Dynamic modeling and simulation of a proton exchange membrane electrolyzer for hydrogen production

Computational model of a proton exchange membrane (PEM) water electrolyzer is developed to enable investigation of the effect of operating conditions and electrolyzer components on its performance by expending less time and effort than experimental investigations. The work presents a dynamic model of a PEM electrolyzer system based on MATLAB/Simulink software. The model consists mainly of four blocks - anode, cathode, membrane and voltage. Mole balances on the anode and cathode blocks form the basis of the model along with Nernst and Butler-Volmer equations. The model calculates the cell voltage by taking into account the open circuit voltage and various over-potentials. The model developed predicted well the experimental data on PEM water electrolyzer available in the literature. The dynamic behavior of the electrolyzer system is analyzed and the effects of varying electrolyzer temperature and pressure on electrolyzer performance and over-potentials are presented.     

A parametric study of polymer membrane electrolyser performance,energy and exergy analyses

In this paper, a mathematical model is developed to study the performance of a polymer membrane electrolyser (PEM) and the effect of different parameters including operating temperature, cathode pressure, membrane thickness, the width and height of channel and current density on the performance and energy and exergy efficiency of PEM electrolyser are investigated. In addition to the resistance overvoltage of components, the concentration overvoltage is modeled using an accurate equation. The model is validated against experimental data. The results indicate that by increasing current density, the voltage of the electrolyser increases, and energy and exergy efficiencies reduce. Increase of temperature from 313 K to 353 K, and decrease of cathode pressure from 40 bar to 1 bar lead to decrease of voltage of the PEM electrolyser by 8.3% and 4.8%, respectively. Moreover, energy and exergy efficiencies increase between 2% and 6% in the range of working temperature and pressure. It is concluded that decrease of membrane thickness, height and width of channel, and increase of exchange current density of the anode and cathode electrodes lead to decrease of voltage of the electrolyser and increase of energy and exergy efficiencies. However, the effect of temperature and cathode pressure and the exchange current densities is greater than the effect of geometric parameters.     

Effect of primary parameters on the performance of PEM fuel cell

A one-dimensional, steady-state and isothermal model for a proton exchange membrane (PEM) fuel cell has been developed to investigate the effects of various parameters such as the molar fraction of nitrogen gas, relative humidity, temperature, pressure, membrane thickness, anode and cathode stoichiometric flow ratio and the distribution of oxygen in the cathode catalyst while water transfer in membrane is produced by diffusion, pressure gradient and electro-osmotic drag. The most critical problems to overcome in the proton exchange membrane (PEM) fuel cell technology are the water and thermal management. The results show that the cell performance increases as operating pressure and temperature are increased. The performance of cell can decrease by decreasing the relative humidity of inlet gases and increasing the membrane thickness. Increasing the anode and cathode stoichiometric flow ratio can also improve the cell performance. As the oxygen concentration becomes zero in about 8 percent depth of cathode catalyst layer, the thickness of cathode catalyst layer can be reduced 92 percent without any potential loss in output voltage. The cathode activation loss also becomes high by increasing the molar fraction of nitrogen gas. The modeling results agree very well with experimental results.     

Performance assessment of gas crossover phenomenon and water transport mechanism in high pressure PEM electrolyzer

To improve proton exchange membrane (PEM) electrolyzes’ performance the voltage loss through them should be avoided. In this work, it is intended to analyze losses including of diffusion loss, ohmic loss due to electrode, bipolar plate (BP), and membrane resistances, and gas crossover associated with the water transferring mechanisms. All of the losses are associated with water transferring mechanisms, which is created due to electro-osmoic drag, pressure differential between the anode and cathode sides, and diffusion. Furthermore, the effect of membrane thickness, cathode pressure, and operating temperature on the hydrogen crossover is examined. In addition, the contribution of ohmic loss due to electrode bipolar plate (BP), and membrane resistances is studied and, the contribution of different losses on the cell performance is discussed. Results show that raising cathode pressure from 1 to 40 bar lead to the increment of anodic hydrogen content from 1.038% to 21% at the specific current density of 10,000 A/m2. Enhancing the thickness of membrane has considerable impact on decrementing anodic hydrogen content, but the mass transfer loss rises from 0.022 to 0.027 V with enhancing membrane thickness from 50 to 300 μm, respectively. Furthermore, the contribution of voltage losses, assigned to each of losses are equal to 85%, 3%, and 12% for activation, diffusion and ohmic losses, respectively. It is found that, from the reported contribution for ohmic loss, the contribution of electrode BP, and membrane resistances are 31% and 69%, respectively.     

Electrochemical characteristics of (PEM) electrolyzer under influence of charge transfer coefficient

In this paper a systematic understanding of how charge transfer coefficient (CTC) and exchange current density contributes to polarization and performance characteristics of PEM electrolyzer has been investigated. A detail discussion on the role played by charge transfer coefficient in influencing operating characteristics of PEM electrolyzer has been presented in this article. Experimental data was used to validate the accuracy of the finding of this research. Main interesting insights are that at CTC of 0.5 and 0.2 for anode and cathode respectively, the operating voltage at 1 A/cm² (current density) is around 2.0 V, however at CTC of 2 and 0.5 for anode and cathode respectively, there was significant drop in operating voltage up to 1.62 V with current density of 1 A/cm², this accounts for about 27% reduction in operating voltage. It was also discovered that with exchange current density of 1 × 10–7 for a Pt–Ir anode based electrode the CTC value for anode increase from 0.27 to 0.34 at current density of 0.05 A/cm2 to 2 A/cm2 respectively, whereas for Pt cathode catalyst with exchange current density of 1.8 × 10–3 the CTC values for cathode increased from 0.02 to 0.14 at current density of 0.1 A/cm2 to 2 A/cm2 respectively, these findings were in agreement with the CTC values reported in the literature.     

Exergetic performance analysis of a PEM fuel cell

In this paper we investigate the effects of thermodynamic irreversibilities on the exergetic performance of proton exchange membrane (PEM) fuel cells as a function of cell operating temperature, pressures of anode and cathode, current density, and membrane thickness. The practical operating conditions are selected to be 3–5 atm for anode and cathode pressures, and 323–353 K for the cell temperatures, respectively. In addition, the membrane thicknesses are chosen as 0.016, 0.018 and 0.02 cm, respectively. Moreover, the current density range of the PEM fuel cell is selected to be 0.01–2.0 A cm^?2. It is concluded that exergy efficiency of PEM fuel cell decreases with a rise in membrane thickness and current density, and increases with a rise of cell operating pressure and with a decrease of current density for the same membrane thickness. Thus, it can be said that, in order to increase the exergetic performance of PEM fuel cell, the lower membrane thickness, the lower current density and the higher cell operating pressure should be selected in case PEM fuel cell is operated at constant cell temperature. Copyright © 2005 John Wiley & Sons, Ltd.     

Proton exchange membrane (PEM) electrolyzer operation under anode liquid and cathode vapor feed configurations

Proton exchange membrane (PEM) electrolysis is a potential alternative technology to crack water in specialty applications where a dry gas stream is needed, such as isotope production. One design proposal is to feed the cathode of the electrolyzer with vapor phase water. This feed configuration would allow isotopic water to be isolated on the cathode side of the electrolyzer and the isotope recovery system could be operated in a closed loop. Tests were performed to characterize the difference in the current–voltage behavior between a PEM electrolyzer operated with a cathode water vapor feed and with an anode liquid water feed. The cathode water vapor feed cell had a maximum limiting current density of 400 mA/cm² at 70 °C compared to a current density of 800 mA/cm² for the anode liquid feed cell at 70 °C. The limiting current densities for the cathode water vapor feed cell were similar to those predicted by a water mass transfer model. It is estimated that a cathode water vapor feed electrolyzer system will need to be between 5 and 8 times larger in active area or number of cells than an anode liquid feed system.     

Analysis of water transport in a high pressure PEM electrolyzer

This paper analyzes, through experimental data and a transport model, the water transported through the membrane under different operating conditions in a on a Proton Exchange Membrane (PEM) electrolyzer operating with a high-pressure gradient across the membrane from the cathode (high-pressure) side to the anode (nearly ambient-pressure) side. The phenomena involved in this movement are described and analyzed, with a focus on the electro-osmotic drag coefficient, n_eo. We have observed that the behavior of the hydraulic percolation determines the results obtained for the electro-osmotic drag, while the contribution of the water diffusion is negligible. In general, the cathode pressure significantly reduces the water transport (a positive effect). Also, operation at lower current density reduces the net electro-osmotic drag coefficient, n_g; therefore, the best operation strategy for obtaining dried hydrogen at the cathode is to impose high cathode pressure and low current density.     

Design and characterization of compact proton exchange membrane water electrolyzer for component evaluation test

In this study, we designed and developed a compact electrolyzer for the evaluation of components in proton exchange membrane (PEM) water electrolysis. First, this electrolyzer features a precise pressure-control system that controls the active electrode area and facilitates setting the desired clamping pressure. This mechanism makes it possible to optimize the electrolyzer performance. Second, it has two reference electrodes that are connected on the faces of the active electrode area of the anode and the cathode on the PEM. The polarizations at the anode and the cathode, the membrane resistivity, and the porous transport layer (PTL) overpotential were measured. The details of the design are described, and the electrochemical performance was measured. The optimized clamping pressure for this electrolyzer component was obtained as the specific value. A new measurement method was developed for estimating polarizations at the anode and the cathode, membrane resistance, and PTL overpotential using two reference electrodes.     

Pressurized PEM water electrolysis: Dynamic modelling focusing on the cathode side

This paper describes a lumped dynamic model for a high pressure PEM water electrolyzer. Since the electrolyzer under analysis is characterized by unbalanced pressure configuration with high cathodic working pressure, the model focuses on the cathode side to adequately predict the electrolyzer performance, analyzing and highlighting the importance of the cathodic activation overpotential term. The model is calibrated using experimental data from a 5.6 kW PEM water electrolyzer stack. A very good fit can be observed between the model and the experimental data, not only at different temperatures, but also at different pressures. It is found that the rise of temperature affects mainly the ohmic overpotential, while increasing the cathode pressure leads to an increment in the cathode activation overpotential that is not negligible for the electrolyzer performance. By rising the operating current, the cathode activation overpotential becomes 63% of that of the anode (at 70 bar, 1.2 A/cm² and 50 °C).     

Dynamic modelling of a proton exchange membrane (PEM) electrolyzer

This paper describes a dynamic model for PEM electrolyzer based on conservation of mole balance at the anode and the cathode. A further feature of the model is it includes water phenomena, electro-osmotic drag and diffusion, through the membrane. The model considers PEM electrolyzer to be composed of four ancillaries: anode, cathode, membrane and voltage ancillary. Additionally, hydrogen storage dynamics is presented. The developed model is suitable for determining control strategy that will ensure efficient and reliable operation of the electrolyzer. Moreover, the dynamic model can be integrated with renewable energy systems models to design, analyze and optimize sustainable energy systems. The study illustrates the dynamic interactions within a PEM electrolyzer and shows the necessity of the proposed approach of separate ancillaries.     

Numerical simulation and exergoeconomic analysis of a high temperature polymer exchange membrane electrolyzer

In this paper, a finite volume numerical method is developed to investigate a high temperature polymer exchange membrane (PEM) electrolyzer cell using a three-dimensional and non-isothermal model. The results that are obtained for the single cell are generalized to a full stack of electrolyzer and an exergoeconomic analysis is performed based on the numerical data. The effects of operating temperature, the pressure of cathode, gas diffusion layer (GDL) thickness, and membrane thickness on the energy and exergy efficiencies and exergy cost of the electrolyzer are examined. This study reveals that by increasing the working temperature from 363 K to 393 K, the exergy cost of hydrogen decreases from 23.16 $/GJ to 22.39 $/GJ, and the exergy efficiency of PEM electrolyzer stack at current density of 10,000 A/m² increases from 0.56 to 0.59. The results indicate that increase of pressure deteriorates the system performance at voltages below 1.4 V. It is concluded that operation of the electrolyzer at higher pressures results in decrease of the exergy cost of hydrogen. Increase of membrane thickness from 50 μm to 183 μm leads to increase of the exergy cost of hydrogen from 23.24 $/GJ to 35.99 $/GJ.     

Two-phase flow in a proton exchange membrane electrolyzer visualized in situ by simultaneous neutron radiography and optical imaging

In proton exchange membrane (PEM) electrolyzers, oxygen evolution in the anode and flooding due to water cross-over in the cathode yields two distinct two-phase transport conditions which strongly affect the performance. Two-phase transport in an electrolyzer cell is visualized by simultaneous neutron radiography and optical imaging. Optical and neutron data are used in a complementary manner to aid in understanding the two-phase flow behavior. Two different patterns of gas-bubble evolution and departure are identified: periodic growth/removal of small bubbles vs. prolonged blockage by stagnant large bubbles. In addition, the bubble distribution across the active area is not uniform due to combined effects of buoyancy and proximity to the inlet. The effects of operating parameters such as current density, temperature and water flow rate on the two-phase distribution are investigated. Higher water accumulation is detected in the cathode chamber at higher current density, even though the cathode is purged with a high flow rate of N₂.     

Experimental analysis of dynamic characteristics on the PEM fuel cell stack by using Taguchi approach with neural networks

This study determines the optimum operating parameters for a proton exchange membrane fuel cell (PEMFC) stack to obtain small variation and maximum electric power output using a robust parameter design (RPD). The operating parameters examined experimentally are operating temperatures, operating pressures, anode/cathode humidification temperatures, and reactant flow rates. First, the dynamic Taguchi method is used to obtain the maximum and stable power density against the different current densities, which are regarded as the systemic inputs considered a signal factor. The relationship between control factors and responses in the PEMFC stack is determined using a neural network. The discrete parameter levels in the dynamic Taguchi method can be divided into desired levels to acquire real optimum operating parameters. Based on these investigations, the PEMFC stack is operated at the current densities of 0.4–0.8 A/cm². Since the voltage shift is quite small (roughly 0.73–0.83 V for each single cell), the efficiency would be higher. In the range of operation, the operating pressure, the cathode humidification temperature and the interactions between operating temperature and operating pressure significantly impact PEMFC stack performance. As the operating pressure increasing, the increments of the electric power decrease, and power stability is enhanced because the variation in responses is reduced.     

SO2-depolarized electrolysis using porous graphite felt as diffusion layer in proton exchange membrane electrolyzer

The hybrid sulfur (HyS) process, which is composed of SO₂-depolarized electrolysis (SDE) reaction and sulfuric decomposition reaction, is one of the simplest thermochemical cycles for producing hydrogen by water splitting. SDE is currently conducted in a proton exchange membrane (PEM) electrolyzer. In this work, a novel PEM electrolyzer structure is proposed. Graphite felt with large void content is used as the diffusion layer. In the electrolyzer, porous graphite felt plays the role of evenly distributing fluid and conducting electricity. The gap between the polar plate and the catalytic layer is occupied by the electrolyte solution and graphite felt, which effectively reduces the ohmic impedance of the electrolyzer. The effects of the main parameters including graphite felt compression ratio, anodic fluid flow rate, and sulfuric acid concentration, as well as temperature are investigated. Under optimized operating conditions, the current density reaches 800 mA/cm² at cell voltage of 1.094 V, which is remarkably better than reported SDE performance using conventional PEM electrolyzers.     

考虑多变量因素影响的光伏PEM制氢系统建模与分析

针对复杂工况对光伏制氢系统性能产生不确定性的影响,提出考虑多变量因素影响的光伏制氢系统模型,探索辐照度、温度、膜厚、压力等因素对光伏质子交换膜（PEM）制氢系统的影响。系统首先建立考虑辐照度、温度、膜厚、压力等因素影响的光伏-质子交换膜电解槽-氢储罐的光伏制氢模型,之后对系统进行定量计算和定性分析,并依据实际光伏数据进行实验验证。结果表明,在额定功率范围内,太阳电池输出电流和功率随辐照度的增加而增大,随温度的升高而降低。质子交换膜电解槽电压随辐照度、膜厚、压力的增加而增大,随温度的升高而减小。太阳电池输出功率、质子交换膜电解槽电压的变化趋势与辐照度变化趋势具有一致性。最终计算得到太阳电池系统、质子交换膜电解槽系统和总系统效率分别为16.8%、72.2%和12.1%。     

Operation-relevant modeling of an experimental proton exchange membrane fuel cell

A current–voltage (I–V) curve, also known as a polarization curve, is generally used to express the characteristics of a proton exchange membrane (PEM) fuel cell system. The behavior of a PEM fuel cell is highly nonlinear and it is important to incorporate process nonlinearity for control system design and process optimization. Therefore, it is essential to generate the I–V curve from the model as the operating condition changes. A first principle one-dimensional water and thermal management model is developed to generate the I–V curve. The model considers the effects of water transport across the membrane, activation overpotential, ohmic overpotential, concentration overpotential, pressure drops, and current density distribution along the channel of a PEM fuel cell. Design and modeling parameters are obtained via regression from four sets of experimental data. They are further validated as operating conditions (e.g., fuel cell temperature, anode pressure, cathode pressure, hydrogen stoichiometric ratio, air stoichiometric ratio, hydrogen humidification temperature, and air humidification temperature) change. A sensitivity analysis example is used to illustrate the usefulness of the predictive model.     

Dynamic behaviors of PEM fuel cells under load changes

In this study, a one-dimensional isothermal single-phase transient model considering the finite-rate water absorption/desorption of membrane was established to study the dynamic behaviors of polymer electrolyte membrane (PEM) fuel cells under different cathode inlet humidity conditions in the presence of voltage step changes. Both the overshoot and undershoot phenomena were observed. Moreover, the distributions of water inside the electrolyte and the influence of that on the response current density of fuel cells were analyzed. When voltage stepped up/down, the water content in anode generally increased/decreased, and the water content in cathode is reversed. If the cathode intake is fully humidified, the water vapor in cathode is always over-saturated causing the change of ionic resistance is determined by that of the water content in anode. If the cathode intake is partially humidified, the change of ionic resistance could maintain within a small range owing to the change of water content in anode can be balanced by that of the water content in cathode.     

Model prediction of effects of operating parameters on proton exchange membrane fuel cell performance

The performance of a proton exchange membrane (PEM) fuel cell is greatly affected by the operating parameters. Appropriate operating parameters are necessary for PEM fuel cells to maintain stable performance. A three-dimensional multi-phase fuel cell model (FCM) is developed to predict the effects of operating parameters (e.g. operating pressure, fuel cell temperature, relative humidity of reactant gases, and air stoichiometric ratio) on the performance of PEM fuel cells. The model presented in this paper is a typical nine-layer FCM that consists of current collectors, flow channels, gas diffusion layers, catalysts layers at the anode and the cathode as well as the membrane. A commercial Computational Fluid Dynamics (CFD) software package Fluent is used to solve this predictive model through SIMPLE algorithm and the modeling results are illustrated via polarization curves including I–V and I–P curves. The results indicate that the cell performance can be enhanced by increasing operating pressure and operating temperature. The anode humidification has more significant influences on the cell performance than the cathode humidification, and the best performance occurs at moderate air relative humidity while the hydrogen is fully humidified. In addition, the cell performance proves to be improved with the increase of air stoichiometric ratio. Based on these conclusions, several suggestions for engineering practice are also provided.     

Performance assessment of a four-pass serpentine proton exchange membrane fuel cell with non-humidified cathode and cell state estimation without special measurement

Proton exchange membrane fuel cells are promising electrochemical energy conversion devices especially important for mobile technologies, including the automotive industry thanks to their quick start-up, low operation temperature, and relatively higher energy density characteristics. However, cell performance depends on many parameters like reactant temperature and humidification ratio, cell operating temperature, reactant feeding pressure, and flow field. In this study, the performance of a 50 cm² active area four-pass serpentine flow field hydrogen-air proton exchange membrane (PEM) fuel cell experimentally investigated for various cell operating temperatures and reactant back pressures without humidification on the cathode side. Dehydration or flooding condition of the cell is showed to be determined with tafel slope, limiting current density and types of voltage losses without using a special measurement. The results show that flooding, which is called mild flooding, is possible to be seen even at high cell temperature in a non-humidified cathode fuel cell, in case of exceeding operating pressures. Behavior of cell parameters under mild flooding and ongoing severe flooding are different from each other. Pressure increase at above 45 °C operating temperature is seen to served higher power output. However, at low back pressure with escalated operating temperature doesn't result with a substantial increase on performance since less amount of water is produced as a product of reaction causing membrane dehydration at relatively low current density levels thus increasing ohmic loss.