Abstract
The electrode performance and degradation of 1:1 La2−xNiTiO6−δ:YSZ composites (x = 0, 0.2) has been investigated to evaluate their potential use as SOFC cathode materials by combining electrochemical impedance spectroscopy in symmetrical cell configuration under ambient air at 1173 K, XRD, electron microscopy and image processing studies. The polarisation resistance values increase notably, i.e., 0.035 and 0.058 Ωcm2 h−1 for x = 0 and 0.2 samples, respectively, after 300 h under these demanding conditions. Comparing the XRD patterns of the initial samples and after long-term exposure to high temperature, the perovskite structure is retained, although La2Zr2O7 and NiO appear as secondary phases accompanied by peak broadening, suggesting amorphization or reduction of the crystalline domains. SEM and TEM studies confirm the ex-solution of NiO with time in both phases and also prove these phases are prone to disorder. From these results, degradation in La2−xNiTiO6−δ:YSZ electrodes is due to the formation of La2Zr2O7 at the electrode–electrolyte interface and the ex-solution of NiO, which in turn results in the progressive structural amorphization of La18NiTiO6−δ phases. Both secondary phases constitute a non-conductive physical barrier that would hinder the ionic diffusion at the La2−xNiTiO6−δ:YSZ interface and oxygen access to surface active area.
Highlights
Solid oxide fuel cells (SOFCs) are unique electrochemical devices for combined heat and electricity generation in terms of efficiency and environmentally friendly
Considering these results, the use of these materials as cathode for SOFC operation at 1173 K is not feasible and should be kept at lower temperatures. This process may occur in other systems where nanoparticle exsolution is considered as a strategy to produce in situ catalysts and boost the electrochemical performance in SOFC electrodes and an evaluation of the materials structure after long-term tests would be desirable
The degradation of the polarisation resistance in La2−x NiTiO6− δ :YSZ composite electrodes (x = 0, 0.2) for SOFC cathode applications has been assessed by a combination of long-term impedance spectroscopy measurements at 1173 K with XRD and electron microscopy
Summary
Solid oxide fuel cells (SOFCs) are unique electrochemical devices for combined heat and electricity generation in terms of efficiency and environmentally friendly. These costly requirements can be partly achieved overusing alternative accelerated lifetime tests (ALTs) to force the operative degradation mechanisms and accelerate the components stress; it would be possible to obtain illustrative and comparably features about the performance losses in the long-term operative SOFC procedure [40,41,42] Within this context, this research outlines a new degradation study on alternative cathode materials, i.e., La2−x NiTiO6−δ [43,44,45], as they exhibited good thermal and chemical stability and a very promising polarisation resistance at 1073 K, ~0.5 Ω cm , which makes them prospective cathode materials. This test, performed at temperatures higher than the usual working SOFC temperatures, i.e., 1173 K, allow us to shed light on the degradation mechanism involved in the cathodic reactions related with these compounds and define their potential working conditions
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