Due to the micro-pillar-structured electrodes were made in the gas diffusion layer (GDL) of the proton exchange membrane fuel cell (PEMFC), the cell performance was raised significantly; the study therefore aims to understand whether the same cell performance can be achieved if the micro-pillar-structures were made in the direct methanol fuel cell (DMFC) of the anode. At room temperature and naturally breathed air, the performance of the micro-pillar-structured electrodes was the same as the conventional electrodes. The performance of the electrodes does not rely on the surface area between the micro porous layers and the catalyst. The experimental results inference indicates that no efficiency can be completed. The study then changed the experimental condition, i.e. increased the temperature of the methanol-water solution to 50¢J and reduced the methanol concentrations to 0.5M. The purpose was to carry out the reaction of the surface between the methanol and the catalyst layer. However, the experimental result shows no variation between the micro-pillar- structured electrodes and the conventional electrodes. Because of the test of the current density of the DMFC was carried out in a small power (0~25mW/cm2). The current density of the PEMFC was carried out in a high power (400mW/cm2 ~). The study proposed that the cell operating temperature can be raised and the oxygen can be put in the cathode, the performance of the micro-pillar-structured electrodes can thus be enhanced if the reaction was in a high current density. At the finals, the study tried to compare the efficiency between self-made electrodes and commercial electrodes (E-TEK). The result showed that both max power densities can reach 17mW/cm2 at room temperature and naturally breathed air.

The development of improved water management strategies for the polymer electrolyte membrane fuel cell (PEMFC) could stand to benefit from an improved understanding of the surface and internal structure of the gas diffusion layer (GDL). The GDL is a fibrous porous material enabling mass transport between the PEMFC catalyst layer and flow fields. Fluorescence-based visualizations of liquid water droplet evaporation on GDL surfaces were performed to investigate water droplet pinning behaviours. The heterogeneous in-plane and through-plane porosity distributions of untreated GDLs were studied using computed tomography visualizations. The through-plane porosity distributions were utilized to calculate heterogeneous local tortuosity, relative diffusivity, and permeability distributions. Finally, the heterogeneous through-plane porosity distributions of GDLs treated for increased hydrophobicity were investigated. This work provides new insight into GDL material properties to better inform future PEMFC models.

The development of improved water management strategies for the polymer electrolyte membrane fuel cell (PEMFC) could stand to benefit from an improved understanding of the surface and internal structure of the gas diffusion layer (GDL). The GDL is a fibrous porous material enabling mass transport between the PEMFC catalyst layer and flow fields. Fluorescence-based visualizations of liquid water droplet evaporation on GDL surfaces were performed to investigate water droplet pinning behaviours. The heterogeneous in-plane and through-plane porosity distributions of untreated GDLs were studied using computed tomography visualizations. The through-plane porosity distributions were utilized to calculate heterogeneous local tortuosity, relative diffusivity, and permeability distributions. Finally, the heterogeneous through-plane porosity distributions of GDLs treated for increased hydrophobicity were investigated. This work provides new insight into GDL material properties to better inform future PEMFC models.

Direct methanol fuel cell (DMFC) were characterized with low operation temperature, high energy density, rapid activation, easy to obtain, easy to carry, safety, stability and low pollution. Therefore, DMFCs were thought as the next generation of power suppliers to replace lithium battery in the future. In order to meet the miniaturization demand of portable electronic devices, this research tried to fabricate a £gDMFC, simplify component, and lower cost by using MEMS technique. This research used TMAH etching, PEACE, and KOH etching, CNT growth technique to fabricate the hill-like diffusion layer (HDL) electrode which combined the channel structure and through-hole silicon (THS) electrode. Another emphasis of this research was to improve the bubble cover problem for £gDMFCs. The bubble cover problem resulted from the CO2 bubble generated in methanol oxidation reaction difficultly removed and resulted in adverse effect for reaction. This research tried to use the surfactants which used in electroforming to improve the bubble cover problem by improvement surface tension of fuel. Experiments show that using the HDL electrode in anode and the THS electrode in cathode would get the maximum power density (0.186 mW/cm2). The powder density of the design £gDMFC is 10 and 2.5 times larger than the one with pure carbon paper electrodes and the HDL electrodes. Surfactant MA was suitable as a wetting of methanol. Bubble size could reduce 1/2 to 1/3 and bubble cover area could reduce 20% by adding MA. Add MA in the fuel cell could help the bubbles remove to avoid the bubble cover problem. Though MA addition would have the adverse effect for methanol reaction, could get the stabile voltage and extend the discharge time.

The excessive presence of liquid water in a gas diffusion layer (GDL) hinders the access of reactant gases to the active sites of the catalyst layer leading to decreased performance of a polymer electrolyte membrane fuel cell (PEMFC). Therefore, GDLs are usually treated with a hydrophobic agent to render their fibres more hydrophobic in order to facilitate gas transport and water removal. Numerous studies have been conducted to investigate water transport in PEMFCs in recent years; however, the behaviour of liquid water in a GDL at a pore-level is poorly understood. Macroscopic models fail to incorporate the influence of the structural morphology of GDLs on liquid water transport behaviour. Experimental methods are not conducive towards a good understanding at a microscopic level because of the diminutive size of the GDLs porous structure. Alternatively, the Lattice Boltzmann (LB) method has gathered interest as it is found to be particularly useful in fluid flow simulations in porous media due to its capability to incorporate the complex boundaries of actual GDL structures. To date, most studies on fluid transport in GDLs integrated artificial structures generated by stochastic simulation techniques to the LB models. The stochastic-based model, however, does not represent closely the microscopic features of the actual GDL as manufactured. In addition, comparison of liquid water transport behaviour in different GDL structures using the LB method is rare since only a single GDL material has been utilised in most of those studies. This thesis aims to develop our understanding of liquid water transport behaviour in GDLs with morphologically different structures under varying wettability conditions based on the LB method and the X-ray computed tomography (XCT) technique. GDLs with paper and felt structures were reconstructed into 3D digital volumetric models via the XCT process. The digital models were then incorporated into a LB solver to model water saturation distribution through the GDL domains. The GDL wettability was also altered so that the effect on liquid water behaviour in the GDL could be examined. This project is divided into three main sections. In the sensitivity analysis, the effect of image resolution on gas permeability through the X-ray reconstructed GDL was carried out using a single-phase LB model. It was found that the resolution variation could significantly affect the resulting gas permeability in both principal and off-principal directions, as well as computational time. An optimum resolution, however, exists at 2.72 μm/pixel, which consumed 400 times less computational time with less than 8% difference in the resulting permeability compared to the base resolution. This study also served as a guideline for selecting a resolution for generating the XCT images of the GDLs which were utilised in the following studies. In the structure analysis, the structures of the paper and felt GDLs were generated using the XCT and the key properties of each GDL, including thickness, porosity, permeability and tortuosity, were characterised. The thickness and the through-plane porosity distributions of each GDL were examined based on the tomography images. The resulting local through-plane porosity distributions were then used to calculate through-plane permeability and tortuosity distributions using an analytical model available in the literature. This study revealed the heterogeneity of the GDLs and how the heterogeneous nature of the GDL structures affects others properties of the GDLs. In this study, the absolute through-plane permeability and tortuosity of the X-ray-reconstructed GDL samples were also characterised using the single-phase LB model. The results from the two models were then compared and validated against data in the literature. In the water transport analysis, the two-phase LB model was employed to examine the effects of GDL structures on the behaviour of liquid water in the GDLs, including invasion patterns, saturation distribution and breakthrough behaviour under varying GDL wettability conditions. It was found that wettability was responsible for invasion patterns and water saturation levels whilst the GDL structure was mostly responsible for breakthrough occurrence and saturation distribution. It was observed that water travelled with stable displacement saturating all pores in hydrophilic GDLs, while it travelled with capillary fingering causing decreased saturation in hydrophobic GDLs, about 50% in the highly hydrophobic cases. The GDL structure was found to play a key role in breakthrough behaviour in the hydrophilic GDL as it was seen that the through-plane fibres in the felt structure and the through-plane binders in the paper structure encouraged water removal from the GDL in the thickness direction. Conversely, the GDL structure was found to have negligible influence on breakthrough in the hydrophobic GDL. Each GDL structure, however, contributed to a distinct difference in water distribution in the GDL with hydrophobic wettability. The work presented in this thesis contributes to the understanding of liquid water transport behaviour in the GDLs under the combined effects of the GDL structures and wettability conditions, which is essential for the development of effective PEMFC water management and the design of future GDL materials.

While there is a substantial amount of information regarding the electrochemical behavior of fuel cells and there components little to no information is available regarding the mechanical properties of fuel cell materials in stack setups. This set of experiments was set up to test mechanical properties of gas diffusion layer and bipolar plate materials in a one cell setup. Samples were clamped to specified pressures and deformation properties were observed and measured. Measurements were taken of impingements of the gas diffusion layers into the gas flow channels. A limit for compression of cell configurations was found to be approximately 300psi. Upon reaching the compression limit bipolar plates collapse and materials between plates show signs of breakage. Under compression diffusion media showed impingement into the gas flow channels as well as substantial compression of the three layer stack.

A single polymer electrolyte membrane fuel cell (PEMFC) is comprised of several sub-millimetre thick layers of varying porosity sandwiched together. The thickness of each layer, which typically ranges from 10 to 200μm, is kept small in order to minimize the transport resistance of heat, mass, electrons, and protons, that limit reaction rate. However, the thickness of these materials presents a significant challenge to engineers characterizing the transport properties through them, which is of considerable importance to the development and optimization of fuel cells. The objective of this research is to address the challenges associated with measuring the heat conduction and gas diffusion transport properties of thin porous media used in PEMFCs. An improvement in the accuracy of the guarded heat flow technique for measuring thermal conductivity and the modified Loschmidt Cell technique for measuring gas diffusivity are presented for porous media with a sub-millimetre thickness. The improvement in accuracy is achieved by analyzing parameters in each apparatus that are sensitive to measurement error and have the largest contribution to measurement uncertainty, and then developing ways to minimize the error. The experimental apparatuses are used to investigate the transport properties of the gas diffusion layer (GDL) and the microporous layer (MPL), while the methods would also be useful in the study of the catalyst layer (CL). Gas diffusion through porous media is critical for the high current density operation of a PEMFC, where the electrochemical reaction becomes rate-limited by the diffusive flux of reactants reaching reaction sites. However, geometric models that predict diffusivity of the GDL have been identified as inaccurate in current literature. Experimental results give a better estimate of diffusivity, but published works to date have been limited by high measurement uncertainty. In this thesis, the effective diffusivity of various GDLs are measured using a modified Loschmidt cell and the relative differences between GDLs are explained using scanning electron microscopy and the method of standard porosimetry. The experimental results from this study and others in current literature are used to develop a generalized correlation for predicting diffusivity as a function of porosity in the through-plane direction of a GDL. The thermal conductivity and contact resistance of porous media are important for accurate thermal analysis of a fuel cell, especially at high current densities where the heat flux becomes large. In this thesis, the effective through-plane thermal conductivity and contact resistance of the GDL and MPL are measured. GDL samples with and without a MPL and coated with 30%-wt. PTFE are measured using the guarded steady-state heat flow technique described in the ASTM standard E 1225-04. Thermal contact resistance of the MPL with the iron clamping surface was found to be negligible, owing to the high surface contact area. Thermal conductivity and thickness of the MPL remained constant for compression pressures up to 15bar at 0.30W/m°K and 55μm, respectively. The thermal conductivity of the GDL substrate containing 30%−wt. PTFE varied from 0.30 to 0.56W/m°K as compression was increased from 4 to 15bar. As a result, the GDL contain- ing MPL had a lower effective thermal conductivity at high compression than the GDL without MPL. At low compression, differences were negligible. The constant thickness of the MPL suggests that the porosity, as well as heat and mass transport properties, remain independent of the inhomogeneous compression by the bipolar plate. Despite the low effective thermal conductivity of the MPL, thermal performance of the GDL can be improved by exploiting the excellent surface contact resistance of the MPL while minimizing its thickness.

This research mainly investigated how the hydrophilic and hydrophobic properties of gas diffusion layer, and the different open ratio of the flowfield may affect the performance of the micro proton exchange membrane fuel cell (£gPEMFC). The flow plate used in this experiment was made through deep UV lithography manufacturing processes and micro-electroforming manufacturing processes. Four different open ratios, 52.8 %, 50.8 %, 75.2 % and 75.75 %, of the flowfield were designed for the flow plate composed of serpentine-parallel and serpentine geometrical micro configurations. Acrylic (PMMA: Polymethylmethacrylate) was used to make the terminal plate placed on both sides of the micro proton exchange membrane fuel cell. By varying values of the hydrophilic and hydrophobic properties of the anode gas diffusion layer, the effects of these two parameters on the polarization curve and power density of the cell were explored. All results obtained in the experiment are presented by P-I curve and V-I curve. The experiment results show that, with 1: 5 flow ratio of anode to cathode, a design with the gas diffusion layer made of the material with hydrophobic factor 20 wt.% and with open ratio of 50.8 % for anode flow channel as well as open ratio of 75.75 % for cathode flow channel may have the best performance.

Due to escalating energy costs and limited fossil fuel resources, much attention has been given to polymer electrolyte membrane (PEM) fuel cells. Gas diffusion layers (GDLs) play a vital role in a fuel cell such as (1) water removal, (2) cooling, (3) structural backing, (4) electrical conduction and (5) transporting gases towards the active catalyst sites where the reactions take place. The power density of a PEM fuel cell in part is dependent upon how uniform the gases are distributed to the active sites. To this end, research is being conducted to understand the mechanisms that influence gas distribution across the fuel cell. Emerging PEM fuel cell designs have shown that higher power density can be achieved; however this requires significant changes to existing components, particularly the GDL. For instance, some emerging concepts require higher through-plane gas permeability than in-plane gas permeability (i.e., anisotropic resistance) which is contrary to conventional GDLs (e.g., carbon paper and carbon cloth), to obtain a uniform gas distribution across the active sites. This is the foundation on which this thesis is centered. A numerical study is conducted in order to investigate the effect of the gas permeability profile on the expected current density in the catalyst layer. An experimental study is done to characterize the effects of the weave structure on gas permeability in woven GDLs. Numerical simulations are developed using Fluent version 6.3.26 and COMSOL Multiphysics version 3.5 to create an anisotropic resistance profile in the unconventional GDL, while maintaining similar performance to conventional GDL designs. The effects of (1) changing the permeability profile in the in-plane and through-plane direction, (2) changing the thickness of the unconventional GDL and (3) changing the gas stoichiometry on the current density and pressure drop through the unconventional GDL are investigated. It is found that the permeability profile and thickness of the unconventional GDL have a minimal effect on the average current density and current density distribution. As a tradeoff, an unconventional GDL with a lower permeability will exhibit a higher pressure drop. Once the fuel cell has a sufficient amount of oxygen to sustain reactions, the gas stoichiometry has a minimal effect on increases in performance. Woven GDL samples with varying tightness and weave patterns are made on a hand loom, and their in-plane and through-plane permeability are measured using in-house test equipment. The porosity of the samples is measured using mercury intrusion porosimetry. It is found that the in-plane permeability is higher than the through-plane permeability for all weave patterns tested, except for the twill weave with 8 tows/cm in the warp direction and 4 tows/cm in the weft direction, which exhibited a through-plane permeability which was 20% higher than the in-plane permeability. It is also concluded that the permeability of twill woven fabrics is higher than the permeability of plain woven fabrics, and that the percentage of macropores, ranging in size from 50-400 µm, is a driving force in determining the through-plane permeability of a woven GDL. From these studies, it was found that the graduated permeability profile in the unconventional GDL had a minimal effect on gas flow. However, a graduated permeability may have an impact on liquid water transport. In addition, it was found that graduating the catalyst loading, thereby employing a non-uniform catalyst loading has a greater effect on creating a uniform current density than graduating the permeability profile.

Fibrous porous media are widely used in various industries such as biomedical engineering, textiles, paper, and alternative energy. Often these porous materials are formed into composite materials, using subsequent manufacturing steps, to improve their properties. There is a strong correlation between system performance and the transport and mechanical properties of the porous media, in raw or composite form. However, these properties depend on the final pore structure of the material. Thus, the ability to manufacture fibrous porous media, in raw or composite forms, with an engineered structure with predictable properties is highly desirable for the optimization of the overall performance of a relevant system. To date, the characterization of the porous media has been primarily based on reverse design methods i.e., extracting the data from existing materials with image processing techniques. The objective of this research is to develop a methodology to enable the virtual generation of complex composite porous media with tailored properties, from the implementation of a fibrous medium in the design space to the simulated coating of this media representative of the manufacturing space. To meet this objective a modified periodic surface model is proposed, which is utilized to parametrically generate a fibrous domain. The suggested modeling approach allows for a high-degree of control over the fiber profile, matrix properties, and fiber-binder composition. Using the domain generated with the suggested geometrical modeling approach, numerical simulations are executed to simulate transport properties such as permeability, diffusivity and tortuosity, as well as, to directly coat the microstructure, thereby forming a complex composite material. To understand the interplay between the xxiii fiber matrix and the transport properties, the morphology of the virtual microstructure is characterized based on the pore size, chord length and shortest path length distributions inside the porous domain. In order to ensure the desired properties of the microstructure, the fluid penetration, at the micro scale, is analyzed during the direct coating process. This work presents a framework for feasible and effective generation of complex porous media in the virtual space, which can be directly manufactured.