Fuel cells with solid electrolytes

The solid electrolyte fuel cells which are presently in the most advanced stages of development are those which employ Zr02 -based electrolytes. Porous platinum or nickel are used 

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Mobius H and Roland B, 1968, Method of Producing Fuel Cells with Solid Electrolytes and Ceramic Oxide Electrode Layers. US Patent 3,377,203. 

Current research is centred on making compact cells of high efficiency. They are described in terms of the electrolyte that is used. The principle types are alkali fuel cells, described above, with aqueous KOH as electrolyte, MCFCs (molten carbonate fuel cells), with a molten alkali metal or alkaline earth carbonate electrolyte, PAFCs (phosphoric acid fuel cells), PEMs (proton exchange membranes), using a solid polymer electrolyte that conducts ions, and SOFCs, (solid oxide fuel cells), with solid electrolytes that allow oxide ion, 0 , transport The... 

It is interesting to note that Walter Schottky, a prominent specialist in the field of solid electrolytes, in his 1936 paper thought fuel cells with solid electrolytes to be unpromising, and favored those with salt melts. 

In general, losses due to polarization are less in high-temperature fuel cells than in low-temperature cells. Satisfactory electrocatalysis is a minor problem. Corrosion in the liquid phase has to be overcome in fuel cells with aqueous electrolytes and carbonate electrolytes while corrosion of the electrocatalyst in the gaseous phase of the fuels is one of the major problems of the fuel cells with solid electrolyte. 

The efficiency of fuel cells with solid electrolytes was discussed in detail by Takahashi, Ito, and Iwahara [9] under the assumption of negligible losses due to polarization. Defining the efficiency as the ratio between the power output W of the fuel cell and the sum of all the partial energies generated, the following expression was derived [9] ... 

Processes in Fuel Cells with Solid Electrolytes... 

Figure2.2 First diagram (Haber, 1905) of a fuel cell with solid electrolytes. Generator gas passed from 1 to 2 through chamber A (440° C) with parallel glass tubes g covered on both sides with thin layers of noble metal...

When Wagner had recognised the mechanism of conduction in the Nernst glower, he pointed out in 1943 For fuel cells with solid electrolytes anion conductors are to be considered exclusively. From this point of view a systematic investigation of the mixed crystal systems of the type of the Nernst mass with roentgenographic and electrical methods seems to be desirable [22]. This was the start of concentrated work on solid oxide fuel cells (SOFCs). 

H.-H. MSbius and B. Rohland, Method of producing fuel cells with solid electrolytes and ceramic oxide electrode layers. US Patent 3,377,203, filed November 18,1964, DDR-P 46 300, filed June 27,963. 

Figure 11.53. Schematic diagram of a fuel cell with solid electrolyte...

Zhang X, Robertson M, Deces-Petit C, Qu W, Kesler O, Marie R et al. Internal shorting and fuel loss of a low temperature solid oxide fuel cell with SDC electrolyte. J. Power Sources 2007 164 668-677. 

High temperature cells with solid electrolytes of zirconium dioxide have been investigated for the electrolysis of H2O vapor and as fuel cells for the generation of electric power. Examples include the combustion of synthesis gas (CO-H2 mixtures) in cells at temperatures of 1300 K. 

Jayashree RS, Egas D, Spendelow JS, Natarajan D, Markoski LJ, Kenis PJA (2006) Air-breathing laminar flow-based direct methanol fuel cell with alkaline electrolyte. Electrochem Solid State Lett 9(5) A252-A256... 

Geneva presented a thin film fuel cell concept in a 1962 patent [12]. Also in 1962, Sandstede from the Battelle Institute in Frankfurt gave the first report on the use of hydrocarbons as fuel in solid oxide cells [13]. At about the same time, fuel cell work was started in France by Kleitz [14], and in Britain, a patent was filed in 1963 [15] to form fuel cells by depositing layers on a porous metallic carrier. In Japan, Takahashi published in 1964 his first results obtained on fuel cells with solid oxide electrolytes [16]. 

Goodenough, J., Solid Oxide Fuel Cells with Gallate Electrolytes, summary data on research supported by EPRI, 1998. 

Solid Electrolytes Versus Fuel Cells Ceramic solid electrolytes are used in the production of electricity in high-temperature solid oxide fuel cells (SOFC), in which electrochemical combustion reactions occur. With around 60 % efficiency of generation (compared to 35 % in conventional methods), the SOFC have already become a useful secondary source of electric energy. Single cells are, as a mle, miniature devices (Fig. 1.11). In local power plants with power outputs of 1-10 MW... 

The design of fuel cells with solid oxide electrolyte must be based on the concept of oxygen ion conduction through the electrolyte, with ions CF- migrating from the cathode to the anode, where they react with the fuel (H2, CO, etc..) generating an electrical current. 

In Japan, Takahashi, after investigations with alkali carbonate electrolytes, published in 1964 his first results obtained on fuel cells with solid oxide electrolytes [66]. 

As with batteries, differences in electrolytes create several types of fuel cells. The automobile s demanding requirements for compactness and fast start-up have led to the Proton Exchange Membrane (PEM) fuel cell being the preferred type. This fuel cell has an electrolyte made of a solid polymer. 

In recent years it was shown that solid electrolyte fuel cells with appropriate electrocatalytic anodes can be used for chemical cogeneration i.e. for the simultaneous production of electrical power and useful chemicals. 

Table 3.2. Electrocatalytic reactions investigated in doped Zr02 solid electrolyte fuel cells with external potential application...

In this section we treat some electrochemical reactions at interfaces with solid electrolytes that have been chosen for both their technological relevance and their scientific relevance. The understanding of the pecularities of these reactions is needed for the technological development of fuel cells and other devices. Investigation of hydrogen or oxygen evolution reactions in some systems is very important to understand deeply complex electrocatalytic reactions, on the one hand, and to develop promising electrocatalysts, on the other. 

Leng YJ, Chan SH, Khor KA, and Jiang SP. Performance evaluation of anode-supported solid oxide fuel cells with thin-film YSZ electrolyte. Int J Hydrogen Energy 2004 29 1025-1033. 

Progress continues in fuel cell technology since the previous edition of the Fuel Cell Handbook was published in November 1998. Uppermost, polymer electrolyte fuel cells, molten carbonate fuel cells, and solid oxide fuel cells have been demonstrated at commercial size in power plants. The previously demonstrated phosphoric acid fuel cells have entered the marketplace with more than 220 power plants delivered. Highlighting this commercial entry, the phosphoric acid power plant fleet has demonstrated 95+% availability and several units have passed 40,000 hours of operation. One unit has operated over 49,000 hours. 

Shukla, A.K., Jackson, C.L., Scott, K., Murgia, G. 2002. A solid-polymer electrolyte direct methanol fuel cell with a mixed reactant and air anode. J Power Sources 111 43-51. 

It must be remembered that in aqueous systems the redox process occurs over the entire electrode area, whereas in solid electrolyte systems the redox process occurs only in the three-phase or charge-transfer region. The technique has been used with solid electrolyte systems for sometime to study the oxidation and reduction of metals and metal oxides in inert atmospheres,94,95 the behaviour of solid oxide fuel cell (SOFC) electrodes and has also been applied to the in-situ study of catalysts.31,32,95... 

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