Oxide ion and proton conductors, which exhibit high conductivity at intermediate temperature, are necessary to improve the performance of ceramic fuel cells. The crystal structure plays a pivotal role in defining the ionic conduction properties, and the discovery of new materials is a challenging research focus. Here, we show that the undoped hexagonal perovskite Ba7Nb4MoO20 supports pure ionic conduction with high proton and oxide ion conductivity at 510 °C (the bulk conductivity is 4.0 mS cm−1), and hence is an exceptional candidate for application as a dual-ion solid electrolyte in a ceramic fuel cell that will combine the advantages of both oxide ion and proton-conducting electrolytes. Ba7Nb4MoO20 also showcases excellent chemical and electrical stability. Hexagonal perovskites form an important new family of materials for obtaining novel ionic conductors with potential applications in a range of energy-related technologies.
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The data that support the findings of this study are available from the authors on reasonable request.
Steele, B. C. H. & Heinzel, A. Materials for fuel-cell technologies. Nature 414, 345–352 (2001).
Duan, C. et al. Readily processed protonic ceramic fuel cells with high performance at low temperatures. Science 349, 1321–1326 (2015).
Wachsman, E. D. & Lee, K. T. Lowering the temperature of solid oxide fuel cells. Science 334, 935–939 (2011).
Jacobson, A. J. Materials for solid oxide fuel cells. Chem. Mater. 22, 660–674 (2010).
Abraham, F., Boivin, J. C., Mairesse, G. & Nowogrocki, G. The BIMEVOX series: a new family of high performances oxide ion conductors. Solid State Ion. 40-41, 934–937 (1990).
Huang, K., Tichy, R. S. & Goodenough, J. B. Superior perovskite oxide-ion conductor; strontium- and magnesium-doped LaGaO3: I, phase relationships and electrical properties. J. Am. Ceram. Soc. 81, 2565–2575 (1998).
Li, M. et al. A family of oxide ion conductors based on the ferroelectric perovskite Na0.5Bi0.5TiO3. Nat. Mater. 13, 31–35 (2013).
Shin, J. F., Orera, A., Apperley, D. C. & Slater, P. R. Oxyanion doping strategies to enhance the ionic conductivity in Ba2In2O5. J. Mater. Chem. 21, 874–879 (2011).
Kendrick, E., Islam, M. S. & Slater, P. R. Developing apatites for solid oxide fuel cells: insight into structural, transport and doping properties. J. Mater. Chem. 17, 3104–3111 (2007).
Kendrick, E., Kendrick, J., Knight, K. S., Islam, M. S. & Slater, P. R. Cooperative mechanisms of fast-ion conduction in gallium-based oxides with tetrahedral moieties. Nat. Mater. 6, 871–875 (2007).
Kuang, X. et al. Interstitial oxide ion conductivity in the layered tetrahedral network melilite structure. Nat. Mater. 7, 498–504 (2008).
Yang, X. et al. Cooperative mechanisms of oxygen vacancy stabilization and migration in the isolated tetrahedral anion Scheelite structure. Nat. Commun. 9, 4484 (2018).
Kreuer, K. D. Proton-conducting oxides. Annu. Rev. Mater. Res. 33, 333–359 (2003).
Fabbri, E., Pergolesi, D. & Traversa, E. Materials challenges toward proton-conducting oxide fuel cells: a critical review. Chem. Soc. Rev. 39, 4355–4369 (2010).
Zhang, G. B. & Smyth, D. M. Protonic conduction in Ba2In2O5. Solid State Ion. 82, 153–160 (1995).
Haugsrud, R. & Norby, T. Proton conduction in rare-earth ortho-niobates and ortho-tantalates. Nat. Mater. 5, 193–196 (2006).
Bae, K. et al. Demonstrating the potential of yttrium-doped barium zirconate electrolyte for high-performance fuel cells. Nat. Commun. 8, 14553 (2017).
Choi, S. et al. Exceptional power density and stability at intermediate temperatures in protonic ceramic fuel cells. Nat. Energy 3, 202–210 (2018).
Zakowsky, N., Williamson, S. & Irvine, J. T. S. Elaboration of CO2 tolerance limits of BaCe0.9Y0.1O3–δ electrolytes for fuel cells and other applications. Solid State Ion. 176, 3019–3026 (2005).
Bhide, S. V. & Virkar, A. V. Stability of BaCeO3-based proton conductors in water-containing atmospheres. J. Electrochem. Soc. 146, 2038–2044 (1999).
Sažinas, R., Bernuy-López, C., Einarsrud, M. & Grande, T. Effect of CO2 exposure on the chemical stability and mechanical properties of BaZrO3-ceramics. J. Am. Ceram. Soc. 99, 3685–3695 (2016).
Jankovic, J., Wilkinson, D. P. & Hui, R. Proton conductivity and stability of Ba2In2O5 in hydrogen containing atmospheres. J. Electrochem. Soc. 158, B61–B68 (2011).
Shin, J. F. & Slater, P. R. Enhanced CO2 stability of oxyanion doped Ba2In2O5 systems co-doped with La, Zr. J. Power Sources 196, 8539–8543 (2011).
D’Epifanio, A., Fabbri, E., Di Bartolomeo, E., Licoccia, S. & Traversa, E. Design of BaZr0.8Y0.2O3–δ protonic conductor to improve the electrochemical performance in intermediate temperature solid oxide fuel cells (IT-SOFCs). Fuel Cells 8, 69–76 (2008).
Yang, L. et al. Enhanced sulphur and coking tolerance of a mixed ion conductor for SOFCs: BaZr0.1Ce0.7Y0.2-xYbxO3-δ. Science 326, 126–129 (2009).
Zhou, C. et al. New reduced-temperature ceramic fuel cells with dual-ion conducting electrolyte and triple-conducting double perovskite cathode. J. Mater. Chem. A. 7, 13265–13274 (2019).
Katz, L. & Ward, R. Structure relations in mixed metal oxides. Inorg. Chem. 3, 205–211 (1964).
Darriet, J. & Subramanian, M. A. Structural relationships between compounds based on the stacking of mixed layers related to hexagonal perovskite-type structures. J. Mater. Chem. 5, 543–552 (1995).
Fop, S. et al. Oxide ion conductivity in the hexagonal perovskite derivative Ba3MoNbO8.5. J. Am. Chem. Soc. 138, 16764–16769 (2016).
McCombie, K. S. et al. The crystal structure and electrical properties of the oxide ion conductor Ba3WNbO8.5. J. Mater. Chem. A. 6, 5290–5295 (2018).
Garcia-González, E., Parras, M. & González-Calbet, J. M. Crystal structure of an unusual polytype: 7H-Ba7Nb4MoO20. Chem. Mater. 11, 433–437 (1999).
Irvine, J. T. S., Sinclair, D. C. & West, A. R. Electroceramics: characterization by impedance spectroscopy. Adv. Mater. 2, 132–138 (1990).
Chambers, M. S. et al. Hexagonal perovskite related oxide ion conductor Ba3NbMoO8.5: phase transition, temperature evolution of the local structure and properties. J. Mater. Chem. A. 7, 25503–25510 (2019).
Auckett, J. E., Milton, K. L. & Evans, I. R. Cation distributions and anion disorder in Ba3NbMO8.5 (M = Mo, W) materials: implications for oxide ion conductivity. Chem. Mater. 31, 1715–1719 (2019).
Yashima, M. et al. Direct evidence for two-dimensional oxide-ion diffusion in the hexagonal perovskite-related oxide Ba3MoNbO8.5-δ. J. Mater. Chem. A. 7, 13910–13916 (2019).
Islam, M. S. Computer modelling of defects and transport in perovskite oxides. Solid State Ion. 154-155, 75–85 (2002).
Wind, J., Mole, R. A., Yu, D., Avdeev, M. & Ling, C. D. Hydration mechanisms and proton conduction in the mixed ionic-electronic conductors Ba4Nb2O9 and Ba4Ta2O9. Chem. Mater. 30, 4949–4958 (2018).
Kim, G., Griffin, J. M., Blanc, F., Haile, S. M. & Grey, C. P. Characterization of the dynamics in the protonic conductor CsH2PO4 by 17O solid-state NMR spectroscopy and first-principles calculations: correlating phosphate and protonic motion. J. Am. Chem. Soc. 137, 3867–3876 (2015).
Huse, M. et al. Neutron diffraction study of the monoclinic to tetragonal structural transition in LaNbO4 and its relation to proton mobility. J. Solid State Chem. 187, 27–34 (2012).
Yamazaki, Y., Babilo, P. & Haile, S. M. Defect chemistry of yttrium-doped barium zirconate: a thermodynamic analysis of water uptake. Chem. Mater. 20, 6352–6357 (2008).
Noirault, S. et al. Water incorportation into the (Ba1-xLax)2In2O5+x□1-x (0 ≤ x ≤ 0.6) system. Solid State Ion. 178, 1353–1359 (2007).
Bielecki, J., Parker, S. F., Mazzei, L., Börjesson, L. & Karlsson, M. Structure and dehydration mechanism of the proton conducting oxide Ba2In2O5(H2O)x. J. Mater. Chem. A. 4, 1224–1232 (2016).
Dunstan, M. T. et al. Phase behavior and mixed ionic–electronic conductivity of Ba4Sb2O9. Solid State Ion. 235, 1–7 (2013).
Rahman, S. M. H. et al. Proton conductivity of hexagonal and cubic BaT1-xScxO3-δ (0.1 ≤ x ≤ 0.8). Dalton Trans. 43, 15055–15064 (2014).
Tabacaru, C. et al. Protonic and electronic defects in the 12R-type hexagonal perovskite Sr3LaNb3O12. Solid State Ion. 253, 239–246 (2013).
Kultz. Unti, L. F., Grzebielucka, E. C., Antonio Chinelatto, A. S., Mather, G. C. & Chinelatto, A. L. Synthesis and electrical characterization of Ba5Nb4O15 and Ba5Nb3.9M0.1O(15-δ) (M = Ti, Zr) hexagonal perovskites. Ceram. Int. 45, 5087–5092 (2019).
Nomura, K. & Kageyama, H. Transport properties of Ba(Zr0.8Y0.2)O3−δ perovskite. Solid State Ion. 178, 661–665 (2007).
Fop, S. et al. Investigation of the relationship between the structure and conductivity of the novel oxide ionic conductor Ba3MoNbO8.5. Chem. Mater. 29, 4146–4152 (2017).
Fop, S., McCombie, K. S., Wildman, E. J., Skakle, J. M. S. & Mclaughlin, A. C. Hexagonal perovskite derivatives: a new direction in the design of oxide ion conducting materials. Chem. Commun. 55, 2127–2137 (2019).
This research was supported by the Leverhulme trust and EPSRC (MISE). We also acknowledge STFC-GB for provision of beamtime at the Institut Laue Langevin.
The authors declare that they have no competing interests.
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Fop, S., McCombie, K.S., Wildman, E.J. et al. High oxide ion and proton conductivity in a disordered hexagonal perovskite. Nat. Mater. (2020). https://doi.org/10.1038/s41563-020-0629-4