Water Electrolysis System Research Articles

An Analysis of the Conceptual and Functional Factors Affecting the Effectiveness of Proton-Exchange Membrane Water Electrolysis

Hydrogen has the potential to decarbonize the energy and industrial sectors in the future, mainly if it is generated by water electrolysis. The proton-exchange membrane water electrolysis (PEMWE) system is regarded as a propitious technology to produce green hydrogen from water using power supplied by renewable energy sources. It offers many benefits, such as high performance, high proton conductibility, quick response, compact size, and low working temperature. Many conceptual and functional parameters influence the effectiveness of PEM, including temperature, pressure of anode and cathode regions, water content and wideness of the layer, and cathode and anode exchange current density. In addition, the anodic half-reaction (known as the oxygen evolution reaction (OER)) and cathodic half-reaction (known as the hydrogen evolution reaction (HER)) perform an important function in the development of PEMWE. The current study aims to present these parameters and discuss their impacts on the performance of PEM. Also, the PEM efficiency is presented. The different methods used to enhance the scattering of OER electrocatalysts and minimize catalyst loading to minimize the price of PEMWE are also highlighted. Moreover, the alternative noble metals that could be used as electrocatalysts in HER and OER to minimize the cost of PEM are reviewed and presented.

Parameter Analysis of Anion Exchange Membrane Water Electrolysis System by Numerical Simulation

Anion exchange membrane electrolysis, which combines the advantages of both alkaline electrolysis and proton-exchange membrane electrolysis, is a promising technology to reduce the cost of hydrogen production. The present work focused on the study of the electrochemical phenomena of AEM electrolysis and the investigation of the key factors of the AEM hydrogen production system. The numerical model is established according to electrochemical reactions, polarization phenomena, and the power consumption of the balance of plant components of the system. The effects of operation parameters, including the temperature and hydrogen pressure of the electrolyzer, electrolyte concentration, and hydrogen supply pressure on the energy efficiency are studied. The basic electrochemical phenomena of AEM water electrolysis cells are analyzed by simulations of reversible potential and activation, and ohmic and concentration polarizations. The results reveal that increasing the operating temperature and hydrogen production pressure of the AEM electrolyzer has positive effects on the system’s efficiency. By conducting an optimization analysis of the electrolyzer temperature—which uses the heat energy generated by the electrochemical reaction of the electrolyzer to minimize the power consumption of the electrolyte pump and heater—the AEM system with an electrolyzer operating at 328 K and 30 bar can deliver hydrogen of pressure up to 200 bar under an energy efficiency of 56.4%.

Fluorine-Induced Lattice Oxygen Participation in 2D Layered Double Hydroxide/MXene Hybrids for Efficient Oxygen Evolution.

In oxygen evolution reaction (OER), the participation of lattice oxygen can break the limitation of adsorption evolution mechanism, but the activation of lattice oxygen remains a critical challenge. Herein, a surface fluorinated highly active 2D/2D FeNi layered double hydroxide/MXene (F-LDH/MX) is demonstrated, boosting OER with the enhanced lattice-oxygen-mediated path. The introduction of fluorine promotes the self-evolution of catalyst in an alkaline environment, even without an external current. It further accelerates the formation of active metal oxyhydroxides with abundant oxygen vacancies under the operating potential. The introduced oxygen vacancy activates the lattice oxygen, increasing the proportion of lattice oxygen mechanism in OER. Owing to the synergistic effects of the 2D/2D hierarchical structure and the modulated active surface, F-LDH/MX possesses excellent electrochemical performances, including a low overpotential of 251 mV at 10 mA cm-2, a low Tafel slope of 40.28 mV dec-1, and robust stability. The water electrolyzer system with F-LDH/MX as the anode offers the benchmark current density at a low cell voltage of 1.53 V, while the Zn-air battery with F-LDH/MX as the air electrode exhibits a higher power density of 75.43 mW cm-2. This study presents a promising strategy to design highly active electrocatalysts for energy conversion and storage.

Optimization of chemical engineering control for large-scale alkaline electrolysis systems based on renewable energy sources

In the context of renewable energy, dynamic control is crucial for large-scale alkaline water electrolysis systems. Under traditional Proportional-Integral-Derivative (PID) control, the system's temperature and impurity levels may exceed safe limits during sudden load changes, compromising system safety. Therefore, this study proposes a control strategy based on mathematical models of system temperature and impurities, including Model Predictive Control (MPC) for temperature and Optimal Curve Tracking (OCT) for impurities. The MPC controller offsets the disturbances in temperature caused by current fluctuations through state prediction, while the OCT controller ensures that impurity levels remain within safe limits. Real-time application of these control strategies is achieved through MATLAB-PLC communication, validating controller performance. Experimental results show that the MPC controller exhibits excellent dynamic response and stability in controlling the stack temperature, with a maximum temperature peak deviation of only 2.9 K and a temperature fluctuation range of 5.9 K. This represents a reduction of 1.6 K in peak deviation compared to traditional PID controllers and significantly decreases the temperature fluctuation range. The OCT controller also demonstrates good safety and stability in controlling hydrogen to oxygen (HTO) impurity levels, consistently maintaining the HTO content at the set upper limit of 1.5%, thereby expanding the safe operational range of the system and reducing the need for frequent adjustments to the system setpoints.

Integrated solar-powered freeze desalination and water electrolysis system with energy recovery and storage for sustainable agriculture in desert environments

Integrated solar-powered freeze desalination and water electrolysis system with energy recovery and storage for sustainable agriculture in desert environments

Enhanced Oxygen Evolution Reaction Performance of NiMoO4/Carbon Paper Electrocatalysts in Anion Exchange Membrane Water Electrolysis by Atmospheric-Pressure Plasma Jet Treatment.

NiMoO4 was grown on carbon paper (CP) by a hydrothermal method. A rapid and high-temperature atmospheric-pressure plasma jet (APPJ) process was used to generate more oxygen-deficient NiMoO4 on the CP surface to serve as an electrode material for the oxygen evolution reaction (OER). After 60 s of APPJ treatment, the overpotential of the electrode at 100 mA/cm2 decreased to 790 mV and that at 10 mA/cm2 decreased to 368 mV. Additionally, the charge transfer resistance decreased from 2.8 to 1.2 Ω, indicating that APPJ treatment effectively reduced the electrode overpotential and impedance. The effect of NiMoO4/CP/APPJ-60 s on the anion exchange membrane water electrolysis (AEMWE) system was also tested. At a system temperature of 70 °C and current density of 100 mA/cm2, the energy efficiency reached 95.1%, and the specific energy consumption decreased from 4.02 to 3.83 kWh/m3. These results demonstrate that the APPJ-treated NiMoO4/CP electrode can effectively enhance the OER performance in water electrolysis and improve the energy efficiency of the AEMWE system. This approach shows promise in replacing precious metal electrodes, thereby potentially reducing the cost and providing an environmentally friendly alternative.

Tantalum-induced reconstruction of nickel sulfide for enhanced bifunctional water splitting: Separate activation of the lattice oxygen oxidation and hydrogen spillover

Designing highly active and stable bifunctional catalysts for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) under alkaline conditions is crucial for sustainable overall water splitting. Herein, we present a targeted reconstruction of Ni3S2 by introducing tantalum, achieving remarkable overall water splitting performance through the separate activation of the lattice oxygen mechanism and hydrogen spillover. Electrochemical Mass Spectrometry and in-situ Raman spectroscopy reveal that tantalum induces Ni3S2 to reconstruct into nickel hydroxide during OER, thereby enhancing catalytic activity via the activation of the lattice oxygen mechanism. In the corresponding HER, tantalum promotes the reconstruction of Ni3S2 into oxysulfide, facilitates hydrogen spillover, and acts as an anchor to shorten the spillover distance, improving the HER catalytic performance, as verified by the kinetic isotope effect and theoretical calculations. Therefore, the catalyst-based anion exchange membrane water electrolyzer system achieves a current density of 1 A cm−2 at just 1.97 V, maintaining continuous operation for 500 h. This study offers new insights into the design of bifunctional catalysts, advancing the development of efficient and robust overall water splitting catalysts.

Intermittent polarity inversion of stainless-steel paired electrodes for efficient and durable water electrolysis

Designing robust and cost-effective catalysts through straightforward and replicable techniques is crucial for advancing water electrolysis. In this study, we introduce a dynamic polarization control method for the continuous activation of stainless steel (SS) substrates to achieve high water-splitting performance and durability. By applying periodic inverted current density during high-current–density operation (0.5 or 1 A cm−2) on bare SS adopted as both cathode and anode substrates, a NiFe-based oxide structure favorable for the hydrogen evolution reaction is formed at the cathode, while a Fe-incorporated NiOOH structure with high efficacy for the oxygen evolution reaction develops at the anode. Implemented in an anion exchange membrane water electrolysis system, this inverted polarization approach applied for the SS paired electrolyzer system successfully maintains a cell voltage of approximately 1.9 V for 500 h at a current density of 1 A cm−2 using bare SS for both electrodes.

Membrane-Free Water Electrolysis for Hydrogen Generation with Low Cost.

Conventional water electrolysis relies on expensive membrane-electrode assemblies and sluggish oxygen evolution reaction (OER) at the anode. Here, we develop an innovative and efficient membrane-free water electrolysis system to overcome these two obstacles simultaneously. This system utilizes the thermodynamically more favorable urea oxidation reaction (UOR) to generate clean N2 over a new class of Cu-based catalyst (CuXO), fundamentally eliminating the explosion risk of H2 and O2 mixing while removing the need for membranes. Notably, this membrane-free electrolysis system exhibits the highest H2 Faradaic efficiency among reported membrane-free electrolysis work. In situ spectroscopic studies reveal that the new N2Hy intermediate-mediated UOR mechanism on the CuXO catalyst ensures its unique N2 selectivity and OER inertness. More importantly, an industrial-type membrane-free water electrolyser (MFE) based on this system successfully reduces electricity consumption to only 3.87 kWh Nm-3, significantly lower than the 5.17 kWh Nm-3 of commercial alkaline water electrolyzers (AWE). Comprehensive techno-economic analysis (TEA) suggests that the membrane-free design and reduced electricity input of the MFE plants reduce the green H2 production cost to US$1.81 kg-1, which is lower than those of grey H2 while meeting the technical target (US$2.00-2.50 kg-1) set by European Commission and United States Department of Energy.

Membrane‐Free Water Electrolysis for Hydrogen Generation with Low Cost

Conventional water electrolysis relies on expensive membrane‐electrode assemblies and sluggish oxygen evolution reaction (OER) at the anode. Here, we develop an innovative and efficient membrane‐free water electrolysis system to overcome these two obstacles simultaneously. This system utilizes the thermodynamically more favorable urea oxidation reaction (UOR) to generate clean N2 over a new class of Cu‐based catalyst (CuXO), fundamentally eliminating the explosion risk of H2 and O2 mixing while removing the need for membranes. Notably, this membrane‐free electrolysis system exhibits the highest H2 Faradaic efficiency among reported membrane‐free electrolysis work. In situ spectroscopic studies reveal that the new N2Hy intermediate‐mediated UOR mechanism on the CuXO catalyst ensures its unique N2 selectivity and OER inertness. More importantly, an industrial‐type membrane‐free water electrolyser (MFE) based on this system successfully reduces electricity consumption to only 3.87 kWh Nm−3, significantly lower than the 5.17 kWh Nm−3 of commercial alkaline water electrolyzers (AWE). Comprehensive techno‐economic analysis (TEA) suggests that the membrane‐free design and reduced electricity input of the MFE plants reduce the green H2 production cost to US$1.81 kg−1, which is lower than those of grey H2 while meeting the technical target (US$2.00–2.50 kg−1) set by European Commission and United States Department of Energy.

Water electrolysis using fluorine-free, reinforced sulfo-phenylated polyphenylene membranes

Fluorinated proton-exchange membranes (PEMs), such as Nafion™, which is the current state-of-the-art polymer, present environmental challenges, driving the need for more sustainable alternatives for proton-exchange membrane water electrolysis (PEMWE) systems. However, fluorine-free membranes like sulfo-phenylated polyphenylene biphenyl (sPPB-50) often suffer from mechanical instability, excessive swelling, and limited cell durability, which hinder their practical applications. This study explores reinforced fluorine-free sulfo-phenylated polyphenylene membranes (Pemion™) with thicknesses of 15 µm (Pemion-15) and 40 µm (Pemion-40) as a potential solution to these issues. Pemion membranes were compared with both sPPB-50 and Nafion™ 112 (N112), focusing on key properties such as water uptake, dimensional swelling, proton conductivity, and durability in PEMWE applications. The results show that Pemion-reinforced membranes exhibit good performance for PEMWE allowing high current densities at lower voltages. Pemion-40 exhibited a low hydrogen gas crossover compared to sPPB-50 and N112. Under a constant current of 1 A cm−2, Pemion-40 exhibited a voltage loss rate of 1.46 mV h−1 over 100 h of operation. This study highlights the importance of structural reinforcement in enhancing the stability and efficiency of fluorine-free membranes, providing a promising route for sustainable alternatives in PEMWE systems.

Insights into kinetic and transfer mechanisms for alkaline decoupled water electrolysis based on distribution of relaxation times

Electrochemical water splitting is crucial for the decarbonization of industrial processes and the coupling of renewable energy sources. Evaluation of individual HER and OER contributions to the transfer process is essential for optimizing electrolysis system performance. This study uses nickel-cobalt layered double hydroxide (NiCo-LDH) as a solid-state redox mediator (SRM), achieving efficient H2 and O2 separation. This study provides an in-depth analysis of kinetic and ion/charge/mass transfer mechanisms linked to various characteristic impedances in alkaline decoupled water electrolysis (DWE) system by integrating Electrochemical Impedance Spectroscopy (EIS) and Distribution of Relaxation Times (DRT) methods. The characteristic frequency evolution is consistent with the charge-discharge state of SRM and mass transfer frequency is related to the bubble size and gas diffusion rate of electrocatalysts at different current densities. The charge transfer Rct dominates the total polarization impedance in decoupled HER, and mass transfer Rm decreases remarkably in decoupled OER. OER shows lower Rct with Fe species existence and lower total polarization impedance than HER. Rm in decoupled HER increases by 38.24% and OER by 29.82% during prolonged decoupled test. This study provides valuable insights into the impedance contributions and kinetic mechanisms through novel electrolysis approaches, guiding further optimization of decoupled electrolyzer and electrode.

Efficient Oxygen Evolution Reaction on Catalyst‐Free Acid‐Functionalized Plastic Chip Electrodes

Innovative electrode design is critical for improving the oxygen evolution reaction (OER) and meeting rising global energy demands. Despite the development of numerous carbon materials for water splitting, their potential is hampered by sluggish kinetics, primarily due to high activation energy compounded by various smaller factors, including additives or binders used in electrode modification. To address these limitations, a catalyst‐free plastic chip electrode (PCE) for OER is developed. PCE is functionalized by oxidizing it in acidic media at 1.8 V versus Ag/AgCl and eliminates the need for additives, offering a more accurate industrial representation. The oxidation process enhances the electrode's surface area and introduces electrochemically active oxygen‐containing functional groups. Characterization of the modified PCE is conducted using scanning electron microscope, X‐ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, X‐ray diffraction, Raman, and thermogravimetric analysis, while electrolyte analysis utilizes UV–vis spectroscopy and NMR. The PCE oxidized for 6 h (PCE@6) demonstrates improved OER performance, with an onset overpotential of 260 mV, an overpotential of 1.06 V versus reversible hydrogen electrode at 10 mA cm−2, and a Tafel slope of 494 mV decade−1. The modified PCE reduces overpotential and minimizes bubble formation, enhancing efficiency and showcasing its potential as a cost‐effective solution for alkaline water electrolysis systems.

An Overview of Different Water Electrolyzer Types for Hydrogen Production

While fossil fuels continue to be used and to increase air pollution across the world, hydrogen gas has been proposed as an alternative energy source and a carrier for the future by scientists. Water electrolysis is a renewable and sustainable chemical energy production method among other hydrogen production methods. Hydrogen production via water electrolysis is a popular and expensive method that meets the high energy requirements of most industrial electrolyzers. Scientists are investigating how to reduce the price of water electrolytes with different methods and materials. The electrolysis structure, equations and thermodynamics are first explored in this paper. Water electrolysis systems are mainly classified as high- and low-temperature electrolysis systems. Alkaline, PEM-type and solid oxide electrolyzers are well known today. These electrolyzer materials for electrode types, electrolyte solutions and membrane systems are investigated in this research. This research aims to shed light on the water electrolysis process and materials developments.

Doping-mediated interface engineered Ni3S2: Economically viable electrochemical methanol-mediated water splitting

Electrochemical water splitting is the front runner to meet the global green hydrogen demand. The development of a noble metal-free earth-abundant electrocatalyst is desired to rationalize an economically viable electrochemical water-splitting system. The sluggish anodic oxygen evolution reaction (OER) is the bottleneck of the electrochemical water-splitting system. Herein, to improve OER kinetics, group VIB elements such as chromium (Cr), molybdenum (Mo), and tungsten (W) doped nickel sulfides (Ni3S2) nanosheets (NSs) are synthesized by two-step hydrothermal method to modulate the intrinsic electrocatalytic activity of the pure Ni3S2. Among all the doped samples, the Cr-doped Ni3S2 catalyst exhibited excellent OER with an ultra-low overpotential of 248 mV and MOR with a potential of 1.36 V @ 10 mA cm−2 vs RHE achieving a lower Tafel slope of 95.5 mV/dec and 46.4 mV/dec and outstanding durability with negligible degradation respectively. Furthermore, the Pt/C||Cr-Ni3S2 (1.48 V) system outperforms commercial Pt/C||RuO2 (1.53 V @ 10 mA cm−2) in a two-electrode configuration. The methanol-mediated hybrid water splitting system only warranted a cell voltage of 1.38 V to attain 10 mA cm−2 for the Pt/C||Cr-Ni3S2 system in the presence of 0.1 M methanol (MeOH). The methanol oxidation reaction (MOR) mediated the hybrid water electrolyzer system demonstrates reduced operation cell voltage while additionally electro-synthesizing formate as a value-added chemical. The overall work is motivated to rationalize the importance of doping-mediated interface-engineered catalyst synthesis to improve the electrocatalytic efficiency of the hybrid water electrolyzer.

Development of a Superior Anion Exchange Membrane with Hyperbranched Polymer for Anion Exchange Membrane Water Electrolysis

The production of hydrogen using membrane-based electrolyzersposes significant advantages and benefits compared to traditionalelectrolysis methods. Among the electrolyzers, anion exchangemembrane water electrolysis (AEMWE) has emerged as one of thepromising technologies owing to its unique advantages. However,the development of efficient AEMs for water electrolysis presentssignificant challenges, particularly in achieving enhanceddimensional stability and conductivity. In this study, ahyperbranched polyesteramide (HPEA) was synthesized andblended with poly(ether sulfone) (PES) to address the challenges.The resulting QPES-HPEA blend membrane exhibited a lowswelling ratio and high water uptake, which are critical formaintaining dimensional stability and enhancing the hydroxide iontransport efficiency of AEM. The enhanced physical properties andoptimized structure of the membrane make it a promising candidatefor next-generation AEMs in water electrolysis systems.

Investigation of the Effect of Initial Anode Structures on the Durability of Water Electrolysis Cells

Water electrolysis systems directly using renewable energy have been focused on this study. From our previous finding in the long-term accelerated voltage fluctuation test using actual wind power voltage fluctuations, increasing hydrophobicity and reducing gas stagnation within the anode catalyst layer were suggested. Then, controlling hydrophobic characters was considered in this study. Hydrophobic materials, such as polytetrafluoroethylene and polypyrrole, were chosen and added to the anode layers. As expected, the addition of 30% polytetrafluoroethylene improved hydrophobicity but also increased ohmic resistance, lowering IV performance. On the other hand, the use of polypyrrole was found to improve hydrophobicity while maintaining IV performance. However, the slight increase in activation and diffusion overvoltages was also observed, which was most likely owing to poor distribution of polypyrrole in the anode layer and possibly improved by adding a milling process.

Room-temperature rapid oxygen monitoring system in high humidity hydrogen gas environment towards water electrolysis application

Water electrolysis is one of the key processes for carbon-free hydrogen (H2) generation, yet it inherently presents the risk of oxygen (O2) permeation, a significant concern that must be addressed. Contrary to external atmospheric conditions, the environment within a water electrolysis system is characterized exclusively by high-purity H2, little O2, and moisture (H2O). However, there has been limited research on sensors capable of detecting O2 crossover in such a pure H2 atmosphere under high humidity conditions. In this study, we developed an electrolysis O2 monitoring (E-OM) sensor based on a semiconducting metal oxide (SMO) that can operate at a room-temperature with such high humidity through photoactivation with 365 nm LED light. A porous In2O3 nanofilm, prepared by glancing angle deposition (GLAD), was used as the gas sensing material, and copper nanoparticles (Cu NPs) were decorated on the In2O3 surface through electron beam evaporation to accelerate the O2 adsorption. Remarkably, the E-OM sensor showed a humidity-independent response to O2 gas in the H2 atmosphere. Meanwhile, since the response of the E-OM sensor itself was not fast enough for water electrolysis system application, convolutional neural network (CNN)-based signal processing in the time domain was applied. As a result, our E-OM sensor system could predict O2 concentrations from 0 to 2 vol% in an H2 environment with a relative humidity (RH) of 30–90 %, and the detection time was under 5 s. This development could enable safe, rapid, and cost-effective monitoring of O2 crossover in H2 production infrastructure.

Response characteristics of platinum coated titanium bipolar plates for proton exchange membrane water electrolysis under fluctuating conditions

Voltage fluctuations in energy input not only impact the overall hydrogen production efficiency and stability of Proton Exchange Membrane Water Electrolysis (PEMWE) systems but also pose significant challenges to the long-term service life of individual components. This study focuses on the key component − bipolar plates and investigates the response behavior of platinum-coated titanium bipolar plates under simulated fluctuating voltage conditions. By integrating surface phase analysis and electrochemical testing results, this research elucidates the response characteristics of the bipolar plates to different voltage waveforms and frequencies. And the findings hold substantial significance for the upstream energy control in hydrogen production through water electrolysis.

Evaluation of hydrogen evolution activity by bubbles growth rates as descriptor

Evaluation of the electrocatalytic behavior in the high current density region is critical toward the applications in the industrial water electrolysis system. Here, we utilized the bubble growth rate as descriptor for evaluation of hydrogen evolution reaction. Ag electrode was selected as a model electrode. Pressure-controlled cell was used for the evaluation of the bubble behavior under the wider range in the overpotential. Hydrogen bubble evolution behavior was evaluated by video observation under electrochemical potential control. Even in the presence of the complex processes such as nucleation, growth and detachment of the bubbles, the hydrogen evolution behavior is evaluated with respect to the classical Tafel analyses even in high overpotential region. These analyses provide the methods for the rapid screening toward the material discovery of the green hydrogen production in high current density region.