Theoretical Analysis And Design Optimization Of Solid Oxide Fuel Cell And Magnetron Sputtering Cathode

Solid oxide fuel cell (SOFC) is one kind of high temperature fuel cell, whichshows great potential applications in military, power generation and transport and isan important part of the new energy technologies. Physical, chemical andelectrochemical processes occurring in SOFC are not independent but stronginteraction. It is costly and time consuming to study the interaction between allprocesses in SOFC by experimental approach. Modeling and simulation techniques,on the other hand, are valuable in enhancing understanding of phenomenon occurringin SOFC and optimizing various key parameters. With the development of computerand commercial modeling software, simulation techniques become more and morepowerful and accurate. Hence, simulation techniques will play an increasinglyimportant role in the commercialization process of SOFC.This Ph.D. dissertation focuses on optimizing and designing of Solid oxide fuelcell and magnetron sputtering cathode by simulation techniques. There are sixchapters in this Ph.D. dissertation. A brief introduction of each chapter is given asfollowing part.In the first chapter, we firstly briefly introduced the fuel cell background and thedevelopment history of fuel cell. In addition, the basic working principle of SOFC,Nernst potential, activation polarization, ohmic polarization, concentrationpolarization, efficiency, stack structures of SOFC and the theory fundamental ofSOFC models are respectively described in detail. Finally, a brief literature review ofSOFC simulation and the application of magnetron sputtering in SOFC arerespectively presented.In the second chapter, we firstly describe the three distinct mass-transfermechanisms including Knudsen diffusion, molecular diffusion, as well as viscousflow. Comparing Fick's model (FM), Advective-diffusive model (ADM),Stefan–Maxwell model (SMM) and Dusty gas model, DGM is required to estimateaccurately the transport of gases in SOFC anode. However species fluxes are coupledwith each other in DGM, moreover it is quite difficult to solve DGM. Therefore,based on a reasonable approximation that is exact for binary mixtures, DGM isreformulated in the form of Fick's law named as DGMFM that gives explicitanalytical expression for each species'flux. Models for mass transport inside a porous SOFC anode are developed based on the DGMFM and the DGM in order to verify theDGMFM, which take into account methane steam reforming and water gas-shiftreaction in anode. The effects of various parameters on the accuracy of DGMFM aresystematically examined such as the pore radius, the porosity, the tortuosity factor andso on. The comprehensive study shows conclusively that the DGM and DGMFMresults match quite well for the practical SOFC operation condition.In the third chapter, a two dimensional comprehensive mathematical model isdeveloped for anode-supported SOFC with composite electrodes. The model not onlytakes into account the electric contact resistance between the electrode andinterconnect rib and microstructure parameters but also couples the intricateinterdependency among the ionic conduction, electronic conduction, gas transport, theelectrochemical reaction in function layer and the electrochemical reaction at interfacebetween electrolyte and electrode. Comparing the gases concentration distribution andvoltage distribution in single cell and stack cell, we find one of the primary causesaccounting for the lowered cell performance at the stack level is the additional lossescaused by interconnector the geometry. In addition, the impact of anode rib width andcathode rib width are studied at different contact resistances, different fuelcompositions, and different electrodes conductivities respectively. Results show thatthe influence of the anode or cathode rib width on SOFC performance can not beneglect for any practical SOFC working condition. Finally, a simple equation for theoptimal anode or cathode rib width is presented.In the fourth chapter, we firstly describe SOFC different parts involved equations.Based on planar anode-supported solid oxide fuel cell (SOFC) with compositeelectrode, a 3D multi-scale mathematic model has been developed for theperformance characteristics of planar anode-supported solid oxide fuel cell (SOFC)with composite electrode, which couples the intricate interdependency among theionic conduction, electronic conduction, gas transport, energy transport and theelectrochemical reaction processes. The developed model is then applied to analyzesome key physical quantities distributions and the effect of contact resistance on theperformance of SOFC. Average current increases from 3679 A/m2to 4000 A/m2byoptimizing CCCL thickness, mean electronic conductor particles radii in CCCL and inASL. Finally, the dependence of the performance of SOFC on the ionic conductivityof cathode functional layer (CFL) is analyzed; we conclude that the ionic conductivityof CFL is of significant influence on the performance of SOFC. In the fifth chapter, we firstly briefly introduced the basic working principle ofthe magnetron sputtering and the simulation approach. In addition, verified oursimulation approach, the result testifies that our simulation approach is right.Comparing different magnet magnetization directions designs, we find that it is easyto change the shape of horizontal component of the magnetic field distribution fromconvex to concave via altering magnet magnetization directions, so it is not necessaryto add shunt bar between target and magnet. Moreover, we analysis the effect ofmagnetic plank and yoke on magnet distribution for different magnet magnetizationdirections designs respectively. We conclude that the magnetic plank opens themagnetic closed-loop of center magnet self or edge magnet self for the magnetizationdirection of center magnet and edge magnet at least one along the horizontal direction,increases the magnetic closed-loop between center magnet and edge magnet andimproves the horizontal component of the magnetic field at target surface.Furthermore, the effect of the relative permeability and high of magnetic plank onmagnetic field is presented. At last but not least, comparing the target utilization ofour design to that of Sierra Inc is presented.In the sixth chapter, a brief summary of the research results is presented.