Alkaline Water Electrolysis System Research Articles

Dynamic fault detection and diagnosis of industrial alkaline water electrolyzer process with variational Bayesian dictionary learning

Alkaline Water Electrolysis (AWE) is one of the simplest green hydrogen production method using renewable energy. AWE system typically yields process variables that are serially correlated and contaminated by measurement uncertainty. A novel robust dynamic variational Bayesian dictionary learning (RDVDL) monitoring approach is proposed to improve the reliability and safety of AWE operation. RDVDL employs a sparse Bayesian dictionary learning to preserve the dynamic mechanism information of AWE process which allows the easy interpretation of fault detection results. To improve the robustness to measurement uncertainty, a low-rank vector autoregressive (VAR) method is derived to reliably extract the serial correlation from process variables. The effectiveness of the proposed approach is demonstrated with an industrial hydrogen production process, and RDVDL can efficiently detect and diagnose critical AWE faults.

Reverse‐Current Tolerance for Hydrogen Evolution Reaction Activity of Lead‐Decorated Nickel Catalysts in Zero‐Gap Alkaline Water Electrolysis Systems

AbstractAlkaline water electrolysis (AWE) systems offer a cost‐effective and scalable approach for large‐scale hydrogen production using renewable energy sources. However, their susceptibility to load fluctuations, particularly the reverse‐current (RC) phenomenon during shutdown events, poses a significant challenge to the long‐term stability and scalability of these systems. Herein, a catalytic approach for enhancing the RC tolerance in AWE systems by using Pb‐decorated Ni cathode catalysts (Pb/Ni) is introduced. The oxidation of Pb/Ni by repeated RC lowers the electromotive force for the reverse current operation, and consequently, imparts RC tolerance. Intriguingly, contrary to the expectation that the decoration with lead, an inert material for the hydrogen evolution reaction (HER), will interfere with the hydrogen generation of the Ni catalyst, the presence of Pb on the Ni cathode after the RC flow promotes both the proton desorption and water‐dissociation steps, improving the HER activity. Furthermore, the AWE stack testing with Pb/Ni catalysts is perfectly operated, demonstrating remarkably enhanced RC tolerance during startup/shut‐down (SU/SD) testing protocol. This paper presents a new strategy for mitigating the AWE performance degradation induced by RC flow and for achieving Pb/Ni catalysts with improved operational durability against RC flow in AWE systems.

Considerations of Reference Electrodes and Liquid Junction Potentials for Accurate Electrocatalysis Studies

For lab-scale electrocatalysis studies, one typically uses a three-electrode system, which consists of working, counter (auxiliary), and reference electrodes, an electrolyte solution, and a reactor. In this system, it is important for accurate electrochemical studies to select an appropriate reference electrode for a particular electrolyte solution and recognize the presence/absence of liquid junction potential at the frit of a reference electrode. For instance, in alkaline water electrocatalysis experiments, Hg/HgO, Ag/AgCl, or saturated calomel electrode (SCE) is generally used as a reference electrode, and 1 M KOH/NaOH aqueous solution is utilized as an electrolyte solution.1 In this regard, the Ag/AgCl electrode and SCE are unsuitable for electrochemical studies with alkaline electrolytes, and among them, only the Hg/HgO electrode can be used instead.1 Furthermore, if the internal solution of a reference electrode and the external electrolyte solution are different in constituent and/or concentration, the liquid junction potential will be established at the frit of a reference electrode. In this case, to accurately know the potential applied to a working electrode, this liquid junction potential as well as the iR drop caused by solution resistance need to be considered and corrected appropriately. However, the liquid junction potential has so far been ignored in most of the electrocatalysis studies.In this work, we will discuss a method to experimentally estimate the liquid junction potential at the reference electrode frit using three-electrode systems with different combinations of electrolytes and reference electrodes. Herein, we will deal with alkaline water electrolysis systems as representatives. The as-estimated values of various liquid junction potentials will be compared with the theoretical values obtained using the Henderson equation2 and the stationary Nernst–Planck equation.3 Additionally, the guideline for selecting an appropriate reference electrode depending on the types of external electrolyte solutions will be discussed briefly. We believe that these findings can improve the accuracy of reporting potential-related parameters (e.g., overpotential, half-wave potential, onset potential, etc.) in three-electrode system-based electrocatalysis studies. References K. Kawashima et al., ACS Catal., 13, 1893–1898 (2023).R. G. Bates, Determination of pH, 2nd ed., p. 36–44, A Wiley-Interscience Publication, New York, New York, (1973).M. Marino, L. Misuri, and D. Brogioli, (2014) https://arxiv.org/abs/1403.3640v2.

Mitigating the Degradation of Electrodes in Alkaline Water Electrolysis during Shutdown Mode by Interrupting Reverse Current

Alkaline water electrolysis (AWE) is a promising technology for large-scale hydrogen production using renewable energy sources (RES). However, AWE integrated with RES experiences shutdown mode due to their intermittency, resulting in reverse current through open flow path of high ionic conductivity. This induces irreversible phase changes, which lead to electrode degradation and inevitably reduce the performance of the AWE. Therefore, it is important to examine the degradation mechanism and identify effective methods to reduce reverse current in AWE. In this work, we developed AWE system which impedes hydroxide ion transfer using deionized (DI) water circulation when it undergoes a shutdown mode. Cutting off the flow of ionic charges prevents the electrodes from forming irreversible phase change, making long-term operation possible while securing durability. We examined how reduced ionic conductivity mitigates the side effects of reverse current using phase characterization and electrochemical performance tests. Based on these results, we established an optimal way to impede hydroxide ion transfer in shutdown condition of an AWE system integrated with RES. Our findings will overcome fatal shortcomings and operate more efficiently in AWE industry.

Study on the synergistic regulation strategy of load range and electrolysis efficiency of 250 kW alkaline electrolysis system under high-dynamic operation conditions

Alkaline water electrolysis (AWE) has the highest technological maturity among all the water electrolysis technologies for hydrogen production, however, reducing the minimum load boundary and improving the electrolysis efficiency are the technical challenges of the AWE system that still exist and urgently require optimization. The minimum load is primarily limited by the hydrogen to oxygen (HTO) from cross-diaphragm transfer and lye mixing, with HTO above 2.0% being a significant safety risk. Reducing the lye flow rate and pressure are effective while two of the few ways by regulating the operating parameters to improve the HTO thus extend the minimum load boundary, but will worsen electrolysis efficiency. Therefore, this study proposes a synergistic regulation strategy of pressure and lye flow rate: maximizing pressure and lye flow rate during high load period to ensure high electrolysis efficiency; adjusting lye flow rate and pressure during medium load period to ensure HTO≤2.0% and maximize the electrolysis efficiency; and reducing lye flow rate and pressure to a low level during the low load period to broaden the minimum load so as to improve overall efficiency of AWE system when loading with fluctuant green electric. This work elaborates the HTO routes, influencing factors and parameter optimization mechanism by building a system-level steady-state and dynamic gas purity model. The optimal combination curve of pressure and lye flow rate is obtained and its control effect on performance parameters, in terms of minimum load, system energy consumption, energy utilization, electrolysis efficiency and so on, is compared and verified in high dynamic wind and photovoltaic (PV) power scenarios. Finally, the optimal wind & PV power ratios are explored based on the optimal operation curve, which will provide a reference for the future large-scale development of hydrogen production scenarios direct-coupled with wind and PV power. The minimum load is extended from 42.0% in the lye flow rate alone control to 21.2% in the pressure alone control and finally to 15.6% in the lye flow rate and pressure synergistic control method. In the absence of electrical replenishment, wind and PV energy utilization efficiency can reach up to 98.3% and 95.6%, respectively.

Experimental studies on dynamic performance of 250-kW alkaline electrolytic system

Alkaline water electrolysis is a mature hydrogen production technology and an important means for future large-scale green hydrogen production and electrical energy storage, while enhancing and optimizing its dynamic characteristic speed is the urgent problem to achieve this goal. In this study, the dynamic response characteristics of the system current, voltage, temperature, hydrogen to oxygen (HTO) and pressure parameters are experimentally investigated at two levels (start-stop and variable load processes) and three-time scales (hours, minutes and seconds) based on the 250-kW industrial alkaline water electrolysis system. The experimental study of cold start (25 °C)→full load (90 °C)→hot shutdown (75 °C)→hot start (70 °C)→full load (90 °C)→cold shutdown (30 °C) revealed that the response time of start-stop process is hourly and temperature is the main limiting factor. The response time of HTO is on the order of minutes based on the variable load test: full load (3500 A, 1.7 MPa)→minimum load (1400 A, 1.7 MPa)→full load (3500 A, 1.7 MPa)→minimum load (800 A, 0.6 MPa). The response of HTO to parameter changes has severe time delay and inertia links, and the latter with significantly longer response time. The response time for different current step is in the order of seconds. This experimental study points out the dynamic performance level of industrial-scale alkaline water electrolysis system at the present stage and provides directions for the optimization of dynamic performance indexes, which is an important guideline for designing control strategies that integrate with renewable energy sources.

Synergistically enhanced electrocatalytic performance of NiO infused crystalline graphitic carbon towards overall water splitting

Developing high-performance electrocatalysts to achieve catalytically active and kinetically feasible reaction sites with structural strength is challenging. Herein, a facile hydrothermal method is reported for compositing the NiO nanoparticles with high crystalline graphitic carbon (GC). With superior electronic conductivity, GC is functionalized with active NiO (NiO/GC) to improve electrocatalytic activity both intrinsically and extrinsically. The NiO/GC electrocatalyst exhibits a minimal overpotential of 260 mV and 177 mV at 10 mA cm−2 with a Tafel slope value of 63 mV dec−1 and 119 mV dec−1 during the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), respectively. The alkaline water electrolysis system designed with NiO/GC as a bifunctional electrocatalyst performs overall water splitting at a low cell voltage of 1.7 V to deliver 10 mA cm−2.

Hierarchical consistency tracking (HCT) model: A rapid and efficient approach for dynamic thermal analysis of alkaline water electrolysis

The intermittent power output of renewable energy sources necessitates alkaline water electrolysis (AWE) systems to operate under fluctuating conditions, emphasizing the need for a comprehensive understanding of their dynamic thermal behavior. However, current methods for dynamic thermal detection in AWE systems suffer from limitations such as limited temperature signals, insufficient temperature distribution analysis, and a lack of dynamic thermal analysis methods. To address these challenges, a hierarchical consistency tracking (HCT) model is proposed, which incorporates three hierarchical procedures: segmental characteristic temperatures (CT) extraction, surface consistency extraction, and dynamic consistency tracking. By analyzing infrared images captured from the electrolyzer, the HCT model extracts CT, quantifies temperature distribution patterns, and enables the assessment of thermal consistency during dynamic processes. This model offers a rapid and efficient approach with several advantages, including a more comprehensive understanding of temperature distribution, quantification of dynamic thermal consistency, and optimization of operating parameters and internal structures to improve temperature uniformity. Moreover, the HCT model provides a cost-effective and efficient solution for thermal characterization by eliminating the need for additional temperature sensors during dynamic operation.

Optimization of alkaline electrolyzer operation in renewable energy power systems: A universal modeling approach for enhanced hydrogen production efficiency and cost-effectiveness

This study presents a comprehensive analysis of an Alkaline Water Electrolysis System (AWES) for hydrogen production, focusing on thermal balance, operating conditions, efficiency, and lifecycle cost. A thermal balance model was developed and further refined using machine learning techniques based on experimental data, to accurately calculate electrolysis power, cooling requirements, and temperature maintenance, enabling cost-effective operation. This study provides insights for optimizing AWES performance and economic feasibility in hydrogen production. Selecting appropriate operating conditions considering current density, inlet temperature, and electricity price is crucial. Implementing these optimizations improves energy efficiency, reduces lifecycle hydrogen production costs, and enables integration with renewable energy systems.

A thin and flexible composite membrane with low area resistance and high bubble point pressure for advanced alkaline water electrolysis

Green hydrogen plays a pivotal role in the decarbonizing process. Hydrogen production by alkaline water electrolysis (AWE) is the most promising way for large-scale hydrogen production because of the merits of high-efficient and cost-effective. In the AWE system, the membrane is used to conduct hydroxide ions and block the interpenetration of hydrogen and oxygen, which is a crucial component. However, the current membranes are limited by either the high area resistance or inadequate gas-blocking ability. Herein, we proposed a thin (∼268 μm) and flexible composite membrane featuring both low area resistance (∼0.14 Ω cm2 in 30 wt% KOH solution) and high bubble point pressure (BPP, ∼24 bar). When applied in alkaline water electrolysis, the composite membrane with the commercial NiMo and NiFe catalysts shows a current density of 2.3 A cm-2 at the voltage of 2 V in 30 wt% KOH solution at 80 °C, surpassing the capabilities of the ZIRFON UTP 500 membrane. Notably, the in-situ gas purity tests reveal an impressive hydrogen purity of ∼99.997%, much higher than that of the state-of-the-art membranes. Additionally, the stability tests conducted more that 600 h at 80 °C without performance attenuation highlight the membrane's competitiveness and promising commercial prospects.

Correlating the influence of the purity of hydrogen produced by a surplus power on the production of green ammonia

Abstract Carbon dioxide is the primary greenhouse gas contributing to climate change. Furthermore, due to the surplus power generated by renewable energy resources, various approaches have been developed to handle this overproduction. This study verifies via a correlation analysis the influence of the purity of hydrogen produced by a continuous surplus power on the sustainable ammonia production. The influence of the temperature and pressure of the hydrogen treatment system on the purity of the hydrogen gas produced in the alkaline water electrolysis system was investigated, where the purity increased with a decrease in temperature and an increase in pressure. The purity of the produced ammonia was positively correlated with the purity of hydrogen. Furthermore, the energy consumption of the ammonia production process increased when the purity of hydrogen was low. In the case of storing the surplus power as ammonia, the effect of hydrogen purity was less affected by the hydrogen production system than by the ammonia production system, and it was thus concluded that it is more desirable to determine the hydrogen purity in the hydrogen production system prior to employing it in the ammonia production system.

Titanium germanium carbide MAX phase electrocatalysts for supercapacitors and alkaline water electrolysis processes

Developing electrochemically active, stable, and low-cost electrocatalysts for electrochemical devices is a significant breakthrough. Accordingly, MAX phases, emerging three-dimensional materials, are considered outstanding candidates due to their excellent electrocatalytic and electrochemical properties. Herein, the titanium germanium carbide (Ti3GeC2) MAX phase with a layered structure manufactured through reactive sintering was regarded as the electrocatalyst. In the current work, the electrocatalytic activity of the Ti3GeC2 was investigated for electrochemical devices. It was observed that adding activated carbon to the Ti3GeC2 enhances the conductivity and active area, leading to an excellent specific capacitance (349 Fg-1) for supercapacitors. Also, the capacitance of Ti3GeC2 was increased by increasing the number of cyclic voltammetry cycles. In another application, Ti3GeC2 showed substantial activity for hydrogen and oxygen evolution reactions in alkaline media. As a result, the alkaline water electrolysis system using Ti3GeC2 showed the highest current density of 10 mA cm−2 at 1.36 V and outstanding stability over 400 cycles.

Hydrogen production by water electrolysis technologies: A review

Hydrogen as an energy source has been identified as an optimal pathway for mitigating climate change by combining renewable electricity with water electrolysis systems. Proton exchange membrane (PEM) technology has received a substantial amount of attention because of its ability to efficiently produce high-purity hydrogen while minimising challenges associated with handling and maintenance. Another hydrogen generation technology, alkaline water electrolysis (AWE), has been widely used in commercial hydrogen production applications. Anion exchange membrane (AEM) technology can produce hydrogen at relatively low costs because the noble metal catalysts used in PEM and AWE systems are replaced with conventional low-cost electrocatalysts. Solid oxide electrolyzer cell (SOEC) technology is another electrolysis technology for producing hydrogen at relatively high conversion efficiencies, low cost, and with low associated emissions. However, the operating temperatures of SOECs are high which necessitates long startup times. This review addresses the current state of technologies capable of using impure water in water electrolysis systems. Commercially available water electrolysis systems were extensively discussed and compared. The technical barriers of hydrogen production by PEM and AEM were also investigated. Furthermore, commercial PEM stack electrolyzer performance was evaluated using artificial river water (soft water). An integrated system approach was recommended for meeting the power and pure water demands using reversible seawater by combining renewable electricity, water electrolysis, and fuel cells. AEM performance was considered to be low, requiring further developments to enhance the membrane's lifetime.

Investigation of the operation characteristics and optimization of an alkaline water electrolysis system at high temperature and a high current density

Increasing the operating temperature of water electrolysis is an effective way to improve its performance. When the available region of the operating current density is extended, the stack can generate an increased amount of hydrogen. This can directly contribute to green hydrogen being highly competitive compared to other kinds of hydrogen. In this study, numerical analysis was conducted to investigate and optimize the operational characteristics of alkaline water electrolysis (AWE) under high temperature and high current density conditions. The numerical model of the AWE developed in our previous study has been upgraded by considering the crossover of hydrogen gas through the membrane to more accurately determine the Faraday efficiency of hydrogen production and the available safe operating range. Simulation results show that saturated vapor generation significantly affected the performance of both stack and system components in high-temperature environments. Therefore, pressurization is important to ensure the high efficiency of high-temperature water electrolysis, but it must be appropriately adjusted in consideration of gas crossover. In this study, the highest efficiency of 78.52% was captured at 120 °C and 10 bar for 1 A/cm2 operation.

Analysis of the total energy consumption through hydrogen compression for the operating pressure optimization of an alkaline water electrolysis system

Analysis of the total energy consumption through hydrogen compression for the operating pressure optimization of an alkaline water electrolysis system

Experimental and modeling study on energy flow of 250 kW alkaline water electrolysis system under steady state conditions and cold start process

Improving the energy utilization efficiency of alkaline water electrolysis system (AWE) is one of the urgent problems at this stage. This study explores the heat flow and energy distribution under steady state and cold start processes by establishing a multi-physical field coupled AWE system model including heat transfer, mass transfer and electrochemistry, based on this, the methods to improve energy utilization efficiency are proposed. The system power consumption at full load is 272.7 kW, the electrolyzer accounts for up to 88.4%, of which, the useless heat production and parasitic current are the main factors that cause the electrolyzer energy loss, accounting for 21.2% and 3.1% of the total power consumption, respectively. The electrolyzer useless heat production also significantly contributes to the chiller energy consumption, which accounts for 5% of the system power consumption. Improving the electrolyzer performance and minimizing its heat production is essential to optimize the system efficiency. During the AWE cold start process, the constant voltage control has a shorter cold start time than the constant current control, but their power consumption differences in terms of heat and hydrogen production are small. Reducing the system thermal capacity is extremely effective in speeding up the cold start process compared to optimizing the power load type, which can cut the cold start time to less than 1 h.

Model-Based Analysis and Optimization of Pressurized Alkaline Water Electrolysis Powered by Renewable Energy

Alkaline water electrolysis is a key technology for large-scale hydrogen production. In this process, safety and efficiency are among the most essential requirements. Hence, optimization strategies must consider both aspects. While experimental optimization studies are the most accurate solution, model-based approaches are more cost and time-efficient. However, validated process models are needed, which consider all important influences and effects of complete alkaline water electrolysis systems. This study presents a dynamic process model for a pressurized alkaline water electrolyzer, consisting of four submodels to describe the system behavior regarding gas contamination, electrolyte concentration, cell potential, and temperature. Experimental data from a lab-scale alkaline water electrolysis system was used to validate the model, which could then be used to analyze and optimize pressurized alkaline water electrolysis. While steady-state and dynamic solutions were analyzed for typical operating conditions to determine the influence of the process variables, a dynamic optimization study was carried out to optimize an electrolyte flow mode switching pattern. Moreover, the simulation results could help to understand the impact of each process variable and to develop intelligent concepts for process optimization.

Dynamic modelling of an alkaline water electrolysis system and optimization of its operating parameters for hydrogen production

Dynamic modelling of an alkaline water electrolysis system and optimization of its operating parameters for hydrogen production

Tert-Butyl-alcohol-induced breakage of the rigid bubble layer that causes overpotential in the oxygen evolution reaction during alkaline water electrolysis

Alkaline water electrolysis (AWE) requires low current densities (≤0.6–1.0 A cm–2) to proceed efficiently because a dense bubble layer covers the electrode surface at high current densities. Herein, we report on a simple method for promoting bubble detachment from an electrode surface and reducing the overpotential of the oxygen evolution reaction during AWE. This method involves the addition of tertiary alcohols that exhibit surfactant properties and are resistant to oxidation in the electrical field. Based on a dual-bubble layer model for reactant transfer, the increased ohmic resistance and diffusion resistance of the hydroxide ions induced by the bubbles attached to the electrode surface were alleviated by adding tert-butyl alcohol (TBA), while also retaining the charge transfer resistance. Consequently, the overpotential was reduced drastically at current densities of >2.0 A cm−2, and the tertiary alcohol effect was stable over several hours. The decomposition product of TBA was not detected after electrolysis at 3.0 A cm−2 for 10 h. We clarified that the addition of tertiary alcohols will improve the current density and productivity of the AWE system.

Magnetic field Pre-polarization enhances the efficiency of alkaline water electrolysis for hydrogen production

Water electrolysis can become a promising mean to produce clean hydrogen. Improving the efficiency of water electrolysis is of great significance for accelerating the development of large-scale hydrogen production equipment and low-carbon economy. This paper presents a novel method for enhancing the alkaline water electrolysis (AWE) efficiency by Magnetic Field Pre-polarization (MFPP), which is easily matched to high-power industrial AWE system. Firstly, compactly-assembled structure and energy consumption of industrial AWE electrolyzer are analyzed. Secondly, the MFPP method was proposed to enhance the efficiency of AWE. The structure parameters of MFPP equipment are optimized by simulation and the physical model is designed. Finally, a system-level equipment was developed to evaluate the effect of MFPP on the performance of the alkaline water electrolysis (AWE) system. Repeatability measurement, I-V characteristic analysis and error statistics were carried out under different working conditions. The effectiveness of MFPP method has been proved on industrial electrolyzer (with 22 cells). Compared with the electrolysis voltage of 40 V-42 V@22_cell, the efficiency improvement is more significant when the voltage is in the range of 42–46 V@22_cell. Under the 0.75 T MFPP, the maximum hydrogen production efficiency increased by 9.2 %. The mean absolute deviation (MAD) of test results is less than 1.88 (with a proportion of 0.11 %) and the mean squared error (MSE) is less than 0.49.