(Invited) Proton Transport Properties of Yb-Doped BaZrO₃ and Its Application to High Efficiency Proton Ceramic Fuel Cell

Barium zirconate have high chemical stability with CO2 comparison with barium cerate. Acceptor doped barium zirconate show high proton conductivity [1]. The proton conductivity of yttrium doped barium zirconate is 1×10-2 Scm-1 at 600 ℃ and it is attracted as the electrolyte of fuel cell and water vapor electrolysis cell. The fuel cell using proton conducting oxide was called to PCFC (proton ceramic fuel cell) and work at the intermediate temperature. PCFC is expected to be the energy conversion device in future because of high efficiency [2] and low production cost [3]. Generally, nickel is used as anode of PCFC. The anode overpotential of nickel is lower than that of the other metals. However, the nickels dissolve to the proton conducting oxide and possibly increase the ohmic resistance of electrolyte. Moreover, the nickel and the electrolyte possibly form the blocking layer such as the complex oxide. Although the proton conductivity of yttrium doped barium zirconate is highest in the zirconate-type proton conductor, BaY2NiO5 is formed between the nickel and the yttrium doped barium zirconate [4] and it might work as the blocking layer of proton. In this study, the reaction product between NiO and BaZr0.8 M 0.2O3-δ (M=Sc, In, Yb, Y, Gd) were confirmed by X-ray diffraction analysis. In order to clarify the NiO dissolution effect on the proton transport properties of BaZr0.8 M 0.2O3-δ (M=Sc, In, Lu, Yb, Y), the partial conductivity of the proton and the hole for BaZr0.8 M 0.2O3-δ (M=Sc, In, Lu, Yb, Y) with NiO were measured at temperature range of 200-600 ℃ by impedance analysis. The current efficiency on the polarization properties, then was examined for the fuel cell system using Acceptor-doped barium zirconate with NiO as electrolyte. Moreover, we investigated the effect of dopants on the ease of cell fabrication. The conventional ceramic tape-casting and firing process for fabricating laminated ceramic electronic devices was used, which is important for practical use. The power generation performance of planer cells fabricated by this process was also measured. The X-ray diffraction patterns of 0.4 mol% NiO doped BaZr0.8 M 0.2O3-δ (M= Sc, In, Yb, Y, Gd) were measured for the the samples as-sintered and annealed under 1%H2 at 873K. The peak of the NiO or Ni phase except the barium zircanate phase was observed for 0.4 mol% NiO doped BaZr0.8 M 0.2O3-δ (M= Sc, In, Yb). On the other hand, the BaM 2NiO5 phase was observed for M=Y, Gd. When the ionic radius of dopant is in excess of the size of Yb, the BaM 2NiO5 was formed as the reaction product between NiO and BaZr0.8 M 0.2O3-δ. The proton conductivity of the series of BaZr0.8 M 0.2O3-δ containing no NiO increased in the order of In更多