Metal-electrolyte interface electron transfer

Two charge-transfer semicircles are expected, which correspond to two RC parallel combinations of the doublelayer capacitance and charge-transfer resistance at the electrode-polymer interface and the double-layer capacitance and charge-transfer resistance at the polymer-electrolyte interface. At the metal-polymer interface, electron transfer would occur while at the polymer-electrolyte interface anion transfer is expected. 

Proposed intermediates in the above reaction include atomic hydrogen [27, 28], hydride ions [29, 30], metal hydroxides [31], metaphosphites [32, 33], and excitons [34]. In general, the postulated mechanisms are not supported by direct independent evidence for these intermediates. Some authors [35] maintain that the mechanism is entirely electrochemical (i.e. it is controlled by electron transfer across the metal-electrolyte interface), but others [26] advocate a process involving a surface-catalyzed redox reaction without interfacial electron transfer. 

Chidsey CED (1991) Free energy and temperature dependence of electron transfer at the metal-electrolyte interface. Science 251 919-922... 

Figure 5.2 Tafel plots of In k versus overpotential for a mixed self-assembled monolayer containing HS(CH2)i600C-ferrocene and HS(CH2)isCH3 in 1.0 M HCIO4 at three different temperatures V, 1 °C O/ 25 °C , 47°C. The solid lines are the predictions of the Marcus theory for a standard heterogeneous electron transfer rate constant of 1.25 s-1 at 25 °C, and a reorganization energy of 0.85 eV (= 54.8 kj moh1). Reprinted with permission from C. E. D Chidsey, Free energy and temperature dependence of electron transfer at the metal-electrolyte interface, Science, 251, 919-922 (1991). Copyright (1991) American Association for the Advancement of Science...

Adiabatic Outer-Sphere Electron Transfer Through the Metal-Electrolyte Interface. 

Sections 3.2.1 and 3.2.2 dealt with electrochemical reactions at metal electrodes where metal ions were transferred across the metal-electrolyte interface. Redox couples are characterized by molecules or ions in a solution which can be reduced and oxidized by a pure electron transfer. The corresponding reaction is given by... 

Since the externally applied voltage occurs only across the Helmholtz layer at the metal electrolyte interface, the energy levels on both sides of the interface are shifted against each other as illustrated in Fig. 7.5. Upon cathodic polarization, an electron transfer occurs from the occupied states in the metal where the latter overlap with the... 

If gaseous, electrochemicaUy active components of the measuring environment are not dissolved in the electrode, then the electrode process will consist of the following stages (also shown in Figure 1.18). They are adsorption-desorption of electrochem-icaUy active gaseous components on gas-electrolyte (GE) and gas-metal (GM) interfaces, ionization reaction (with electron transfer) on the metal-electrolyte (ME) and gas-electrolyte interfaces, and mass-transfer processes on all boundaries of three phases (gas-metal, gas-electrolyte, and metal-electrolyte). Furthermore, mass transfer of electrons and holes on the surface electrolyte layer may also occur. It is evident that the quantity of the current in the stationary state is equal to the quantity of the nonmetal component adsorbing on the gas-metal and gas-electrolyte surfaces as a result of ionization of this component on the ME and GE surfaces. 

There is no doubt that the variants described above cannot comprehend aU the possible ways of the reaction zone extension, even for the relatively simple electrode system. It is possible that some of the electrode processes can take place simultaneously on the gas-electrolyte, gas-metal, and metal-electrolyte interfaces. The removal of oxygen in the second variant, for instance, can be represented by the following reactions diffusion of subions along the metal-electrolyte interface, and diffusion of oxygen atoms on the gas-metal interface. Prior to this, the oxidation reaction of subion to atom O should take place with the transfer of electrons into the metal. 

Electrosorption and Electron Transfer Reactions of Some Blood Coagulation Factors at Metal-Electrolyte Interfaces... 

As in the cases of fibrinogen, prothrombin, and thrombin, the cyclic voltammetric results obtained with Factors V and VIII provide evidence for their electron transfer reactions at metal-electrolyte interfaces. There is a significant influence of adsorption involved in these reactions, as can be expected for large organic molecules with a number of different amino acid... 

It is instructive to first examine the historical evolution of this field. Early work in the fifties and sixties undoubtedly was motivated by application possibilities in electronics and came on the heels of discovery of the first transistor. Electron transfer theories were also rapidly evolving during this period, starting from homogeneous systems to heterogeneous metal-electrolyte interfaces leading, in turn, to semiconductor-electrolyte junctions. The 1973 oil embargo... 

Dissolution of an active metal (active dissolution), involves a charge transfer at the metal-electrolyte interface. Soluble ions, either hydrated or complexed, are formed and dissolve into the electrolyte, while the liberated electrons either flow to the cathode or are taken up by an oxidizing agent. 

Electrochemical reactions are heterogeneous chemical reactions in which electrons are exchanged between the electrode and the molecules or ions in the electrolyte. The electrode is metal or other electronic conductive material, while the electrolyte is purely ionic conductor which includes water and nonaqueous solvents and melt or solid electrolytes. In the course of an electrochemical reaction, the electron transfer occurs through the electrode/electrolyte interface. Electrons can be transferred through the interface in both directions. Particle in the electrolyte becomes either reduced when it accepts an electron from the electrode or oxidized when it gives... 

Chidsey, C. E. D. (1991) Free Energy and Temperature Dependence of Electron Transfer at the Metal-Electrolyte Interface, Science 251, 919-922. 

FIGURE 1.12 Schematic of a simple outer-sphere one-electron transfer process at the metal/electrolyte interface. 

The Temperature and Potential Dependence of Electrochemical Reaction Rates, and th Real Form of the Tafel Equation Theoretical Aspects of Semiconductor Electrochemistry Theories for the Metal in the Metal-Electrolyte Interface Theories of Elementary Homogeneous Electron-Transfer Reactions Theory and Applications of Periodic Electrolysis... 

In a PEC, light is incident on the n-type semiconductor/electrolyte junction (photoanode), where light absorption occurs and an electron-hole pair is formed. The pair is separated by the strong electric field found just beneath the semiconductor surface, and the hole is driven towards the interface between semiconductor and electrolyte. Charge transfer to the redox species A contained in the electrolyte results in the oxidation to Conversely, the electron is driven to the metal/electrolyte interface (counter electrode), where the redox species is reduced. No net chenaical work is done and we can extract the energy as a current from the cell. 

It is thus clear from the previous discussion that the absolute electrode potential is not a property of the electrode material (as it does not depend on electrode material) but is a property of the solid electrolyte and of the gas composition. To the extent that equilibrium is established at the metal-solid electrolyte interface the Fermi levels in the two materials are equal (Fig. 7.10) and thus eU 2 (abs) also expresses the energy of transfering an electron from the Fermi level of the YSZ solid electrolyte, in equilibrium with po2=l atm, to a point outside the electrolyte surface. It thus also expresses the energy of solvation of an electron from vacuum to the Fermi level of the solid electrolyte. 

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