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.     

Optimization of operating parameters of a polymer exchange membrane electrolyzer

In this research, the operating parameters of proton exchange membrane (PEM) electrolyzer are optimized in order to decrease the required input voltage using Taguchi method. The considered parameters include the operating temperature, the pressure of cathode and anode, membrane water content, membrane thickness, and cathode and anode exchange current density. First, a thermodynamic model is developed for the PEM electrolyzer, and then the Taguchi method is applied for optimization of the electrolyzer performance. The signal to noise ratio (SNR) and the analysis of variance (ANOVA) method are also performed to determine the contribution ratio of effective parameters. The results reveal that the optimal condition is achieved at maximum working temperature, membrane water content, and cathode and anode exchange current density and at minimum membrane thickness, cathode pressure, and anode pressure. The anode exchange current density has considerable effect on the electrolyzer voltage with contribution of 67.15% while the membrane water content and the anode pressure have a minor influence with contribution of 1.1% and 0.42%, respectively.     

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).     

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.     

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.     

Numerical simulations of the energy performance of a PEM water electrolysis based high-pressure hydrogen refueling station

The present paper proposes an energy analysis on a hydrogen production and storage system. The dynamic and multi-physical investigation is inherent to an energy system composed of a PEM electrolyzer, a diaphragm compressor, a gaseous storage system, ancillaries, and control procedures. To perform this investigation, a model previously developed by the authors has been used. The case-study simulation shows how the electrolyzer has the predominant rate, accounting for 88.5% of the daily 24-h energy demand (13 MWh). The electrolyzer specific energy consumption for 205 kg of hydrogen generated resulted to be 56.3 kWh/kg. The other components have required 1.5 MWh, with a specific energy of about 7.5 kWh/kg. The overall system efficiency resulted to be 52.9%, including all the components and their energy consumption and guaranteeing 14.9 metric tons of avoided carbon dioxide.     

Design and economic analysis of high-pressure proton exchange membrane electrolysis for renewable energy storage

The proton exchange membrane (PEM) electrolysis with a high-pressure cathode can help avoid the utilization of a hydrogen compressor and improve the efficiency of hydrogen transmission. The economic analysis of the entire process from hydrogen production to transportation was conducted in this study, and the advantages of high-pressure PEM electrolysis were proved. The economic analysis has also illustrated the influence of the cathode pressure and membrane thickness involved in PEM electrolysis on the energy consumption and capital expenditure of the electrolyzer from the perspectives of hydrogen permeability, ohmic impedance, and structural design. Although the output pressure of hydrogen is increased several tens of times, the proper structure and unchanged thickness of the membrane can help satisfy the strength and safety requirements of the electrolyzer simultaneously. In addition, the energy consumption and cost increase associated with the high-pressure electrolyzer can be limited to an acceptable range. The impact of the renewable energy scale on the decision and selection for PEM or ALK is also analyzed; PEM has an advantage over ALK in large-scale renewable energy hydrogen production scenarios because of its own wider upper and lower load limits compared to those of ALK.     

A simple electric circuit model for proton exchange membrane fuel cells

A simple and novel dynamic circuit model for a proton exchange membrane (PEM) fuel cell suitable for the analysis and design of power systems is presented. The model takes into account phenomena like activation polarization, ohmic polarization, and mass transport effect present in a PEM fuel cell. The proposed circuit model includes three resistors to approach adequately these phenomena; however, since for the PEM dynamic performance connection or disconnection of an additional load is of crucial importance, the proposed model uses two saturable inductors accompanied by an ideal transformer to simulate the double layer charging effect during load step changes. To evaluate the effectiveness of the proposed model its dynamic performance under load step changes is simulated. Experimental results coming from a commercial PEM fuel cell module that uses hydrogen from a pressurized cylinder at the anode and atmospheric oxygen at the cathode, clearly verify the simulation results.     

Modeling and control of air stream and hydrogen flow with recirculation in a PEM fuel cell system—I. Control-oriented modeling

Transient behavior is one of the key requirements for the vehicular application of proton exchange membrane (PEM) fuel cell. The goal of this study is to develop a dynamic model of PEM fuel cell system (FCS) that is capable of characterizing the mixed effects of gas flow, pressure and humidity. In addition to the model of air supply system, the anode recirculation is also presented in this paper by an analytical model of injection pump. A steady-state, isothermal analytical fuel cell model is adopted to analyze the mass transfer in the diffusion layer and water transportation in the membrane. The liquid water accumulation in the cathode flow channel is described by a finite-rate phase-change model and the cathode flooding in the diffusion layer is also discussed. The transient phenomena in FCS are captured by the mechanical inertia of compressor and flow filling in lumped-parameter volumes of manifolds, anode and cathode.     

Improving dynamic performance of proton-exchange membrane fuel cell system using time delay control

Transient behaviour is a key parameter for the vehicular application of proton-exchange membrane (PEM) fuel cell. The goal of this presentation is to construct better control technology to increase the dynamic performance of a PEM fuel cell. The PEM fuel cell model comprises a compressor, an injection pump, a humidifier, a cooler, inlet and outlet manifolds, and a membrane-electrode assembly. The model includes the dynamic states of current, voltage, relative humidity, stoichiometry of air and hydrogen, cathode and anode pressures, cathode and anode mass flow rates, and power. Anode recirculation is also included with the injection pump, as well as anode purging, for preventing anode flooding. A steady-state, isothermal analytical fuel cell model is constructed to analyze the mass transfer and water transportation in the membrane. In order to prevent the starvation of air and flooding in a PEM fuel cell, time delay control is suggested to regulate the optimum stoichiometry of oxygen and hydrogen, even when there are dynamical fluctuations of the required PEM fuel cell power. To prove the dynamical performance improvement of the present method, feed-forward control and Linear Quadratic Gaussian (LQG) control with a state estimator are compared. Matlab/Simulink simulation is performed to validate the proposed methodology to increase the dynamic performance of a PEM fuel cell system.     

Solar-powered regenerative PEM electrolyzer/fuel cell system

An electrolyzer/fuel cell energy storage system is a promising alternative to batteries for storing energy from solar electric power systems. Such a system was designed, including a proton-exchange membrane (PEM) electrolyzer, high-pressure hydrogen and oxygen storage, and a PEM fuel cell. The system operates in a closed water loop. A prototype system was constructed, including an experimental PEM electrolyzer and combined gas/water storage tanks. Testing goals included general system feasibility, characterization of the electrolyzer performance (target was sustainable 1.0 A/cm² at 2.0 V per cell), performance of the electrolyzer as a compressor, and evaluation of the system for direct-coupled use with a PV array. When integrated with a photovoltaic array, this type of system is expected to provide reliable, environmentally benign power to remote installations. If grid-coupled, this system (without PV array) would provide high-quality backup power to critical systems such as telecommunications and medical facilities.     

Energy and exergy analyses of hydrogen production via solar-boosted ocean thermal energy conversion and PEM electrolysis

Energy and exergy analyses are reported of hydrogen production via an ocean thermal energy conversion (OTEC) system coupled with a solar-enhanced proton exchange membrane (PEM) electrolyzer. This system is composed of a turbine, an evaporator, a condenser, a pump, a solar collector and a PEM electrolyzer. Electricity is generated in the turbine, which is used by the PEM electrolyzer to produce hydrogen. A simulation program using Matlab software is developed to model the PEM electrolyzer and OTEC system. The simulation model for the PEM electrolyzer used in this study is validated with experimental data from the literature. The amount of hydrogen produced, the exergy destruction of each component and the overall system, and the exergy efficiency of the system are calculated. To better understand the effect of various parameters on system performance, a parametric analysis is carried out. The energy and exergy efficiencies of the integrated OTEC system are 3.6% and 22.7% respectively, and the exergy efficiency of the PEM electrolyzer is about 56.5% while the amount of hydrogen produced by it is 1.2 kg/h.     

One-dimensional dynamic modeling of a high-pressure water electrolysis system for hydrogen production

Research on high-pressure water electrolyzers is under way worldwide as the economic production of hydrogen from renewable energy sources becomes more important. With increases in operating pressures, new safety issues have emerged, for which a reliable dynamic model of the electrolyzers is important for predicting their behavior. In this paper, a one-dimensional dynamic model of a high-pressure proton exchange membrane water electrolyzer is proposed. The model integrates various important physico-chemical phenomena inside the electrochemical cell that have been investigated individually into a dynamic model framework. Water transport, gas permeation, gas volume variation in anode/cathode channels, gas compressibility, and water vaporization are considered to formulate the model. Numerical procedures to handle and solve the model and the model performance for the prediction of steady and dynamic state behaviors are also presented.     

A solid oxide membrane electrolyzer for production of hydrogen and syn-gas from steam and hydrocarbon waste in a single step

This paper describes a novel solid oxide membrane (SOM) electrolyzer that can utilize the energy value in any hydrocarbon waste or reductant to lower the energy requirement for hydrogen production from steam. The SOM electrolyzer consists of a one-end closed oxygen-ion-conducting yttria stabilized zirconia (YSZ) tube with Ni-YSZ cathode coated on the outside and liquid metal anode inside the tube. The SOM electrolyzer is operated by feeding steam on the cathodic side and hydrocarbon reductant in the liquid metal anode. By feeding hydrocarbon waste it is possible to lower the chemical potential of oxygen in the liquid metal such that the SOM electrolyzer can spontaneously dissociate steam and generate hydrogen on the cathodic side and oxidize the hydrocarbon waste on the anodic side to produce syn-gas. The rate of these reactions can be increased by applying a small potential across the electrodes.     

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.     

A stacked interleaved DC-DC buck converter for proton exchange membrane electrolyzer applications: Design and experimental validation

Since the two last decades, hydrogen production has been attracting the attention of the scientific community thanks to its inherent very low pollution when energy coming from renewable energy sources (RESs) are used. However, it implies the use of DC/DC converters to interface source and load. These conversion systems must meet several requirements from current ripple point of view, energy efficiency, and performance to preserve the sustainability of hydrogen production. This article proposes the design and realization of a stacked interleaved buck converter to supply a proton exchange membrane electrolyzer. The converter is designed to ensure a low output current ripple and a suitable dynamic response to guarantee the reliability of the electrolyzer. A theoretical analysis of the converter, taking into account the dynamic model of the electrolyzer, and the design of the control system based both on feedforward and a feedback action is provided. The stability of the control system is discussed as well. The effectiveness of the model and the control algorithm has been verified by simulation and experimental results on a PEM electrolyzer at laboratory scale; the extension to higher power levels is discussed at the end.     

Analysis and modeling of high-performance polymer electrolyte membrane electrolyzers by machine learning

In this study, box and whisker and principal component analysis, as well as classification and regression tree modeling as a part of machine learning were performed on a database constructed on PEM (polymer electrolyte membrane) electrolysis with 789 data points from 30 recent publications. Box whisker plots discovered that pure Pt at the cathode surface, Ti at the anode support, the existence of Pt, Ir, Co, Ru at the anode surface, Ti porous structures at the electrodes, pure water-electrolyte and Nafion and Aquivion type membranes in proton exchange electrolyzer provide the highest performances. Principal component analysis indicated that when cathode surface consists of mostly pure Ni, when anode electrode has no support or vanadium (10–20%) doped TiO₂ support and when anode electrode surface consists of cobalt-iron alloys (0.5:0.5 and 0.333:0.666 mol ratio) or RuO₂, there is a risk for low-performance. Classification trees revealed that other than current density and potential, cathode surface Ni mole fraction, anode surface Co mole fraction are the most important variables for the performance of an electrolyzer. Finally, the regression tree technique successfully modeled the polarization behavior with a RMSE (root mean square error) value of 0.18.     

A nonlinear control strategy for fuel delivery in PEM fuel cells considering nitrogen permeation

Hydrogen energy shows its great potential to be one of the future sustainable energies with abundant storage and high energy content. Proton exchange membrane (PEM) fuel cells, as a hydrogen energy conversation plant with high efficiency, becomes a hot topic of many researches. This paper proposes a multi-input-multi-output (MIMO) nonlinear control strategy for fuel delivery in PEM fuel cell systems. Specifically, a control oriented dynamic model is developed for the fuel delivery system (FDS) with anode recirculation and anode bleeding. Based on the model, a MIMO nonlinear state feedback controller is proposed to maintain adequate hydrogen supply and suitable anode hydrogen concentration. Moreover, an optimized output feedback controller is proposed to improve the state feedback controller, where the unknown hydrogen partial pressures utilized are estimated by developed observers. Lyapunov based stability analysis is carried out to analyze the proposed output feedback controller and the observers. Simulation results show the effectiveness of the proposed controller under various current demands.     

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.