Electrode electrolyte movement

Cell normally divided Electrolyte movement Electrode movement High electroactive area... 

In a SOFC, there is no liquid electrolyte present that is susceptible to movement in the porous electrode structure, and electrode flooding is not a problem. Consequently, the three-phase interface that is necessary for efficient electrochemical reaction involves two solid phases (solid electrolyte/electrode) and a gas phase. A critical requirement of porous electrodes for SOFC is that they are sufficiently thin and porous to provide an extensive electrode/electrolyte interfacial region for electrochemical reaction. 

Similar types of electric double layer may also be formed at the phase boundary between a solid electrolyte and an aqueous electrolyte solution [7]. They are formed because one electrically-charged component of the solid electrolyte is more readily dissolved, for example the fluoride ion in solid LaFs, leading to excess charge in the solid phase, which, as a result of movement of the holes formed, diffuses into the soUd electrolyte. Another possible way a double layer may be formed is by adsorption of electrically-charged components from solution on the phase boundary, or by reactions of such components with some component of the solid electrolyte. For LaFa this could be the reaction of hydroxyl ions with the trivalent lanthanum ion. Characteristically, for the phase boundary between two immiscible electrolyte solutions, where neither solution contains an amphiphilic ion, the electric double layer consists of two diffuse electric double layers, with no compact double layer at the actual phase boundary, in contrast to the metal electrode/ electrolyte solution boundary [4,8, 35] (see fig. 2.1). Then, for the potential... 

There is therefore one essential conclusion from the comparison of electrodic e-i junctions and semiconductor n-p junctions The symmetry factor P originates in the atomic movements that are a necessary condition for the charge-transfer reactions at electrode/electrolyte interfaces. Interfacial charge-transfer processes that do not involve such movements do not involve this factor. By understanding this, ideas on P become a tad less underinformed. Chapter 9 contains more on this subject. 

The impedance of an electrode/electrolyte interface is one of the characteristic quantities that reveals the electrical nature of the interface. The electrical structure of the interface layers and the resistance to charge storage and movement can be analyzed by determining the impedance as a function of frequency. The characteristics of the electrochemical impedance of the silicon/electrolyte interface are different for n-Si and p-Si and depend on among other factors, electrolyte composition and partiodarly the concentration of fluoride. 

Chemelec cell with fluidized-bed glass beads within electrodes. The cell performance is achieved mainly by electrolyte movement. The cathode product is removed by scraping or used as anodes. 

ER cell with packed bed of carbon particles within parallel-plate electrodes. The cell performance is achieved by electrolyte movement and high electroactive... 

So far as lithium intercalation/deintercalation into/from transition metal oxides and graphite proceeds under the cell-impedance controlled constraint Eq. (8), it is unlikely that the disturbance of lithium diffusion inside the electrode due to the presence of the phase boundary and the phase boundary movement causes any significant change in the CTs. It is likely predicted from Eq. (8) that unlike the case of the diffusion controlled phase transformation, the flux of lithium at the electrode/electrolyte interface under the cell-impedance controlled constraint is hardly dependent on the location of the phase boundary within the electrode. 

The potential gradient that exists in the elextrolyte contributes negligibly to the movement of minor ionic species their transport is almost entirely by convection and diffusion. Therefore, the equations that are used for neutral species, such as for dissolved molecular oxygen, are also valid for minor ionic species. Convection refers to the macroscopic movement of a fluid under the influence of a mechanical force (forced convection) or of gravity force (free convection). At solid surfaces the velocity of fluids is zero and as a consequence only diffusion contributes to the flux at the electrode-electrolyte interface. This allows us to write the following expression for the flux of a minor ionic species B ... 

It is expected that the high prevalence of large pores in the polymer grown on platinum or gold enables easier passage of electrolyte into the bulk of the polymer, thus improving the rate of diffusion of ions into the sub-micron sized free volume of the polymer and improving the actuation strain rate. An earlier study by Pandey et al. [53] showed that the polymerization electrode also influenced the balance of anion/cation movement in the polymer. In this case PPy doped with naphthalene sulfonic acid (NSA) was prepared on three different electrodes. Anion movement was favoured in those films that had a more open, porous structure. The actuation was performed in aqueous NaCl electrolyte, so that the mobile cation (Na ) was smaller than the mobile anion (NSA). 

The treatment of mass transport, more than any other aspect of the subject, highlights the diflercnces between laboratory experiments and industrial-scale electrolyses. In the former, there is great concern to ensure that the mass transport conditions may be described precisely by mathematical equations (which, moreover, are soluble) since this is essential to obtain reliable mechanistic and quantitative kinetic information. The need in an industrial cell is only to promote the desired effect within technical and economic restraints and this permits the use of a much wider range of mass transport conditions. In particular, a diverse range of electrode-electrolyte geometry and relative movement are possible. 

Horita T, Yamaji K, Kato T, Sakai N, Yokokawa H (2004) Imaging of labeled gas movements at the SOFC electrode/electrolyte interfaces. Solid State Ionics 169 105—113... 

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