Alkaline Water Electrolysis Research Articles

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.

Integration of Multifunctionality in a Colloidal Self‐Repairing Catalyst for Alkaline Water Electrolysis to Achieve High Activity and Durability

Self‐repairing catalysts are useful for achieving alkaline water electrolyzers with long lifetimes under intermittent operation. However, rational methodologies for designing self‐repairing catalysts have not yet been established. Herein, hybrid cobalt hydroxide nanosheets (Co‐ns), with a high deposition (repairing) rate, and β‐FeOOH nanorods (Fe‐nr), with high oxygen evolution reaction (OER) ability, are electrostatically self‐assembled into composite catalysts. This strategy is developed to integrate multifunctionality in self‐repairing catalysts. Positively charged Co‐ns and negatively charged Fe‐nr form uniform composites when dispersed in an electrolyte. These composites are electrochemically deposited on a nickel electrode by electrolysis at 800 mA cm−2. Co‐ns form a conductive mesoporous assembly of CoOOH nanosheets as a support. Fe‐nr are then distributed on the CoOOH nanosheets as active sites for the OER. Because of the high deposition rate of Co‐ns, the amount of Fe‐nr deposited increases 22 times compared to when Fe‐nr is deposited alone, and the OER current density increases 14 times compared to that of Co‐ns alone. The composite self‐repair catalyst shows the highest activity and durability under an accelerated durability test (ADT), and its degradation rate decreases from 84 μV cycle−1 (Fe‐nr only) to 60 μV cycle−1 (composite catalyst) under ADT conditions without repair.

Unveiling the bi-functional electrocatalytic properties of rhenium di-sulfide nanostructures towards the development of high-rate alkaline water electrolyzer

Alkaline water electrolyzer (AWE) offers a unique solution for generating hydrogen (H2) gas via an electrochemical water-splitting process. The major drawback of the AWE is its limitations in driving high-current densities, an important criterion for the industry standard. In this work, we have demonstrated the bi-functional electrocatalytic properties of ReS2 nanosheets towards hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) with low overpotential (139.2 and 258.89 mV for HER and OER) and Tafel slopes, respectively. The micro/nano electrocatalytic activity of the ReS2 electrocatalyst was examined using a scanning electrochemical microscope (SECM) and Kelvin probe force microscope (KPFM). A lab-scale AWE fabricated using prototype ReS2 electrocatalyst demonstrated that they could drive the benchmark current density (10 mA cm−2) with a low cell voltage of 1.645 V. Further, we also demonstrated a self-powered system comprising an on-shore wind-energy driven ReS2 AWE for sustainable H2 production. Further, the experimental results based on industrially recommended conditions for AWE illustrated that they need only 1.85 V to drive a current density of 500 mA cm−2; thus, ensuring their candidature towards high-rate AWE for clean hydrogen production.

Green hydrogen production from thermoelectric condensation of ambient moist air

As the world transitions towards reducing carbon emissions, green hydrogen produced through solar-powered alkaline water electrolysis (AWE) presents a promising eco-friendly fuel option. In response to the challenges caused by global warming, including air moisture saturation leading to unbalanced rainfall, flooding, concern for freshwater depletion and the limited availability of water and energy sources in arid regions. The present study introduces a novel method of integrating thermoelectric water condenser (TEWC) and AWE for green hydrogen production in remote and arid regions where both the water and the conventional energy sources are scarce. Numerical simulations of the present study show that the impact of relative humidity, temperature, and air flow rate significantly affect water condensation, energy requirement, and hydrogen production. The TEWC and AWE models showed excellent agreement with the experimental data. TEWC model reveled that the highest water production rate of 1.50 kg/(m2h) is achieved at ambient air temperature of 308 K and relative humidity of 80%. Furthermore, increasing the moist air flow from 1 m/s to 2 m/s results in a 47.5% increase in water production rate. The AWE model showed that cell's performance improved with higher temperatures, lower electrode-separator gap, and overpotentials. The hydrogen evolution rate reached a maximum of 5.2 kg/(m2h) at current density of 1.4 A/cm2 and potential of 3.96 V. By optimizing the TEWC and AWE systems the integrated method proved to be an efficient way of converting moist air into green hydrogen using solar energy, making it a viable and sustainable setup in remote arid regions.

Eco-friendly and facile nanomanufacturing of amorphous Co-Ce-Fe trimetallic molybdates composites for accelerated anodic oxygen evolution in alkaline water electrolysis: Evaluation of active sites performance

Currently, endeavors to scale up the production of amorphous catalysts are still impeded by intricate synthesis conditions. Here, we have prepared a series of metal-based molybdate via one-step coprecipitation method. After ingredient optimization, amorphous Co2CeFe2-MoO4 was identified as exhibiting the highest intrinsic activity among its counterparts. Modulation of electron structure enables Co2CeFe2-MoO4 to balance the adsorption behavior towards reactive intermediates. Ultimately, the obtained Co2CeFe2-MoO4 molybdate demonstrated a captivating OER performance, showcasing a low overpotential of 230 mV at 10 mA cm-2. Moreover, the alkaline electrolyzer employing the Co2CeFe2-MoO4 anode exhibited a low cell voltage of 1.50 V for water splitting and underwent an acceptable attenuation of 4.99% after 165 hours of continuous operation, demonstrating its favorable catalytic activity and durability. This work provides a facile and eco-friendly synthesis pathway for crafting cost-effective and durable earth-abundant OER electrocatalysts tailored for water splitting to produce clean hydrogen.

Advanced characterization of alkaline water electrolysis through electrochemical impedance spectroscopy and polarization curves

Improved electrolyzer components are needed to make alkaline water electrolyzers more flexible and durable. The performance of these new components can be assessed through in situ electrochemical characterization in the form of polarization curves and electrochemical impedance spectroscopy (EIS). Presently, EIS is still mostly used for the IR-correction of the polarization curve, but more valuable information can be extracted. In this work we show how EIS data can be used to determine the dependence of ohmic resistance on current density, to derive anodic and cathodic Tafel slopes and exchange current densities from fitted charge transfer resistances and to derive anodic and cathodic capacitances from fitted constant phase elements. We do this for both a two electrode alkaline electrolysis flow cell setup as well as for a three electrode beaker type setup with 2D nickel electrodes. The presented tools can be used in performance studies of new and existing electrodes and membranes in alkaline water electrolysis.

Electronic modulation towards MOFs as template derived CoP via engineered heteroatom defect for a highly efficient overall water splitting

The reasonable design of material morphology and eco-friendly electrocatalysts are essential to highly efficient water splitting. It is proposed that a promising strategy effectively regulates the electronic structure of the d‐orbitals of CoP using cerium doping in this paper, thus significantly improving the intrinsic property and conductivity of CoP for water splitting. As a result, the as-synthesize porous Ce-doped CoP micro-polyhedron composite derived from Ce-ZIF-67 as bifunctional electrocatalytic materials exhibits excellent electrocatalytic performance in both the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER), overpotentials of about 152 mV for HER at 10 mA cm−2 and about 352 mV for OER at 50 mA cm−2, and especially it shows outstanding long-term stability. Besides, an alkaline electrolyzer, using Ce0.04Co0.96P electrocatalyst as both the anode and cathode, delivers a cell voltage value of 1.55 V at the current density of 10 mA cm−2. The calculation results of the density functional theory (DFT) demonstrate that the introduction of an appropriate amount of Ce into CoP can enhance the conductivity, and can induce the electronic modulation to regulate the selective adsorption of reaction intermediates on catalytic surface and the formation of O* intermediates (CoOOH), which exhibits an excellent electrocatalytic performance. This study provides novel insights into the design of an extraordinary performance water-splitting of the multicomponent electrocatalysts.

Unlocking OER potential: Tailoring layered double perovskites through self-reconstruction

The sluggish rate of the anode oxygen evolution reaction (OER) is a major bottleneck for green hydrogen production, making a room-temperature alkaline water electrolyser critical to unlocking the full potential of this technology. Using a perovskite oxide as an electrochemical matrix and forming a self-assembled oxyhydroxide (OOH) layer on the surface via a self-reconstruction activation process (SRAP) is a promising strategy to enhance OER catalytic activity. However, the mechanistic details and long-term impact of SRAP, especially its relationship to catalytic activity, oxygen collection efficiency, and catalyst dissolution, are not fully understood. To address this knowledge gap, we used layered double perovskite (LDP) PrBa0·75Ca0·25Co1·5Fe0·5O5+δ(PBCCF) and PrBa0·75Ca0·25Co1·5Fe0·4Ni0·1O5+δ (PBCCFN) as model electrochemical catalysts and then triggered SRAP. Subsequently, chronoamperometry (CA), rotating ring disk electrode (RRDE) and in-situ electrochemical quartz crystal microbalance (EQCM) were used to study the effect of the Ni-doping on PBCCF SRAP in terms of catalytic activity, oxygen collection efficiency and catalyst stability. The results showed that the OER catalytic current of the LDP PBCCF and PBCCFN was enhanced via SRAP and the oxygen collection efficiency can be maintained, suggesting that the increase in catalytic current is attributed to OER catalytic activity increase rather than electrochemical catalyst dissolution. Additionally, the effect of the catalytic activity enhancement was more significant in PBCCFN. More importantly, the stability of the LDP PBCCF and PBCCFN after SRAP are higher than simple perovskite Ba0·5Sr0·5Co0·8Fe0·2O3-δ (BSCF) because of the increase in the redeposition rate. The observations suggest that using LDP PBCCF and PBCCFN as matrices followed by triggering SRAP can provide valuable insights for designing LDP based OER electrocatalysts.

Study on Titanate perovskites with different morphologies for oxygen-evolution reaction catalysts

Metal exsolution from perovskite oxides has been used to produce well-designed electro-catalysts where metal nanoparticles are homogeneously distributed on the surface of perovskites. Our previous works revealed that the metal exsolution concept is effective not only for high-temperature system such as solid oxide fuel/electrolysis cells but also for alkaline water electrolysis at near-ambient temperatures. In this study, we prepare cuboidal and spherical Ni-doped CaTiO3 to investigate the effects of the different perovskite morphologies on Ni exsolution and catalytic activity for OER. Ni ions seem to be incorporated into the A-site of CaTiO3 with structural OH ions via solvothermal route, and the stoichiometry of spheres and cubes were confirmed as (Ca0.82Ni0.04)Ti1O2.63(OH)0.46 and (Ca0.90Ni0.04)Ti1O2.88(OH)0.12, respectively. The spheres show random distribution of Ni nanoparticles along grain boundaries, whereas Ni nanoparticles are ex-solved along the edges in the cubes. With the small amount of Ni contents (∼4 mol %), geometric current density of each cube and sphere exhibits comparable OER activities of ∼10 mA cm−2 and ∼7 mA cm−2 at 1.7 V to previously reported catalysts such as transition metals or perovskites. We suppose from Tafel slope that different A-site and oxygen stoichiometry of the CaTiO3 may affect deprotonation step during OER in terms of proton conduction.

High-current decoupled hydrogen and oxygen evolution via nickel–cobalt based redox mediators and bifunctional catalyst of 3D printing substrates

The conversion of renewable energy sources with relatively large energy fluctuations into hydrogen represents a crucial aspect of energy storage. Nevertheless, the direct water electrolysis process is known to require excessive instantaneous energy consumption and high cost. Two-step alkaline water electrolysis is regarded as a secure and effective method of generating hydrogen from renewable energy sources when compared to direct water electrolysis. Here we propose a two-step alkaline water electrolysis using nickel–cobalt based hydroxide (Ni0.9Co0.1(OH)2) as a redox mediator, and a high-performance bifunctional catalyst as gas evolution electrodes (GEE). The substrates for the GEE were prepared using 3D printing and then loaded with in-situ grown Ru-doped MoS2/NiFe-LDH hierarchical heterostructure catalysts (MS-NiFe-Ru-3D). The oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) of the MS-NiFe-Ru-3D catalyst can reach up to 500 mA cm−2 at 300 and 250 mV overpotentials, respectively. It can meet the requirement of high catalyst performance for two-step alkaline water electrolysis. The direct water electrolysis using the bifunctional MS-NiFe-Ru-3D catalyst only requires a voltage of 1.85 V at 500 mA cm−2 with minimal attenuation over 300 h. For the two-step alkaline water electrolysis using MS-NiFe-Ru-3D as bifunctional catalysts and Ni0.9Co0.1(OH)2 as redox mediator, only 1.70 V and 0.27 V were required for HER and OER at 500 mA cm−2, respectively. This work offers a promising avenue for the efficient conversion of renewable secondary energy sources into hydrogen.

Diaphragm and Membrane for Alkaline Water Electrolysis with Zirconium Hydroxide Hydrogel as Hydrophilic Filler

Diaphragm and Membrane for Alkaline Water Electrolysis with Zirconium Hydroxide Hydrogel as Hydrophilic Filler

Development of a free-standing flexible electrode for efficient overall water-splitting performance via electroless deposition of iron-nickel-cobalt on polyacrylonitrile-based carbon cloth

Developing cost-effective and highly efficient electrodes for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is crucial, particularly for alkaline OER and HER. Herein, electroless plating of iron-nickel–cobalt (Fe–Ni–Co) electrocatalyst on a flexible polyacrylonitrile (PAN)-based carbon cloth (CC) was performed to synthesize a free-standing catalytic electrode for bifunctional electrocatalysts. The three-dimensional porous backbone of PAN-based CC and the synergistic effect between Fe-Ni-Co and corresponding hydroxides result in outstanding OER and HER activities, that is low overpotentials of 230 and 150 mV at 10 mA cm−2 and Tafel slopes of 63 and 57.1 mV dec–1, respectively. Additionally, a complete alkaline electrolyzer was constructed using Fe-Ni-Co plated PAN-based CC as both the cathode and anode. When operated at 10 mA cm−2, this setup enabled efficient water splitting at a low potential of 1.57 V. This study provides new opportunities for the development of advanced Fe-Ni-Co electrocatalyst with superior bifunctional OER and HER performance and cost-effectiveness that are suitable for integration into PAN-based CC via electroless plating.

Comparative thermoeconomic analysis of integrated hybrid multigeneration systems with hydrogen production for waste heat recovery in cement plants

The cement industry is a widely used and energy-consuming sector, making it one of the largest CO2 emitters, primarily to meet its energy demands. Therefore, this research aims to evaluate the waste heat recovery process from a cement factory to fulfill a portion of its energy requirements. In this study, four scenarios have been evaluated, including power production scenarios, hydrogen production scenarios, methanation production process evaluation scenarios, blending hydrogen with natural gas, oxy-fuel combustion scenarios, and scenarios for producing the required freshwater for the factory and the water electrolysis process. The results show that the steam Rankine cycle with the reheating process and the organic Rankine cycle with methanol working fluid with a production capacity of 24.35 MW, and a payback period of 2.4 years with levelized cost of energy being 0.005809 $/kWh, is the most favorable scenario for the power generation cycle. Also, the process of alkaline electrolysis with a hydrogen production rate of 0.1648 kg/s, and a payback period of 5.816 years, and also with the levelized cost of hydrogen being 1.001 $/kg, happened to be the most suitable hydrogen production scenario compared to other electrolysis scenarios such as PEM and SOEC. Moreover, the process of water desalination by reverse osmosis with the energy consumption of 2.7 MW of power is capable of supplying all the required water of the factory and the water electrolysis process, and it was determined as the most suitable scenario for supplying the required water.

Dynamic Simulation and Performance Analysis of Alkaline Water Electrolyzers for Renewable Energy-Powered Hydrogen Production

This paper presents a comprehensive study on the dynamic simulation modeling of alkaline water electrolyzers. Detailed experimental testing and characteristic analysis reveal that alkaline water electrolyzers have long startup times, rapid dynamic responses, and poor dynamic stability. These characteristics are critical for the development of accurate models and effective strategies. A dynamic simulation model was established in MATLAB R2022b and Simulink, enabling standalone simulation operation and module encapsulation. This model facilitates the construction of hydrogen production clusters and serves as a foundational tool for system strategy research. Simulations of rated current loading and unloading for four electrolyzers over 6 h showed significant differences in startup and operation. Key parameters such as cell voltage, maximum loadable power, hydrogen production efficiency, and energy consumption were analyzed. Temperature simulations indicated significant differences in thermal equilibrium points and cooling modes among the electrolyzers, as determined by structural design and cooling system efficiency. These findings highlight the need for efficiency improvements in high-current density electrolyzers. Overall, the model effectively represents commercial electrolyzer characteristics and offers a reliable tool for future research on control strategies for adapting hydrogen production systems to renewable energy power fluctuations, laying a solid foundation for the optimization of electrolyzer design and operation strategies.

Induction heating boosts water splitting on iron-coated nickel foam

Abstract Alkaline water electrolysis at high temperatures can rival acidic proton-exchange membranes.
However, they suffer from increased energy consumption, reduced lifespan of materials and heightened safety risks. Magnetic hyperthermia is a method of localizing intense heating in the presence of an external high-frequency alternating magnetic field. In this study, we developed a custom electromagnetic induction device capable of generating a small magnetic field of about 2 µT. High-permeability nickel foam is used as electrodes. Results show that the iron coated nickel foam decreases the overpotential of the hydrogen evolution reaction and oxygen evolution reaction by ~150 mV and 60 mV, respectively, at 20 mAcm−2 when subjected to magnetic heating in a high-frequency alternating magnetic field. The overall water splitting current of Ni foam/Fe increases 540% under intermittent induction. The enhanced stability of Ni foam/Fe is attributed to the high binding energy of metal-O on the surface. The density function theory calculations further indicates that the lattice expansion of the metal electrode under induction heating optimizes the adsorption and desorption of H*, thereby enhancing the HER performance.

Thermodynamic and Economic Analysis of the Green Ammonia Synthesis System Driven by Synergistic Hydrogen Production Using Alkaline Water Electrolyzers and Proton Exchange Membrane Electrolyzers

Green ammonia and hydrogen from renewable energy sources have emerged as crucial players during the transition of the chemical industry from a fossil energy‐dominated economy to one that is environmentally friendly. This work proposes a green ammonia synthesis system driven by synergistic hydrogen generation using alkaline water electrolyzers (AWE) and proton exchange membrane electrolyzers (PEMEC). The effects of hydrogen‐production ratios of PEMEC and AWE on the thermodynamic and economic performance of the system are compared and analyzed via multi‐objective optimization. The findings showed that an increase in the amount of hydrogen produced by PEMEC improves the system's energy efficiency, but the payback period is delayed because of the PEMEC high initial investment cost. The techno‐economic performance of the system at a 1:1 ratio of PEMEC to AWE hydrogen production are investigated considering the system level heat integration based on the pinch point analysis method to maximize the heat recovery. The results show that increasing the operational temperature, the pressure of the electrolyzer, and the ammonia synthesis pressure will enhance the system's thermal performance. Economic analysis shows that reducing electricity prices and electrolyzer investment costs will be the key to achieving the economic feasibility of the green ammonia system.

Evaluating the techno-economic potential of large-scale green hydrogen production via solar, wind, and hybrid energy systems utilizing PEM and alkaline electrolyzers

The study evaluates the potential of solar, wind, and hybrid PV/WT renewable energy systems for green hydrogen production in four Iraqi cities. Through a comparative analysis of six distinct scenarios involving the deployment of 60 MWp solar panels, 30 MWp wind turbines, and 45 MWp hybrid PV/WT systems, the research aims to ascertain the most energy-efficient and cost-effective strategy for hydrogen generation. This evaluation is aligned with the operational capacities of two types of water electrolyzers: Alkaline (AWE) and proton exchange membrane (PEM), each with a 17.5 MWp capacity. Employing the HOMER Pro software for system simulation and optimization, and considering a project timeline from 2022 to 2042, the study identifies Anbar City as the prime location for green hydrogen production, highlighting solar PV panels as the most economical option with the lowest levelized cost of energy at US $4.5/MWh. The analysis further demonstrates that hydrogen production costs are US $1.98/kg for AWE electrolyzers and US $2.72/kg for PEM electrolyzers, with net present costs of US $26.31 million and US $35.91 million, respectively. Moreover, the annual hydrogen output is estimated at 1.11 million kg for AWE and 1.19 million kg for PEM electrolyzers. These insights significantly contribute to the strategic planning and development of Iraqi green hydrogen sector, offering a valuable framework for policymakers and stakeholders invested in sustainable energy transitions.

Elucidating the increased ohmic resistances in zero-gap alkaline water electrolysis

This study investigates the increased ohmic resistances observed in zero-gap alkaline water electrolyzers, aiming to provide insights that can help enhance electrolyzer efficiency and enable operation at higher current densities. Electrochemical impedance spectroscopy (EIS) has been employed in combination with chronopotentiometry, utilizing a custom-designed flow cell with nickel perforated electrodes and a Zirfon UTP 500 diaphragm. Observed differences in area-ohmic resistance values obtained through I-V fitting and EIS, are ascribed to a non-linear Tafel slope at higher current densities. Ohmic resistance values measured with EIS are up to 27% higher than the ex-situ determined value, a significantly smaller percentage than expected based on previous studies. The presence of bubbles outside and inside the diaphragm is identified as the key factor contributing to this increased resistance. We recommend the use of an improved fitting approach, accounting for non-linear Tafel behavior, and the use of a 4-terminal configuration when performing EIS measurements to minimize cable and contact resistance.

Computational Fluid Dynamics Analysis of Gas Crossover in an Alkaline Electrolyzer Using a Multifluid Model

A comprehensive three-dimensional, two-phase isothermal model is developed for an alkaline water electrolyzer, aimed to accurately simulate complex interactions at gas-liquid interfaces, ion transport mechanisms, and electrochemical reactions. The present model accounts for the local volume fraction of gas, the species spatial distributions and both electrical and electrolyte potentials. The crossover of the product gases is a result of diffusion of the dissolved species in the liquid phase. This work explores the role of parameters such as mass transfer coefficients and supersaturation within the cell. Despite the model demonstrating trends that are consistent with anticipated physical behaviors, it currently tends to underestimate the crossover effect.

Frequency response coefficient optimal allocation strategy for multi-stacks alkaline water electrolyzer plant

Currently, power discrepancies between stacks are often overlooked when developing frequency response (FR) strategies for multi-stack alkaline water electrolyzer plants (AWEPs), which limits the full utilization of the plant’s FR potential. To address this issue, this paper introduces a stack-level FR coefficient allocation strategy aimed at minimizing post-contingency frequency deviation. Specifically, the quantitative relationship between the operating power of alkaline water electrolyzer (AWE) stacks and steady-state frequency deviation is first derived, followed by the formulation of an optimal FR problem. The solution to this problem is an FR strategy based on the principle of equal frequency deviation, which optimally allocates FR coefficients among AWE stacks according to their operating power, thereby maximizing the plant’s FR support capacity. Equivalent circuit model-based case study demonstrates that, compared to existing strategies, the proposed approach achieves a more balanced power distribution among the stacks during the FR process. This even power allocation not only reduces post-contingency frequency deviation but also enhances productivity and streamlines production management in the AWEP, thereby increasing the plant owner’s willingness to participate in FR. Specifically, the proposed strategy results in a 29.3% reduction in post-contingency frequency deviation, a 1.8% improvement in production efficiency under a 10 MW power imbalance, a 2.3% increase in hydrogen production rate under a 4 MW power imbalance, and more stable operation under a 16 MW power imbalance.