Development and performance evaluation of Proton Exchange Membrane (PEM) based hydrogen generator for portable applications

This paper presents the development of key components, specifications, configuration and operation characteristics of an 80 l/h Proton Exchange Membrane (PEM) water electrolyzer system for portable application. The developed PEM water electrolyzer can produce 80 l/h hydrogen (purity > 99.99%) with moderate pressure range up to 500 kPa (73 psi) at an operating current of 100 A with energy efficiency of 77.48%. The reliability in operation of developed PEM water electrolyzer system is tested for running the stack about 3000 h with 100 A current. The results indicate the reasonable stability of MEA fabrication and cell design method.     

PEM water electrolyzer model for a power-hardware-in-loop simulator

Power-electronics-based power-hardware-in-loop (PHIL) simulator for water electrolyzer emulation with a nominal current of 405 A is developed to study the electrolyzer as part of a smart grid and to analyze the characteristics of various electrolyzer power supply electronics. A simplified model of a proton exchange membrane (PEM) electrolyzer is implemented into the PHIL simulator to describe the voltage and current characteristics of the electrolyzer stack. The model is verified comparing the current and the estimated hydrogen production of the PHIL simulator with the measured values of the commercial PEM electrolyzer following the measured solar photovoltaic (PV) system output power.     

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%。     

Control strategy of electrolyzer in a wind-hydrogen system considering the constraints of switching times

In order to improve the operational performance of alkaline electrolyzers powered by wind power, the influences of the fluctuating wind power on alkaline electrolyzers must be taken in accounts. In pursuing this goal, the influences of fluctuating wind power on both the hydrogen production and the self-safety of alkaline electrolyzer is discussed firstly. And a wind-hydrogen integrated energy system (WHIES) integrated supercapacitor is designed to smooth the fluctuation of wind power. In which, the fluctuation of wind power is divided into two kinds, instantaneous fluctuation and wide power fluctuation, the former is absorbed by supercapacitors, the latter is overcomed by adopting a modular adaptive control strategy to optimize the operation mode of alkaline electrolyzer. A simulation has been developed for a specific wind farm located in Northeast China. The simulation results show that under the condition of fluctuating wind power, the WHIES with the proposed control strategy can reduce the switching times of electrolyzers by 93.5% and increase hydrogen production by more than 44.18% when compared with other control strategies.     

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).     

Methylcyclohexane production under fluctuating hydrogen flow rate conditions

Energy storage using liquid organic hydrogen carrier (LOHC) is a long-term method to store renewable energy with high hydrogen energy density. This study investigated a simple and low-cost system to produce methylcyclohexane (MCH) from toluene and hydrogen using fluctuating electric power, and developed its control method. In the current system, hydrogen generated by an alkaline water electrolyzer was directly supplied to hydrogenation reactors, where hydrogen purification equipment such as PSA and TSA is not installed to decrease costs. Hydrogen buffer tanks and compressors are not equipped. In order to enable MCH production using fluctuating electricity, a feed-forward toluene supply control method was developed and introduced to the system. The electrolyzer was operated under triangular waves and power generation patterns of photovoltaic cells and produced hydrogen with fluctuating flow rates up to 7.5 Nm³/h. Consequently, relatively high purity of MCH (more than 90% of MCH mole fraction) was successfully produced. Therefore, the simplified system has enough potential to produce MCH using fluctuating renewable electricity.     

Performance assessment of solar-powered high pressure proton exchange membrane electrolyzer: A case study for Erzincan

In this study, a performance assessment of a solar-powered high-pressure proton exchange membrane (PEM) electrolyzer for hydrogen production is conducted. The feasibility analysis of photovoltaic systems equipped with a high pressure PEM electrolyzer is presented for a university campus-scale community in Erzincan- Turkey. Variable solar irradiance data sets are utilized to assess the performance of the proposed system. A parametric study is conducted in order to evaluate the influence of some design parameters as well as operating conditions on the efficiency of the system. Efficiency of the overall system in the case of relevant inverter sizing is in the range of 11–12%. An ascent of the number of stacks leads to an increase in production rate which is almost linear by photovoltaic (PV) array size. The results shows that in order to have a higher efficiency, the inverter size should be higher than 0.75% of maximum excess power. The proposed system investigated in this study shows great promise of opening up opportunity to develop the high pressure PEM electrolyzer.     

Failure of PEM water electrolysis cells: Case study involving anode dissolution and membrane thinning

Polymer electrolyte membrane (PEM) water electrolysis is an efficient and environmental friendly method that can be used for the production of molecular hydrogen of electrolytic grade using zero-carbon power sources such as renewable and nuclear. However, market applications are asking for cost reduction and performances improvement. This can be achieved by increasing operating current density and lifetime of operation. Concerning performance, safety, reliability and durability issues, the membrane-electrode assembly (MEA) is the weakest cell component. Most performance losses and most accidents occurring during PEM water electrolysis are usually due to the MEA. The purpose of this communication is to report on some specific degradation mechanisms that have been identified as a potential source of performance loss and membrane failure. An accelerated degradation test has been performed on a MEA by applying galvanostatic pulses. Platinum has been used as electrocatalyst at both anode and cathode in order to accelerate degradation rate by maintaining higher cell voltage and higher anodic potential that otherwise would have occurred if conventional Ir/IrO_x catalysts had been used. Experimental evidence of degradation mechanisms have been obtained by post-mortem analysis of the MEA using microscopy and chemical analysis. Details of these degradation processes are presented and discussed.     

Influence of renewable energy power fluctuations on water electrolysis for green hydrogen production

The development of renewable energy technologies is essential to achieve carbon neutrality. Hydrogen can be stably stored and transported in large quantities to maximize power utilization. Detailed understanding of the characteristics and operating methods of water electrolysis technologies, in which naturally intermittent fluctuating power is used directly, is required for green hydrogen production, because fluctuating power-driven water electrolysis processes significantly differ from industrial water electrolysis processes driven by steady grid power. Thus, it is necessary to overcome several issues related to the direct use of fluctuating power. This article reviews the characteristics of fluctuating power and its generation as well as the current status and issues related to the operation conditions, water electrolyzer configuration, system requirements, stack/catalyst durability, and degradation mechanisms under the direct use of fluctuating power sources. It also provides an accelerated degradation test protocol method for fair catalyst performance comparison and share of effective design directions. Finally, it discusses potential challenges and recommendations for further improvements in water electrolyzer components and systems suitable for practical use, suggesting that a breakthrough could be realized toward the achievement of a sustainable hydrogen-based society.     

A review of accelerated stress tests of MEA durability in PEM fuel cells

This paper is a review of recent work done on accelerated stress tests in the study of PEM fuel cell durability, with a primary focus on the main components of the membrane electrode assembly (MEA). The accelerated stressors for each component under different conditions are outlined, in an attempt to gain a detailed understanding of cell degradation with respect to microstructural change and performance attenuation in the perfluorosulfonic acid membrane, catalyst, and gas diffusion layers. Various techniques for evaluating the components' performance are presented, along with representative mitigation strategies. In addition, different degradation mechanisms proposed in recent publications are briefly reviewed.     

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.     

Failure mechanism of PEM fuel cell under high back pressures operation

Proton exchange membrane fuel cells (PEMFCs) are expected to function under relatively higher back pressures for targeting higher outpower. Under this condition, the durability of fuel cells will be a huge challenge for commercialization. In our study, a 1000-h durability experiment was performed on a PEMFC to investigate the durability under high back pressures. A semi-empirical fuel cell polarization curve model was used to separate the activation and concentration losses, and study their changes with testing time at different current densities. In addition, the charge transfer resistance (R_ct) related to oxygen reduction reaction (ORR) in the catalyst layer was also investigated. Additionally, the mass transfer resistance (Z_d) was investigated using electrochemical impedance spectroscopy (EIS). Moreover, the contact angle and energy-dispersive X-ray spectrum (EDX) of carbon paper surface were characterized. The results indicated that the increase in mass transfer resistance was the biggest contributor to the loss of cell voltage with testing time. The decrease in contact angle of carbon paper surface implied that the weakening of hydrophobicity contributed to an increase in the mass transfer resistance, which comes from the PTFE loss observed from EDX. This may result from the aggravated corrosion of carbon fiber or physical erosion induced by flooding in fuel cell under high back-pressure.     

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.     

Characterisation tools development for PEM electrolysers

Electrochemical impedance spectroscopy (EIS), current interrupt (CI) and current mapping (CM) were investigated as in-situ characterisation tools for PEM electrolysers. A 25 cm² cell with titanium anode and carbon cathode plates were utilised in this study. A commercial MEA consisting of 1 mg IrO₂/cm² on the anode and 0.3 mg Pt/cm² on the cathode was used. The electrocatalyst was deposited on Nafion^® membranes. The electrochemical losses in a PEM electrolyser namely: activation, ohmic and mass transfer losses were identified using EIS and CI and both the advantages and disadvantages of the methods were discussed. The current distribution over the membrane electrode assembly (MEA) at different current densities was measured using the current mapping method. It is also shown that under the given experimental conditions the current density decreases along the serpentine flow field.     

Degradation analysis of the core components of metal plate proton exchange membrane fuel cell stack under dynamic load cycles

The durability of metal plate proton exchange membrane fuel cell (PEMFC) stack is still an important factor that hinders its large-scale commercial application. In this paper, we have conducted a 1000 h durability test on a 1 kW metal plate PEMFC stack, and explored the degradation of the core components. After 1000 h of dynamic load cycles, the voltage decay percentage of the stack under the current densities of 1000 mA cm^?2 is 5.67%. By analyzing the scanning electron microscopy (SEM) images, the surfaces of the metal plates are contaminated locally by organic matter precipitated from the membrane electrode assembly (MEA). The SEM images of the catalyst coated membrane (CCM) cross section indicate that the MEA has undergone severe degradation, including the agglomeration of the catalyst layer, and the thinning and perforation of the PEM. These are the main factors that cause the rapid increase in hydrogen crossover flow rate and performance decay of the PEMFC stack.     

Assessment of hydrogen production from waste heat using hybrid systems of Rankine cycle with proton exchange membrane/solid oxide electrolyzer

A techno-economic assessment of hydrogen production from waste heat using a proton exchange membrane (PEM) electrolyzer and solid oxide electrolyzer cell (SOEC) integrated separately with the Rankine cycle via two different hybrid systems is investigated. The two systems run via three available cement waste heats of temperatures 360 °C, 432 °C, and 780 °C with the same energy input. The waste heat is used to run the Rankine cycle for the power production required for the PEM electrolyzer system, while in the case of SOEC, a portion of waste heat energy is used to supply the electrolyzer with the necessary steam. Firstly, the best parameters; Rankine working fluid for the two systems and inlet water flow rate and bleeding ratio for the SOEC system are selected. Then, the performance of the two systems (Rankine efficiency, total system efficiency, hydrogen production rate, and economic and CO₂ reduction) is investigated and compared. The results reveal that the two systems' performance is higher in the case of steam Rankine than organic, while a bleeding ratio of 1% is the best condition for the SOEC system. Rankine output power, total system efficiency, and hydrogen production rate rose with increasing waste heat temperature having the same energy. SOEC system produces higher hydrogen production and efficiency than the PEM system for all input waste heat conditions. SOEC can produce 36.9 kg/h of hydrogen with a total system efficiency of 23.8% at 780 °C compared with 27.4 kg/h and 14.45%, respectively, for the PEM system. The minimum hydrogen production cost of SOEC and PEM systems is 0.88 $/kg and 1.55 $/kg, respectively. The introduced systems reduce CO₂ emissions annually by about 3077 tons.     

Highly active screen-printed IrTi4O7 anodes for proton exchange membrane electrolyzers

Electroceramic support materials can help reducing the noble-metal loading of iridium in the membrane electrodes assembly (MEA) of proton exchange membrane (PEM) electrolyzers. Highly active anodes containing Ir-black catalyst and submicronic Ti₄O₇ are manufactured through screen printing technique. Several vehicle solvents, including ethane-1,2-diol; propane-1,2-diol and cyclohexanol are investigated. Suitable functional anodic layer with iridium loading as low as 0.4 mg cm^?2 is obtained. Surface properties of the deposited layers are investigated by atomic force microscopy (AFM). The most homogeneous coating with the highest electronic conductivity is obtained using cyclohexanol. Tests in PEM electrolyzer operating at 1.7 V and 40 °C demonstrate that the CCM with anode coated with cyclohexanol presents a 1.5-fold higher Ir-mass activity than that of the commercial CCM.     

Development,analysis and assessment of fuel cell and photovoltaic powered vehicles

This paper deals with a new hybridly powered photovoltaic- PEM fuel cell – Li-ion battery and ammonia electrolyte cell integrated system (system 2) for vehicle application and is compared to another system (system 1) that is consisting of a PEM fuel cell, photovoltaic and Li-ion battery. The paper aims to investigate the effect of adding photovoltaic to both systems and the amount of hydrogen consumption/production that could be saved/generated if it is implemented in both systems. These two systems are analyzed and assessed both energetically and exergetically. Utilizing photovoltaic arrays in system 1 is able to recover 177.78 g of hydrogen through 1 h of continuous driving at vehicle output power of 98.32 kW, which is approximately 3.55% of the hydrogen storage tank used in the proposed systems. While, using the same photovoltaics arrays, system 2 succeeds to produce 313.86 g of hydrogen utilizing the ammonia electrolyzer system 2 appeared to be more promising as it works even if the car is not in operation mode. Moreover, the hydrogen produced from the ammonia electrolyzer can be stored onboard, and the liquefied ammonia can be used as a potential source for feeding PEM fuel cell with hydrogen. Furthermore, the effects of changing various system parameters on energy and exergy efficiencies of the overall system are investigated.     

Durability analysis and degradation mechanism for an electrolytic air dehumidifier based on PEM

Electrolytic air dehumidification (vapor electrolysers) based on proton-exchange membrane (PEM) is competitive to conventional dehumidifiers, but serious degradation has been found in long-running applications. This study conducted the durability test of electrolytic dehumidifier, under continuous operation for more than 250 h. Changes in current and dehumidification rate were analyzed and compared to those for fuel cells and water electrolysers. Physicochemical and electrochemical changes of the materials before and after the test were investigated. Results show that higher applied potential or higher air humidity corresponds to a larger dehumidification amount, while performance attenuates more quickly over time. When the applied potential increased from 2 V to 4 V, the degradation rate increases from 23% to 67% at 90% air humidity. Simultaneously, the internal resistance of PEM element increased from 0.419 to 1.45 Ω and the reaction resistance changed from 1.13 to 2.17 Ω, indicating by in-situ and ex-situ EIS. By characterization analysis, it indicated that the corrosion of the anode-side catalyst IrO₂ is the main reason for the long-term attenuation. The grain size of almost all IrO₂ faces reduced after 250 h dehumidification, and the content of active metal of the catalyst lost by 54.3%. The dissolution rate of IrO₂ also increases with increasing applied potential. Besides, there is almost no physical or chemical damage on PEM or cathode catalyst before and after the durability test. This research clarifies the micro-scale changes of the materials during long-term operation, and discloses the degradation mechanism of PEM-based electrolytic dehumidifiers.     

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.