Numerical analysis of the optimum membrane/ionomer water content of PEMFCs: The interaction of Nafion® ionomer content and cathode relative humidity (original) (raw)
Related papers
Electrochimica Acta, 2012
Performance equations that describe the dependence of cell potential on current density for proton exchange membrane fuel cells (PEMFCs) with feeds of varying degrees of humidification have been formulated in algebraic form. The equations are developed by the reduction of a one-dimensional multi-domain model that takes into account, in details, the transport limitations of gas species, proton migration and electron conduction, electrochemical kinetics, as well as liquid water flow within the cathode, anode, and membrane. The model equations for the anode and membrane were integrated with those of the cathode developed in the previous studies to form a complete set of equations for one-dimensional single cell model. Because the transport equations for the anode diffuser can be solved analytically, calculations of integrals are only needed in the membrane and the two-phase region of cathode diffuser. The proposed approach greatly reduces the complexity of the model equations, and only iterations of a single algebraic equation are required to obtain final solutions. Since the performance equations are originated from a mechanistic one-dimensional model, all the parameters appearing in the equations are endowed with a precise physical significance.
Reactants flow behavior and water management for different current densities in PEMFC
International Journal of Heat and Mass Transfer, 2008
Computational fluid dynamics analysis was carried out to investigate the reactants flow behavior and water management for proton exchange membrane fuel cell (PEMFC). A complete three-dimensional model was chosen for single straight channel geometry considering both anode and cathode humidification. Phase transformation was included in the model to predict the water vapor and liquid water distributions and the overall performance of the cell for different current densities. The simulated results showed that for fully humidified conditions hydrogen mole fraction increases along the anode channel with increasing current density, however, at higher current densities it decreases monotonically. Different anode and cathode humidified conditions results showed that the cell performance was sufficiently influenced by anode humidification. The reactants and water distribution and membrane conductivity in the cell depended on anode humidification and the related water management. The cathode channel-GDL (Gas Diffusion Layer) interface experiences higher temperature and reduces the liquid water formation at the cathode channel. Indeed, at higher current densities the water accumulated in the shoulder area and exposed higher local current density than the channel area. Higher anode with lower cathode humidified combination showed that the cell had best performance based on water and thermal management and caused higher velocity in the cathode channel. The model was validated through the available literature.
Mathematical Model of Proton Exchange Membrane Fuel Cell with Consideration of Water Management
Fuel Cells, 2013
Proton exchange membrane fuel cell (PEMFC) has attracted much attention in recent years, which is considered as one of the most promising energy conversion device to replace conventional combustion engine used in transportation vehicles [1-3]. The heart of PEMFC is the membrane electrode assembly (MEA), composed of solid electrolyte sandwiched between the anode and cathode gas diffusion electrodes. The solid polymer electrolyte is polymeric perfluorosulfonic acid derivative, used as separator and proton conductor. Carbon fiber woven porous gas diffusion layers (GDLs), covered with layers of carbon supported platinum catalyst, are used as the respective cathode and anode gas diffusion electrodes. The deformable MEA, fabricated in a novel configuration, can be constrained in a limited space for both stationary and portable power sources [4-7]. One of the major design considerations is the water flooding in the MEA, arising from the blockage of gas diffusion layer by the generated water in cathode catalyst layer [8, 9]. Mechanistic single cell simulation is the foundation of subsequent optimization study and advanced stack design [10-13]. Bernardi and Verbrugge [14-16] proposed the physical model that predicts the water flux through the MEA. Although water saturation profile was not determined in the gas diffusion layer, a detailed water conservation across the MEA over the whole cell operating range was satisfied. Springer et al. [17, 18] also provided a comprehensive MEA model, the role of water diffusion and electro-osmotic drag through membrane was clarified. It was found that single cell performance is hinged on the relative humidities in the respective anode and cathode feeds and the water distribution across the membrane. However, in their work, liquid water emergence in the cathode gas diffusion layer was only accounted by a reduction in oxygen diffusivity. In addition, effect of pressure gradient across the membrane was not considered.
Flow rate and humidification effects on a PEM fuel cell performance and operation
Journal of Power Sources, 2007
A new algorithm is presented to integrate component balances along polymer electrolyte membrane fuel cell (PEMFC) channels to obtain three-dimensional results from a detailed two-dimensional finite element model. The analysis studies the cell performance at various hydrogen flow rates, air flow rates and humidification levels. This analysis shows that hydrogen and air flow rates and their relative humidity are critical to current density, membrane dry-out, and electrode flooding. Uniform current densities along the channels are known to be critical for thermal management and fuel cell life. This approach, of integrating a detailed two-dimensional across-the-channel model, is a promising method for fuel cell design due to its low computational cost compared to three-dimensional computational fluid dynamics models, its applicability to a wide range of fuel cell designs, and its ease of extending to fuel cell stack models.
Journal of Power Sources, 2006
In this work, the main focus is to measure the optimal cathode fuel flow rate effects with different flow field designs. In addition, the effects of different flow field designs (flow channel number, flow channel length, corner numbers and baffle effects) on the cell performance of the PEM fuel cells under the different operating conditions are examined. The experimental results reveal that the temperature effects generate the same trend in the five cathode flow field designs. When the cell temperature increases from 50 to 70 • C, the proton exchange membrane (PEM) experiences an insufficient hydration which causes an increase in ionic transport resistance. Therefore, the cell performance decreases with an increase in the cell temperature. In addition, increasing the cathode humidification improves the cell performance through enhancing the hydration level of the membrane and hence its ionic conductivity. For the effects of the cathode fuel flow rate on the cell performance, the PEM fuel cell with interdigitated flow field shows a better cell performance than that with the conventional flow field due to the baffle effect which forces the reactant gas through the gas diffuser layer. Furthermore, compared with conventional flow field, the PEM fuel cell with an interdigitated flow field can reach the same cell performance with a lower fuel consumption rate. Under the optimal fuel flow rate conditions, the PEM fuel cell with a parallel flow field with baffle provides the best cell performance among the five flow field designs. (W.-M. Yan). more important. As for water management, this determines the cell performance during cell operation. Water flooding inside the cell would cause dehydration of the PEM and an increase of cell internal resistance, and consequently cell performance degradation. In the case of water flooding inside the cell, the cathode gas diffuser layer would be blocked and the cathode gas would not be able to diffuse to the catalyst layer and take part in electrochemical reactions, causing degradation of the overall cell performance. Nguyen [1] analyzed the influences of different humidity conditions on the water and thermal management in a PEMFC. The results showed that hydration and ionic conduction are better in the portion of the membrane close to the fuel inlet, which increases the electro-osmosis coefficient and electricity carrying ability of the membrane, and the consumption rate of the anode hydrogen and the cathode oxygen. In the downstream flow field, less water is held by the membrane, and hydration and ionic conduction are weaker, which implies a lower fuel consumption and thereby lower cell performance. In addition, a high humidity temperature is required at high current density so 0378-7753/$ -see front matter
Transport parameters for the modelling of water transport in ionomer membranes for PEM-fuel cells
2004
The water transport number (drag coefficient) and the hydraulic permeability were measured for Nafion. The results show a significant increase of both parameters with increasing water content indicating that they are strongly influenced by the membrane microstructure. Based on these experimental studies a new model approach to describe water transport in the H 2-PEFC membrane is presented. This approach considers water transport by electro-osmosis caused by the proton flux through the membrane and by osmosis caused by a gradient in the chemical potential of water. It is parametrized by the measured data for the water transport number and the hydraulic permeability of Nafion. First simulation results applying this approach to a one-dimensional model of the H 2-PEFC show good agreement with experimental data. Therefore, the developed model can be used for a new insight into the dominating mechanisms of water transport in the membrane.
An analytic model of membrane humidifier for proton exchange membrane fuel cell
Environmental Engineering Science, 2014
An essential requirement for an operating PEM fuel cell is providing proper water content in the membrane. To avoid water flooding an appropriate water balance is required. Here, an analytic model of a planar membrane humidifier for PEM fuel cell is proposed where the effect of dimensional parameters includes membrane thickness, membrane area and channel hydraulic diameter are investigated. A Non-linear governing equations system is developed and solved. At each stage, the outlet temperatures, the water and heat transfer rates, relative humidity and the dew point at dry side outlet are presented and discussed. The humidifier is evaluated based on the decrease in difference between the dew point at wet side inlet and dry side outlet which leads to humidifier better performance. The results show that an increase in membrane thickness results in a decrease in dew point at dry side outlet which indicates a weak humidifier performance. Vaster membrane area can enhance humidifier performa...
Influence of Operating and Electrochemical Parameters on PEMFC Performance: A Simulation Study
Membranes
Proton exchange membrane fuel cell, or polymer electrolyte fuel cell, (PEMFC) has received a significant amount of attention for green energy applications due to its low carbon emission and less other toxic pollution capacity. Herein, we develop a three-dimensional (3D) computational fluid dynamic model. The values of temperature, pressure, relative humidity, exchange coefficient, reference current density (RCD), and porosity values of the gas diffusion layer (GDL) were taken from the published literature. The results demonstrate that the performance of the cell is improved by modifying temperature and operating pressure. Current density is shown to degrade with the rising temperature as explored in this study. The findings show that at 353 K, the current density decreases by 28% compared to that at 323 K. In contrast, studies have shown that totally humidified gas passing through the gas channel results in a 10% higher current density yield, and that an evaluation of a 19% higher R...