Solid oxide cells

The high-temperature fuel cell to which most attention is paid at present is the solid electrqlyte cell. Solid oxide fuel cells (SOFC) use zirconia compounds as the electrolyte layer to conduct oxygen ions formed at the positive electrode. The electrode reactions involve oxygen ion transport (in contrast to the hydrogen ion transport in the basic scheme given by (3.15) and (3.16)), whence the appearance of oxygen in the cell name. 

These reactions take place at the surface of a solid state electrolyte at a temperature of 600-1000°C. The lower temperatures are desirable, due to a wider choice of materials capable of maintaining integrity. A number of materials have been contemplated for use as electrodes and electrolyte. 

Modelling the behaviour of sohd oxide fuel cells employs a combination of an electrochemical model and a heat and materials flow model. The electrochemical model starts from calculating the internal cell potential by combination of the equations (3.5)-(3.7) with (3.20) and (3.23), 

For the SOFCs, the sums in (3.66) have three terms, two positive ones for Hj and O2 and one negative one for H2O. The constant part of the first terms on the right hand side, deviates from the one given in (3.20) for an ideal gas at ambient pressure and temperature, as it must take into account the high temperature in the SOFC. It is estimated as (Campanari and lora, 2004), 

The second sum on the right-hand side of (3.66) is called the Nemst potential, and finally, the loss term is as in (3.23) made up of contributions from bulk resistive losses and losses occurring at each of the two electrodes. These 

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Two types of continuous flow solid oxide cell reactors are typically used in electrochemical promotion experiments. The single chamber reactor depicted in Fig. B.l is made of a quartz tube closed at one end. The open end of the tube is mounted on a stainless steel cap, which has provisions for the introduction of reactants and removal of products as well as for the insertion of a thermocouple and connecting wires to the electrodes of the cell. A solid electrolyte disk, with three porous electrodes deposited on it, is appropriately clamped inside the reactor. Au wires are normally used to connect the catalyst-working electrode as well as the two Au auxiliary electrodes with the external circuit. These wires are mechanically pressed onto the corresponding electrodes, using an appropriate ceramic holder. A thermocouple, inserted in a closed-end quartz tube is used to measure the temperature of the solid electrolyte pellet. 

A high-temperature seal for a solid oxide cell needs to be hermetic and be able to withstand thermal cycles. However, there is sparse literature available regarding seal... 

N.Q. Minh, "High-Temperature Fuel Cells, Part 2 The Solid Oxide Cell," ChemTech,... 

Mogensen, M., S.H. Jensen, A. Hauch, I. Chorkendorff, T. Jacobsen (2008), Reversible Solid Oxide Cells , Ceramic Engineering and Science Proceedings, Vol. 28, No. 4, Advances in Solid Oxide Fuel Cells III - A Collection of Papers Presented at the 31st International Conference on Advanced Ceramics and Composites, pp. 91-101. 

The high-temperature solid oxide cell would be suitable for electric locomotives, with on-board re-forming of methanol or diesel oil within the cell. 

For cargo and passenger boats, conversion to fuel cells and electric drive will follow as a consequence of the more favorable economics of the lessened fuel consumption. Hence, the rate-determining step is the manufacture of sufficiently large fuel cells once more the prospects look good for the monolithic solid oxide cell. 

Fig. 9. Schematic of high-temperature electrolysis in a solid-oxide cell. The geometry can be planar or tubular as in the case of the first demonstration of the hybrid solar concentrator PV system. Operating the electrolysis cell in reverse corresponds to electricity and heat production...

The big investment is in the PEMFC, but Ceres Power in the UK is using its 500°C solid oxide cell to enter many applications (Bance etah, 2004). 

There are four types of fuel cells in development. They differ in the electrolyte they use, but the mechanical and chemical fundamentals are similar. The electrolytes under investigation are Phosphoric Acid, Molten Carbonate, Solid Oxide and Solid Polymer. The Phosphoric acid cells operate at temperatures of 180 to 210 degrees Celsius. Molten carbonate cells operate at 600 to 700 degrees Celsius. Solid oxide Cells operate at 650 to 1000 degrees Celsius. These temperatures are uncomfortably high for home use and impractically high for automotive use. Only the Solid Polymer cells operate at a temperature range, 80 to 100 Celsius, a suitable for use in the home or automobile. 

The operative temperature could play a crucial role for the development of a very efficient electrolyser plant. Solid oxide cells (scheme c in Fig. 2.4) have been proposed for high temperature electrolysis (HTE), because of the strong resistance at high temperatures of the related electrolytes. With respect to traditional room-temperature electrolysis HTE modules presents two main advantages [87] ... 

The fuel cell has already proved its usefulness in space technology and there are excellent prospects for its commerical application. Application on a large scale is not expected during the 20th century. The alkaline cell and the phosphoric acid cell are technically well developed, but from a commerical point of view it is questionable whether or not they will be of interest when other types reach technical maturity. The molten carbonate cell and the solid oxide cell seem to have the best prospects. For mobile application the solid polymer cell is a strong candidate. 

Figure 14.20 Model solid oxide fuel cell studied using APXPS. (a) Schematic of the cell design. Solid oxide cells have a 200 nm Pt counter electrode, a 300 nm Au current collector on top of a 30 nm alumina film (black) and a 50, 100, or 250 nm ceria working electrode patterned onto a polycrystalline YSZ substrate. This geometry exposes all cell components to the X-ray beam. The drawing is not to scale, (b) During operation, the...

T. (2006) Performance of reversible solid oxide cells a review. Proceedings, 7th European Fuel Cell Forum 2006, Lucerne. 

High-Temperature CO2 Electrolysis, Fig. 2 Working principle of a reversible solid oxide cell (SOC). The cell can be operated as a SOFC (a) and as a SOEC (b). The operation temperature is typically in the range of 650-850 °C. The blue-colored layer is the oxygen... 

Schefold J, Brisse A, Zahid M, Ouweitjes JP, Nielsen JU (2011) Long term testing of short stacks with solid oxide cells for water electrolysis. ECS Trans 35 2915... 

Schefold J, Brisse A, Tietz F (2012) Nine thousand hours of operation of a solid oxide cell in steam electrolysis mode. JElectrochem Soc 159 A137... 

Ebbesen SD, Mogensen M (2011) Method and system for purification gas streams for solid oxide cells. EPO patent EP2362475A1... 

Bierschenk DM, Wilson JR, Barnett SA (2011) High efficiency electrical energy storage using a methane-oxygen solid oxide cell. Energy Environ Sci 4 944... 

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