Proton-conducting yttrium-doped barium cerate ceramics synthesized by a cost-effective solid-state reactive sintering method

Ceramic pellets of the prototypical proton conductor BaCe0.8Y0.2O3 − δ (BCY20) were synthesized using the recently developed solid-state reactive sintering (SSRS) method [J. Tong et al., Solid State Ionics, 2010, 181, 496–503] from inexpensive raw materials of BaCO3, CeO2, and Y2O3 with less than 2 wt.% NiO as a sintering aid. The sintering aid amount, sintering temperature, and sintering time were optimized by analyzing the crystal structure, relative density, and morphology for a series of as-sintered BCY20 ceramic pellets. High-quality, fully-densified BCY20 ceramic pellets were successfully prepared using 1.0 wt.% NiO loading at a sintering temperature of 1400 °C for 12 h. In order to examine the fate of the NiO addition in the as-fabricated (oxidized) pellets and under reducing conditions, the microstructure of several as-sintered and reduced BCY20 ceramic pellets were investigated in detail by EDS mapping and compared with as-sintered and reduced control BCY20 ceramic pellets obtained from polymeric sol–gel powder. Upon reduction, nanosized nickel particles were accumulated in grain boundary regions of the NiO-modified BCY20 pellets, while Y2O3 second-phase impurities were identified in the sol–gel BCY20 control pellets. The conductivities of both the NiO-modified SSRS and sol–gel control BCY20 ceramic pellets were investigated from 150 to 650 °C under H2O saturated (PH2O~ 0.025 atm) atmospheres of UHP Ar and 5 vol.% H2 + 95 vol.% Ar. The NiO-modified SSRS-fabricated BCY20 pellets demonstrated significantly higher conductivities than the sol–gel fabricated control BCY20 pellets.