Cell performance

With its reactant and product connections isolated, but equilibrium concentrations remaining in the cell, the cell voltage is a maximum, namely V , at open-circuit, zero-flow equilibrium (Table A.1). Equilibrium entails the presence of a thermodynamically reversible, symmetrical or balanced exchange current, described by Marcus (1964 1982) as being an equilibrium exchange between electrode electrons and vibrating 

See Atkins (1995), Koryta (1991 1993) and Bard and Falkener (1980) for the Butler-Volmer theory and Tafel slopes. 

As the oxygen ions are transported across the electrolyte between adjacent anode and cathode, the ionic conduction path is mainly determined by the size of the inter-electrode gap. Several experimental studies performed under different operating conditions (gas composition, temperature) and for cells constructed from different cell component materials showed that a decrease in the inter-electrode gap leads to a decrease in the ohmic cell resistance and an increase in power output [9, 20, 62, 68]. These observations were also confirmed by a computational analysis where maximum cell performance was obtained for the smallest gap size studied [64]. The OCV, however, was found to be independent of changes of the inter-electrode gap [20]. When the anode and cathode are located in grooves in the electrolyte, ions can also be transferred through the electrolyte material filling the inter-electrode gap, and a reduction in ohmic cell resistance can be achieved [65]. 

OCVs of 0.7 V [74] and 0.9 V [75] confirmed that the complexity of the electrode geometry did not impede the establishment of a reasonable OCV. Additionally, SC-SOFCs with curvilinear microelectrodes of different geometries but similar electrode dimensions (electrode width, inter-electrode gap, and electrode surface area) exhibited similar OCVs and power densities, indicating that the electrode shape did not significantly affect the cell performance. 

Series connection of two single cells with side-by-side electrodes on the same electrolyte substrate produced double the voltage of the single cell [69]. Similarly, the power output was doubled for two cells coruiected in parallel and further increased for a three-ceU stack [68, 69]. 

In addition to cell design and geometry, the ceU performance also depends on the testing conditions. Especially the gas composition and orientation of the electrodes with respect to the incoming gas stream were found to affect the OCV and cell power. 

There are three possibilities for the electrode alignment of SC-SOFCs with coplanar electrodes with respect to the gas flow direction (i) parallel gas flow where the gas mixture reaches both electrodes simultaneously, (ii) perpendicular gas flow with anode first (the gas mixture encounters the anode first), and (iii) perpendicular gas flow with cathode first [68]. Perpendicular gas flow with cathode first [64, 68, 

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The electrolyte feed to the cells is pretreated to remove impurities, and/or additives are added to the feed to improve cell performance (94). The cell hquor leaving the cell is evaporated, crystallised, and centrifuged to remove soHd sodium perchlorate. The clarified cell Hquor can undergo reaction in a double metathesis reactor to produce NH CIO, KCIO or other desired perchlorates. 

Ren, X. Springer, T. E. and Gottesfeld, S. (1998). Direct Methanol Fuel Cell Transport Properties of the Polymer Electrolyte Membrane and Cell Performance. Vol. 98-27. Proc. 2nd International Symposium on Proton Conducting Membrane Euel Cells. Pennington, NJ Electrochemical Society. 

Figure 21. Cell performance of LiMnO, oxide. The anode is metallic Li [26].

It is possible that all three phenomena contribute to the capacity loss of 4V Lix[Mn2]04 electrodes. Nonetheless, all three can be at least partly circumvented by slightly modifying the composition of the spinel electrode. For example, cell performance can be improved by increasing the amount of lithium in the spinel structure [107, 123, 130] and, in particular, by substituting a small amount of manganese on the B sites with lithium [107], which drives the composition a small way down the stoichiometric spinel tie-line, towards... 

Repeat Example 8-3 but now with unequal initial concentrations of A and B. Use [A]o = 400 cells and [B]o = 600 cells. Perform the same tests as before and comment on the results. In particular, determine Kgq. 

Nonmuscle cells perform mechanical work, including self-propulsion, morphogenesis, cleavage, endocytosis, exocytosis, intracellular transport, and changing cell shape. These cellular functions are carried out by an extensive intracellular network of filamentous structures constimting the cytoskeleton. The cell cytoplasm is not a sac of fluid, as once thought. Essentially all eukaryotic cells contain three types of filamentous struc-mres actin filaments (7-9.5 nm in diameter also known as microfilaments), microtubules (25 nm), and intermediate filaments (10-12 nm). Each type of filament can be distinguished biochemically and by the electron microscope. 

Two major types of muscle fibers are found in humans white (anaerobic) and red (aerobic). The former are particularly used in sprints and the latter in prolonged aerobic exercise. During a sprint, muscle uses creatine phosphate and glycolysis as energy sources in the marathon, oxidation of fatty acids is of major importance during the later phases. Nonmuscle cells perform various types of mechanical work carried out by the structures constituting the cytoskeleton. These strucmres include actin filaments (microfilaments), micrombules (composed primarily of a- mbulin and p-mbulin), and intermediate filaments. The latter include keratins, vimentin-like proteins, neurofilaments, and lamins. 

Sol-gel technique has been used to deposit solid electrolyte layers within the LSM cathode. The layer deposited near the cathode/electrolyte interface can provide ionic path for oxide ions, spreading reaction sites into the electrode. Deposition of YSZ or samaria-doped ceria (SDC, Smo.2Ceo.8O2) films in the pore surface of the cathode increased the area of TPB, resulting in a decrease of cathode polarization and increase of cell performance [15],... 

Sol-gel techniques have been successfidly applied to form fuel cell components with enhanced microstructures for high-temperature fuel cells. The apphcations were recently extended to synthesis of hybrid electrolyte for PEMFC. Although die results look promising, the sol-gel processing needs further development to deposit micro-structured materials in a selective area such as the triple-phase boundary of a fuel cell. That is, in the case of PEMFC, the sol-gel techniques need to be expanded to form membrane-electrode-assembly with improved microstructures in addition to the synthesis of hybrid membranes to get higher fuel cell performance. 

The single cell thus fabricated was placed in a single chamber station as illustrated in Fig. 2. A humidified mixture of methane and oxygen was supplied to the station so that both electrode compartments were exposed to the same composition of methane and oxygen. For the measurement of the cell temperature, a thermocouple (TC) was placed approximately 4 mm away from the cathode site. For the evaluation of the fuel-cell performance, Ft wires and Inconel gauzes were used as the output terminals and electrical collectors, respectively. 

We reported the dotted and dash performance curves illustrated in Fig. 5 for an anode-supported Ni5Al (SDC) / SDC / LSM (SDC) cell running on humidified methane and air mixtures in mixed-gas mode at 700°C with 02 C ratio of 1.5 and 1.67, respectively [6]. In the previous paper, we suggested that the decrease of cell performance for mixed-gas SOFC results from an increase in the anode polarization and is due to the low catalytic activity of the... 

It is well established that sulfur compounds even in low parts per million concentrations in fuel gas are detrimental to MCFCs. The principal sulfur compound that has an adverse effect on cell performance is H2S. A nickel anode at anodic potentials reacts with H2S to form nickel sulfide. Chemisorption on Ni surfaces occurs, which can block active electrochemical sites. The tolerance of MCFCs to sulfur compounds is strongly dependent on temperature, pressure, gas composition, cell components, and system operation (i.e., recycle, venting, and gas cleanup). Nickel anode at anodic potentials reacts with H2S to form nickel sulfide. Moreover, oxidation of H2S in a combustion reaction, when recycling system is used, causes subsequent reaction with carbonate ions in the electrolyte [1]. Some researchers have tried to overcome this problem with additional device such as sulfur removal reactor. If the anode itself has a high tolerance to sulfur, the additional device is not required, hence, cutting the capital cost for MCFC plant. To enhance the anode performance on sulfur tolerance, ceria coating on anode is proposed. The main reason is that ceria can react with H2S [2,3] to protect Ni anode. 

A study on surface treatment of Nation membrane and its effects on cell performance... 

Design parameters of the anode catalyst for the polymer electrolyte membrane fiiel cells were investigated in the aspect of active metal size and inter-metal distances. Various kinds of catalysts were prepared by using pretreated Ketjenblacks as support materials. The prepared electro-catalysts have the morphology such as the sizes of active metal are in the range from 2.0 to 2.8nm and the inter-metal distances are 5.0 to 14.2nm. The electro-catalysts were evaluated as an electrode of PEMFC. In Fig. 1, it looked as if there was a correlation between inter-metal distances and cell performance, i.e. the larger inter-metal distances are related to the inferior cell performance. 

But when the contents of Nafion ionomer was increased from 30 to 45 % to find out the better electrode structures, the Pt-Ru/SRaw, which had showed the lowest single cell performance, became the best electro-catalyst. By this result one can conclude that as long as the structure of the electrode can be optimized for the each of new electro-catalysts, the active metal size is a more important design parameter rather than inter-metal distances. Furthermore, when the electro-catalysts are designed, the principal parameters should be determined in the consideration of the electrode structures which affect on the electron conduction, gas permeability, proton conductivity, and so on. 

Primarily connected to corrosion concepts, Pourbaix diagrams may be used within the scope of prediction and understanding of the thermodynamic stability of materials under various conditions. Park and Barber [25] have shown this relevance in examining the thermodynamic stabilities of semiconductor binary compounds such as CdS, CdSe, CdTe, and GaP, in relation to their flat band potentials and under conditions related to photoelectrochemical cell performance with different redox couples in solution. 

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