Correlation Studies of Electrochemical and Crystallographic Properties on SOFC and SOEC Related Materials by Simultaneous EIS and XRD in-operando Measurements

NAPOLITANO F.; MONTENEGRO HERNANDEZ A.; BASBUS J.F.; ARCE M.D.; MOGNI L.V; SERQUIS A,

Congreso; 229th ECS Meeting; 2016

Thecomplexity of the process involved in the development of new technologicaldevices requires the use of complementary characterization techniques in orderto understand the whole phenomena. A usual approach to study materials fordevices with non-ambient working conditionsis to perform the experimentsimulating the same environment (temperature, atmosphere, pressure, magneticfield, etc.). Although being a reasonable approach, this could fall short whenreal working conditions are more complex[1, 2].Nowadays, the implementation of in-operando characterization techniques is amajor field of capabilities development at world-wide large facilities[3-5] and, in lesser scale, at laboratory level[6].Thesituation afore described is particularly applicable to the field of hightemperature electrochemical devices such as Solid Oxide Fuel Cells (SOFC) andSolid Oxide Electrolyzer Cells (SOEC) where the different materials involved inthe device are exposed to extreme environments and, moreover, could exists astrong correlation between different properties. For example, it is well knownthe dependence of the crystallographic parameters with several relevantelectrochemical properties such as electrical conductivity, chemicalcompatibility, electrode reaction performance, etc[7, 8]. The simultaneous characterization of such properties in anin-operando condition allows gaining insight into some still not wellunderstood phenomena.In thiswork, we present the simultaneous crystallographic and electrochemical characterizationthrough X-ray Diffraction and Electrochemical Impedance Spectroscopy,respectively, of three different materials: a proton conductor electrolyte, anO2 electrodematerial, and a symmetrical (H2 and O2)electrode material. In order to study these materials we use a home-made sampleholder specifically designed to study the electrical resistivity and theelectrode polarization resistance evolution simultaneously with structuralproperties, under in-situ or in-operando conditions. Firstly,we followed a second order phase transition found on the proton conductor electrolytematerial BaCe0.4Zr0.4Y0.2O3-δ at around 400°C under wetoxidizing and reducing atmospheresand its influenceon its ionic conductivity. This phase transition(related to a crystallographicdistortion coming from the hydration/dehydration process) affects the latticeparameters and, therefore,the ionic transport properties.  The utilization of the in-operando sampleholder allow us to get direct information about how this structural distortionaffects the transport properties.Secondly,we studied the electrochemical performance of Nd2NiO4+δelectrode material and its crystallographic parameters under anin-operando condition through the simultaneous EIS and XRD measurements of ahalf cell applying several electrode potentials.While their ionic conductivitycombines the migration of interstitial oxygen (δ) in the rock-salt layer and the migration of oxygen vacancies in theperovskite layer, it is actually dominated by the former due to the highermobility of these defects. Therefore, the O-content play a fundamental role inthe O2 electrode activity(specially working under anodicpolarization) and, moreover, is the driven force of a first order phasetransition from an orthorhombic (Fmmm) to a tetragonal (I4/mmm)symmetry at 505°C.Lastly,we also followed the second order phase transition exhibited by the symmetricalelectrode La0.4Sr0.6Ti0.5Co0.5O3at around 300°C (in both oxidizing and reducing atmospheres), passing from arhombohedral perovskite structure (R-3c) to the ideal cubic perovskite (Pm-3m)as temperature is increased. This phase transition is mediated by the rigidrotation of the oxygen octahedra (around a-a-a- direction, in Glazer?snotation)[9].The correlationbetween the electrochemical properties and structural parameters on each systemis discussed. 1.            Zhang,C., et al., Nature Materials, 2010. 9(11):p. 944-949.2.            Kirtley,J.D., et al., Analytical Chemistry, 2012. 84(22):p. 9745-9753.3.            Peterson,V.K. and C.M. Papadakis, IUCrJ, 2015. 2(2):p. 292-304.4.            Gallo,E. and P. Glatzel, Advanced Materials, 2014. 26(46): p. 7730-7746.5.            Mueller,D.N., et al., Nature Communications, 2015. 6.6.            Brightman,E., et al., Review of Scientific Instruments, 2012. 83(5).7.            Imada,M., A. Fujimori, and Y. Tokura, Reviews of Modern Physics, 1998. 70(4 PART I): p. 1039-1263.8.            Fagg,D.P., et al., Solid State Ionics, 2003. 156(1-2):p. 45-57.9.            Napolitano,F., et al., ECS Transactions, 2013. 58(3):p. 185-193.