High-pressure Water Electrolysis Research Articles

Low hydrogen permeability and high durability proton exchange membrane with three-dimensional acid-base crosslink structure for water electrolysis

Introducing a acid–base cross-linked network structure and reinforcement layer into a proton exchange membrane (PEM) can effectively improve its performance, durability, and hydrogen permeability for high-pressure PEM water electrolysis (PEMWE). Here, a hyperbranched polymer containing imidazole terminal groups (HBP-MZ) is designed and prepared, then is used to form a novel PEM possessing a cross-linked network structure consisting of HBP-MZ, perfluorosulfonic acid (PFSA) and reinforced with a poly(ether-ether-ketone) (PEEK) mesh. The microstructure of the PEM is characterized using thermal performance analysis. Benefiting from the acid–base crosslinked structure, the obtained PEM has a more compact structure, induces a drastic increase in dimensional stability, mechanical properties, proton conductivity and stability in water. The HBP-MZ/PFSA@PEEK membrane exhibits excellent water electrolysis performance, low high-frequency impedance, and superior stability: the HBP-MZ/PFSA@PEEK membrane provides an electrolytic performance of up to 1.76 V at 2.0 A cm−2 and 1.84 V at 3.0A cm−2 (60 °C, with an IrO2 loading of 1.0 mg cm−2), and exhibits a 6.2 μV h−1 average voltage degradation rate during durability testing. Benefiting from the characteristics of HBP and the existing cross-linked structures, the obtained HBP-MZ/PFSA@PEEK membrane exhibits a lower hydrogen crossover current density of 1.06 mA cm−2 and maintains a lower hydrogen content in oxygen under conditions of high current density and high pressure. This work provides a promising way to prepare a PEM with high durability and low gas permeability that could be applied in high-pressure water electrolysis.

(Invited) Regenerative Fuel Cell System Utilizing a High Differential Pressure Water Electrolysis Technology

The expansion of manned activities in space requires energy system technology that utilizes sunlight, and hydrogen fuel cells are one such means. By electrolyzing water with sunlight, energy is stored with oxygen and hydrogen, and electricity is generated by fuel cells. The generated water can be recycled, and energy can be stored and supplied without external replenishment. This is commonly called a regenerative fuel cell. In the space domain, such energy systems must be compact and lightweight, and gas must be stored under high pressure. However, mechanical compressors that are generally used for compressing are heavy, and there are also issues of vibration and noise.Since the 1990s, Honda has worked on the development of high-differential-pressure water electrolysis technology that generate hydrogen from renewable energy and compress without a mechanical compressor, in parallel with the development of fuel cell technology. High-differential-pressure water electrolysis is a technology that generates high pressure hydrogen by moving the protons generated by electrolysis to the cathode through the Proton exchange membrane (PEM) . The energy required is only the potential generated by the difference in hydrogen concentration, which is superior to small mechanical compressors whose efficiency is reduced by friction loss. However, a large differential pressure is generated across the PEM because only one side is at a high pressure. Honda has achieved a maximum pressure increase of 70 MPa by using its own structure. Moreover, this principle can be applied not only to the generation and pressurization of hydrogen, but also to oxygen. Honda is working on the development of RFC technology that integrates these hydrogen technologies with the aim of applying them not only to sustainability on Earth, but also to the space domain. Currently, we are undertaking a JAXA project and are promoting the production of a breadboard model.The feature of Honda's RFC technology is that it applies high-differential-pressure water electrolysis technology, not only to generate oxygen and hydrogen, but also to pressurize each gas. By not using a mechanical compressor, it is possible to downsize the system, and it is also no vibration or noise. Utilizing the characteristics of this technology, we are planning to build an energy system that can store energy at high density and apply it to various manned missions.Honda's RFC consists of the high-differential-pressure water electrolysis system that simultaneously electrolyzes water and pressurizes oxygen, a Electrochemical hydrogen compressor system (EHC system) that electrochemically pressurizes the hydrogen and a fuel cell system. In the electrolysis stack, oxygen is generated and compressed to the target pressure by the differential pressure water electrolysis. The generated hydrogen is sent to the EHC stack that also applies the technology of high-differential pressure water electrolysis, where the hydrogen is pressurized. As a result, both oxygen and hydrogen gases were generated and compressed without a mechanical compressor. For the fuel cell system, the compact and highly efficient fuel cell technology that has been developed for FCVs is applied. When the fuel cell is used on the ground, oxygen is supplied from the atmosphere, but in space RFC it is necessary to generate electricity using pure oxygen and to circulate the system. A dedicated circulating FC system was constructed to achieve stable power generation. The water produced by power generation is used in the next water electrolysis cycle, and the proof of principle as RFC has been completed. In addition to these basic functions, for space application, we must address issues not found on Earth, such as heat management in a vacuum, radiation, and vibrations during launch. Starting with the lunar exploration mission scheduled for 2030, Honda will develop this technology for the spread of manned activities. Figure 1

The case for high-pressure PEM water electrolysis

Hydrogen compression is a key part of the green hydrogen supply chain, but mechanical compressors are prone to failure and add system complexity and cost. High-pressure water electrolysis can alleviate this problem through electrochemical compression of the gas internally in the electrolyzer and thereby eliminating the need for an external hydrogen compressor. In this work, a detailed techno-economic assessment of high-pressure proton exchange membrane-based water electrolysis (PEMEL) systems was carried out. Electrolyzers operating at 80, 200, 350, and 700 bar were compared to state-of-the-art systems operating at 30 bar in combination with a mechanical compressor. The results show that it is possible to achieve economically viable solutions with high-pressure PEMEL-systems operating up to 200 bar. These pressure levels fit well with the requirements in existing and future industrial applications, such as e-fuel production (30–120 bar), injection of hydrogen into natural gas grids (70 bar), hydrogen gas storage (≥200 bar), and ammonia production (200–300 bar). A sensitivity analysis also showed that if the cost of electricity is sufficiently low (<0.1 €kWh−1), it may even be economical to operate PEMEL systems with hydrogen outlet pressures up to 350 bar.

Catalyst-coated proton exchange membrane for hydrogen production with high pressure water electrolysis

Green hydrogen is currently enjoying a worldwide momentum due to its potential in supporting the United Nations Sustainable Development Goals. It is one of key technologies toward the establishment of a global low-carbon energy infrastructure. As a viable solution to achieve green hydrogen from renewable sources such as wind and solar powers, the process of proton exchange membrane (PEM) water electrolysis enables scalable stacked devices and systems for high pressure hydrogen production. By developing a catalyst-coated proton exchange membrane, we constructed membrane electrode assemblies (MEAs) and assembled them into a five-cell stack device to optimize the materials and components. After device characterization and optimization, a 20 kW PEM water electrolysis system was built, which, under high pressure operating conditions, exhibited favorable hydrogen production performance with 82.9% energy efficiency at the current density of 1000 mA/cm2 and reaction temperature of 70 °C. The resulting hydrogen production rate of the system with catalyst-coated membranes reached 3.09 N m3/h, while the power consumption for hydrogen production was 4.39 kWh/N m3. The results indicate the feasibility of PEM water electrolysis technology for green hydrogen production, for which we envision development into commercial applications in the near future.

Capabilities and Limitations of 3D-CFD Simulation of Anode Flow Fields of High-Pressure PEM Water Electrolysis

In this work, single-phase (liquid water) and two-phase (liquid water and gaseous oxygen) 3D-CFD flow analysis of the anode of a high pressure PEM electrolysis cell was conducted. 3D-CFD simulation models of the anode side porous transport layer of a PEM electrolyzer cell were created for the flow analysis. For the geometrical modelling of the PTL, two approaches were used: (a) modelling the exact geometry and (b) modelling a simplified geometry using a porosity model. Before conducting two-phase simulations, the model was validated using a single-phase approach. The Eulerian multiphase and the volume-of-fluid approaches were used for the two-phase modelling and the results were compared. Furthermore, a small section of the PTL was isolated to focus on the gas bubble flow and behaviour in more detail. The results showed plausible tendencies regarding pressure drop, velocity distribution and gas volume fraction distribution. The simplified geometry using the porous model could adequately replicate the results of the exact geometry model with a significant reduction in simulation time. The developed simulation model can be used for further investigations and gives insight into two-phase flow phenomena in the PTL. Additionally, the information obtained from simulation can aid the design and evaluation of new PTL structures.

Numerical modeling and analysis of the effect of pressure on the performance of an alkaline water electrolysis system

Hydrogen is considered a promising green energy carrier due to its long storage period and zero harmful emissions. The green hydrogen produced by water electrolysis using renewable energy is indispensable for expanding the renewable energy grid and establishing a clean energy society. As renewable power sources are widely deployed, hydrogen can be utilized to connect the energy demand section with the energy supply section. To transport hydrogen to demand sites, one of the most common commercial methods is hydrogen compression. Notably, high-pressure water electrolysis does not need to additionally compress hydrogen, which can significantly diminish the cost of hydrogen production. In this study, to evaluate the effect of the operating pressure on the performance of an alkaline water electrolysis (AWE) system, a numerical model of the AWE system was developed using Aspen Plus®. The AWE system is comprised of the AWE stack, water pumps, heat exchangers, separator, condenser, and electric heat pump (EHP) system. The AWE stack model is validated by comparing the current–voltage polarization curve with experimental data. Simulation results show that an appropriate pressure makes the system more efficient due to decreasing the power consumption of the balance of plant (BOP). Furthermore, high-pressure water electrolysis has a large advantage for obtaining high-purity hydrogen (over 99.9%) without using a water adsorption device.

High Pressure Water Electrolysis Using a Hydrophobic Gas Diffusion Layer with a New Cell Structure of Water Absorbing Electrolyte Cell

Nowadays, the usage of fossil fuel has been raised as a non-sustainable resource, account for the main contributor to global warming (CO2 emission) and environmental pollutions. In this regard, the hydrogen production through polymer electrolyte membrane (PEM) water electrolysis is an industrially important approach to resolving the above energy issues. Precious metals are the top metal-catalysts that can offer to generate hydrogen efficiently and earth-abundant nonprecious metal catalyst has large overpotential issues because of a low electro-activity. Therefore, the production of pressurized hydrogen through polymer exchange membrane (PEM) water electrolysis without the usage of the external compressor is an industrially important approach to maximize energy efficiency. Because hydrogen is believed to be a clean energy carrier to store the excess renewable energy to resolve its intermittent issues. Although over 96% of the current hydrogen produced is via the reformation of natural gas and the remaining 4% produced from water electrolysis and it is the “green” approach to produce hydrogen without CO2 emission. In this report, we demonstrated the operation of a new water electrolysis cell at high water support pressure with the assistance of a hydrophobic gas diffusion layer (H-GDL) and demonstrated a high-pressure PEM water electrolysis experiment with the assistance of a newly structured water electrolysis cell (Fig.1a). The membrane electrode assemblies (MEAs) was prepared using H-GDL, membrane, Pt-C//IrO2 and the electrolysis experiment was performed at different temperature and water support pressure (ΔP = 0.05-0.4 MPa). The current density obtained at 1.6 V were 117, 188, 262 mA cm-2 at 25, 60, and 80oC (Fig.1b), respectively, and the generated gas evolution rates (hydrogen and oxygen) were consistent with theoretical value with efficiencies up to 87%. It was found that increasing water pressure is beneficial to the electrode kinetics and mass-transportation due to an increase in water transport to the electrode surface and efficient gas separation. The benefits of using GDL is, therefore, lying on two points. Firstly, high pressure can be applied to the water, which allows the operation of the cell at a temperature higher than 100℃, while maintaining the water in the liquid phase and secondly the high-pressure operation using H-GDL is the production of pressurized hydrogen gas without the use of an external compressor. As advantages, in the future, it can be directly used to fuel cell and that can be stored in a hydrogen tank without further purification process. Figure 1

Theoretical and experimental analysis of an asymmetric high pressure PEM water electrolyser up to 155 bar

In this paper a semi-empiric zero-dimensional steady state simulation model of an asymmetric high pressure proton exchange membrane water electrolyser is being presented. Based on experimental investigations on a 9.6 kW asymmetric high pressure water electrolysis module, empirical parameters were determined. Measurements were taken by varying the production pressure between 70 bar and 155 bar, the process temperature between 45 °C and 75 °C and the current density from 0.81 A cm−2 to 1.85 A cm−2. Stack efficiency and hydrogen diffusion from the cathode to the anode side were determined and expressed by the faradaic efficiency. Stack efficiencies of up to 74.8% were achieved at 0.81 A cm−2, 75 °C and 155 bar. As expected the stack efficiency decreases with increasing hydrogen production pressure. A temperature decrease of 30 °C has greater impact on the efficiency than an increase of pressure from 70 to 155 bar. The faradaic efficiency at 1.85 A cm−2, 155 bar and 45 °C is higher than 99% and even at a high operating temperature of 75 °C higher than 97%. The presented model can be used for prediction of the stack voltage, gas production flow rates, water consumption and stack efficiency as function of input current, process temperature and production pressure. Results show a very satisfactory consistency of measurement and simulation.

Overpotential Analysis in High Pressure Water Electrolysis

To store or transport hydrogen (and optionally oxygen) in high pressure tanks or pipelines pressures up to 1000 bar are needed. Pressurized polymer electrolyte electrolyzers are typically operated at around 30 bar to reduce downstream mechanical compression and gas drying stages. Interestingly, often the cell voltage does not show the expected thermodynamic voltage increase [1,2]. Consequently beneficial influences are compensating the compression work, at the expense of higher faradaic losses due to increased gas crossover. In this work we analyze cell voltages at gas pressures up to 100 bar as function of temperature up to 70 °C and current densities up to 4 A/cm2, considering the three main overpotentials (ohmic, kinetic, mass transport) using a zero-order analysis based on the Tafel kinetics model. As expected, the ohmic overpotential is mainly a function of temperature and almost independent from pressure. Therefore the overpotential gains with increasing pressure, observed for current densities above about 0.8 A/cm2, stem from the kinetics and/or the mass transport. Both overpotentials decrease with increasing pressure, but over a wide current density region kinetics contribute about two thirds to the voltage gain. The improved kinetics can be attributed to an increased apparent exchange current density, whereas the increased mass transport might be related to smaller gas volumes or velocities resulting in an improved two-phase flow in the porous structures. Literature: [1] S.A. Grigoriev, V.I. Porembsky, V.N. Fateev, Pure hydrogen production by PEM electrolysis for hydrogen energy, Int J of Hydrogen Energy, 31 (2006) 171-175. [2] P. Millet, R. Ngameni, S.A. Grigoriev, N. Mbemba, F. Brisset, A. Ranjbari, C. Etiévant, PEM water electrolyzers: From electrocatalysis to stack development, Int J of Hydrogen Energy, 35 (2010) 5043-5052.

High-pressure water electrolysis: Electrochemical mitigation of product gas crossover

Hydrogen produced by water electrolysis can be used as an energy carrier storing electricity generated from renewables. During water electrolysis hydrogen can be evolved under pressure at isothermal conditions, enabling highly efficient compression. However, the permeation of hydrogen through the electrolyte increases with operating pressure and leads to efficiency loss and safety hazards. In this study, we report on an innovative concept, where the hydrogen crossover is electrochemically mitigated by an additional electrode between the anode and the cathode of the electrolysis cell. Experimentally, the technique was applied to a proton exchange membrane water electrolyzer operated at a hydrogen pressure that was fifty times larger than the oxygen pressure. Therewith, the hydrogen crossover was reduced and the current efficiency during partial load operation was increased. The concept is also discussed for water electrolysis that is operated at balanced pressures, where the crossover of hydrogen and oxygen is mitigated using two additional electrodes.

Thermodynamics of high-temperature, high-pressure water electrolysis

We report on a thermodynamic analysis for water electrolysis from normal conditions (P = 0.1 MPa, T = 298 K) up to heretofore unaddressed temperatures of 1000 K and pressures of 100 MPa. Thermoneutral and reversible potentials are determined using equations-of-state published by the International Association for the Properties of Water and Steam and the National Institute of Standards and Technology. The need for using accurate property models at these elevated temperatures and pressures is exemplified by contrasting results with those obtained via ideal assumptions. The utility of our results is demonstrated by their application in an analysis comparing pressurized electrolysis versus mechanical gas compression. Within the limits of our analysis, pressurized electrolysis demonstrates lower energy requirements albeit with electrical work composing a greater proportion of the total energy input.

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.

Dual-Feed Balanced High-Pressure Electrolysis of Water in a Lightweight Polymer Electrolyte Membrane Stack

Efficient water electrolyzers that generate high-pressure hydrogen and oxygen are useful for aerospace and civilian applications. A lightweight polymer-electrolyte-membrane electrolyzer capable of producing oxygen and hydrogen at a balanced pressure of 13.8 MPa has been designed and fabricated by Hamilton Sundstrand Space Systems International (HSSSI). This electrolyzer uses a unique metal-laminate cell design that reduces the weight of traditional high-pressure water electrolysis stacks by eliminating the need to place the stack within a pressure vessel. The electrolyzer operates on water fed to the anode and cathode (dual-feed mode). This design simplifies the balance of plant for a regenerative fuel cell system and enhances system safety. The electrolyzer was tested at balanced pressure in the range of 1.72–13.8 MPa using a test system designed and constructed at the Jet Propulsion Laboratory. Current efficiency of 96 to 97% was achieved at a balanced product pressure of 13.8 MPa. The polarization characteristics were governed by the kinetics of oxygen evolution and the ionic resistance of the membrane electrolyte. The electro-osmotic water drag coefficient was determined to be in the range of 2.3–2.4 and this value did not vary with the operating pressure up to 13.8 MPa. The dual-feed electrolyzer is a promising design for achieving high energy efficiencies at high product pressure.

High-pressure PEM water electrolysis and corresponding safety issues

In this paper, safety considerations related to the operation of proton-exchange membrane (PEM) water electrolysers (hydrogen production capacity up to 1Nm3/h and operating pressure up to 130bars) are presented. These results were obtained in the course of the GenHyPEM project, a research program on high-pressure PEM water electrolysis supported by the European Commission. Experiments were made using a high-pressure electrolysis stack designed for operation in the 0–130bars pressure range at temperatures up to 90°C. Besides hazards related to the pressure itself, hydrogen concentration in the oxygen gas production and vice-versa (resulting from membrane crossover permeation effects) have been identified as the most significant risks. Results show that the oxygen concentration in hydrogen at 130bars can be as high as 2.66vol%. This is a value still outside the flammability limit for hydrogen–oxygen mixtures (3.9–95.8vol%), but safety measures are required to prevent explosion hazards. A simple model based on the diffusion of dissolved gases is proposed to account for gas cross-permeation effects. To reduce contamination levels, different solutions are proposed. First, thicker membranes can be used. Second, modified or composite membranes with lower gas permeabilities can be used. Third, as reported earlier, external catalytic gas recombiners can be used to promote H2/O2 recombination and reduce contamination levels in the gas production. Finally, other considerations related to cell and stack design are also discussed to further reduce operation risks.

Mathematical modeling of high-pressure PEM water electrolysis

This paper is devoted to the modeling and numerical optimization of proton-exchange membrane (PEM) water electrolysers for operation at elevated pressures (up to 130 bars). The model takes into account different geometrical parameters of the PEM cell, the kinetics of the hydrogen and oxygen evolution reactions, the electro-osmotic drag of water molecules, the permselectivity of the solid polymer electrolyte and associated gas cross-over phenomena. The role of various operating parameters (such as pressure, temperature, current density, flow rate of water) on cell efficiency, faradaic yield and heat produced during water electrolysis is evaluated and discussed. The model is also used for the purpose of optimizing the performances of PEM cells. In particular, optimal values of some critical operating parameters (current density, rate of water supplied to the anodes) are recommended.

Hydrogen safety aspects related to high-pressure polymer electrolyte membrane water electrolysis

Abstract Polymer electrolyte membrane (PEM) water electrolysis has demonstrated its potentialities in terms of cell efficiency (energy consumption ca. 4.0–4.2 kW/Nm 3 H 2 ) and gas purity (>99.99% H 2 ). Current research activities are aimed at increasing operating pressure up to several hundred bars for direct storage of hydrogen in pressurized vessels. Compared to atmospheric pressure electrolysis, high-pressure operation yields additional problems, especially with regard to safety considerations. In particular the rate of gases (H 2 and O 2 ) cross-permeation across the membrane and their water solubility both increase with pressure. As a result, gas purity is affected in both anodic and cathodic circuits, and this can lead to the formation of explosive gas mixtures. To prevent such risks, two different solutions, reported in this communication, have been investigated: first, the chemical modification of the solid polymer electrolyte, in order to reduce cross-permeation phenomena; second, the use of catalytic H 2 /O 2 recombiners to maintain H 2 levels in O 2 and O 2 levels in H 2 at values compatible with safety requirements.

Backwards Runs the Reaction

This article describes various electrochemical programs that could enable advanced vehicles to generate critical gases directly from water. Energy storage solutions using water electrolysis and fuel cell systems are being examined for applications ranging from backup power systems and lighter-than-air vehicles to extraterrestrial bases on the moon and Mars. The basic architecture of a regenerative fuel cell energy storage system includes a high-pressure water electrolysis system, a fuel cell, a fluid management and storage system, a thermal management system, and a power management system. For extraterrestrial applications, the system would be used in tandem with a photovoltaic array. Recent studies have focused on oxygen and hydrogen storage pressures of between 1000 and 2000 psi, requiring the development of a high, balanced-pressure water electrolysis cell stack and balance of plant to safely manage these fluids. Fuel cell-powered vehicles hold the promise of reducing greenhouse gas emissions from the transportation sector, provided the hydrogen fuel is produced from a renewable energy source, such as a high-pressure water electrolyzer operating from wind, solar, or nuclear power.

Thermodynamics aspect of high pressure hydrogen production by water electrolysis

Hydrogen can be produced from water electrolysis which can operate at atmospheric pressure or high pressure. Today’s industry including vehicle one, devotes efforts to produce high pressure hydrogen by using pressurized electrolyser. The purpose of this work is to estimate the ideal electrical energy needed for high pressure hydrogen under high pressure water electrolysis conditions. Calculations are based on the estimation of the enthalpy and free Gibbs energy of water electrolysis at various pressures and temperatures, referring to both the work of LeRoy &amp; Onda.

Prediction of production power for high-pressure hydrogen by high-pressure water electrolysis

Recent attention focused on fuel cell electric vehicles (FCEVs) has created demand for the construction of hydrogen supply stations for FCEVs throughout the world. The hydrogen pressure supplied at the supply stations is intentionally high to increase the FCEVs driving mileage. Water electrolysis can produce clean hydrogen by utilizing electricity from renewable energy without CO 2 emission to the atmosphere when compared with the industrial fossil fuel reforming process. The power required for high-pressure water electrolysis, wherein water is pumped up to a high-pressure, may be less than the power required for atmospheric water electrolysis, wherein the produced atmospheric hydrogen is pumped by a compressor, since the compression power for water is much less than that for hydrogen-gas. In this study, the ideal water electrolysis voltage of up to 70 MPa and 250 °C is estimated by referring to both the results of LeRoy et al. up to 10 MPa and 250 °C, and the latest steam tables. Using this high-pressure water electrolysis voltage, the power required to produce high-pressure hydrogen by high-pressure water electrolysis is estimated to be about 5% less than that required for atmospheric water electrolysis, assuming compressor and pump efficiencies of 50%.

高圧水電解による高圧水素の製造動力の推定

高圧水電解による高圧水素の製造動力の推定