The Fabrication And Characterization For PEFC With Fiber Alignment Electrodes

The proton exchange membrane fuel cell is the development direction of the future vehicle power technology,and the catalyst layer as the core component of the fuel cell is the key to determine the performance,durability,cost and subzero start-up capability of the fuel cell.After nearly two hundred years of development,there are three kinds of structure of catalyst layer:particle stack,column array and fiber alignment.Among them,the fiber alignment catalyst layer has outstanding advantages in performance,durability and water management.The fiber alignment catalyst layer is mainly fabricated by the electrospinning method,and the preparation process is directly the key to determine the performance of the catalyst layer.However,the solution formulation and procedures in the electrospinning preparation process still need further research.In addition,the subzero start-up capability is currently the key to limiting the promotion of fuel cell vehicles in the cold zone.However,little research has been reported on the subzero start-up characteristics of the fiber-discharged catalyst layer and the subzero start-up aging characteristics.The core innovation of this paper is to study the subzero start-up characteristics and its subzero start-up aging characteristics for fiber-alignment catalyst layer,and lay the foundation for improving the performance and subzero start-up capability of vehicle fuel cells.This paper mainly consists of four chapters.In the second chapter,the preparation method of the fiber alignment catalyst layer was studied.The preparation of the slurry,the dispersion of the slurry,the electrospinning process and the hot pressing process were studied,and the key preparation parameters of each process were determined.In the process of electrospinning,the phenomenon of fiber "instability" was introduced,and the temperature and humidity boundaries of the fiber "instability" were determined by experiments of controlling variables.In the third chapter,for the characteristics above zero of the fiber alignment catalyst layer,the research is carried out from two aspects of structure and functional properties.In terms of structure,firstly,the diameter and distribution of platinum particles of the fiber alignment catalyst layer and the commercial particle stack catalyst layer were studied;then the thickness and pore-size characteristics of the two types of catalyst layers were measured;finally,the distribution of elements within the single fiber cross section of the layer is observed.In terms of functional properties,first,the electrochemical active areas of the two types of catalyst layers were studied by cyclic voltammetry;secondly,the polarization curves of the two types of catalyst layers were tested and compared.A large number of experiments have shown that the fiber diameter in the fiber alignment catalyst layer is within 100-800 nm,and there are more pore diameters in the single fiber less than 7 nm.At the same time,compared to commercial particle stack catalyst layers,the higher performance and electrochemically active area of fiber alignment catalyst layer under 70?-100%RH.In the fourth chapter,based on the characteristics of the fiber-discharged catalyst layer above zero,the subzero start-up characteristics of the fiber alignment catalyst layer and the particle stack catalyst layer at various temperatures were studied by isothermal thermal boundary experiments.When the starting current is below 40 mA·cm-2,the fiber-alignment catalyst layer has a longer running time than the commercial particle stack catalyst layer,which is inferred to be due to the fact that the fiber alignment catalyst layer has bigger pore volume within 7 nm,which reduces the randomness of chilling in super-cooling water and increases the capability of subzero start-up.In addition,by the hot pressing of the catalyst layer and the proton exchange membrane,the running time of the fiber alignment catalyst layer is remarkably improved,mainly because the hot pressing improves the interface between the catalyst layer and the membrane.In the fifth chapter,the aging test procedure was determined for the aging characteristics of the fiber alignment catalyst layer under subzero-start-up process,and the fiber alignment catalyst layer and commercial particle stack catalyst layer were compared from physical characterization and electrochemical characterization.The aging phenomenon of the layer during the subzero start-up process.Under the same aging test procedure,the fiber arrangement catalyst layer has a small change in diameter and pore before and after subzero start-up.The performance after multiple subzero start-up is basically close to that before subzero start-up,indicating that there is basically no aging;however,the performance of the commercial particle stack catalyst layer is drastically reduced and the particle diameter is significantly increased.The work of this paper preliminarily studied the preparation process of the fiber alignment catalyst layer,and conducted a systematic experimental study on its subzero start-up characteristics and aging characteristics during subzero start-up from a new perspective.Combined with the literature results,the fiber alignment catalyst layer has better performance and durability above and below zero than the current commercial particle stack catalyst layer.This paper studies the design and application of a catalyst layer for a proton exchange membrane fuel cell for vehicles.