Anodes modelling

An examination of the catalyst-layer models reveals the fact that there are many more cathode models than anode ones. In fact, basically every electrode-only model is for the cathode. This arises because the cathode has the slower reaction it is where water is produced, and hence, mass-transfer effects are much more significant and it represents the principal inefficiency of the fuel cell. In other words, while the cathode model can be separate from the anode model, the converse is not true due to the... 

Figure 12(a) shows the typical distributions in local current for a first order reaction with different values of v 2 and applied dimensionless overpotentials ° for the coupled anode model, including mass transfer parameter y. The values of °, in the range of 0.5 to 16 typically represent overpotentials in the approximate range of 25 to 800 mV. The total current flows fromX = 0 (anode fed plane) to X= 1 (membrane). Current is much higher at the face of the electrode adjacent to the membrane or free electrolyte solution and decreases towards the current collector. An increase in potential increases the local current density and thereby increases the overall variation in current density throughout the electrode. 

Figure 12(b) shows the local current distribution of first and second order reactions and applied over potentials ° for the coupled anode model without the mass transfer parameter y. The figure also shows the effect of a change in the electrode kinetics, in terms of an increase in the reaction order (with respect to reactant concentration) to 2.0, on the current distribution. Essentially a similar variation in current density distribution is produced, to that of a first order reaction, although the influence of mass transport limitations is more severe in terms of reducing the local current densities. 

The steady-state anode model is derived from a dynamic, spatially two-dimensional description of a single cross-flow MCFC in terms of dimensionless variables [7, 8] under the following assumptions ... 

Fig. 2.3. Flow scheme and assigned variables of the steady-state anode model.

The steady-state anode model can be applied for various purposes. In the following section, three applications are demonstrated, namely ... 

As indicated in Fig. 2.2, three different reforming concepts are available for high-temperature fuel cells. The steady-state anode model presented above allows a comparison of various combinations of reforming concepts. First, a system without a reforming catalyst inside the anode channel is considered - that is, a fuel cell without DIR. Three alternatives for fuel gas treatment are discussed ... 

These considerations clearly show the advantage of the DIR concept. Independent of the pre-treatment of the feed gas, the application of DIR always leads to a high degree of fuel utilization. As shown here, the steady-state anode model and the representation of its solutions in the conversion diagram are useful tools for evaluation and comparison of different process configurations. 

All three systems - that is, the single cell and the two cell cascades in either configuration - are simulated with the steady-state anode model. They are optimized to yield an optimum of electric power at a given feed rate. The optimization variables are the cell voltage for the single cell system, and both cell voltages plus the size of the first cell for both cascade configurations. 

Mascia M, Vacca A, Palmas S, Polcaro AM (2007) Kinetics of the electrochemical oxidation of organic compounds at BDD anodes modeling of surface reactions. J App Electrochem 37 71-76... 

Bessler WG, Vogler M, Stormer H, Gerthsen D, Utz A, Weber A and Ivers-Tiffe E Model anodes and anode models for understanding the mechanism of hydrogen oxidation in solid oxide fuel cells Phys. Chem. Chem. Phys., 2010,12, 13888-13903... 

The HU-type cells are offered to cover the 30—150-kA range. All of the different cell types are equipped with cathodes and anodes of identical height and width. The only difference between the various models is the number of anode—cathode elements and consequently the length of the cell. Table 11 hsts the characteristics of the various HU cells. 

Fig. 8. Model of the conductivity profile in an anodic oxide film on tantalum after heat treatment, where Tj < r, < T,.

The platinum anode used was Model 611 obtained from Engelhard Industries. This eleetrode has a height of 5.6 cm. and a diameter of 5.1 em. The total surface area claimed by the supplier is 200 cm.. ... 

Complex computer models are now available to assist in defining the optimum anode distribution . 

Currem field characteristics measured wiih conjugated polymers sandwiched between an indium-tin oxide (ITO) anode and an aluminum cathode are usually hole dominated and are, consequently, appropriate for testing injection/lransport models for the case of unipolar current How. Data shown in Figure 12-1 refer to injection-limited currents recorded on typically 100 nm thick spin-coated films of derivatives of poly(y d/"fi-phenylenevinylene) (PPV) and a planarized poly(/ /" -pheny-leue) employing a Keilhley source measure unit. The polymers were ... 

The early literature (until 1982) is summarized in Refs. [1] and [2], Hundreds of papers have been published since then (most of them in since 1994) and it is impossible to summarize all of them here. The Proceedings of the conferences mentioned above are good, sources of recent developments though sometimes incomplete. Since the early 1980s new systems have been introduced. The most important of these are lithium-ion batteries (which have lithiated carbonaceous anodes) and polymer-electrolyte batteries. Until 1991 very little was published on the Li/polymer-electrolyte interface [3, 4], The application of the SEI model to Li-PE batteries is ad-... 

The first two models are irrelevant to lithium-battery systems since the PEIs are not thermodynamically stable with respect to lithium. Perchlorate (and other anions but not halides) were found to be reduced to LiCl [15, 16, 22-27]. It is commonly accepted that in lithium batteries the anode is covered by SEI which consists of thermodynamically stable anions (such as 02, S2-, halides). Recently, Aurbach and Za-ban [25] suggested an SEI which consists of five different consecutive layers. They represented this model by a series of five... 

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