High Temperature Proton Conductors (HTPCs) can be used as electrolytes in a Protonic Ceramic Fuel Cell (PCFC) or, in case of a mixed ionic and electronic conductivity, as membranes for hydrogen separation.

Solid solutions of barium cerate and zirconate have been widely studied because they represent a compromise between the relatively high proton conductivity of cerate and the chemical/mechanical stability of zirconate [1-2]. But the very high sintering temperatures required limit their use from an economic but also practical point of view. Indeed, in case of anode supported cells, potential electrode materials can’t resist these high temperatures. Doping with transition metals has been shown to promote sintering, for example, a 400°C decrease of the sintering temperature for Zn doped barium zirconate [3-4].

In this study, nickel and cobalt doping (from 1 to 5% of the B-site) is studied with two compositions: BaZr_0.9Y_0.1O_3-δ (BZY10) and BaCe_0.2Zr_0.7Y_0.1O_3-δ (BCZY27). The powders were synthesized by a solid state reaction at 1400°C and pellets sintered in air at temperature between 1350°C and 1450°C. Density percentages of about 95% could have been achieved for doped samples, compared to only 80% for the undoped ones. The conductivity of the samples has been determined using impedance spectroscopy. Measurement of the conductivity isotope effect by exchange with heavy water vapour has been used to identify the protonic component of the ionic conductivity.

References:

[1] K.H. Ryu, S.M. Haile, Solid State Ionics 125 (1999) 355

[2] K. Katahira, Y. Kohchi, T. Shimura, H. Iwahara, Solid State Ionics 138 (2000) 91

[3] P. Babilo, S.M. Haile, Jounal of American Ceramic Society 88 (2005) 2362

[4] S. Tao, J.T.S. Irvine, Journal of Solid State Chemistry 180 (2007) 2493

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