Improving commercial-scale alkaline water electrolysis systems for fluctuating renewable energy: Unsteady-state thermodynamic analysis and optimization

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

The circular economy offers a vital avenue for sustainable development by optimizing resource utilization through reusing and recycling materials. This study focuses on the lifecycle assessment (LCA) of a 5 MW alkaline water electrolysis (AWE) system, emphasizing end-of-life (EoL) strategies, material recovery, and their environmental implications. Focusing on the recycling and reuse of critical materials—including stainless steel and nickel—we argue that enhancing material efficiency in AWE systems can lead to significant reductions in global warming potential (GWP). Our LCA reveals that manufacturing an AWE system from recycled materials results in a 50% decrease in GWP compared to virgin materials. Despite the operational focus of previous studies, our research uniquely incorporates comprehensive EoL considerations, assessing realistic recycling scenarios that highlight potential material recovery and component reuse after the system’s 20-year lifespan. Notably, 77% of materials in the AWE system can be recycled or reused, though the substantial environmental impacts of certain components, particularly the inverter and nickel, necessitate ongoing research and improved recycling technologies. This study underscores the critical role of systematic recycling and the strategic selection of materials to enhance the sustainability profile of hydrogen production technologies. By bridging the gap between operational efficiency and EoL management in AWE systems, our findings contribute to the broader aim of advancing circular economy principles in clean energy transitions. Ultimately, the research emphasizes the need for integrating innovative recycling methods and material reuse strategies to lower carbon footprints and enhance resource security, aligning with sustainable industrial practices and future energy demands.

Power controller design for electrolysis systems with DC/DC interface supporting fast dynamic operation: A model-based and experimental study

Direct operational data-driven workflow for dynamic voltage prediction of commercial alkaline water electrolyzers based on artificial neural network (ANN)

Overview of alkaline water electrolysis modeling

Hydrogen production by water electrolysis technologies: A review

Green hydrogen from water electrolysis coupled with renewable energy is important to overcome the climate change crisis and drives the energy paradigm shift from fossil fuels to eco-friendly energy. Water electrolysis technology was first discovered in the 19th century, and hydrogen for ammonia synthesis was produced in a 165 MW water electrolysis system linked to the Aswan Dam in Egypt in the early 20th century. Currently, research is being actively conducted to implement a water electrolysis system using wind and solar power generation. Among water electrolysis technologies, alkaline water electrolysis has a high technological maturity based on its long history and has the advantage of being highly economical as it does not use precious metal catalysts. However renewable energy has intermittent and irregular power production characteristics, the water electrolysis system must include load-following technology that can follow load changes when connected to renewable energy.Most electrode materials used in alkaline water electrolysis are Ni-based catalysts, and Raney-Ni is an advanced catalyst through the enlarged specific surface area by forming an intermetallic compound layer such as combined with Ni, Al, and Zn on the surface of the Ni electrode. Complex structural electrodes including many pores are generally used in order to realize a zero-gap design in alkaline water electrolysis. VPS (vacuum plasma spraying), PVD (physical vapor deposition), and electroplating are generally used to form Raney-Ni on the surface of a complex structural substrate. However, above mentioned methods have a technical issue for scaling up the area of the electrode because certain conditions must be established in the vacuum chamber or plating bath.In this study, high-performance Raney-Ni electrode was manufactured using a dip-coating method which is to soak the Ni substrate in the slurry consisted of Al powder and polymeric binder. Heat treatment condition was adjusted to find the optimal temperature range for forming suitable Ni-Al intermetallic compounds on the Ni foam (NF) surface. As a result, the appropriate heat treatment temperature was 700 oC, and the prepared electrode was evaluated by linear sweep voltammetry (LSV) to confirm the hydrogen generation reaction performance. The ratio of polymer binder and Al was adjusted to confirm the optimal slurry viscosity to determine the optimal Al loading conditions on the surface of the complex structural NF. LSV, electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV) were conducted to measure HER performance of prepared Raney-Ni electrodes. Fig. 1a. shows a comparison of HER performance between conventional NF and prepared electrode, and the Raney Ni/NF is achieved for low overpotential of more than 170 mV at the current density of -0.3 A/cm2. In addition, the outstanding kinetics of Raney-Ni were confirmed on the Tafel slope (Fig. 1b). Performance improvement was investigated through CV analysis by improving the electrochemically active area due to the Ni-Al intermetallic compound layer formed on the Ni surface. As shown in 1c, the improvement in surface roughness was confirmed through SEM analysis (Fig. 1c).It is important to respond to load fluctuations from renewable energy and the durability of components in electrolytic stack because the value of alkaline water electrolysis lies in high economy for utilizing surplus energy from renewable energy. Durability and responsiveness were confirmed by repeatedly applying currents from -0.03 to -0.3 mA/cm2 of electrolytic cell equipped with the manufactured Raney-Ni electrode for 100 cycles. The excellent HER performance of the Raney-Ni electrode, which was already confirmed through the previous electrochemical analysis, was also confirmed in repeated current application experiments, and excellent responsiveness and durability were also confirmed (Fig. 1d). It was confirmed that the prepared Raney-Ni electrode showed high responsiveness, with voltage appearing immediately according to the applied current (Fig. 1e). Additionally, there was small or no changes of performance despite repeated load fluctuations during 100 cycles (Fig. 1f).In the previous experiment, HER performance, responsiveness, and durability were confirmed through a half-cell experiment. The water electrolysis efficiency of the prepared electrode was confirmed through in-situ analysis, and durability was confirmed for over 100 hours in a constant current condition. In addition, the electrode corrosion resistance caused by shunt current, which is important in the alkaline water electrolysis stack, was confirmed through the alkaline water electrolysis stack equipped with the prepared electrode and stack was performed on/off test over 100 cycles. As a result, the electrode showed only low performance degradation. Finally, an m2 electrode was manufactured by dip-coating method, and to conduct performance evaluation through the sample which is at a random location with a size of 25 cm2. Samples achieved uniform performance, although efficiency difference was observed. Figure 1

<div class="section abstract"><div class="htmlview paragraph">The development of hydrogen economy is an effective way to achieve peak carbon emission and carbon neutralization. Therein, the green production of hydrogen is a prerequisite to reach the goal of decarbonization. As an ideal route, water electrolysis has triggered intense responses under the strong support from policies, which further presenting a phenomenon of water electrolysis equipment manufactures competing to enter the market. However, the extensive growth mode is not conducive to a long term healthy development of the water electrolysis hydrogen production market where products can be sold without requiring compulsory inspection or quality inspection process due to the absence of laws and test & evaluation standards. Considering the market status and technology maturity, the main working principles and characteristics of alkaline water electrolysis (AWE) and proton exchange membrane (PEM) hydrogen production systems are summarized, and the test frameworks of the AWE and PEM hydrogen production systems are mainly introduced. Combining the current technology and market status of water electrolysis system, and referring to the progress of its test & evaluation methods, this study analyzed the test & evaluation methods of the whole product chains from material, single cell, stack, balance of plant (BOP) to the system levels. At the same time, referring to the progresses in the test & evaluation methods, relevant suggestions are given for the establishment of test specifications and standards of water electrolysis hydrogen production system in emerging technology countries. The present study is significant to the improvement of water electrolysis technology and the standardized development.</div></div>

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

Increasing demand for clean energy have triggered researches on alternative energy sources and devices to reduce use of fossil fuel. Hydrogen has been considered as one of the most promising energy source for future due to its high energy density and no air pollutant emission. Splitting water into hydrogen and oxygen is an environmentally friendly method for producing hydrogen gas. This technology can store excess electric energy in the form of chemical bonds of hydrogen, which can resolve an issue about surplus electric power of present renewable energy systems caused by irregular energy source such as airflow and sunlight. Water electrolysis reaction is divided into two half reactions; hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). High overpotential of both HER and OER is the most significant problems to hamper reaction rate and overall efficiency of water electrolysis, especially OER has much higher overpotential than HER. Therefore, recently major efforts have been devoted to exploring active catalysts for the OER in water electrolysis cell. Among many kinds of candidate materials for OER catalyst, cobalt (Co) and various Co based materials, including nanostructured Co3O4, CoSe2, Co based perovskites, CoP, CoB and Co/N-doped carbon, have drawn much attention for use in the alkaline water electrolysis system. These Co based catalysts have low OER ovepotential in alkaline media comparable with precious metal based catalysts, such as IrO2 and RuO2. However, previous studies has focused mainly on the exploring desirable composites for high OER activity without careful mechanistic study. OER mechanism on Co based catalysts and descriptors for designing more efficient catalysts have been unclear yet. Herein, we report novel hybrid type catalysts, which composed of Co and molybdenum carbide (Mo2C), as efficient OER catalysts for alkaline water electrolysis, and evaluate the OER mechanism by investigating the effects of surface acidity of the catalysts on the OER activity in alkaline media. Mo2C has very similar electronic structure with platinum (Pt) group metal. So, it can be promising candidate as an efficient electrocatalyst for water electrolysis system. We synthesized Co-Mo2C hybrids using facile solution based process. Synthesized Co-Mo2C hybrids exhibit enhanced activity and durability compared with Co and ruthenium dioxide (RuO2) catalysts in alkaline media (0.1 and 1 M KOH). This result is ascribed to increase in surface acidity by formation of Co-Mo bimetallic surface on the Co-Mo2C hybrids. Increase in surface acidity leads to increase in hydroxide ion (OH-) adsorption on the catalyst surface, which can promote the OER kinetics in alkaline media. Fig. 1. XRD patterns of Co-Mo2C hybrids. Fig. 2. OER activities of Co-Mo2C hybrids, Co, RuO2 and Mo2C in 0.1 M KOH solution. Figure 1

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

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.

Water electrolysis to produce hydrogen using electric energy is classified into polymer electrolyte water electrolysis, alkaline water electrolysis, solid oxide water electrolysis, and anion exchange membrane water electrolysis according to the type of electrolyte applied. Among them, polymer electrolyte membrane water electrolysis has a lower operating temperature than other types of water electrolysis, and it is possible to operate high-efficiency, high-power density hydrogen production with high current density. In addition, polymer electrolyte water electrolysis has the advantage of fast response to changes in power supply, so empirical studies for green hydrogen production linked to renewable energy are being conducted most actively compared to other water electrolysis. However, research on coupling polymer electrolyte water electrolysis with renewable energy generation with intermittent and irregular power generation has mainly focused on materials, cells, and stacks. In order to keep the hydrogen production reaction of water electrolysis stack stable under the condition of supply power fluctuation, the peripheral devices should be optimally installed and controlled.In this study, a dynamic model of a polymer electrolyte water electrolysis system was developed using Aspen HYSYS®. To accurately predict the hydrogen production efficiency, a stack model considering electrochemical reactions and crossovers through the electrolyte was developed and internalized in a spread sheet. A heat exchanger model from the model library was used to simulate dynamic changes in the electrolyte temperature flowing through the water electrolysis stack. The developed stack model was extended to a system model by integrating the feed pump, separator, condenser, heater, and cooling system. The developed water electrolysis system model was simulated in connection with power ramp variations and renewable energy output, and the optimal operation strategy of each module unit was derived to ensure the stability of high-purity hydrogen production under transient conditions.

Self-repairing hybrid nanosheet anode catalysts for alkaline water electrolysis connected with fluctuating renewable energy

Green hydrogen production via alkaline water electrolysis (AWE) powered by renewable electricity is a promising pathway for societal decarbonization. Despite its technological maturity, widespread AWE adoption would face challenges due to the intermittent nature of renewable energy, necessitating frequent start-up/shutdown (on/off) cycles. During shutdown, reverse currents generated in industrial AWE systems—where cathodes and anodes are interconnected through bipolar plates and electrolyte in manifolds—trigger unfavorable redox reactions, accelerating catalyst degradation.1 This study investigates the reverse current dynamics and potential shifts of AWE electrodes during on/off cycles by employing an internal reversible hydrogen electrode (RHE) reference. We identify the double-layer capacitance (C dl) of the electrodes as a reasonable descriptor influencing potential changes during shutdown, and demonstrate that balancing the C dl values of the anode and cathode prevents unfavorable redox reactions, thereby enhancing electrode stability.Nickel-supported ruthenium (Ru) and lanthanum nickel oxide (LaNiO₃) were chosen as cathode and anode catalysts, respectively. Ru was deposited onto nickel felt (NF) via cathodic electrodeposition, while LaNiO₃ was synthesized by thermal decomposition. The electrodes were assembled into a single-cell configuration, with an external resistance mimicking the electrolyte manifold connection in industrial AWE systems, enabling reverse current measurement. First, electrode potential changes upon shutdown were recorded for various cathode-anode combinations, in which the cathode was fixed to Ru while the anode was varied among LaNiO3, porous nickel electrodeposited on NF, and the bare NF. Notably, as shown in figure 1a, Ru cathode paired with LaNiO₃ anode exhibited significant potential increases (up to 1.0 V vs. RHE) while Ru cathode’s potential increases less when the anode is replaced to the Porous Ni and the bare NF. The potential changes of anode and cathode depend on the balance of their discharge capacities.2 Thus, we employed the C dl of the electrodes as an indicator, which may be proportional to the total charge accumulation that leads to the reverse current during shutdown condition. It was found that C dl widely varies among the tested anodes (Bare NF: 1.7 mF cm−2, Porous Ni: 41 mF cm−2, LaNiO3: 280 mF cm−2) while the cathode was maintained to Ru (141 mF cm−2).Stability test with dynamic on (CP 1 A cm−2 10 min) and off cycles revealed that the Ru cathode activity deteriorated with LaNiO3 anode (figure 1b) due to Ru dissolution at the resting potentials above 1.0 V vs. RHE as shown in figure 1a. This is consistent with previous study on Ru’s CV which clarified Ru dissolution in highly alkaline solution as a ruthenate RuO4 2− species around 1.0 V vs. RHE.3 However, as the grey plot shows, pairing the Ru cathode with NF substrates (lower C dl) mitigated potential increases upon on/off cycles, preserving catalyst stability. This is because unlike the case of LaNiO3, Ru cathode’s potential did not reach 1.0 V vs. RHE upon shutdown. To address the issue caused by LaNiO3 catalysts, we developed a porous RuNi catalyst with a higher C dl (464.4 mF cm⁻²) via cathodic electrodeposition in a mixture of NiCl2 and RuCl3 solution. The porous RuNi potential during shutdown was successfully maintained below 0.5 V vs. RHE, which is below the dissolution threshold, even when paired with LaNiO3 anode. The porous RuNi catalyst exhibited excellent stability under dynamic conditions (green symbols in figure 1c), validating the proposed strategy.Finally, a linear correlation between the ratio of potential shifts (ΔE a/ΔE c) and C dl ratios (C dlc/ C dla) was observed (figure 1c), confirming that the C dl reasonably represents the charge accumulation. Here, subscripts ‘a’ and ‘c’ indicate the anode and the cathode, respectively.This work highlights the critical role of C dl in determining electrode potential changes during shutdown. By balancing anode and cathode C dl values, we successfully mitigated unfavorable redox reactions and prolonged catalyst lifespan in AWE systems operating under intermittent conditions. These findings provide valuable insights for optimizing electrode design in dynamic water electrolysis processes.Reference: A. Haleem et al., J. Power Sources 2022, 535, 231454.Oda et al., Electrocatalysis 2023, 14, 499–510.Chalupczok et al, Int. J. Electrochem. 2018, 1273768. Figure 1