Electrode is where electricity is generated. Its quality is important to the entire battery performance. In this study, we are going to establish a stable and automatic process for making electrodes as well as required equipment. By this way, the instability in the electrode process can be improved. Electrospray technology is developed to spray the catalyst and reduce the agglomeration. It is shown that the electrode performance is 37% better than before after electrospray is adopted for producing catalyst layer. If we check the catalyst grains by AFM and TEM, we can find that the electrospray does scatter the polymers containing Nafion effectively. Under SEM, the catalyst grains are small and well proportioned on the carbon cloth. Obviously, catalysts are better utilized. All of the above can be used to explain the performance boost.

The catalyst layer of a proton exchange membrane (PEM) fuel cell is a mixture of polymer, carbon, and platinum. The characteristics of the catalyst layer play a critical role in determining the performance of the PEM fuel cell. This research investigates the role of catalyst layer composition using a Central Composite Design (CCD) experiment with two factors which are Nafion content and carbon loading while the platinum catalyst surface area is held constant. For each catalyst layer composition, polarization curves are measured to evaluate cell performance at common operating conditions, Electrochemical Impedance Spectroscopy (EIS), and Cyclic Voltammetry (CV) are then applied to investigate the cause of the observed variations in performance. The results show that both Nafion and carbon content significantly affect MEA performance. The ohmic resistance and active catalyst area of the cell do not correlate with catalyst layer composition, and observed variations in the cell resistance and active catalyst area produced changes in performance that were not significant relative to compositions of catalyst layers. / Master of Science

In this work, a micro-model of the catalyst layer of polymer electrolyte membrane fuel cell (PEMFC) was developed. The micro-model includes the transport phenomena and the reaction kinetics within a three dimensional micro-structure representing a sample of PEMFC catalyst layer. Proper physical boundary conditions have been described on the surfaces of the sample as well as on the interfaces between the regions through which all constituents are solved in a coupled manner. A four-phase micro-structure of CL was reconstructed, the platinum particles were resolved in the computational grid generation and the governing equations were solved within platinum region. A body-fitted computational mesh was generated for the reconstructed micro-structure of CL. The number of computational cells were optimized based on how close to an analytical sphere the magnitude of the surface area of a sphere can be captured after generating the computational cells. The interfaces with important physical phenomena were more refined than the rest of the interfaces, specially the electrochemically active reaction surface. The computational mesh was checked for a grid independent numerical solution. The Knudsen effects was included by calculating the characteristic length in the pore region. Four different cases of including Knudsen effects were studied. Also, a comparison was made between solution with and without Knudsen effects. A physical model of oxygen dissolution was developed, the oxygen dissolution at the interface between pore and ionomer was treated as an superficial phenomenon. The performance curves were produced and provided for the reconstructed micro-structure along with the distribution of field variables. A length study of the reconstructed micro-structure was conducted such that the results from the micro-modeling can capture the trend in variable distributions observed in the macro-modeling of CL or experiments. A platinum loading study was preformed and the anomalous phenomena of dramatic increase in oxygen transport resistance observed in some experimental works was explained by isolating the ionomer region of the CL micro-structure and numerically calculating the shape factor for diffusive transport. It was found that the increase in oxygen transport resistance is due to the increase in diffusion pathway and decrease in the transport surface area. / Thesis (Ph.D, Mechanical and Materials Engineering) -- Queen's University, 2013-03-06 15:55:21.564

This thesis presents a framework for a microstructural model of a catalyst layer in a proton exchange membrane (PEM) fuel cell. In this study, a stochastic model that uses individual carbon, platinum and ionomer particles as building blocks to construct a catalyst layer geometry, resulting in optimal porosity and material mass ratios has been employed. The construction rule set in this design is easily variable, enabling a wide range of catalyst layer geometries to be made. The generated catalyst layers were found to exhibit many of the features found in currently poduced catalyst layers. The resulting geometries were subsequently examined on the basis of electronic percolation, mean chord length and effective diffusivity of the pore phase. Catalyst layer percolation was found to be most effected by the number of carbon see particles used and the specified porosity. The mean chord lengths of all of the catalyst layer geometries produced Knudsen numbers ranging in order of magnitude between 0.1 and 10, thus indicating that gas diffusion within the catalyst layers lies in the transition regime between bulk and Knudsen diffusion. Calculated effective diffusivities within the pore space of the model were shown to be relatively insensitive to changes in the catalyst layer composition and construction rule set other then porosity, indicating that the pore size distribution does not significantly vary when the catalyst layer mass ratios vary. / Thesis (Master, Mechanical and Materials Engineering) -- Queen's University, 2012-08-31 08:52:55.747

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A transient model of the cathode catalyst layer of a proton exchange membrane fuel cell is presented. The catalyst layer structure can be described as a superposition of the polymer membrane, the backing layer, and some additional platinum particles. The model, which incorporates some of the features of the pseudo-homogeneous models currently present in the literature, considers the kinetics of the electrochemical reaction taking place at the platinum surface, the proton transport through the polymer agglomerates, and the oxygen and water transport within the pores as well as the membrane material of the catalyst layer. Due to the lower porosity of this region and the higher liquid water content, the catalyst layer can be current limiting in the fuel cell. Furthermore, since the cost of the catalyst material is critical, it is important to have a model predicting the effective utilization of this catalyst layer as well as one, which gives insights into how it might be improved. Equations are presented for the mass conservation of reactants and products, the electrical and ionic currents, and the conservation of energy. A discussion of a number of the closure relations such as the Butler-Volmer equation employed is included as is a discussion of the initial and boundary conditions applied. The mathematical model is solved using a finite elements approach developed at the I.U.S.T.I. / Master of Science

The catalyst layer of a proton exchange membrane (PEM) fuel cell is a porous mixture of polymer, carbon, and platinum. The characteristics of the catalyst layer play a critical role in determining the performance of the PEM fuel cell. In this research, sample membrane electrode assemblies (MEAs) are prepared using various combinations of polymer and carbon loadings while the platinum catalyst surface area is held constant. For each MEA, polarization curves are determined at common operating conditions. The polarization curves are compared to assess the effects of the catalyst layer composition. The results show that both Nafion and carbon content significantly affect MEA performance. The physical characteristics of the catalyst layer including porosity, thickness, active platinum surface area, ohmic resistance, and apparent Nafion film thickness are investigated to explain the variation in performance. The results show that for the range of compositions considered in this work, the most important factors are the platinum surface area and the apparent Nafion film thickness. / Master of Science

Catalyst layer modeling can be a useful tool for fuel cell design. By comparing numerical results to experimental results, numerical models can provide a better understanding of the physical processes occurring within the fuel cell catalyst layer. This can lead to design optimization and cost reduction. The purpose of this research was to compare, for the first time, a direct numerical simulation (DNS) model for the cathode catalyst layer of a PEM fuel cell to a newly developed experimental technique that measures the ionic potential through the length of the catalyst layer. A new design for a microstructured electrode scaffold (MES) is proposed and implemented. It was found that there is a 25%-27% difference between the model and the experimental measurements. Case studies were also performed with the DNS to compare the effects of different operating conditions, specifically temperature and relative humidity, and different reconstructed microstructures. Suggested operating parameters are proposed for the best comparison between numerical and experimental results. Recommendations for microstructure reconstruction, MES construction and design, and potential measurement techniques are also given. / Master of Science

Understanding how the water produced in an operating polymer electrolyte membrane fuel cell (PEMFC) is transported in cathode catalyst layer (CCL) is crucial to improving performance and efficiency. In this thesis, a multiple-relaxation-time (MRT) lattice Boltzmann method (LBM) is employed to simulate the high density ratio, multiphase water transport in in the CCL. The three-dimensional structure of the catalyst layer is reconstructed based on experimental data acquired with a dual beam scanning electron microscope/focused ion beam system and a stochastic method using lower order statistical functions (e.g. porosity and two point correlation functions). Simulations of the water transport dynamics are performed to examine the effect of a range of physical parameters: wettability, viscosity ratio, pressure gradient, and surface tension. The water penetration patterns in the catalyst layers reveal a complex fingering process and transition of the water transport pattern from a capillary fingering regime to a stable displacement regime is observed when the wettability potential of the catalyst layer changes. The second part of the analysis focuses on quantifying the impact of liquid water distribution and accumulation in the catalyst layer on effective transport properties by coupling two numerical methods: the two-phase LBM is used to determine equilibrium liquid water distribution, and then a finite volume-based pore-scale model (FV-PSM) is used to compute transport of reactant and charged species in the CL accounting for the impact of liquid water saturation .The simulated results elucidate and quantify the significant impact of liquid water on the effective oxygen and water vapor diffusivity, and thermal conductivity in CLs. / Graduate

Indiana University-Purdue University Indianapolis (IUPUI) / There are three parts in this work centered on the catalyst layer of Polymer Electrolyte Fuel Cell (PEFC) in this thesis. The first part is for making best MEA structure. One of the major aims of this investigation is to understand the micro-structural organization of ionomer particles and Pt/C aggregates dispersed in a catalyst ink. The dispersion of Nafion® ionomer particles and Pt/C catalyst aggregates in liquid media was studied using ultra small angle x-ray scattering (USAXS) and cryogenic TEM technologies. A systematic approach was taken to study the dispersion of each component (i.e. ionomer particles and Pt/C aggregates) first, then the combination, last the catalyst ink. A multiple curve fitting was used to extract the particle size, size distribution and geometry from scattering data. The results suggests that the particle size, size distribution and geometry of each system are not uniform, rather, vary significantly. The results also indicate that interaction among components (i.e. ionomer particles and Pt/C aggregates) exists. The cryogenic TEM, by which the size and geometry of particles in a liquid can be directly observed, was used to validate the scattering results, which shows the excellent agreement. Based on this study, a methodology of analyzing dispersion of Pt/C particles, Nafion® particles in a catalyst ink has been developed and can serve as a powerful tool for making a desired catalyst ink which is a critical step for making rational designed MEA. The carbon corrosion process is the second part of the thesis. The carbon corrosion process of low–surface-area Pt/XC72 and high-surface-area Pt/BP2000 was investigated xi using an developed accelerated durability testing (ADT) method under simulated fuel cell conditions (a Rotating Disk Electrode (RDE) approach). Compared with the complex MEA system, this innovated approach using RDE can simply focus on carbon corrosion process and avoid the use of MEA in which many degradation/corrosion processes simultaneously occur. It was observed that different carbon corrosion processes resulted in different performance (electrochemical active surface area, mass activity and double layer capacity) decay of catalysts. The corrosion process was studied using TEM. It was found that in the case of Pt/XC72, major corrosion occurred at the center of the Pt/XC72 particle, with some minor corrosion on the surface of the carbon particle removing some amorphous carbon black filaments, while in the case of Pt/BP2000, the corrosion started on the surface. The understanding of carbon corrosion process provides the guidance for making high corrosion resistance catalysts to increase the durability performance of PEFC. Based on the second work, XC72 carbon blacks were etched using steam under different time and used as a new high corrosion resistance catalysts support for the oxygen reduction reaction. TEM results show that the center part of the XC72 particle was more easily etched away. XRD results show that the 002 and 10 peaks of the XC72 based samples are initially sharp, but then broaden during the corrosion process. TEM results of Pt particles show that the steam etching can improve dispersion uniformity of Pt nanoparticles on the surface of carbon support and reduce the Pt particles size. Electrochemical characterization results show that the mass activity of etched carbon black for 1 hour was 1.3 and 34 times greater than that of the carbon blacks etched for 3h and that of carbon blacks non-ecthed. ECSA of the carbon blacks was also significantly increased after etching. MEA test showed after 45 hours testing, the performance MEA with steam etching 1 hour XC72 based catalyst decreases much less than the MEA with commercial catalyst. Clearly, steam etching is a simple and efficient method to increase the performance and durability of the fuel cells catalysts.