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Higher N/O increases significantly the V(O,N) oxidation resistance.

Gd-doped ceria (Ce 1-x Gd x O 2-d ; x = 0, 0.1 and 0.2) is one of the best ceramic electrolytes for application in solid oxide electrochemical devices. This work reports an innovative and environmentally friendly route known as ''proteic sol-gel synthesis'' using gelatin for their preparation. Materials are characterized via thermogravimetric analysis, X-ray diffractometry, scanning electron microscopy, Raman and X-ray photoelectron spectroscopies, and electrochemical impedance spectroscopy. The proposed method allows to produce pure phase nanosized powders at 400 °C that exhibit excellent sinterability at 1350 °C. Significant differences are found in the bulk at lower temperatures, with estimated defect association enthalpies of 0.45 and 0.56 eV for the compositions containing 10 and 20 mol% Gd, respectively, leading to an increased bulk conductivity in the first case. In contrast, identical grain boundary Schottky barrier height values of around 0.2 V are a possible result of the relatively low sintering temperature, decreasing the extent of the acceptor dopant segregation to the grain boundaries due to insufficient cation mobility. This leads to similar specific grain boundary characteristics in both doped compositions. Overall, this work provides a rational understanding of a novel route for the synthesis of CGO ceramics with competitive performance and decreased sintering temperature.

In this work, we demonstrate that the introduction of a small amount of NiO (1.8 wt%) to the proton-conducting perovskite yttrium-doped barium (BaCe 0.9 Y 0.1 O 3−δ , BCY10) can radically improve its chemical stability, even in conditions of very high carbon dioxide partial pressure (p O2 = 1 atm) and wet conditions (p H2O = 0.033 atm). To this end, we test sets of unmodified and NiOmodified 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 a NiO /a BaO 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 O 2 (p H2O = 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.

Layered Ruddlesden-Popper (RP) lanthanide nickelates, Lnn+1NinO3n+1 (Ln = La, Pr, and Nd; n = 1, 2, and 3) have generated great interest as potential cathodes for proton conducting fuel cells (PCFCs). The high-order phase (n = 3) is especially intriguing, as it possesses the property of a high and metallic-type electronic conductivity that persists to low temperatures. To provide the additional requirement of high ionic conductivity, a composite electrode is here suggested, formed by a combination of La4Ni3O10±δ with the proton conducting phase BaCe0.9Y0.1O3-δ (40 vol%). Electrochemical impedance spectroscopy (EIS) is used to analyse this composite electrode in both wet (pH2O ~ 10−2 atm) and low humidity (pH2O ~ 10−5 atm) conditions in an O2 atmosphere (400–550 °C). An extended analysis that first tests the stability of the impedance data through Kramers-Kronig and Bayesian Hilbert transform relations is outlined, that is subsequently complemented with the distribution function of relaxation times (DFRTs) methodology. In a final step, correction of the impedance data against the short-circuiting contribution from the electrolyte substrate is also performed. This work offers a detailed assessment of the La4Ni3O10±δ-BaCe0.9Y0.1O3-δ composite cathode, while providing a robust analysis methodology for other researchers working on the development of electrodes for PCFCs.