Toward improved chemical stability of yttrium‐doped barium cerate by the introduction of nickel oxide

Abstract

AbstractIn this work, we demonstrate that the introduction of a small amount of NiO (1.8 wt%) to the proton‐conducting perovskite yttrium‐doped barium (BaCe0.9Y0.1O3−δ, BCY10) can radically improve its chemical stability, even in conditions of very high carbon dioxide partial pressure (pO2 = 1 atm) and wet conditions (pH2O = 0.033 atm). To this end, we test sets of unmodified and NiO‐modified BCY samples sintered at different temperatures to achieve different grain sizes. Long‐term stability measurements up to 720 h at 400°C, under these conditions, reveal a noticeable drop in conductivity for the unmodified samples, scaling with decreasing grain size, due to the formation of barium carbonate. Conversely, the NiO‐modified samples show no apparent degradation, with a stable conductivity performance retained over 720 h, irrespective of grain sizes. We tentatively attribute this unusual behavior to the increased chemical resistance of the perovskite phase due to an increase in the aNiO/aBaO activity ratio at the bulk surfaces, which can prevent surface attack. Such an effect is supported by an observed increase in the Schottky barrier height, revealing a change in the specific grain boundary properties of the NiO‐modified samples. Conductivity measurements in wet O2 (pH2O = 0.033 atm) underscore that both the bulk and grain boundary terms of the conductivity of the NiO‐modified sample, sintered at 1350°C, are competitive with the unmodified BCY sample, sintered at 1450°C, even at temperatures as low as 400°C. The results here reported, thus, unlock a different perspective for these transition metal additives, to improve the chemical resistance of proton‐conducting ceramics perovskites.