First Principles Research On Hydration Performance Of Mixed-Conductors And Its Application To Solid Oxide Fuel Cells

Solid oxide fuel cells can breakthrough the limitations of the Carnot cycle and convert chemical energy directly into electrical energy with high efficiency,which make them an efficient and clean energy conversion device.However,conventional solid oxide fuel cells can only be used in high temperatures(800-1000℃),which leads to high costs,and therefore,the development of low-intermediate temperature solid oxide fuel cells is essential.An important factor limiting the performance of low temperature solid oxide fuel cells is the lack of cathode materials with high catalytic activity toward oxygen reduction reaction.The electrochemical polarisation resistance of the cathode increases rapidly when the operating temperature decreases,leading to a rapid degradation of the cell performance.This thesis explores the relevant material systems in terms of defect behaviour,electronic structure and cathode surface processes using first principles simulations,with the aim of deepening the understanding of cathode reaction processes and providing new ideas for the design and development of highly active cathodes.Its main contents include the following:Chapter 1 reviews the basic principles of solid oxide fuel cells and provides a brief introduction to the key materials in proton-based solid oxide fuel cells from an application-component-structure-property perspective.This is followed by a brief introduction to the basic principles of density functional theory and the idea of numerical solution based on the development history,highlighting its applicability scenarios and error sources.Finally,the current status of the application of density functional theory in the field of solid oxide fuel cell research is summarised in terms of the key problems of the fuel cell material system,and the theme of this thesis is made.In Chapter 2,a new iron-based simple perovskite cathode system is developed using a combination of first-principles calculations and experimental methods.Firstly,the stability,electronic structure and defect behaviour(mainly the formation and conduction of oxygen vacancies and proton defects)of a series of component cathodes are modelled using first-principles calculations;then their potential application as proton involved conducting cathodes is evaluated,followed by their characterisation of the structural and electrochemical properties from an experimental point of view;and finally,a new cathode material with excellent electrochemical properties was successfully developed.Chapter 3 presents the evaluation of the intrinsic properties of strontium-iron oxides with a higher ordering RP structure using first principles calculations and proposes a modification scheme for their application in fuel cell cathodes.Then,the material modification scheme is evaluated from a computational(defect behaviour,surface catalytic activity)point of view,and the electrochemical properties of the materials before and after modification are further investigated experimentally.Chapter 4 focuses on the development of a new model for the prediction of hydration properties of mixed ionic electronic conductors,as well as the use of the new model to carry out studies on the factors affecting the hydration properties of the materials.Possible models for the calculation of hydration enthalpies of mixed conductors are firstly proposed by comparing the differences in structure and properties between the electrolyte and cathode systems.Secondly,the rationality and validity of each model are evaluated in the light of experimental data,and the new model that fits the experimental results best is identified.And,the new model is applied to the design of the component system,and the factors influencing the hydration properties of the cathode are investigated.Chapter 5 provides a systematic summary of the whole text and provides an outlook on related issues that need further research.