Oxide proton-conducting

Mother compounds like SrCeOs or BaCe03 are not good conductors in themselves. However, after doping with aliovalent cations, mainly rare earth cations such as Y or Yb, electron hole conductivity appears. For example, 

BaTh03 and BaTb03 doped with Gd are also reported as possible protonconducting electrolytes for intermediate temperature SOFCs [106, 107], Sammells et al. reported that BaTho.9Gao.3O3, Sr2Gd20s, and Sr2Dy 205 were 

During the past decades, many oxide formulations have been extensively examined in the search for candidate SOFC electrolyte materials. Zirconia-based compositions are still the best electrolytes at present owing to their good stability under reducing atmospheres, low electronic conductivity, and acceptable oxide ion conductivity above 800°C. The recent trend of SOFC development is to operate at lower temperatures. The lowest operation temperature limit of the cell, for thin YSZ electrolytes, is estimated to be about 700°C from YSZ conductivity and mechanical property data. Scandia-doped zirconia, which shows a higher conductivity than that of YSZ, could be preferred at temperatures below 700°C, if the cost of scandia was acceptable. 

Ceria-based electrolytes could be used at 550°C or less. To operate at higher temperatures, a dual layer electrolyte, with a thin YSZ layer on CGO, has been proposed to avoid the electronic current leakage. The interdiffusion issues at the interface are important in this case for long-life electrolytes. 

Another possibility is to use perovskite compositions. The most promising candidate at this time is LaGaOj doped with Sr and Mg. Other possible perovskites are Ba2 In205 doped with Ce or La. Other ionic conducting oxides have also been found including La ioSi6026 composition. Proton conductors such as SrCeOs, SrZrOs or BaCeOs doped with Y or Yb may also be effective electrolytes, but reaction with CO2 has to be resolved first. 

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Figure 22. Partially self-regulated methane reforming in an SOFC operating with a proton conducting oxidic electrolyte as suggested by Coors163 (see text) top) the overall cell reaction and bottom) the back diffusion step.164 Reprinted from K.D. Kreuer, Arum. Rev. Mater. Res., 33 (2003) 333-359. Copyright 2003 with permission from Annual Reviews.

Keywords Compact fuel cell Proton conductive oxide Radiation induced conductivity Radiation enhanced diffusion... 

Iwahara, H., High temperature proton conducting oxides and their applications to solid electrolyte fuel cells and steam electrolyzer for hydrogen production. Solid State Ionics, 28/30, 573, 1988. 

Synthesize cerate and zirconate proton-conducting oxides from the component oxides. 

Synthesized SrCeo 95Ybo,o503-x nd SrZrg 9Y0 1O3.X proton-conducting oxides. 

Confirmed the orthorhombic crystal structure of the proton-conducting oxides using X-ray diffraction. The lattice parameters of the proton-conducting oxides were also measured. 

In investigations of proton conducting and mixed proton conducting oxides, one is usually interested in finding the concentration of protons and their role in the defect structure. Absolute measures of the proton content can be determined with a number of methods, most commonly and simply by thermogravimetry (TG). Various procedures are in use ... 

Acceptor-doped SrCe03 is, without doubt, the mixed electron-proton conducting oxide system most studied, both with respect to actual measurements of... 

Okada S, Mineshige A, Kikuchi T, Kobune M, Yazawa T (2007) Cermet-type hydrogen separation membrane obtained from fine particles of high temperature proton-conductive oxide and palladium. Thin Solid Films 515 7342-7346... 

The high temperature proton conducting oxides described here are perovskites based on SrCe03 or BaCeO in which some trivalent cations... 

In this experiment, undoped SrCeOj released little water vapour, but Yb-doped proton conducting oxides evolved a substantial amount of water vapour on raising the temperature. The 5% Yb-doped oxide released a larger amount of water vapour than the 3% doped specimen. This indicates that the higher the vacancy concentration produced by Yb-doping, the higher the proton concentration in the oxides. 

Sensors based on protonically conducting oxides 7.4.1. Hydrogen sensors... 

Many perovskite-type (ABO3) oxides show high proton conductivity in a reducing atmosphere. The most common proton-conducting oxide is BaCeOs, which has been doped with various oxides, including those of samarium (Ranran et al, 2006), neodymium (Schober, 2003 Kobayashi et al, 2005 Gorbova et al, 2006 Su et al, 2006) and ytterbium (Taherparvar et al,... 

Other proton-conducting oxides for potential use in SOFCs include BaScosZrosOs, (La,Pr)o.9Bai iGaOj 95 and Ndo.9BanGa03 95 (Kendrick et al, 2005). 

Tao S W and Irvine ITS (2006), A stable, easily sintered proton-conducting oxide electrolyte for moderate-temperature fuel cells and electrolyzers , Adv Mater, 18,1581-1584. 

In proton-conducting oxides, the increase of oxygen partial pressure when using high partial pressure of water will decrease the proton conductivity of the electrolyte according to the following equation ... 

At the moment, highly Y-doped BaZr03 seems to be the only proton-conducting oxide, which meets the essential requirements for SOFC electrolyte materials. Surprisingly, the development of this material required very little compromising, which can be understood from the above considerations. 

Yamaguchi, S, Yamamoto, S, Tsuchiya, B., Nagata, S, ShiShido, T. Construction of fuel reformer using proton conducting oxides electrolyte and hydrogen-permeable metal membrane cathode. J. Power Sources 2005 145 712-715. 

Kreuer KD (2003) Proton-conducting oxides. Annu Rev Mater Res 33 333-359... 

Fabbri E, Pergolesi D, Traversa E (2010) Materials challenges toward proton-conducting oxide fuel cells a critical review. Chem Soc Rev 39 4366-4369... 

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