Performance of SOFC

This volume shows how the performance of SOFCs can be improved through novel materials and methods, thereby, bringing them closer to commercialization. 

Hydrogen sulfide (H2S), hydrogen chloride (HCl) and ammonia (NH3) are impurities typically found in coal gas. Some of these substances may be harmful to the performance of SOFCs. Recent experiments (35) have used a simulated oxygen-blown coal gas containing 37.2% CO/34.1% H2/0.3% CH4 /14.4% C02/13.2% H2O/0.8% N2. These experiments have shown no... 

Figure 2 illustrated two dominant strategies that have been used to enhance the performance of SOFC cathodes. One has been the introduction of ionic... 

The performance of SOFCs with Cu—ceria—YSZ anodes has been tested with a wide variety of hydrocarbon fuels, and this has been documented elsewhere.With the exception of methane, which is known to be relatively unreactive in normal heterogeneous reactions as well, all of the hydrocarbons we examined appear to give similar performance characteristics. The fuels that were tested include /2-butane, /2-decane, toluene, and a synthetic diesel. The main difference observed between the various fuels is that some fuels tend to form tars more readily via gas-phase free-radical chemistry. Otherwise, with the exception of CH4, all hydrocarbons that were investigated showed similar power densities. This is shown in Figure 20, which displays the voltage and current densities for /2-decane, toluene, and synthetic diesel as a function of time. In this case, the hydrocarbon fuels were diluted in dry N2 to a concentration of 40 wt % hydrocarbon to prevent condensation of unreacted fuels that leave the cell. (In our studies, the active area for the fuel cell is typically 0.5 cm, and a current density of 1 A/cm would require a flow... 

Perovskite materials show outstanding thermal and mechanical stability at temperatures typical for the performance of SOFCs in contrast with the standard Ni/YSZ cermet, where nickel sintering and agglomeration are latent risks [144],... 

Although the current performance of SOFC anodes is still far from satisfactory, they are mainly being studied solely in terms of the electrochemically active area, the electric conductivity, thermal expansion, stability and reactivity with the solid electrolyte. It is... 

Ni-GDC cermet not only lowered the operating temperature of SOFC but also allowed the use of CH4 as a fuel. The direct use of CH4 or hydrocarbon provides a number of significant advantages elimination of the use of reformer, improvement of the energy efficiency, and reduction in fabrication cost. Table 3 summarizes the performance of SOFC for the direct oxidation of hydrocarbon fuels. ... 

Cell design is also an important factor to improve the performance of SOFC stack/module [15-18]. Use of small diameter SOFC may also give opportunity to reduce operating temperature by increasing the volumetric power density [19]. Thus, they are expected to accelerate the progress of SOFC systems which can be applied to portable devices and auxiliary power units for automobile. 

Macroscale cell-level models are able to provide a great amount of insight into the operation and performance of SOFCs. With the newer mesoscale electrochemistry models, information about the conditions within the SOFC electrodes and electrolytes can even be resolved. However, due to the continuum-scale treatment of the SOFC, these models stiU rely on effective parameters, which need to be determined through smaller scale modehng or by fitting the models to experimental data. 

Trembly JP, Gemmen RS, Bayless DJ (2007) The effect of coal syngas containing AsHs on the performance of SOFCs Investigations into the effect of operational temperature, current density and ASH3 concentration. J Power Sources 171 818-825... 

This section provides empirical information that can be used to estimate the performance of SOFCs based on various operating parameters. The SOFCs being developed, particularly the planar types, have unique designs, are constructed of various materials, and are fabricated by different techniques. This development process will result in further evolution of the performance trends summarized here. The electrochemical reactions associated with hydrogen fuel are expressed in equations (7-4) to (7-6) ... 

Madi et al. [42] report the study of the impact of silica contamination on the performance of SOFC Ni anodes. Haga et al. [48] observed the effect of feeding 10 ppm of D5 on a Ni anode showing how the SOFC performance is rapidly falling (within hours). The analysis revealed the plugging of the anode structure with Si02 deposits [47]. They concluded that the presence of siloxane can cause... 

In a review paper, Cayan et al. (2008) summarized study results on the identification of impurities in coal syngas on the performance of SOFCs. 

In order to improve the performance of SOFC, a thirmer yttria-stabilized zirconia (YSZ) electrolyte is considered for lower ohmic resistance and for operation in the intermediate temperature range of 500°C-800°C. Ionic conductivity decreases with decrease in temperature and hence the area-specific resistance (ASR) of an electrolyte increases with lower operating temperature. Fabricating the electrolyte in a dense and thinner film reduces the ASR or the resistance to ionic transport, allowing a lower operating temperature. For this purpose, efforts are being made in fabricating SOFC cell on the basis of either a thicker anode-supported or a thicker cathode-supported SOFC... 

The preparation, stmcture, and performance of SOFC used for power generation is described in Chapter 12 of this handbook. Both the electrocatalysis and the catalysis of the NiAi"SZ anode are reasonably well understood and the same applies for the electrocatalysis of the Lai xSrxMn03 5 and Lai xSrxCo03 g cathodes. State-of-the-art SOFC units with anodic and cathodic overpotentials of less than 150 mV each at current densities up to 0.5 AJcm at T = 950°C are currently available. ... 

Operating temperatures below 973 K are preferred to use metallic SOFC components (e.g., interconnects) and reduce the start-up time. Decrease of the operating temperature can be achieved by using LaGaOg thin films. In this section, the preparation of LSGM films is briefly described, and performance of SOFC cells using the LSGM thin-film electrolytes is discussed. 

Concerning the Ruddlesden-Popper series, Laberty et alP reported on the performance of SOFC cathodes with lanthanum-nickelate-based composites. They showed that lanthanum nickelate performs poorly when used as a single-phase cathode in yttria-stabilised, zirconia-based air-H2 button cells at 800 °C. However high power densities of up to 2.2 W cm were measured using a La2Ni04+ -CS0 composite bilayer cathode. 

Electrode-level models describe the performance of SOFC electrodes in detail. They take into account the distribution of species concentrations, electric potential, current, and even temperature in the electrode. Their purpose is to (i) interpret the performance (polarisation curve) of electrodes in terms of rate-limiting resistances such as kinetic (activation), mass transfer, and ohmic resistance and (ii) predict the local polarisation in full-scale cell and stack models. 

This chapter first considers the trends in the energy markets that are driving towards utilisation of SOFC technology for electricity generation in various applications, Then SOFCs are compared with combustion engine generators and the potential application areas of SOFC systems are explored in detail. Designs and performance of SOFC systems are then analysed, followed by examples of SOFC systems and their demonstrations. 

This book is intended primarily for use by researchers, engineers and other technical people who wish to determine the basic performance of SOFCs through advanced computational methods and examine issues of combination with other power devices. While the content will inevitably age from the moment it is published, we hope it has a universal quality that will enable adaptation to new conditions. 

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