Anodic half-cell reaction

This section addresses the role of chemical surface bonding in the electrochemical oxidation of carbon monoxide, CO, formic acid, and methanol as examples of the electrocatalytic oxidation of small organics into C02 and water. The (electro)oxidation of these small Cl organic molecules, in particular CO, is one of the most thoroughly researched reactions to date. Especially formic acid and methanol [130,131] have attracted much interest due to their usefulness as fuels in Polymer Electrolyte Membrane direct liquid fuel cells [132] where liquid carbonaceous fuels are fed directly to the anode catalyst and are electrocatalytically oxidized in the anodic half-cell reaction to C02 and water according to... 

The anodic half-cell reaction occurring at the photoanode/ electrolyte interface may be written ... 

In this PEVD system, the source (O) will be a vapor phase, which contains elemental solid-state transported reactant (A), and an anode half-cell reaction... 

Under open circuit conditions, the PEVD system is in equilibrium after an initial charging process. The equilibrium potential profiles inside the solid electrolyte (E) and product (D) are schematically shown in Eigure 4. Because neither ionic nor electronic current flows in any part of the PEVD system, the electrochemical potential of the ionic species (A ) must be constant across both the solid electrolyte (E) and deposit (D). It is equal in both solid phases, according to Eqn. 11, at location (II). The chemical potential of solid-state transported species (A) is fixed at (I) by the equilibrium of the anodic half cell reaction Eqn. 6 and at (III) by the cathodic half cell reaction Eqn. 8. Since (D) is a mixed conductor with non-negligible electroific conductivity, the electrochemical potential of an electron (which is related to the Eermi level, Ep) should be constant in (D) at the equilibrium condition. The transport of reactant... 

Following the procedure described previously (using ideal gas as secondary reference state for the SHE) it is easy to show that for the anode half-cell reaction (Eq. 3), the standard cell potential with respect to SHE is given by... 

Alkaline batteries A more efficient alkaline dry cell, shown in Figure 20.9, is replacing the standard zinc-carbon dry cell in many applications. In the alkaline cell, the zinc is in a powdered form, which provides more surface area for reaction. The zinc is mixed in a paste with potassium hydroxide, a strong base, and the paste is contained in a steel case. The cathode mixture is manganese(IV) oxide, also mixed with potassium hydroxide. The anode half-cell reaction is as follows. 

Fig. 3 Electrochemical framework for intergranular corrosion described by an Evans diagram depicting the anodic half-cell reaction kinetics for the grain boundary zone and the grain matrix. In this case, enhanced active dissolution occurs in both the grain boundary region and in the matrix. At a fixed potential, given by Egpp, the anodic dissolution rate is accelerated along the grain boundary compared to the matrix.

In the presence of reducible aqueous metal species, additional reactions resulting in the oxidation of Fe(II) oxide surfaces can occur. Anodic half cell reactions describing the oxidation of Fe(II) on the surfaces of magnetite and ilmenite can be decoupled from the corresponding reductive half cell reactions (equations 6 and 8) and linked to the reduction of aqueous metal species at the mineral surfaces (10). 

Anodic half-cell reaction Fe Fe ++2e Cathodic half-cell reaction H2O -I- l/202+2e —... 

The relations established in the following are developed on the example of Equation (17.1) for the anodic half-cell reaction or Equation (17.3) for the overall cell reaction. 

Entropy change in the anodic half-cell reaction. -27... 

Strategy Use the tabulated values of E° to determine which electrode is the cathode and which is the anode, combine cathode and anode half-cell reactions to get the overall cell reaction, and use Equation 19.1 to calculate . ... 

The anode catalyzes the oxidation of the fuel using 02- ions delivered through the electrolyte-producing electrons that flow through the external circuit to the cathode. If H2 is used as the fuel, the anode half-cell reaction is as follows ... 

Although SOFCs that rely on reforming of hydrocarbons to produce synthesis gas are a viable technology, it would be much simpler and more efficient if the reforming step could be avoided and the fuels used directly. Thus, one would prefer to have an anode half-cell reaction that involves the direct oxidation of a hydrocarbon fuel, such as the following ... 

Use of reduction potential tables—It can be determined which species is reduced or oxidized in a redox couple from standard tables, as exempHfied by the brief listing given in Table 19. The cathode and anode half-cell reactions are noted and added algebraically as noted for Pb and Sn. Note that the algebraic sign of the Sn electrode potential is also reversed (i.e., from —0.136 to +0.136) ... 

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