In a proton exchange membrane fuel cell (PEMFC), the water removal from the cathode to reactant flow channels is a critical aspect of cell operation. This is an active area of research to understand the transport mechanisms of water. In the available literature, it has been shown that a significant portion of the product water is removed in vapor form by the heat pipe effect through the gas diffusion layer (GDL). The intensity of the heat pipe effect is dependent on the local mean temperature and the through-plane temperature gradient across the GDL. This gradient is spatially affected by the reactant channel-land patterns of the bipolar plate (BPP) and the coolant plate operation. Therefore, the heat pipe effect can have spatial variances depending on the BPP design and cooling method. In order to show the local temperature and through-plane temperature gradient distribution in a GDL, a numerical approach was taken in this work using a commercially available software package, COMSOL Multiphysics ® 4.2a. A repetitive cathode section of the PEMFC was modeled in 3D with domains of a GDL and BPP. In-plane thermal conductivity of the GDL was incorporated by using experimentally obtained values from the available literature. By changing the design and operating conditions of the coolant system, the thermal profile and so, the vapor flux across the GDL were investigated. It was found that the increasing temperature non-uniformity on coolant plates leads to less uniform distribution of vapor flux. This is expected to lead to more condensation of water vapor under the lands.

Micro-porous layers (MPLs) play an important role in the water management of polymer electrolyte fuel cells (PEFCs), but details of the mechanism that works to suppress water flooding has not been fully understood. In this study, the authors investigated water distribution at the interface between the MPL and the catalyst layer (CL) at the cathode side to clarify the effect of the MPL on the discharge of produced water. A freezing method was applied to observe the distribution of the condensed water, and the ice distribution on the CL surface was quantified by image processing. The effects of operating conditions on the water distribution were examined at normal temperature conditions. The distribution of ice formed on the surface of the CL with and without MPL after −10°C cold start operation was also established. Water transport rate in the vapor phase was analyzed based on temperature and vapor pressure gradient considerations. The experiments and the analysis showed that the MPL functions to prevent accumulation of water on the surface of the CL, resulting in less water flooding.

A prodigious amount of research has been conducted to study and measure the different properties associated with the mass transfer phenomenon inside the GDL like diffusivity, permeability, porosity, thickness. However, the functional relationship of these parameters with the limiting current; the effect of the individual factor over others; and the interaction, correlation and interdependence of these factors have been subject of little work. Using the experimental data presented in the literature, this paper presents a methodology developed based on a regression model to predict the limiting current from GDL properties. Statistical techniques like factorial design and response surface methodology are used to perform the sensitivity analysis of relevant parameters. The emphasis will be on factor screening to identify efficiently the parameters with most dominant effects. The results obtained will then be used to select the most effective GDL (among those characterized) based on multi criteria decision making tools like weighting sum method (WSM) and TOPSIS with entropy weight. The final goal is to elucidate the impact of each property, and hence to identify the most important parameters that need to be studied and characterized to engineer a better GDL with enhanced water management capabilities.

In the present work, a chip embedded thin film current collector for vanadium fueled microfluidic fuel cells is proposed. Embedded current collectors are expected to increase the number of contact points with the porous electrodes and thereby reduce the overall contact resistance and ohmic losses of the cell. The micromachining based thin film process is compatible with the overall cell fabrication scheme, which is based on soft lithography, and does not require a substantial modification of the original cell design. The flow-through microfluidic fuel cell architecture with porous carbon paper electrodes is used as a proof-of-concept in this study. Our preliminary study shows that the peak power density of the cell with the current collector is increased by 79% at 300 μL min −1 compared to an otherwise identical cell without current collector, indicating that the contact resistance is significantly reduced. Electrochemical impedance spectroscopy analysis is carried out to estimate the overall cell ohmic resistance and confirms a 32% reduction using the current collectors.

In the microscale structure of a porous electrode, the transport processes are among the least understood areas of SOFC. The purpose of this study is to evaluate the Lattice Boltzmann Method (LBM) for a porous microscopic media and investigate mass transfer processes with electrochemical reactions by LBM at a mesoscopic and microscopic level. Part of the anode structure of an SOFC for two components is evaluated qualitatively for two different geometry configurations of the porous media. The reaction-diffusion equation has been implemented in the particle distribution function used in LBM. The LBM code in this study is written in the programs MATLAB and Palabos. It has here been shown that LBM can be effectively used at a mesoscopic level ranging down to a microscopic level and proven to effectively take care of the interaction between the particles and the walls of the porous media. LBM can also handle the implementation of reaction rates where these can be locally specified or as a general source term. It is concluded that LBM can be valuable for evaluating the risk of local harming spots within the porous structure to reduce these interaction sites. In future studies, the information gained from the microscale modeling can be coupled to a macroscale CFD model and help in development of a smooth structure for interaction of the reforming reaction and the electrochemical reaction rates. This can in turn improve the cell performance.

This paper investigates numerical simulation of one-dimensional homogeneous adiabatic gas-liquid two-phase flow in a rectangular microchannel with one boundary porous wall under the assumption of hydrophobic condition. Gas enters the microchannel with a uniform velocity and liquid is injected through the porous side wall. The present approach is to simulate water injection effects and developing mechanism of two-phase flow. The modeling and solution of the conservation equations provide pressure drop, vapor quality, void fraction and tow-phase mixture velocity for different water injection rates. The results show that velocity and pressure drop significantly perturbed when the water injection rate exceeds a critical value. Comparison between the results of the present work with the previous experimental work shows a good agreement.

The appropriate blend proportional factor value which combines two kinds of staggered grids used in Lattice Boltzmann Method (LBM) for simulating the multiphase flow phenomena with large density ratio in the Polymer electrolyte fuel cell (PEFC) is fixed on. The shape deformation of the water droplet is found when using the two kinds of staggered grids to prevent the pressure oscillation when solving the Poisson equation of this LBM model and the shape of the water droplet varies with the changes of the blend proportional factor values. Two methods are adopted to find out the two staggered grids’ appropriate blend proportional factor value that can diminish or minimize the deformation of the droplet. The first one is to compare the simulation results of different blend proportional factors with the theoretical value and find the one mostly approaches the theoretical value; the second one is to compare the current velocity divergences of the two staggered grids using the results calculated by different blend proportional factor values. A water droplet resting in a tunnel is simulated with different blend proportional factor values and the appropriate value is decided.

The polymer electrolyte membrane (PEM) fuel cell is a zero emission power generation system that has long been considered as a replacement for conventional fossil fuel combustion systems. However, before constituting a viable market for commercial use, the fuel cell’s efficiency and reliability need to be improved significantly. It has been shown that water management has a significant effect on the power and reliability of the cell as the electrolyte membrane must be well hydrated to allow for ion transfer while excess water blocks the activation sites on the cathode side. The latter effect is known as flooding which occurs at large current densities and compromises the normal operation of the fuel cell. To enhance water management, a prodigious amount of studies have been conducted to optimize the properties and structures of different layers. One of the key results of these studies has been the design of a flow field pattern on the relatively hydrophobic surface of a graphite plate which is believed to provide a better mechanism for removing water droplets from the cathode flow channel. However, the wettability gradient between the catalyst layer (i.e., hydrophilic) and the flow channel (which is currently more hydrophobic) introduces problems as the water droplets formed at the catalyst layer will not likely detach, and hence create a film of liquid that will block the activation sites. If the flow channel is made out of a material that is more hydrophilic than the catalyst layer, water removal and transport will be enhanced as water naturally moves from low surface energy to high surface energy sites. However, recent numerical studies conducted on simulation of water transport in the channels show that removing the water film formed on the hydrophilic channels is limited due to the pressure of the gas flow in the channels. To resolve this problem, the use of compact aluminum foams in the flow channels is studied in this paper. It is shown that the hydrophilicity of the foam-filled flow channel helps the transport of the water droplets at the catalyst layer to the channel in which a liquid film is formed. This film is then removed due to the increased pressure developed in the porous media of the foam (as opposed to the regular open flow channel). The paper includes the experimental results obtained for the fuel cell performance using the new geometry with and without the gas diffusion layers (GDLs). These results will be compared to a similar flow channel that does not include the compressed aluminum porous structure. This work will result in finding the optimum geometry for achieving maximum performance in the flooding regime.

Porous transport layers are an integral part of polymer electrolyte fuel cells (PEMFC). In order to optimize the catalyst layer performance and reduce catalyst consumption, a thorough understanding of mass transport through porous media is necessary. Currently, there is a lack of experimental measurements of effective mass transport properties of porous transport layers. Further, mass transport theories in the literature, such as the binary friction model by Kerkhof [1], have not been extensively validated for porous media. In the present study, mass transport measurements have been performed on the porous media of a PEMFC, namely a GDL and an MPL. The experimental setup described by Pant et al. [2] has been used. The setup uses the diffusion bridge/counter-diffusion technique for the mass transport measurements. The experimental setup has the advantage that it can be used to perform studies for pure diffusion and convection-diffusion mass transport. The setup also facilitates measurement of permeability of porous media, which can then be used in convection-diffusion studies. Preliminary permeability measurements of GDL and MPL from the setup show good agreement with values available in literature. In preliminary experimentation, the conventional diffusivity correlations like Bruggeman equation have been found to overpredict the diffusivities.

A novel method has been implemented for measuring the concentration of various gas species (water vapor, carbon dioxide) within fuel cell gas channels and other minichannel applications in a non-invasive manner through the use of tunable diode laser absorption spectroscopy (TDLAS). An optically accessible test cell has been designed to allow for the passage of 1–0.5 millimeter diameter laser beams along 12 mm-12 cm long flow paths, while also allowing for visual observation of the channels in order to detect the formation of liquid water. Concentrations of water vapor and carbon dioxide have been measured in situ within the test cell with a temporal resolution of 0.5 secs and 2.5 secs respectively. The technique is portable to high aspect ratio channels yielding concentration measurements of species over 1 mm long passages with an experimental uncertainty of 5%.

Water management is a critical factor in the performance and durability of a proton exchange membrane (PEM) fuel cell. In situ experiments are needed to gain a better understanding of water transport within the channels of the cell during operation. In this work a 50 cm 2 fuel cell with optical access is designed and tested in an in situ experimental facility. Two-phase flow in the cathode channels of the cell is observed, and flow patterns are characterized. Three primary two-phase structures are identified — slug flow, film flow, and mist flow — and a flow pattern map is developed. A comparison between in situ and ex-situ flow pattern maps shows that ex-situ experimentation can be used to predict some in situ flow characteristics, but cannot capture the effects of reaction kinetics or relative humidity. The total pressure drop signature is seen to be a useful parameter for predicting two-phase flow dynamics in the gas channels. In addition, channel to channel flow variation caused by the presence of liquid water in the cathode channels is investigated using entrance region pressure drop measurements.

In the paper, a two-phase, one-dimensional steady model of a proton exchange membrane fuel cell is developed for the porous cathode electrode. The interacted phenomena of cathode flooding and mass-transport limiting are investigated. In the model, the catalyst layer is treated as a separate computational domain with finite thickness and structure. Furthermore, through the Tafel kinetics, the mass transport processes of oxygen and liquid water are coupled. The transport of liquid water across the porous electrode is driven by the capillary force based on the Darcy’s law. However, the transport of gas is driven by the concentration gradient based on the Fick’s law. From the simulated results, it is found that the thin catalyst layer is very detriment for better understanding of the concurrent phenomena inside the electrode of a fuel cell, particularly, the flooding phenomena. More importantly, the saturation-level jump at the gas diffusion layer and catalyst layer interface is attained in order to satisfy the continuity of the capillary pressure on both sides of the GDL and CL interface. Meanwhile, the results show that the flooding phenomenon within the CL is more serious than that in the GDL, which has a significant influence on the mass transport of oxygen. Finally, the effect of some important parameters, such as the boundary value of saturation, absolute permeability, the cathode surface overpotential, on the saturation distribution inside the electrode is also obtained.

Polymer electrolyte fuel cells (PEFCs) are one of the most interesting alternatives for a pollution-free electrical energy production in many applications where a highly reliable source of electricity is needed. One of the major challenges in the development of PEFCs is to exploit the whole capacity that is inherent to a given membrane electrode assembly (MEA). In practice, certain obstacles remain to be overcome like local mass transport effects, non-uniformly manufactured MEAs, locally varying contact resistances, water management and temperature gradients. All these parameters lead to an inhomogeneous electrochemical activity over the electrode area. Consequently, a variation and a gradient of the current density over the cell area occurs which tends to result in inferior performance and low durability of a PEFC. For the determination of current density distribution different in-situ methods and measurement techniques are applied. Results can be used to improve cell components, to validate models and to detect inappropriate detrimental operating conditions of the fuel cell.

Fuel cells are clean and efficient power generation devices which are being widely investigated under the efforts to reduce the impact of greenhouse gases on the environment. Solid oxide fuel cells (SOFCs), especially, are suitable for stationary power generation using a wide range of alternative fuels. Performance of a SOFC strongly depends on the mass transport inside the porous electrodes which are essentially composed of a network of microchannels. In this study the mass transport inside a SOFC cathode is studied using direct simulation of mass transport in microchannels along with statistical analysis. A virtual cathode is built using microchannels that are representative of continuous flow paths between the cathode/air stream interface and cathode/electrolyte interface of a SOFC. Different representative microchannel flow paths are built with varying tortuosity and channel diameters. The numbers of channels of each kind are chosen according to a normal distribution and they are randomly arranged in an appropriately sized cuboid to construct a unit block of the virtual cathode. The normal distribution is modulated with average and standard deviation values for real world electrodes found in literature. Microchannels are tightly packed to achieve the desired porosity. Mass transport in each of the channels is studied separately using commercial CFD software FLUENT. Three dimensional simulations of momentum and specie transport equations (for oxygen and nitrogen) are performed. The results from individual channel simulations are used to assess the global mass transfer characteristics of the virtual cathode. Results obtained using this approach will be compared with those from a continuum Fick’s law type diffusion model used to simulate mass transport in porous media. The primary objective is to test the assumptions employed within the context of continuum mass transport model.

In this investigation, X-ray microscopy (7B2) in Pohang Accelerator Laboratory was employed to visualize the water distribution in operating PEMFC which had 2cm × 2cm active area. This X-ray microscopy has 1μm spatial resolution with 1.5mm × 1.2mm view area. Each image spent about 1.3 second, 0.65 second for exposure and about 0.6 second for data read out. The resistance of the electric loader was changed and electric current and voltage was measured during images were recorded. The water distribution in PEMFC was analyzed with this I-V curve. Water distribution was depend on current density and aggregated on interfaces of layers (GDL, MPL, MEA).

Water management in a polymer electrolyte fuel cell (PEFC) was experimentally investigated using an X-ray microscopy technique. Recently, fuel cell has been receiving large attention as an important renewable energy due to its efficiency, clearness and sustainability. Among various types of fuel cells, PEFC can be used as a power source of transport vehicles and home applications. In recent commercial development of PEFC, water management is one of the major problems to be solved. In fact, proper water management is vital to enhance performance and durability of PEFC. In this study, transport of water inside MEA (membrane electrode assembly) and GDL (gas diffusion layer) layers of an operating ( in situ ) fuel cell was observed using the synchrotron X-ray micro-imaging technique. As the synchrotron X-ray imaging technique has very high spatial and temporal resolutions, it is suitable for observing the dynamic movement and behavior of liquid layer and water distribution inside the PEFC. For this X-ray micro-imaging experiment, a single cell test kit of PEFC was specially designed for convenient capturing of X-ray images. Temporal variation of gray level in the PEFC components, such as MEA, GDL and endplate, was investigated with varying loading condition. As a result, X-ray images of the PEFC components were clearly distinguished by image pattern and gray level difference. The gray level shows roughly symmetric distribution with respect to MEA layer. The gray level at GDL decreases with lapse of time, indicating the increase of H 2 O concentration with time.

Proton Exchange Membrane (PEM) fuel cells are gaining popularity as a replacement to the internal combustion engine in automobiles. This application will demand high levels of performance from the fuel cell making it critical that proper water management is maintained. One of the areas of interest in water management is the transport of water through the Gas Diffusion Medium (GDM) on the cathode side of the cell. Research is currently being conducted to understand how water moves through the porous structure of the GDM. Due to the small scale of the GDM, most work done is analytical modeling. This paper will focus on reviewing current models for water transport within the GDM of a PEM fuel cell to address state of the art and provide recommendations for future work to extend current models.

The flow behavior in the separator channel and gas diffusion layer (GDL) of a polymer electrolyte fuel cell (PEFC) has been investigated by using a transient, isothermal and three-dimensional numerical model. Gas channel and gas diffusion layers are considered as the important parts of PEFC as they transport reactant gases to the catalyst layer and also byproduct from the catalyst layer. The deformation of GDL plays an important role on the performance of polymer electrolyte fuel cell since the physical properties such as porosity and permeability of the GDL and the cross sectional area of the gas channel are affected by the structural deformation of GDL. In this present investigation, non-uniform deformations shape of GDL are taken into consideration and chosen as in the experimental data. Numerical simulations are performed for a wide range of porosity and permeability values. Further, the effects of these parameters on the pressure distribution are measured. It is revealed that the increase of porosity and permeability parameter caused the decrease of pressure drop (difference of pressure from inlet and outlet) but the decreasing rate is not uniform. It is also found that there is an effective range of porosity and permeability values for which these parameters have a very strong effect on the pressure drop. The results obtained by numerical simulation are also compared with the experimental as well as theoretical solution.

Flooding within a Polymer Electrolyte Membrane (PEM) fuel cell occurs during operation as a result of product water vapor condensing near the surface of the cathode; this can be detrimental to fuel cell performance due to its role in reducing oxygen transport throughout the GDL. Previous Gas Diffusion Layer (GDL) transport models have made use of a zero-saturation boundary condition at the GDL/Oxygen (O 2 ) gas channel (GC) interface. However, the physical correctness of this saturation boundary condition is still unclear. Further investigation of the saturation boundary condition could lead to a more robust model of the GDL saturation distribution and cathodic flooding. This exploration provides a one-dimensional two-phase transport model for saturation as well as liquid water and gaseous oxygen pressure distributions throughout the cathode-side gas diffusion layer (GDL) within a PEM fuel cell. The focus of this investigation is on the impact of non-zero saturation boundary conditions at the GDL / GC interface, and its impact on two-phase transport within the porous medium, with regard to fuel cell performance. Saturation boundary conditions at this location are determined based on GDL interfacial liquid coverage of water droplets that diffuse through the porous medium during operation and block oxygen transport paths. The results of this investigation suggest that non-zero saturation boundary conditions at the GDL/GC interface are evident when analyzing two-phase phenomena, which affect the overall saturation distribution throughout the GDL, and consequent performance of the fuel cell. In addition, GDL membranes with large porosities were found to improve gas and liquid transport by lowering the saturation at the GDL / Cathode interface that would otherwise impede oxygen transport.

Pore network modelling has traditionally been used to study displacement processes in idealized porous media related to geological flows, with applications ranging from groundwater hydrology to enhanced oil recovery. Very recently, pore network modelling has been applied to model the gas diffusion layer (GDL) of a polymer electrolyte membrane (PEM) fuel cell. Discrete pore network models have the potential to elucidate transport phenomena in the GDL with high computational efficiency, in contrast to continuum or molecular dynamics modelling that require extensive computational resources. However, the challenge in studying the GDL with pore network modelling lies in defining the network parameters that accurately describe the porous media as well as the conditions of fluid invasion that represent realistic transport processes. In this work, we discuss the first stage of developing and validating a GDL-representative pore network model. We begin with a two-dimensional pore network model with a single mobile phase invading a hydrophobic media, whereby the slow capillary dominated flow process follows invasion percolation. Pore network geometries are designed, and transparent hydrophobic microfluidic networks are fabricated from silicon elastomer PDMS using a soft lithography technique. These microfluidic networks are designed to have channel size distributions and wettability properties of typical GDL materials. Comparisons between the numerical and experimental flow patterns show reasonable agreement. Furthermore, the fractal dimension and saturation are measured during invasion, revealing different operating regimes that can be applied to GDL operation. Future work for model development will also be discussed.