NNT : 2015SACLC016 T HESE DE DOCTORAT DE L’UNIVERSITE PARIS-SACLAY PREPAREE A “ECOLE CENTRALESUPELEC” ECOLE DOCTORALE N° 573 Interfaces : approches interdisciplinaires / fondements, applications et innovation Spécialité de doctorat Chimie Par Mme Anastasia Iakovleva Study of novel proton conductors for high temperature Solid Oxide Cells Thèse présentée et soutenue à « Châtenay-Malabry », le « 30 Octobre 2015 » : Composition du Jury : Mme. Irina ANIMITSA Professeur à l’Université Président Fédérale de l'Oural Mme. Rose-Noëlle VANNIER Professeur à L’ENSCL Rapporteur M. Christos ARGIRUSIS Professeur à l’Université Rapporteur Technique Nationale d'Athènes M. Anthony CHESNAUD Responsable Scientifique à Examinateur Ecole des Mines ParisTech M. Guilhem DEZANNEAU Directeur du laboratoire SPMS Directeur de thèse Acknowledgements This work has been done in the Laboratoire “Structures, Propriétés et Modélisation des Solides” (SPMS) of the Ecole CentraleSupelec and Centre National de la Recherche Scientifique (C.N.R.S., U.M.R.8580). My first huge thanks to Guilhem Dezanneau, my supervisor, for giving me the opportunity of doing my PhD in this laboratory and in his group, for guiding me during this thesis, for his help, patience and kind attention. I would like to sincerely thank Mme. Rose-Noelle Vannier, Professor of the University of Lille, and M. Christos Argirusis, Associate Professor at National Technical University of Athens for having accepted to be the reviewers of my thesis, and M. Anthony Chesnaud for accepting as the examiner of my thesis, for his help and collaboration. I am deeply grateful to Irina Evgenievna Animitsa, my russian Professor. Thank you for guiding me during my university years, for introducing me to solid-state electrochemistry, for your help, advices and support during my PhD thesis. I want to say a great thanks to Igor Kornev, Professor at SPMS laboratory, for all our conversations in Russian, attention, your help and advices. I would like to my sincere gratitude to Christine Vinée-Jacquin for all your kindness, attention and invaluable help with my professional and personal issues. I would be absolutely lost in these thousands of french papers without your help. Thank you! I’m also thankful to Ingrid Canero-Infante for your energy, always positive mood and great time we spent together. I would like to thank to all laboratory team: Christine Bogicevic and Fabienne Karolak for their help in experiments; Nicolas Guiblin for the help with X-Ray diffraction experiments; Gilles Boemare for the help with repair of different equipment in the lab, especially isostatic press and nice talks during that; Brahim Dkhil for your sparkling humor, energy and advices. And I would also thank to Jean-Michel Kiat, Jean-Michel Gillet, Pierre-Eymeric Janolin, Pierre Becker, Sandrine Geiger, Hichem Dammak, Pascale Salvini, Pascale Gemeiner, Michel Jouan, Thierry Martin, Agnès Bénard, Claire Roussel, Hubert Jubeau, Xavier Bril. Without their help, I could not have finished my thesis on time. I would also like thank all PhD students and post-docs from the laboratory: Camille Exare, Romain Fayo, Yang Liu, Desirée Ciria, Cintia Hartmann, Fabien Brieuc, Mohamed Ben Hassine, Xiaofai Bai, Gentien Thorner, Bo Bo TIAN, Wen Jing Li, Xiao Xuan SHI, Bertrand Clair, Yang Hu and Michael Anoufa. They gave me many suggestions and help, and we spent a lot of unforgettable time together. A very special thanks to Charles Paillard and Sergei Prokhorenko for your positive mood, support, a lot of serious and funny talks, for your patience and courage during our driving lessons. I would also like to thank Charlotte Cochard for our conversations in French and English and great concerts we attended together. I would like to sincerely thank to my friend Nadia for your help, support and fantastic time we spent together in Russia and Europe. I am deeply grateful to all my family and friends, who stay in Russia but never forget about me. First of all, to my mom, for your love and care, for your wise advices and patience; to my grandparents, uncle, aunt, my sister Julia and brother Danil. Thank you for believing in me, understanding and supporting me in the choices I’ve made even if they kept us far away from each other for a while. Titre : Étude de nouveaux conducteurs protoniques pour des cellules à oxyde solide à haute température Mots clés : Céramique, pile à combustible, conductivité, conducteurs protoniques, des unités tétraédriques, la synthèse de chimie humide Résumé : L'objectif principal de ce travail était En ce qui concerne les propriétés électriques, l'étude systématique de plusieurs groupes de nous avons constaté une augmentation de la matériaux conducteurs protoniques: Gd conduction avec le taux de substitution. Tous 3- Me GaO (Me = Ca2+, Sr2+), Ba Nb Y O , les composés présentent une bonne stabilité en x x 6-δ 2 1-x 1+x 6-δ and BaZr Y O (BZY15). Nous avons milieu humide, sous hydrogène et CO . Dans le 0.85 0.15 3-δ 2 développé une voie de synthèse pour chaque cas des matériaux Ba Y Nb O , les 2 1+x 1-x 6-δ groupe de matériaux tels que le procédé de propriétés physico-chimiques des matériaux combustion sol-gel, la synthèse lyophilisation et synthétisés ont été caractérisées par la le procédé de complexation de citrate-EDTA diffraction des rayons X et par MEB. La taille modifié. Des nanopoudres pures et des moyenne des grains a considérablement céramiques denses ont été obtenus après ces augmenté avec l'augmentation du taux de Y3+. synthèses suives d’un processus de frittage Les propriétés de conduction ont été légèrement classique. La structure et la composition des améliorées avec la substitution partielle de produits obtenues ont été caractérisées par niobium par l'yttrium. La stabilité de diffraction des rayons X (XRD) et microscopie Ba Y Nb O composés a été étudiée sous 2 1+x 1-x 6-δ électronique à balayage (MEB). La variation de différentes atmosphères et conditions. Les la conductivité en fonction de la température a propriétés de conduction ionique restent été étudiée par spectroscopie d'impédance, ainsi modestes ce qui a été explique par des que la dépendance en fonction de pO et pH O. simulations de dynamique moléculaire. Enfin, 2 2 Pour la famille de Gd Me GaO (Me = Ca2+, nous avons étudié l'influence d’emploi d'un 3-x x 6-δ Sr2+), nous avons étudié l'influence de la nature additif ZnO et NiO lors de la synthèse de et la quantité de dopant sur les propriétés BZY15, les adjuvants de frittage pouvant être structurales et électriques. Les résultats utilisés pour abaisser la température de frittage. indiquent une solution solide possible jusqu'à L'oxyde de zinc comme un adjuvant de frittage 10% de taux du substituant. Selon les permet de diminuer de 300 °C la température de observations au MEB, la taille des grains est frittage et d’augmenter légèrement la augmente le taux de substitution. conduction ionique. Title : Study of novel proton conductors for high temperature Solid Oxide Cells Keywords : Ceramics, SOFC, conductivity, proton conductors, tetrahedral units, wet chemistry synthesis Abstract : The main objective of the present Concerning electrical properties, we found an work was the systematic study of several increase of conduction with increasing dopant groups of materials: Gd Me GaO (Me = content. All compounds present a good stability 3-x x 6-δ Ca2+, Sr2+), Ba Y Nb O , and in humid, hydrogen and CO containing 2 1+x 1-x 6-δ 2 BaZr Y O (BZY15) as proton atmosphere. In case of Ba Y Nb O 0.85 0.15 3-δ 2 1+x 1-x 6-δ conductors. We developed a synthesis route for materials, the physico-chemical properties of each group of materials such as microwave- synthesized materials have been - 5 - assisted citric acid combustion method, freeze- characterized by the XRD and SEM drying synthesis and modified citrate-EDTA techniques. The average grain size increased complexing method. Pure nanopowders and significantly with increasing amount of Y3+. dense ceramics were obtained after these Conduction properties were slightly improved syntheses plus a classical sintering process. The with the partial substitution of niobium by structure and composition of the obtained yttrium. The stability of Ba Y Nb O 2 1+x 1-x 6-δ products were characterized by X-Ray compounds was investigated under different diffraction (XRD) and scanning electron atmospheres and conditions. The ionic microscopy (SEM). The temperature conduction in this case is quite low, which has dependences of the conductivity were been explained by futher molecular dynamics investigated by impedance spectroscopy as a simulations. Finally, we studied the influence function of pO and pH O. For the family of of an ZnO and NiO additives on the sintering 2 2 Gd Me GaO (Me = Ca2+, Sr2+), we studied of BZY15, being these sintering aids used to 3-x x 6-δ the influence of dopant nature and content on lower the sintering temperature. Zinc oxide as a the structural and electrical properties. Results sintering aid lowers the sintering temperature indicate that the substitution possible till 10 % by 300 °C and slightly increases the bulk and of doping content. According to the SEM total conductivity of BZY15. observations, the grain size is increased with increasing dopant content. - 6 - Table of contents Acknowledgements ................................................................................................................................. 3 Abstract………………………………………………………………………………………………….5 Résumé……………………………………………………………………………………………….....6 Chapter 1 Introduction .................................................................................................................... 10 1.1 Fuel cells: principle, types, advantages ........................................................................................... 10 1.2 Solid Oxide Fuel Cells (SOFC) and Proton Conducting Fuel Cells (PCFC): principle and components ............................................................................................................................................ 13 1.3 Proton-conducting electrolyte materials for SOFCs ........................................................................ 17 1.3.1 Materials .................................................................................................................................. 17 1.3.2 Mobility of proton defects ....................................................................................................... 19 1.3.3 Hydration thermodynamics ..................................................................................................... 20 1.3.4 Isotope effect ........................................................................................................................... 22 1.4 Objectives ........................................................................................................................................ 25 References ............................................................................................................................................. 27 Chapter 2 Experimental Techniques ............................................................................................ 30 2.1 Introduction ..................................................................................................................................... 30 2.2 Nanopowders synthesis ................................................................................................................... 30 2.2.1 Microwave-assisted citric acid combustion method ............................................................... 30 2.2.2 Modified citrate-EDTA complexing method .......................................................................... 32 2.2.3 Freeze drying synthesis ........................................................................................................... 34 2.3 Preparation of Ceramics .................................................................................................................. 36 2.4 Chemical and structural characterization ........................................................................................ 36 2.4.1 X-Ray diffraction analysis ............................................................................................................ 36 2.4.1.a Routine X-Ray diffraction analysis ...................................................................................... 36 2.4.1.b High-temperature X-Ray diffraction .................................................................................... 36 2.4.2 Scanning electron microscopy (SEM) and Energy dispersive spectroscopy (EDS) .................... 37 2.4.3 Dilatometry analysis ..................................................................................................................... 38 2.4.4 Transmission electron microscopy (TEM) ................................................................................... 39 2.5 Conductivity measurements ............................................................................................................ 40 2.5.1 Fundamentals of electrochemical impedance method ............................................................. 40 2.5.2 Experimental details ................................................................................................................ 43 - 7 - 2.5.3 Controlling of the atmosphere ................................................................................................. 44 2.5.3.a Controlling of oxygen partial pressure ................................................................................. 44 2.5.3.b The humidity controlling ...................................................................................................... 44 References ............................................................................................................................................. 45 Chapter 3 Synthesis, structure and electrical properties of Gd Me GaO (Me=Ca2+, 3-x x 6-δ Sr2+) ...................................................................................................................................................... 46 3.1 Introduction ..................................................................................................................................... 46 3.2 Phase equilibrium in Ln O – Ga O binary systems ...................................................................... 49 2 3 2 3 3.3 Objectives of the study .................................................................................................................... 53 3.4 Structural properties of Gd Me GaO (Me=Ca2+, Sr2+) compounds ............................................ 54 3-x x 6-δ 3.4.1 Structural analysis of Gd Me GaO (Me=Ca2+, Sr2+) powders ........................................... 54 3-x x 6-δ 3.4.2 High temperature X-Ray diffraction and thermal expansion coefficient ................................ 56 3.4.3 Structural analysis of Gd Me GaO (Me=Ca2+, Sr2+) sintered pellets ................................. 57 3-x x 6-δ 3.4.4 Microstructural analysis of Gd Me GaO (Me=Ca2+, Sr2+) sintered pellets ........................ 62 3-x x 6-δ 3.4.5 Chemical stability .................................................................................................................... 67 3.5 Transport and hydration properties ................................................................................................. 69 3.5.1 Impedance spectra of Gd Me GaO (Me = Ca2+, Sr2+) ....................................................... 69 3-x x 6-δ 3.5.2 Transport properties of solid solutions Gd Me GaO (Me = Ca2+, Sr2+) as a function of 3-x x 6-δ temperature ............................................................................................................................................ 70 3.5.3 Transport properties as a function of p(O ) ............................................................................. 74 2 3.6 Conclusion ....................................................................................................................................... 77 References ............................................................................................................................................. 79 Chapter 4 Synthesis, structure and electrical properties of Ba Y Nb O .................... 81 2 1+x 1-x 6-δ 4.1 The perovskite background ............................................................................................................. 81 4.1.1 Simple perovskite structure ..................................................................................................... 81 4.1.2 Double perovskite structure .................................................................................................... 83 4.1.3 Structural properties of Ba LnB'X (Ln=lanthanide, In and Y, B'= Nb5+ and Ta5+) ................ 86 2 6 4.1.4 Electrical properties of A LnB'X (A= Ba2+, Sr2+, Ca2+, Ln=lanthanide, In and Y, B'= Nb5+ 2 6 and Ta5+) ................................................................................................................................................ 93 4.2 Objectives of the study .................................................................................................................... 98 4.3 Structural properties of Ba Y Nb O compounds (x = 0, 0.05, …, 0.25) ................................. 99 2 1+x 1-x 6-δ 4.3.1 Structural characterization of sintered pellets ......................................................................... 99 4.3.2 Microstructural characterization of sintered pellets .............................................................. 107 4.3.3 Chemical stability .................................................................................................................. 109 4.4 Transport properties ...................................................................................................................... 111 4.4.1 Transport properties as a function of T. Analysis of impedance spectra .............................. 111 - 8 - 4.4.2 Transport properties as a function of p(O ) ........................................................................... 115 2 4.5 Molecular dynamics simulations ................................................................................................... 116 4.5.1 Calculations details ............................................................................................................... 116 4.5.2 Results ................................................................................................................................... 117 4.5.2.1 Room temperature simulations ........................................................................................... 117 4.5.2.2 High temperature simulations ............................................................................................ 118 4.6 Transmission Electron Microscopy (TEM) ................................................................................... 121 4.6.1 Objective ............................................................................................................................... 121 4.6.2 Description of the experiment ............................................................................................... 121 4.6.2.1 Principle of the Focus Ion Beam ........................................................................................ 121 4.6.2.2 FIB preparation for TEM ................................................................................................... 122 4.6.3 Results ................................................................................................................................... 122 4.7 Conclusion ..................................................................................................................................... 125 References ........................................................................................................................................... 127 Chapter 5 Synthesis, structure and electrical properties of BZY15 .................................... 130 5.1 Introduction ................................................................................................................................... 130 5.1.1 Structure of Barium Zirconate ............................................................................................... 130 5.1.1 Chemical Stability ................................................................................................................. 131 5.1.2 Conductivity properties of Doped Barium Zirconate ............................................................ 133 5.2 Objectives of the study .................................................................................................................. 135 5.3 Structural and microstructural properties of BZY15 ..................................................................... 135 5.3.1 Enhanced Sintering of Yttrium doped Barium Zirconate by addition of ZnO and NiO ..... 138 5.4 Transport properties ....................................................................................................................... 143 5.5 Conclusion ..................................................................................................................................... 147 References ........................................................................................................................................... 148 Chapter 6 General conclusions and perspectives ..................................................................... 150 6.1 Summary ...................................................................................................................................... 150 6.2 Perspectives ................................................................................................................................... 152 - 9 - Chapter 1 Introduction Chapter 1 Introduction 1.1 Fuel cells: principle, types, advantages Renewable energy sources are an infinite resource unlike energy produced from fossil fuels. Natural phenomena such as sunlight, wind, waves, water flow, biological processes and geothermal heat are some of the renewable energy sources available to mankind. But they are site-specific and intermittent, which is not suitable for continuous energy supply. Therefore storage or energy carriers are needed [1-4]. Hydrogen and fuel cells are seen by many as key solutions for the 21st century, enabling clean efficient production of power and heat from a range of primary energy sources. Hydrogen, which is transportable and storable, could serve as an attractive option for energy carrier, as a precursor for synthetic fuels when combined with CO , as well as a potential clean fuel for many 2 applications, such as for heating, electricity and vehicles [5-7]. Fuel cells will be used in a wide range of products, ranging from very small fuel cells in portable devices such as mobile phones and laptops, through mobile applications like cars, delivery vehicles, buses and ships, to heat and power generators in stationary applications in the domestic and industrial sector. Future energy systems will also include improved conventional energy converters running on hydrogen (e.g. internal combustion engines, Stirling engines, and turbines) as well as other energy carriers (e.g. direct heat and electricity from renewable energy, and bio-fuels for transport) [8]. Fuel cells are electrochemical devices that convert directly chemical energy present in fuels into electrical energy, see Figure 1.1. They are a promising alternative to traditional power generation with high efficiency and low environmental impact. Because the intermediate steps of producing heat and mechanical work typical of most conventional power generation methods are avoided, fuel cells are not limited by thermodynamic limitations of heat engines such as the Carnot efficiency. In principle, fuel cell works like a battery in sense that it also produces electrical energy through electrochemical processes. However, unlike a battery, a fuel cell cannot run out as long as fuel is continuously supplied. This is interesting for applications in which absolutely reliable energy supply is needed like military and health care.