In this work, a systematic work was performed to investigate the electrochemical transport properties of acceptor-doped BaZrO3 by measuring electromotive force on various gas concentration cells. For the measurements in the wet oxidizing atmosphere, where significant hole conduction occurs, the transport numbers of the ionic conduction in the oxidizing atmosphere were corrected by taking the effect of electrode polarization into consideration. The results revealed that regardless of whether Sc, Y, In, Ho, Er, Tm or Yb was doped, proton conduction predominates in the reducing atmosphere with the transport number close to unit. However, the contribution of ionic conduction weakens, and the contribution of hole conduction enhances, when the samples are exposed to the moist oxidizing atmosphere. In addition, introducing Ba-deficiency results in degraded electrochemical conductivity, but the transport number in either the moist reducing or the moist oxidizing atmosphere does not change obviously.

Lanthanum polyphosphate (LaP 3 O 9 ) is an attractive candidate for the electrolytes in fuel cells because of its relatively high proton conductivity. However, the proton conduction mechanism in LaP 3 O 9 (i.e., proton transport pathways and its relationship with the crystal structure) still remains poorly understood; thus, there has been no clear strategy for enhancing the conductivity. In this paper, we show that the fast and anisotropic proton conduction pathways exist along the b-and c-axes in the crystal lattice of LaP 3 O 9 , and the proton conductivity can be remarkably improved by controlling the microstructure of the electrolyte membranes. The first-principles calculations reveal that protons migrate only along the neighbors of specific oxide ions in the PO 4 chains, leading to the conductivity anisotropy, which is readily confirmed using Sr-doped LaP 3 O 9 single crystals. The c-axis oriented, coarse-grained polycrystalline membranes of Sr-doped LaP 3 O 9 prepared by solution synthesis techniques exhibit markedly enhanced conductivity compared to randomly oriented polycrystals prepared by solid state reaction and have direct applicability to fuel cell electrolytes. The discovery of fast proton conduction pathways in LaP 3 O 9 will motivate further development of LaP 3 O 9 -based electrolytes as well as exploration of new proton conducting crystalline polyphosphates with infinite chains of PO 4 tetrahedra.

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BaZr 0.8 Y 0.2 O 3Àd (BZY20) is a promising candidate as an electrolyte in protonic ceramic fuel cells (PCFCs), and nickel (Ni) is known to show good electrode properties for the anode reaction. However, their compatibility seems to be questionable, since during the co-sintering process for cell fabrication, a second phase of BaY 2 NiO 5 formed due to a reaction between BZY20 and NiO. The results in this work revealed that BaY 2 NiO 5 was unstable against high temperature (1500 and 1600 C), and could also be reduced in a hydrogen atmosphere at 600 C. The products of these reactions may affect fuel cell performance. A systematic work was then performed to provide fundamental insight into the reactivity between BZY20 and NiO, which was found to be impacted significantly by the compositional homogeneity of the BZY20 powder used for cell fabrication, and also the BaO activity during the cosintering process. It is concluded that improving the compositional homogeneity of BZY20, by elevating the final heating temperature for BZY20 from 1300 to 1600 C in this work, and choosing a proper sintering strategy may improve effectively the phase purity of the cell.