Solid oxide fuel cells requirements

Similarly, in the development of solid oxide fuel cells (SOFCs), it is well recognized that the microstructures of the component layers of the fuel cells have a tremendous influence on the properties of the components and on the performance of the fuel cells, beyond the influence of the component material compositions alone. For example, large electrochemically active surface areas are required to obtain a high performance from fuel cell electrodes, while a dense, defect-free electrolyte layer is needed to achieve high efficiency of fuel utilization and to prevent crossover and combustion of fuel. 

A solid oxide fuel cell (SOFC) consists of two electrodes anode and cathode, with a ceramic electrolyte between that transfers oxygen ions. A SOFC typically operates at a temperature between 700 and 1000 °C. at which temperature the ceramic electrolyte begins to exhibit sufficient ionic conductivity. This high operating temperature also accelerates electrochemical reactions therefore, a SOFC does not require precious metal catalysts to promote the reactions. More abundant materials such as nickel have sufficient catalytic activity to be used as SOFC electrodes. In addition, the SOFC is more fuel-flexible than other types of fuel cells, and reforming of hydrocarbon fuels can be performed inside the cell. This allows use of conventional hydrocarbon fuels in a SOFC without an external reformer. 

However, in the case of high temperature fuel cells like solid oxide fuel cells (SOFCs) that can utilize CO as a fuel, downstream WGS and preferential CO oxidation are not required and simplify the system. Consider the generalized expression for the POX reaction ... 

A comprehensive analysis of solid oxide fuel cells phenomena requires an effective multidisciplinary approach. Chemical reactions, electrical conduction, ionic conduction, gas phase mass transport, and heat transfer take place simultaneously and are tightly coupled. 

A single-chamber solid oxide fuel cell (SC-SOFC), which operates using a mixture of fuel and oxidant gases, provides several advantages over the conventional double-chamber SOFC, such as simplified cell structure with no sealing required and direct use of hydrocarbon fuel [1, 2], The oxygen activity at the electrodes of the SC-SOFC is not fixed and one electrode (anode) has a higher electrocatalytic activity for the oxidation of the fuel than the other (cathode). Oxidation reactions of a hydrocarbon fuel can... 

Both the 2000 doe analysis and a 2003 analysis by the Fuel Cell and Hydrogen Research Centre in Berlin suggest that solid oxide fuel cells (sofcs) may be a better candidate for home fuel cells because they have higher electric efficiency, they do not need an expensive external reformer, and they have more usable heat.27 For home use, however, sofcs would have their own limitations. Since they operate at very high temperatures, they take a long time (several hours) to warm up, which is why they operate much better in commercial and industrial applications that require high levels of electricity continuously. 

Given these requirements, hybrid and nonhybrid PEMFC systems are the leading contenders for automotive fuel cell power, with additional attention focusing on the direct-methanol fuel cell (DMFC) version of the technology and the possibility of using solid oxide fuel cell (SOFC) systems as auxiliary power units for cars and trucks. 

At 1-10 W (watts), fuel cells could be used as battery replacements at 100 W to 1 kW, fuel cells could find military applications which require lightweight portable power sources for communications and weapon power at 1 - 10 kW, fuel cells could supply power to residential buildings and serve as auxiliary power units in vehicles and trucks. At higher power levels, the solid oxide fuel cell (SOFC) could be an effective approach for the distributed power generation and the cogeneration (i.e., combined heat and power). Above 1 MW, the SOFC could be integrated with a turbine power plant to improve the overall efficiency of power generation and reduce emissions. ... 

Sakaki et al [2] reported that the energy efficiency of a solid oxide fuel cell (SOFC) could be increased by CO separation from its recycling gas at energy requirements of less than two times the theoretical separation energy. It means the possibility of COj capture in fuel ceU systems without the use of additional energy. 

PEM has the disadvantage of requiring high purity hydrogen as fuel. Solid oxide fuel cells can use a variety of fuels and be used in the future [16], however, they are as yet in the intitial stage of development. 

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