Solid oxide fuel cells proton conducting

Iwahara, H., High temperature-type proton conductive solid oxide fuel cells using various fuels,/. Appl. Electrochem., 16, 663-668 (1986). 

Bi, L., Zhang, S., Fang, S., Tao, Z., Peng, R., Liu, W. (2008). A novel anode supported BaCeo.7Tao.iYo,203 5 electrolyte membrane for proton-conducting solid oxide fuel cell. Electrochemistry Commununications, 10, 1598—1601. 

Lu, X., Ding, Y., and Chen, Y. (2009) BaosSto Zno F o-sOs-fi BaCeo.5Zro.3Yo.i6Zno.o403 s composite cathode for proton-conducting solid oxide fuel cells. /, Alloys Compd., 484 (1-2), 856-859. 

Wu,T.Z., Rao,Y.Y., Peng, R.R. Xia, C.R. Fabrication and evaluation ofAg-impregnatedBaCeo.8Smo.202.9 composite cathodes for proton conducting solid oxide fuel-cells. J. Power Sources 195 (2010), pp. 5508-5513. 

Materials for Proton Conducting Solid Oxide Fuel Cells... 

Today, the term solid electrolyte or fast ionic conductor or, sometimes, superionic conductor is used to describe solid materials whose conductivity is wholly due to ionic displacement. Mixed conductors exhibit both ionic and electronic conductivity. Solid electrolytes range from hard, refractory materials, such as 8 mol% Y2C>3-stabilized Zr02(YSZ) or sodium fT-AbCb (NaAluOn), to soft proton-exchange polymeric membranes such as Du Pont s Nafion and include compounds that are stoichiometric (Agl), non-stoichiometric (sodium J3"-A12C>3) or doped (YSZ). The preparation, properties, and some applications of solid electrolytes have been discussed in a number of books2 5 and reviews.6,7 The main commercial application of solid electrolytes is in gas sensors.8,9 Another emerging application is in solid oxide fuel cells.4,5,1, n... 

Figure 29. Conductivity of some intermediate-temperature proton conductors, compared to the conductivity of Nafion and the oxide ion conductivity of YSZ (yttria-stabilized zirconia), the standard electrolyte materials for low- and high-temperature fuel cells, proton exchange membrane fuel cells (PEMFCs), and solid oxide fuel cells (SOFCs).

The purpose of the present review is to summarize the current status of fundamental models for fuel cell engineering and indicate where this burgeoning field is heading. By choice, this review is limited to hydrogen/air polymer electrolyte fuel cells (PEFCs), direct methanol fuel cells (DMFCs), and solid oxide fuel cells (SOFCs). Also, the review does not include microscopic, first-principle modeling of fuel cell materials, such as proton conducting membranes and catalyst surfaces. For good overviews of the latter fields, the reader can turn to Kreuer, Paddison, and Koper, for example. 

The most important fuel cells that are in use nowadays are the polymer electrolyte membrane fuel ceU (PEMFC), the molten carbonate fuel cell (MCFC), and the solid oxide fuel cell (SOFC). In a PEMFC, the electrolyte is a polymer membrane that conducts protons, in an MCFC the electrolyte is a carbonate melt in which oxygen is conducted in the form of carbonate ions, CO , and in an SOFC the electrolyte is a solid oxide that conducts oxygen ions, While a PEMFC can be operated at low temperatures of about 80 °C, an MCFC works at intermediate temperatures of about 650 °C, and an SOFC needs relatively high temperatures of 800-1000 °C (see next sections). 

The low ionic resistivities of these materials (reported to be under 10 Q cm at 1000°C in some compositions) make them very attractive candidates for use in electrochemical devices such as the solid oxide fuel cell. Their proton conductivity is highly dependent on the partial pressure of water in the atmosphere. Whether these materials exhibit longterm stability in highly oxidizing and/or highly reducing atmospheres remains to be seen. Many of the preparation techniques discussed for the oxygen ion conductors should be applicable to this relatively new class of ionic conductors. 

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... 

Figure 5.9 Solid oxide fuel cells schematic (a) oxygen ion conducting electrolyte (b) proton conducting electrolyte, both with gas as fuel...

There are several types of fuel cells, which are classified primarily by the kind of electrolyte they employ. The materials used for electrolytes have their best conductance only within certain temperature ranges (Hirschenhofer 1994). A few of the most promising types include phosphoric acid fuel cell (PAFC), molten carbonate fuel cell (MCFC), solid oxide fuel cell (SOFC), alkaline fuel cell (AFC), proton exchange membrane fuel cell (PEMFC), and direct methanol fuel cell (DMFC). 

Fu X Z, Luo J-L, Sanger A R, Xu Z-R and Chuang K T (2010), Fabrication of bi-layered proton conducting membrane for hydrocarbon solid oxide fuel cell... 

He F, Wu T, Peng R, Xia C (2009) Cathode reaction models and performance analysis of Smo.5Sro.5Co03 5-BaCeo.gSmo.203.s composite cathode for solid oxide fuel cells with proton conducting electrolyte. J Power Sources 194 263-268... 

At the university of Alberta in Canada, Fu et al. (2011) showed the possibility of cogenerating ethylene and electrical power by ethane dehydrogenation over a nano-Cr203 anode catalyst in a proton ceranfic fuel cell reactor having a BaCeOo.s.YOo os NdOo isOs-s (BCYN) perovskite oxide as proton-conducting ceramic electrolyte and Pt as cathode catalyst. The power density increased from 51 mW/cm to 118 mW/cm, and the ethylene yield increased from about 8% to 31% when the operating temperature of the solid oxide fuel cell reactor was increased from 650°C to 750°C. 

Ni, M., Leung, D.Y.C. Leung, M.K.H. Modeling of methane fed solid oxide fuel-cells comparison between proton conducting electrolyte and oxygen ion conducting electrolyte. J. Power Sources 183 (2008), pp. 133-142. 

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