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Protonic and Electronic Conduction in Proton Conductive Solid Oxide Fuel Cells

Published online by Cambridge University Press:  10 August 2011

V. Hugo Schmidt  and
Chih-Long Tsai
V. Hugo Schmidt
Affiliation:
Department of Physics, Montana State University, Bozeman, MT 59717, U.S.A.
Chih-Long Tsai
Affiliation:
Department of Physics, Montana State University, Bozeman, MT 59717, U.S.A.
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Abstract

Protons can fit into the perovskite structure because the O-O distance is approximately that of ice. However, to achieve charge balance, -2e charge must be added for every two protons added. If O2- vacancies are introduced, for instance by doping barium cerate with yttrium to obtain (BCY), each filled vacancy will add -2e charge. Proton concentration and conductivity can be increased by exposing BCY to steam molecules, which dissociate into 2 protons and an O2- ion. Our impedance spectroscopy measurements and solid oxide fuel cell (SOFC) work shows that exposure to H2 on the anode side can add protons. This requires addition of O2- ions on the cathode side from O2 in air. Alternatively, electrons could be added because BCY is a weak electronic semiconductor. BCY is a hole conductor, and this conductivity decreases upon exposure to steam or H2. From our analysis of V(i) curves for SOFCs with BCY electrolyte, at low H2 concentration, increasing this concentration decreases electronic conductivity somewhat, consistent with adding electrons and reducing hole carrier concentration. At higher H2 concentrations, electronic conductivity remains constant.

Proton transfer in perovskites such as BCY resembles that in usual H‑bonded crystals. Such transfer requires two steps, both needed for dc conductivity. One is intrabond proton transfer, O‑H O→O H-O. The other is a proton jump from one H-bond to an adjacent bond, equivalent to rotation of an O-H unit about the O ion. The main difference from usual H-bonded crystals is that the adjacent O-O pair most likely has no proton between the O ions, so that the Pauling ice rule precluding 2 protons in one bond is not much of a restriction in perovskites because the proton concentration is typically below 0.2 per formula unit. Another difference is that, though protonic semiconductor activation energies are high, in the 0.5 to 1 eV range, the high operating temperatures of SOFCs, 600 to 900 oC, give useful amounts of power per unit area, or in the electrolysis mode, useful amounts of H2 out for steam and electric power input.

Two applications for proton-conducting perovskite ceramics are SOFCs and hydrogen separation membranes (HSMs). For SOFCs, we have modeled the V(i) behavior with almost no adjustable parameters, and have succeeded in coming close to the Nernst open‑circuit potential as well as fitting the V(i) curves for a variety of H2/O2 partial pressure combinations. For HSMs, unlike for SOFCs, an electronic conductivity comparable to the protonic conductivity is desirable, to avoid using a cermet which may crack because of differential thermal expansion.

In conclusion, many oxides and fluorides have O-O or F-F separations in the H‑bonding range and will provide a stimulating playground for further basic and applied research on proton incorporation and dynamics in solids.

Keywords

hydrogenationionic conductorelectrical properties
Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 1330: Symposium J – Protons in Solids , 2011 , mrss11-1330-j04-05
Copyright
Copyright © Materials Research Society 2011

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References

REFERENCES

1. Schmidt, V. H., in Physics and Chemistry of Ice, Whalley, E., Jones, S. J., and Gold, L. W., Eds., Royal Society of Canada, Ottawa, 1973, pp. 212–217.Google Scholar
2. Schmidt, V. H. and Uehling, E. A., Phys. Rev. 126, 447–457 (1962).Google Scholar
3. Schmidt, V. H., J. Sci. Instrum. 42, 889–890 (1965).Google Scholar
4. Schmidt, V. H., Western, A. B., and Baker, A. G., Phys. Rev. Lett. 37, 839–842 (1976).Google Scholar
5. Schmidt, V. H., Ferroelectrics 72, 157–173 (1987).Google Scholar
6. Trybula, Z., Schmidt, V. H., and Drumheller, J. E., Phys. Rev. B 43, 1287–1289 (1991).Google Scholar
7. Sinitski, A. and Schmidt, V. H., Phys. Rev. B 54, 842–848 (1996).Google Scholar
8. Schmidt, V. H. and Parker, R. S., J. de Physique, Coll. C2, suppl. 4, 33, C2–109–111 (1972).Google Scholar
9. Vanderkooy, J., Cuthbert, J. D., and Petch, H. E., Canad. J. Phys. 42, 1871–1878 (1964).Google Scholar
10. Kreuer, K. D., Annu. Rev. Mater. Res. 33, 333–359 (2003).Google Scholar
11. Tomita, A., Hibino, T., and Sano, M., Electrochem. and Solid-State Lett. 8, A333–A336 (2005).Google Scholar
12. Fu, X., Luo, J., Sanger, A. R.. Luo, N., and Chuang, K. T., J. Power Sources, 195, 22659‑2663 (2010).Google Scholar
13. Melnik, J., Sanger, A. R., Tsyganok, A., Luo, J. L., and Chuang, K. T., J. Power Sources, 185, 1101–1106 (2008).Google Scholar
14. Xie, K., Yan, R., and Liu, X., J. Alloys and Compounds 47, L40–L42 (2009).Google Scholar
15. Gorelov, V. P., Balakireva, V. B., Kleshchev, Y. N., and Brusentsov, V. P., Inorganic Materials, 37, 535–538 (2001).Google Scholar
16. Fabbri, E., Pergolesi, D., and Traversa, E., Sci. Technol. Adv. Mater. 11, 044301 (2010).Google Scholar
17. Malavasi, L., Fisher, C. A. J., and Islam, M. S., Chem. Soc. Rev. 39, 4370–4387 (2010).Google Scholar
18. Guan, J., Dorris, S. E., Balachandran, U., and Liu, M., J. Electrochem. Soc., 145, 1780–1786 (1998).Google Scholar
19. Katahira, K., Kohchi, Y., Shimura, T., and Iwahara, H., Solid State Ionics 138, 91–98 (2000).Google Scholar
20. Iwahara, H., Solid State Ionics, 77, 289–298 (1995).Google Scholar
21. Babilo, P., Uda, T., and Haile, S. M., J. Mater. Res., 22, 1322–1330 (2007).Google Scholar
22. Ryu, K. H. and Haile, S. M., Solid State Ionics, 125, 355–367 (1999).Google Scholar
23. Coors, W. G. and Zhong, D., Solid State Ionics 162-163, 283–290 (2003).Google Scholar
24. Guan, J., Dorris, S. E., Balachandran, U., and Liu, M., Solid State Ionics 110, 45‑52 (1997).Google Scholar
25. Suksamai, W. and Metcalfe, I. S., Solid State Ionics 178, 627–634 (2007).Google Scholar
26. Tsai, C. L. and Schmidt, V. H., J. Power Sources, 196, 692–699 (2011).Google Scholar
27. Tsai, C. L. and Schmidt, V. H., J. Electrochem. Soc. (accepted) (2011).Google Scholar
28. Wu, Z. and Liu, M., J. Electrochem. Soc., 144, 2170–2175 (1997).Google Scholar
29. Bhide, S. V. and Virkar, A. V., J. Electrochem. Soc. 146, 2038–2044 (1999).Google Scholar
30. Ma, G., Shimura, T., and Iwahara, H., Solid State Ionics 120, 51–60 (1999).Google Scholar
31. Coors, W. G. and Readey, D. W., J. Am. Ceram. Soc. 85, 2637–2640 (2002).Google Scholar
32. Bertolo-Pardo, M. E. et al. ., Proc. 11th Internat. Conf. on Solid State Protonic Conductors, PB3, 27–30 Aug. 2002.Google Scholar