Preparation And Theoretical Research Of Key Materials For Proton Conductor Solid Oxide Fuel Cells

Proton conducting solid oxide fuel cells(H-SOFC)have been playing an essential role in energy storage and transformation,owing to those overwhelming advantages,such as low activity energy,efficient energy consumption,high power generation ability and direct conversion of chemical energy into electrical energy,besides,the only product for energy transformation in H-SOFCs.Thus,it is considered as an effective way for energy transformation,contributing to the sustainable development.This will bring a challenge to numbers of industries and gradually replace conventional equipment.To maintain a good performance in middle temperature(600-800 ℃),we should improve the activity in this condition,more specifically,the proton conducting ability and oxygen reduction reaction(ORR).In this thesis,cathode materials are advanced by doping specific element,crystal facet control and microstructure modification.Furthermore,density functional theory(DFT)based on first principle is applied to predict material properties,such as vacancy formation energy,hydration energy and proton transformation,as the consequence,promising cathode materials in H-SOFC are made and show state-of-the-art properties.Firstly,we introduce the application and perspective proton conducting solid oxide fuel cells,reaction theory,drawbacks and deficiencies;an overview of cathode material is also illustrated in this chapter,we also introduced the reaction mechanism and ratelimiting steps in cathode materials.Furthermore,the use and improvement of the firstand second-generation cathode materials.However,experiment has some essential restrictions,the first principle and density functional theory are used to solve these problems.In this paper,we briefly introduce the first principle and density functional theory and the self-consistent process of density functional theory.Introduction of VASP calculation software and the status and application of this theory in materials science are also demonstrated.By the assistance of computational simulation,we propose a rational design of a high-performance cathode for proton-conducting solid oxide fuel cells(SOFCs)with the aim of improving the hydration properties of conventional perovskite cathode materials,thus leading to the development of new materials with enhanced proton migration.Herein,potassium is used to dope traditional Ba0.5Sr0.5Co0.8Fe0.2O3-δ(BSCF),which is demonstrated to be a beneficial way for improving hydration,both experimentally and theoretically.The theoretical study is needed to overcome practical limits that hindered direct hydrogen mobility measurements.The novel material Ba0.4K0.1Sr0.5Co0.8Fe0.2O3-δ(BKSCF)shows a lower overall proton migration energy compared with that of the sample without K,suggesting that K-doping enhances proton conduction,which shows an improved performance by extending the catalytic sites to the whole cathode area.As a result,a fuel cell built with the novel BKSCF cathode shows an encouraging fuel cell performance of 441 and 1275 m W cm-2 at 600 and 700 °C,respectively,which is significantly higher than that of the cell using the pristine BSCF cathode.This study provides a new and rational way to design a perovskite cathode for proton-conducting SOFCs with high performance.In addition,the first-generation cathode La0.5Sr0.5Fe O3-δ tailored with Pr successfully extends the cathode reaction active area and thus leads to a doubled fuel cell power output,which brings a new life of the cathode for proton-conducting solid oxide fuel cells.At 700 ℃,the peak power density of the new material La0.35Pr0.15Sr0.5Fe O3-δ(LPr SF)is significantly increased to 1083 m W cm-2,which is almost double compared with the H-SOFC using LSF cathode,with a peak power density of 545 m W cm-2 at 700 ℃.Finally,Co3O4 nanoparticles with exposed(001)surfaces is used to accelerate the cathode reactions for solid oxide fuel cells for the first time,which was the key to improving fuel cell performance.LSM-SDC-based SOFC using Co3O4 nanocubes produced peak power densities of 152,248,500,863 and 1126 m W cm-2 at 500,550,600,650 and 700 ℃,respectively.The counterpart using commercial Co3O4 reached only 179 m W cm-2 at 600 ℃.