference just outside the metal, then at the electrode potential = 0 V it should also be equal to the value of A. At other potentials it wiU be determined by an equation analogous to Eq. (29.5) ... 

An electrochemical analog of digital etching can easily be envisioned, where first some reactant is adsorbed in a surface-limited reaction, and then the potential is switched to one where a product species is produced, stoichiometric in the adsorbate and the substrate. The results of the CdTe etching study described above suggested still another scenario, where no adsorbate is involved, just two electrochemical potentials. Figure 68 is a... 

In analogy with the previous discussion, the adsorption isotherms for both, the pairing ion and the counter ion are obtained from the equilibrium condition for the corresponding electrochemical potentials according to the scheme ... 

Virtually all energy transductions in cells can be traced to this flow of electrons from one molecule to another, in a downhill flow from higher to lower electrochemical potential as such, this is formally analogous to the flow of electrons in a battery-driven electric circuit. All these reactions involving electron flow are oxidation-reduction reactions one reactant is oxidized (loses electrons) as another is reduced (gains electrons). 

The reader should be aware that considerable confusion exists with respect to names and definitions.176 For example, the AGH+ of Eq. 18-8 can also be called the proton electrochemical potential Ap,+, which is analogous to the chemical potential p of an ion (Eq. 6-24) and has units of kj/mol (Eq. 18-10). 

In the cases of the cells 5 and 6 the cell voltage is analogously related to Uion (see Appendix 1), which is determined by the difference in the electrochemical potentials of the mobile ions at... 

To find thermodynamic relationships for charged systems, we just replace chemical potentials in equations for uncharged systems by electrochemical potentials. For example, for equilibrium of a charged particle at a phase boundary, we have, in analogy to Eq. (24) of Chapter 6,... 

It may be added that the terms in parentheses in (4.6.511 represent the tangential component of the gradient in the electrochemical potential, V,p,. The formula that is obtained if this is substituted (but without Du) can also be found in O Brien s work, illustrating again that there is analogy between the theories of different Schools. 

An important subject in this chapter on Electron transfer at electrodes and interfaces is to draw an analogy between electrochemical and interfacial electron transfer between two solid phases. Any theory dealing with electron transfer has a thermodynamic and a kinetic basis. In Section 4.2, it was shown that electrons flow or tunnel in the direction of decreasing electrochemical potential the gradient of the electrochemical potential is the driving force behind a directed flow of electrons,... 

The AGo values can be transformed into the corresponding standard electrochemical potentials, (Eq. 4.1). For instance, thc conversion of PTFE (AGr= —365kJ/mol CF2) into polyyne and HI (reaction (4.11b) in a hypothetical cell with standard hydrogen electrode) would have AGo = —71kJ/mol. The corresponding standard redox potential PTFE/polyyne is Eq = 0.74 V, which is just 0.36 V smaller than the standard potential of PTFE/graphite (Eq = 1V) [3]. Apparently, in terms of the reaction thermodynamics, the electrochemical carbyne should be easily accessible via cathodic reduction of PTFE. Analogously, the oxidation of acetylene (AGr = —209.9 kJ/mol) to polyyne (Eq. 4.11a) corresponds to AGo = 2.1kJ/mol, Ea = -0.02 V. 

In analogy with the Fermi level of electrons in solids (calculated per electron), we introduce the quantity /Vedox, which is defined by the relation Fredox == Iand represents the electrochemical potential of electrons in the solution, per particle. The quantity Fredox is frequently called the Fermi level of electrons in solution. We note that this term (and more so the term Fermi level of... 

Equation (55) also suggests the introduction of the name surface-chemical potential for [i thus underlining the facts that fi enters into the fundamental equation for a surface phase in the same manner as enters into the corresponding equation for a bulk phase and that generally /t. In these respects is analogous to the electrochemical potential. However, the counterpart of Eq. (55) in the thermodynamics of electrochemical systems is the well-known relation... 

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