Simulation and experiment of heat and mass transfer in a proton exchange membrane electrolysis cell

A full-scale, two-phase, single-channel model of proton exchange membrane electrolysis cell is established. The electrochemical model and the thermal model are coupled to explore the mass transfer of the channel, catalytic layer and diffusion layer, and the heat transfer of the entire electrolysis cell. Two different calculation models are compared, and it is found that the calculation results of the model with bipolar plates are closer to the actual values. Simultaneously, effective water and thermal management strategies are proposed: The temperature of the electrolysis cell can be reduced effectively by supplying water to the cathode side. The Counter-flow mode has a lower temperature than the Co-flow mode, but the temperature gradient in the Counter-flow mode is greater. Reducing the channel depth and increasing the channel width can improve the water transmission in the electrolysis cell and reduce the temperature of the electrolysis cell, but a larger channel width will increase the electrical loss. Therefore, the selection of appropriate channel size is of great significance to the long-term stable operation of the electrolysis cell.     

Transport phenomena effect on the performance of proton exchange membrane fuel cell (PEMFC)

The aim of this work is to present a two-dimensional transient model, of heat and mass transfer in a proton exchange membrane fuel cell (PEMFC). The model includes various conservation equations such as mass (hydrogen, oxygen, water concentration), Momentum and energy equations this model is combined with the electrochemical model.     

质子交换膜燃料电池的多尺度传热传质

介绍了目前质子交换膜燃料电池(PEMFC)在膜、电极、单电池、电堆或系统等四个结构尺度上的传热传质过程研究;主要讨论了PEMFC内的多组分传输、膜内水管理和多孔电极内的传热、传质过程;认为建立在孔尺度水平的研究方法是深入探讨电池内多孔材料微结构传热传质的有效途径;多维、多尺度模型的建立及其模拟计算能准确反映PEMFC内部的传递过程机理,为进一步优化电池结构和操作条件提供有价值的参考。     

A numerical study on the performance of PEMFC with wedge-shaped fins in the cathode channel

The gas flow field design has a significant influence on the overall performance of a proton exchange membrane fuel cell (PEMFC). A single-channel PEMFC with wedge-shaped fins in the cathode channel was proposed, and the effects of fin parameters such as volume (0.5 mm³, 1.0 mm³, and 1.5 mm³), number (3, 5, and 9), and porosity of the gas diffusion layer (GDL) (0.2, 0.4, 0.6, and 0.8) on the performance of PEMFC were numerically examined based on the growth rate of power density (GRPD) and polarization curve. It was shown that wedge-shaped fins could effectively improve the PEMFC performance. With an increase in fin volume, the distributions of oxygen mass fraction in the outlet area of the cathode channel were lower, the drainage effect of the PEMFC improved, and GRPD also increased accordingly. Similar results were obtained as the number of fins increased. The GDL porosity had a greater effect than the wedge-shaped fins on the improvement in PEMFC performance, but the influence of GDL porosity weakened and the GRPD of porosity decreased as the porosity increased. This study provides an effective guideline for the optimization of the cathode channel in a PEMFC.     

Numerical study of optimized three-dimension novel Key-shaped flow field design for proton exchange membrane fuel cell

Key-shaped three-dimension (3D) flow field channel is designed to improve the performance and mass transfer of proton exchange membrane fuel cell (PEMFC). This study comprehensively analyses the impacts on the performance and mass transfer of the flow channel from multiple dimensions such as the size, shape, and placement of the blocks. In comparison with the conventional straight single flow field channel, the new channel with rectangular blocks can effectively improve performance by 30%. Semi-elliptical and quarter-elliptical blocks are designed to make forced convection and increase the diffusion area of oxygen. The results indicate that the flow velocity in the Z-axis direction can be increased to 0.08–0.2 m/s due to the narrow space formed by variable cross-sections. In conclusion, the Key-shaped design has a potential to improve the performance of mass transfer in the cathode channel, providing a new strategy for the development of flow field design in PEMFC field.     

The voltage characteristics of proton exchange membrane fuel cell (PEMFC) under steady and transient states

In this paper, voltage sensors were developed to explore the voltage distribution characteristics inside the fuel cell under both steady and transient states. The effects of air stoichiometry and current density on the voltage distribution under steady state were discussed, and the dynamic voltage response due to the load change under transient state was also investigated. Results showed that under transient state, the fuel cell would experience a temporary voltage fluctuation due to the air starvation. Thus could probably lead to the degradation of materials, such as the catalyst, membrane, etc. To lessen the degree of air starvation, a method of pre-supplying certain amount of air before loading was adopted. The relationship between the voltage response at the loading transient and the amount of pre-supplied air was also studied, and a minimum value of the pre-supplied air was obtained. The experimental results of this paper could be applied to the optimization of vehicular fuel cell system.     

Water management in a single cell proton exchange membrane fuel cells with a serpentine flow field

Gas and water management is the key to achieving good performance from a polymer electrolyte membrane fuel cell (PEMFC) stack. Imbalance between production and evaporation rates can result in either flooding of the electrodes or membrane dehydration, both of which severely limit fuel cell performance. In the present study, a mathematical model was developed to evaluate moisture profiles of hydrogen and air flows in the flow field channels of both the anode and the cathode. For model validation, a single fuel cell was designed with an active area of 200 cm². Six humidity sensors were installed in the flow fields of both the anode and the cathode at 457 mm, 1266 mm and 2532 mm from the inlets. The experiment was performed using an Arbin Fuel Cell Test Station. The temperature was varied (25 °C, 40 °C, 50 °C and 60 °C), while hydrogen and air velocities were fixed at 3 L min⁻¹ and 6 L min⁻¹, respectively, during the operation of the single cell. The feed relative humidity at the anode was fixed at 1.0, while the feed relative humidity at the cathode was fixed at 0.005 (dry air). All humidity sensor readings were taken at steady state after 2 h of operation. Model predictions were then compared with experimental results by using the least squares algorithm. The moisture content was found to decrease along the flow field at the anode, but to increase at the cathode. The moisture content profile at the anode was shown to depend on the moisture Peclet number, which decreased with temperature. On the other hand, the moisture profile at the cathode was shown to depend on both the Peclet number and the Damkohler number. The trend of the Peclet number in the cathode followed closely that of the anode. The Damkohler number decreased with temperature, indicating increasing moisture mass transfer with temperature. The moisture profile models were successfully validated by the published data of the estimated overall mass transfer coefficient and moisture effective diffusivity of the same order of magnitude. The strategy of saturating the hydrogen feed and using dry air, as in the present work, has been shown to successfully prevent water droplet formation in the cathode, and hence prevent flooding.     

Characteristic simulation and numerical investigation of membrane electrode assembly in proton exchange membrane fuel cell

This study analyzes the characteristic numerical analysis of membrane electrode assembly in Proton Exchange Membrane Fuel Cell (PEMFC) with bipolar plate, flow channel, gas diffusion electrode, and proton exchange membrane. The numerical solution focuses on discussing the effects of different parameters, including permeability, porosity, and operation voltage, on various mass fractions, current-voltage curve, and power-voltage curve.The results show that as the porous medium with high gas permeability is an important factor that affects the mass fraction of hydrogen. Regarding the analyses of various porosities, the fuel cell performance can be effectively promoted with larger ratio of porosity and permeability. However, increasing the porosity will affect the electrical conductivity and increase the flooding of water, which will block the flow channel and reduce efficiency.     

Recent development in design a state-of-art proton exchange membrane fuel cell from stack to system: Theory,integration and prospective

As an efficient energy converter, the proton exchange membrane fuel cell (PEMFC) is developed to couple various applications, including portable applications, transportation, stationary power generation, unmanned underwater vehicles, and air independent propulsion. PEMFC is a complex system consisting of different components that can be influenced by many factors, such as material properties, geometric designs operating conditions, and control strategies. The interaction between components and subsystems could affect the performance, durability, and lifespan of PEMFC system. To design a high performance, long lifespan, high durability PEMFC, it's essential to comprehensively understand the coupling effect of different factors on the overall performance and durability of PEMFCs. This review will present existing research on basis of four aspects, involving fuel cell stack design, subsystems design and management, mass transfer enhancement, and system integration. Firstly, the multi-physics intergradation and component design of PEMFC are reviewed with the designing mechanisms and recent progress. Besides, mass transfer enhancement methods are discussed by bipolar plate design and membrane electrode assembly optimization. Then, water management, thermal management, and fuel management are summarized to provide design guidance for PEMFC. The specifications design and system management for various engineering applications are briefly presented.     

A three-dimensional analysis of the effect of anisotropic gas diffusion layer(GDL) thermal conductivity on the heat transfer and two-phase behavior in a proton exchange membrane fuel cell(PEMFC)

A three-dimensional and two-phase model was employed to investigate the effect of the anisotropic GDL thermal conductivity on the heat transfer and liquid water removal in the PEMFCs with serpentine flow field and semi-counter flow operation. The GDL with different anisotropic thermal conductivity in the three directions (x, y, z) was simulated for four cases. As a result, the water saturation, temperature, species, current, potential distribution and proton conductivity were obtained. According to the comparison between the results of each case, some new conclusions are obtained and listed as below: (1) The anisotropic GDL produces the high temperature difference than that of isotropic case, and the in-plane thermal conductivity perpendicular to the gas channels is more important than that of along channels, which may produce the larger temperature difference. (2) Water saturation decreases due to the large temperature difference in the anisotropic case, but some water vapor may condense in the area neighbor to the channel ribs due to the cool function of the current collector and the great temperature difference. (3) The anisotropic thermal conductivity in the through-plane direction and the in-plane direction perpendicular to the gas channels can lead to the decrease of the membrane conductivity. (4) The isotropic GDL is better than that of anisotropic one for the uniform current density. Also, in-plane thermal conductivity perpendicular to the channels has more negative effect on the current density distribution in the membrane than that of the along channels one.     

Numerical study of PEMFC heat and mass transfer characteristics based on roughness interface thermal resistance model

The thermal contact resistance (TCR) is the main component of proton exchange membrane fuel cell (PEMFC) thermal resistance due to the existence of surface roughness between the components of PEMFC, and the influence of TCR is often ignored in traditional three dimensional PEMFC simulations. In this paper, the heat and mass transfer characteristics including polarization curve, power density curve, temperature distribution, membrane water content distribution, membrane current density are studied under different component surface roughness conditions, and finally the effect of each TCR on the PEMFC performance is studied. It is found that under the same operating conditions, the TCR makes the radial heat transfer of the PEMFC decrease, and the temperature of the membrane electrode and the temperature difference of each component of the PEMFC is higher than that of the model without TCR. When the surface roughness of components in the PEMFC equals 1 μm, 2 μm, 3 μm, the cell current density decreases by 6.56%, 12.46% and 17.17% respectively when the output cell voltage equals 0.3 V, and the cell power density decreases by 3.64%, 7.54%, 13.14% respectively when the cell current density equals 1.2 A·cm^?2. When the TCR between the CL and PEM equals 0.003 K·m²·W^?1, 0.005 K·m²·W^?1, 0.01 K·m²·W^?1, the cell current density is increased by 2.30%, 3.65%, 6.74% respectively under the condition that the output cell voltage equals 0.3 V, and the cell power density is increased by 1.24%, 1.85%, 3.10% respectively when the cell current density equals 1.2 A·cm^?2. The results show that the numerical simulation of PEMFC cannot ignore the effect of TCR.     

Mass transfer characteristics of the hydrophilic membrane with the isolation of heat transfer effect by isothermal bath

The efficiency and lifetime of a proton exchange membrane fuel cell (PEMFC) system is critically affected by the humidity of incoming gas which should be maintained properly for normal operating conditions. But the experimental characteristics of the humidifier are rarely reported. Water transport through the hydrophilic membrane is a coupled phenomenon of heat and mass transport. In this study, a laboratory scale test bench is designed to investigate the characteristics of water transport through the hydrophilic membrane. The mass transfer capability of the hydrophilic membrane is evaluated over various flow rates, temperature, pressure, and flow arrangements. In the experiment, the test bench is submerged in a constant temperature bath in order to isolate the effect of temperature variation between dry air and humid air. The results show the water transport of the hydrophilic membrane is significantly affected by operating temperature and operating pressure. Additionally, the flow arrangement demonstrates a minor effect but it should be considered along with the heat transfer effect.     

A novel online degradation model for proton exchange membrane fuel cell based on online transfer learning

A novel online degradation prediction model is proposed to prognosticate the future degradation trend (FDT) of proton exchange membrane fuel cell (PEMFC) stack in this paper. In order to overcome the fact that existing FDT prediction methods of PEMFC stack based on data-driven model rely on the assumption that the operating conditions of the training data and testing data need to be consistent, an end-to-end prediction algorithm based on the combination of transfer learning and transformer neural network, referred to as TLTNN, is proposed to predict the FDT of PEMFC stack. Besides, in order to demonstrate the effectiveness and superiority of the proposed method in prognostics tasks of PEMFC stack FDT, the prediction performance is validated on the PEMFC test system. The results show that the RMSE, MAE and MAPE values of the predicted degradation voltage are 0.00598 V, 0.004842 V and 0.1518%, respectively, which indicates that the proposed TLTNN strategy based on transfer online learning can be used to predict the degradation voltage of PEMFC stack and the superiority of the proposed method is better, thus solving the problem that the distribution of training and test data must be the same in traditional machine learning models.     

质子交换膜燃料电池建模及水热传输特性分析

针对质子交换膜燃料电池(PEMFC)水管理开展了研究,建立了一维非等温两相流解析模型,研究了不同电流密度、微孔层接触角和不同加湿方案对电池内部水分布和温度分布的影响,提出了更好的进气加湿方案。结果表明:电流密度增大会导致阳极拖干、阴极水淹加剧,导致电池各部分温度上升。因各层材料亲水性不同,在交界面处能观察到液态水阶跃现象。增大微孔层接触角促进阴极液态水反扩散到阳极,一定程度上缓解阳极变干,但过大的接触角可能导致阴极水淹加剧。通过采取"阳极充分加湿、阴极低加湿"的进气加湿方案可以有效提高电池性能,并且能在一定程度改善电池内部受热,提高电池使用寿命。     

Numerical simulation of mass and charge transfer for a PEM fuel cell

A three-dimensional, steady state, single phase model is developed to study the mass and charge transfer within a proton exchange membrane (PEM) fuel cell. A single set of conservation equations is used for all PEM fuel cell layers and the governing equations are solved numerically using a finite-volume-based computational fluid dynamics technique. The numerical results for the flow field, species transport and phase potential are presented for two designs, namely a PEM fuel cell with conventional and interdigitated flow fields for the reactant supply.     

The study on transient characteristic of proton exchange membrane fuel cell stack during dynamic loading

The operations of fuel cell stacks in fuel cell vehicle are dynamic. During dynamic loading, the oxidant starvation often occurs, due to the gas response rate lagging the loading rate. To study the transient behavior of the fuel cell stack at load changes, the measuring methods of current and temperature distribution are developed. In this paper, the current distribution and temperature distribution as well as their dynamic changes in fuel cell stack have been evaluated in situ. The experimental results show that the local current and temperature rise when load rapidly. The extent of temperature fluctuation during dynamic loading is significantly influenced by air stoichiometries, loading rates, and air relative humidities. When air stoichiometry is very low, the temperature of cathode inlet rises sharply. The quicker the loading rate is, the bigger the extent of temperature fluctuation is. With increasing air relative humidity, the transient temperature of cathode inlet rises, while the transient temperature of cathode outlet decreases. This paper will provide reference for durability researches on fuel cell vehicles (FCVs).     

The development of air-breathing proton exchange membrane fuel cell (PEMFC) with a cylindrical configuration

A small air-breathing proton exchange membrane fuel cell with a cylindrical configuration (Cy-PEMFC) and a helical flow-channel was developed to provide a uniform contact pressure to the membrane electrode assembly (MEA) with a thin cathode current collector. A comparison of the contact pressure and performance of the Cy-PEMFC and general planar PEMFC was performed to determine the effect of the cylindrical configuration. For the contact pressure comparison, numerical analysis was performed using commercial software. Numerical analysis showed that the Cy-PEMFC has its own structural advantage of changing the applied clamping pressure to a uniformly distributed contact pressure. The actual pressure measurements were carried out with pressure-sensitive film to support results of numerical analysis. These results also showed that the Cy-PEMFC had a uniformly distributed contact pressure, whereas the planar PEMFC did not. The polarization curves of both PEMFCs were measured to determine the performance variations caused by the uniform contact pressure and better mass transfer. The maximum power density of the Cy-PEMFC was 220 mW/cm², which was approximately 24% higher than the planar PEMFC.     

A transient analysis of three-dimensional heat and mass transfer in a molten carbonate fuel cell at start-up

In this paper, we investigate the time-dependent heat and mass transfer in a molten carbonate fuel cell at start-up. Thus, a three-dimensional, transient mathematical model is presented through a comprehensive inclusion of various physical, chemical and electrochemical processes that occur within the different components of molten carbonate fuel cells. The model is proposed as a predictive tool to provide a three-dimensional demonstration of variable variations at system start-up. The local distribution of field variables and quantities are showcased. It reveals that the electrochemical reaction rate is dominated by the over-potential, not by the reactants' molar fraction. Reversible heat generation and consumption mechanisms of the cathode and anode are dominant in the first 10 s while the heat conduction from the solid materials to the gas phase is negligible. Meanwhile, activation and ohmic heating have nearly the same impact within the anode and cathode. Based on these findings, the importance of heat conduction and its main features are finally assessed.     

Heat and mass transfer influence on potential variation in a PEMFC membrane

Water transport in the membrane of a PEM fuel cell is provided essentially by a convective force, resulting from a pressure gradient, an osmotic force, due to a concentration gradient and an electric force caused by the protons migration from the anode to the cathode. Through these three types of force the two-dimensional behavior of electric potential has been studied in this paper. The adopted model in this work is based on the assumption of single phase and multi-species flow, supposed two-dimensional and transient in a porous medium. The species conservation equation is coupled with the energy equation through the diffusion coefficient of water and the heat convective flux. The set of governing equations in the form of convection–diffusion problem has been solved numerically using the finite volume method. The obtained results show the transient two-dimensional effect of heat and mass transfer on the voltage variation within the membrane.     

Unsteady three-dimensional numerical study of mass transfer in PEM fuel cell with spiral flow field

Bipolar plate design and its flow field shape have an important effect on the fuel cell performance. In this work, a FORTRAN program has been developed to investigate the effects of the channel width, the number of turns of the spiral channel and the flow direction on the reactants consumption in a proton exchange membrane fuel cell (PEMFC) with a spiral flow field design. The governing equations are discretized using the finite volume method in cylindrical coordinates. The results show that the channel-rib width ratio influences the cell performance; the higher ratio, the more important contact area between the channel and the GDL, the more reactants quantity seeped to the GDL and more uniform reactants distribution is. The increasing the spiral channel turns number improves the reactants distribution uniformity. The channel spiral shape engenders a centrifugal force which enhances the cell performances in the case when the reactants are injected from the external side of the spiral channel and ejected from its internal one.