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Microstructure and durability of praseodymium-doped lanthanum nickelate for solid oxide cells

Abstract : Coupling fuel cell and electrolysis technologies provide an attractive solution to absorb the fluctuations induced by the deployement of the intermittent renewable energy sources. In this frame, the technology based on the "Solid Oxide Cells" (SOCs) appears as a promising solution as the same device can be alternatively used in both the electrolysis and fuel cell modes. The SOCs are based on an oxide ceramic electrolyte operating at a high temperature (800-1000 °C) allowing to reach very good efficiency. Hovewer, their durability is still insufficient to envisage their economic deployment. An important issue limiting the SOCs lifetime is the chemical and mechanical destabilizations of the oxygen electrode, as well as its chemical reactivity with the electrolyte upon operation. Moreover, the high operating temperature of SOCs leads to severe constraints on materials assembling and on fabrication processes.The objectives of this PhD thesis are to better understand the role of microstructure and the reaction mechanisms of oxygen electrode in SOCs operating in intermediate temperature (650-800 °C) and to investigate the aging in electrolysis and fuel cell modes through an integrated approach coupling electrochemical and physicochemical characterizations with modeling. In this work, architecturally designed LaPrNiO4+δ, referred to as LPNO, oxygen electrode has been prepared on Ce0.9Gd0.1O2-δ electrolyte by taking advantage of the complementary properties of La2NiO4+δ and Pr2NiO4+δ extremes, i.e. larger chemical stability of La2NiO4+δ and larger electrochemical activity of Pr2NiO4+δ. The performances of SOCs are not only due to the intrinsic properties of materials but also to the association of functional structured materials and the properties of their interfaces. In this frame, novel architectures based on an active functional layer (AFL) fabricated by electrostatic spray deposition (ESD) and topped by an optimized current collecting layer (CCL) deposited by screen-printing (SP) have been optimized aiming to decrease the operating temperature in order to improve the performances and the lifetime. A unique coral-like nanostructured AFL with large porosity and good adhesion on the electrolyte has been proved to be of great importance in the oxygen electrode reactions. The electrode performance and durability in symmetrical SOCs and in a complete electrolysis cell have been investigated in detail in thermal aging and in galvanostatic mode. These data have been thoroughly discussed in relationships with structural and microstructural evolution of LPNO oxygen electrode thanks to post-mortem characterizations using scanning electron microscopy, 3D reconstruction by focused ion beam-SEM, laboratory X-ray diffraction and synchrotron X-ray µ-diffraction and µ-fluorescence.
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Nur Istiqomah Khamidy. Microstructure and durability of praseodymium-doped lanthanum nickelate for solid oxide cells. Mechanics of materials [physics.class-ph]. Université Grenoble Alpes [2020-..], 2020. English. ⟨NNT : 2020GRALI020⟩. ⟨tel-02894862⟩

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