Single Chamber Fuel Cell

Figure 3.3. Electrode configuration for SEP (a) and for electrochemical promotion (or NEMCA) studies (b). The latter can be carried out using the fuel-cell type configuration (c) or the single chamber type configuration (d).

Figure 4.1. Electrode configuration for NEMCA studies using (a) the fuel cell type reactor and (b) the single-chamber type reactor.

Qualitatively similar behaviour for methanol oxidation on Pt/YSZ was reported by Cavalca, Larsen, Vayenas and Haller51 who used the single chamber design51 instead of the fuel-cell type design of the earlier study of Neophytides and Vayenas.50 Cavalca et al51 took advantage of the electrophobic... 

Figure B.l. (Top) Typical reactor designs used in electrochemical promotion studies singlechamber design (left) and fuel cell type design (right). (Bottom) Typical apparatus for electrochemical promotion studies using a three-pellet single chamber reactor.

In the present work, we report results on the fabrication and performance of anode-supported, thin SDC el trolyte fuel cells operated in a single chamber configuration where methane and oxygen served as the gas mixture. 

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. 

Interestingly, research has started on single chamber SOFC (SC-SOFC) concepts. However, the SC-SOFC exhibits inherently low power density and is therefore primarily of academic interest. It has the potential to relax cell component requirements and probably to ease manufacture. The principle of SC-SOFC is that it is fed by an air fuel mixture which flows onto the PEN contained in a single compartment, avoiding the use of gas separator plates and high temperature sealants. The fluid may flow simultaneously or sequentially along the electrodes. Both electrodes are either built onto the same side of the electrolyte some distance apart or on opposite sides. Low temperature operation would apparently suppress direct combustion of the air fuel mixture provided the electrode materials chosen are highly selective towards their respective catalytic reactions. SC-SOFC stacks may hold prospects in specific applications where the reaction products are the prime focus. 

PERFORMANCE OF SINGLE-CHAMBER SOLID OXIDE FUEL CELLS... 

Abstract Single-chamber solid oxide fuel cells (SC-SOFCs) immerse the entire cell in a mixture of fuel and oxidizer gases within a single chamber, which eliminates the need for high temperature sealant, simplifies construction, and increases reliability over traditional double-chamber cells. However, there are challenges, such as low fuel utilization and electrode catalytic selectivity, that need to be overcome. This brief review paper looks at recent improvements in materials, processing, and operation of SC-SOFCs, which are rapidly approaching the performances of the double-chamber fuel cells and may become attractive for specific fuel cell applications. 

Keywords solid oxide fuel cell, SOFC, hydrogen, hydrocarbon, single chamber, SC-SOFC... 

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... 

Hibino, T., Wang, S., Kakimoto, S., and Sano, M. Single Chamber Solid Oxide Fuel Cell Constructed from an Yttria-Stabilized Zirconia Electrolyte, Electrochem. Solid-State Letters, 2, 317 (1999). 

Shao, Z., Kwak, C., and Haile, S. M. Anode-Supported Thin-film Fuel Cells Operated in a Single Chamber Configuration, Solid State Ionics, 175, 39 (2004). 

Suzuki, T., Jasinski, P., Petrovsky, V., Anderson, H., and Dogan, F. Anode Supported Single Chamber Solid Oxide Fuel Cell in CH4-air Mixture, Journal of the Electrochem. Soc., 151, A1473 (2004). 

It has even been proposed to give up the separation of the gas chambers.156-158 Then one has to completely rely on selective catalytic activity of electrocatalysts to activate reduction or oxidation processes. In Ref.158 considerable power densities have been achieved in this way. This single chamber fuel cell concept might be indeed relevant for reduced temperature application. 

Catalysis of Solid Oxide Fuel Cells 6 Single Chamber Fuel Cell... 

The anode catalyst should possess high electrochemical oxidation activity and minimal conventional oxidation activity the cathode catalysts should exhibit selectivity for the reduction of O2 to. Single chamber fuel cell studies using Ni-SDC as an anode and Smo.sSr 0.5C0O3 as a cathode showed that the anode catalyst was active for partial oxidation of C2H6 to produce CO and H2 for further electrochemical oxidation on the anode catalyst surface. 

Table 3 shows that the power density produced from the single chamber is at the level of the conventional double chamber for the direct hydrocarbon fuel cell. Since the fuel utilization data in these studies were not provided, it remains unclear whether the overall efficiency of the single chamber fuel cell is at the level of double chamber. 

The counter- and the reference electrodes can be in a separate gaseous compartment (fuel-cell-type design) or can be in the same gaseous compartment with the catalyst-electrode (single-chamber-type design) [13,27-30]. 

This negative potential is easy to understand and is actually used today in the single-chamber fuel cell [14] oxygen is consumed by the catalytic reaction of CH3OH oxidation much faster on the Pt catalyst-electrode than on the Ag counterelectrode (Ag is also a catalyst for CH3OH oxidation and partial oxidation, but much less... 

The single cells consist of a dense solid electrolyte membrane and two porous electrodes. In most cases, at least one of the electrodes is exposed to an oxygen-containing gas (often, ambient air), while the other electrode is exposed to an inert gas, a liquid metal, a partial vacuum, or a reacting mixture (hydrogen, water vapor, hydrocarbons, CO, CO2, etc.). The single-chamber reactor (SCR) has been also proposed either as a membrane reactor or as a fuel cell. In this case, the solid-electrolyte disk, with two different electrodes that are coated either on opposite sides or on the same side of the pellet, is suspended in a flow of the reacting mixture (see Section 12.6.3). 

Development of Single-Chamber Solid Oxide Fuel Cells... 

Z. P. Shao, J. Mederos, W. C. Chueh, S. M. Haile, High Power-Density Single-Chamber Fuel Cells Operated on Methane. J. Power Sources, 162, 589-96 (2006). 

B. Wei, Z. Lit, X. Huang, M. Liu, K. Chen, W. Su, Enhanced Performance of a Single-Chamber Solid Oxide Fuel Cell with an SDC-Impregnated Cathode. J. Power Sources, 167, 58-63 (2007). 

Other measurements were conducted in an environmental chamber at a variety of temperatures and relative humidity. In the climate chamber the fuel cells were placed in an extra enclosure to keep off any air movement produced by the circulation system. Figure 7-12 shows the F//characteristic of a single cell with an active area of 0.54 cm. ... 

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