Electrolysis System Research Articles

Methods for Enhancing Electrolysis for Hydrogen Production: The Benefits of Applying Magnetic Fields

The electrolysis of water is one of the most promising ways of producing green hydrogen. This produces hydrogen using electricity and does not generate additional carbon dioxide like the more conventional reforming of fossil fuels. However, making electrolysis competitive with conventional methods for hydrogen production is a challenge because of the cost of electricity and because of inefficiencies and costs in electrolysis systems. Initially this review looks at the basic design of water electrolysis and asks where energy is lost. Then, a selection of the latest results in the area of magnetic field-enhanced water electrolysis are examined and discussed, in particular focusing on the empirical results of magnetic field-assisted electrolysis with the aim of comparing findings and identifying limitations of current studies such that recommendations can be made for advanced design of hydrogen producing electrolysis systems.

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.

Investigation into the electrolysis performance of a novel directly solar irradiated solid oxide electrolysis cell

Current coupling methods linking solar energy to solid oxide electrolysis cell (SOEC) mostly involve indirect coupling, with limited studies exploring direct coupling. This study is the first to evaluate a novel directly solar irradiated solid oxide electrolysis cell, anticipating a reduction in polarization loss incurred during the electrolysis process and improving the electrochemical performance of the system through direct solar irradiation. Additionally, it aims to reduce electric energy consumption required to maintain the high-temperature environment for the reaction and enhance the energy conversion efficiency of the electrolysis system, presenting a unique coupling technology. Hence, this paper proposes and develops the inaugural solar SOEC system, directly harnessing sunlight on the SOEC electrode surface, achieving stable and continuous hydrogen production through experimental methods. Experimental results demonstrate that direct solar irradiation increases the SOEC system’s heating rate by 12 times compared to electric heating, with a notably swifter response time. Under identical electrolysis voltages, the system exhibits significantly higher efficiency under direct solar irradiation than under electric heating. Moreover, for equivalent hydrogen production, the total energy input from solar energy is lower than that from electric heating, saving about 76 % of energy. Under specific conditions—solar radiation power of 123.2 W, electrolysis temperature of 655 °C, cathode-side gas input maintaining a water-hydrogen molar ratio of 8:2, and an electrolysis voltage of 1.5 V—the SOEC system sustains a nearly constant current density of about 359 mA/cm2 for 3 h. Comparative experiments conducted under identical working conditions, both in solar and electrically heated environments, reveal that the electrochemical impedance spectroscopy indicates inhibited mass transfer processes during electrolysis under direct solar irradiation. Consequently, the electrochemical performance of the SOEC system operating under direct solar irradiation was lower than that under electrically heated environments, across varying electrolysis temperatures and water contents. This study uncovers the pivotal influence of direct solar irradiation on concentration losses during the electrolysis process. The corresponding concentration losses can be subsequently mitigated by optimizing the reactor structure of the solar SOEC system.

Assessing the Performance of a Proton Exchange Membrane Green Hydrogen Generation System through Stack and Balance of Plant Modeling

The integration of Proton Exchange Membrane electrolyzers into hydrogen generation systems offers significant potential for sustainable energy solutions. Integrating hydrogen production with electricity, heat, and renewable energy sources enhances sustainability. PEM electrolyzers effectively address renewable energy intermittent by converting energy into hydrogen, leveraging their ramp rate and load-following capabilities. However, widespread commercialization hinges on cost reductions through new material development and a comprehensive understanding of the system's heat, mass, and electrochemical processes. This study presents a zero-dimension model developed using the Aspen Custom Modeler, detailing the electrochemical phenomena. A holistic PEM electrolysis model, including the stack and the Balance of Plant, is developed in Aspen Plus, demonstrating an overall system efficiency of 50%, with the BoP accounting for 8% of total electricity consumption. This research underscores the critical role of optimizing BoP subsystems and integrating grid-based backup solutions to enhance the economic viability and resilience of PEM 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.

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.

Assessing the Performance of a Proton Exchange Membrane Green Hydrogen Generation System through Stack and Balance of Plant Modeling

The integration of Proton Exchange Membrane electrolyzers into hydrogen generation systems offers significant potential for sustainable energy solutions. Integrating hydrogen production with electricity, heat, and renewable energy sources enhances sustainability. PEM electrolyzers effectively address renewable energy intermittent by converting energy into hydrogen, leveraging their ramp rate and load-following capabilities. However, widespread commercialization hinges on cost reductions through new material development and a comprehensive understanding of the system's heat, mass, and electrochemical processes. This study presents a zero-dimension model developed using the Aspen Custom Modeler, detailing the electrochemical phenomena. A holistic PEM electrolysis model, including the stack and the Balance of Plant, is developed in Aspen Plus, demonstrating an overall system efficiency of 50%, with the BoP accounting for 8% of total electricity consumption. This research underscores the critical role of optimizing BoP subsystems and integrating grid-based backup solutions to enhance the economic viability and resilience of PEM electrolysis systems.

Hierarchical Superhydrophilic/Superaerophobic Ni3S2/VS2 Nanorod-Based Bifunctional Electrocatalyst Supported on Nickel Foam for Overall Urea Electrolysis.

The design and preparation of effective nonprecious metal-based catalysts for the urea oxidation reaction (UOR) coupled with the hydrogen evolution reaction (HER) are of great significance to solve both energy shortage and environmental pollution problems. In this study, a novel hierarchical superhydrophilic and superaerophobicity three-dimensional nanorod-like bifunctional catalyst with a heterostructure (Ni3S2/VS2) was prepared on nickel foam via a simple one-step hydrothermal method, serving as an excellent electrocatalyst for both UOR and HER. The formed heterostructure significantly alters the electronic structure, optimizing charge transfer and increasing the number of active sites, which enhances the electrocatalytic performance of Ni3S2/VS2. As a result, this catalyst requires an extremely low potential of 1.396 V at the current density of 100 mA cm-2 for UOR and only 164 mV overpotential at -10 mA cm-2 for HER. Notably, a constructed two-electrode electrolyzer system (Ni3S2/VS2∥Ni3S2/VS2) demonstrates extraordinary activity and long-term stability, achieving a current density of 10 mA cm-2 at a low cell voltage of 1.48 V, which is superior to majority of the reported catalysts. This work demonstrates that the formation of heterostructures can effectively enhance the catalytic activity of nanomaterials toward UOR and HER and provides a feasible strategy for fabricating highly efficient nonprecious metal overall urea electrocatalysts.

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.

Solid‐Liquid‐Gas Three‐Phase Indirect Electrolysis Enabled by Affinity Auxiliary Imparted Covalent Organic Frameworks

The design of efficient heterogenous redox mediators with favorable affinity to substrate and electrolyte are much desired yet still challenging for the development of indirect electrolysis system. Herein, for the first time, we have developed a solid‐liquid‐gas three‐phase indirect electrolysis system based on a covalent organic framework (Dha‐COF‐Cu) as heterogenous redox mediator for S‐S coupling reaction. Dha‐COF‐Cu with the integration of high porosity, nanorod morphology, abundant hydroxyl groups and active Cu sites is much beneficial for the adsorption/activation of thiols, uniform dispersion and high wettability in electrolyte, and efficient interfacial electron transfer. Notably, Dha‐COF‐Cu as solid‐phase redox mediator exhibits excellent electrocatalytic efficiency for the formation of value‐added liquid‐phase S‐S bond product (yields up to 99%) coupling with the generation of gas‐phase product of H2 (~1.40 mmol g‐1 h‐1), resulting in a powerful three‐phase indirect electrolysis system. This is the first work about COFs that can be applied in three‐phase indirect electrolysis system, which might promote the development of porous crystalline materials in this field.

Optimization of user-side electrolytic hydrogen production system considering electrolyzer efficiency degradation

This paper proposes an optimized operational strategy for user-side proton exchange membrane (PEM) electrolyzer hydrogen production systems, considering the degradation of hydrogen production efficiency over time. The work is divided into three parts. First, a combined hydrogen production efficiency model based on operational data is established, using polynomial surface fitting (PSF) and gaussian process regression (GPR) to model the electrolyzer's efficiency from two perspectives: operational time and input power. Second, an optimization model for the operational strategy of the user-side electrolytic hydrogen production system is constructed, aiming to enhance overall system efficiency by adjusting the electrolyzer's input power. Finally, the hydrogen efficiency model from the first part is applied to the optimization strategy in the second part for empirical analysis. The results show that the optimized strategy, which accounts for the degradation of hydrogen production efficiency, significantly improves system performance, validating the method's effectiveness and practicality. This study provides theoretical support and practical guidance for the efficient operation of user-side electrolyzers, contributing to the promotion and application of green hydrogen technologies.

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.

Decoupling Electrolytic Water Splitting by an Oxygen-Mediating Process.

Decoupled water electrolysis systems, incorporating a reversible redox mediator that allows for the construction of membrane-free electrolyzers, have emerged as a promising approach to produce high-purity hydrogen with remarkable flexibility. The key factor crucial for practical applications lies in the development of mediator electrodes that possess suitable redox potential, high redox capacity, excellent cycling reversibility and stability. Herein, we introduce a novel concept of oxygen-mediating redox mediators (ORMs) employing Bi2O3 as an example material, which are capable of sequestering oxygen during the hydrogen evolution reaction and subsequently releasing it to generate oxygen gas under alkaline conditions. Thanks to its remarkable reversible redox activity and specific capacity, the Bi2O3 electrode boasts an impressive reversible specific capacity of 300.8 mA h g-1 and delivers outstanding cycling performance for >1000 cycles at a current density of 2.0 A g-1. Furthermore, the implementation of such a decoupled alkaline water electrolysis system can be integrated with a Bi2O3-Zn battery, enabling both power-to-fuel (hydrogen production) and chemical-to-power (rechargeable Bi2O3-Zn battery) conversion. With many oxygen-carrier materials readily available and the potential integration with rechargeable alkaline batteries, this study provides an alternative competitive route for membrane-free decoupled water splitting through the oxygen-mediating mechanism with combined energy transformation and storage.

Electrooxidation of glycerol to formic acid coupled with Energy-Saving hydrogen production over ruthenium doped Cobalt-Based nanosheet arrays

The utilization of small molecule oxidation reactions as a substitute for the sluggish oxygen evolution reaction (OER) in traditional water electrolysis represents an innovative approach to achieve efficient hydrogen production while concurrently generating value-added chemicals. Herein, we report an energy-saving H2 production system utilizing electrooxidation of glycerol to generate valuable formate. Cobalt–ruthenium oxide nanosheet arrays (CoRuO/CF) and cobalt–ruthenium bimetallic nanoparticles wrapped by nitrogen-doped carbon nanosheet arrays (CoRuCN/CF) were synthesized for glycerol oxidation reaction (GOR) and hydrogen evolution reaction (HER), respectively, using Co-ZIF nanosheets precursor material supported on copper foam (Co-ZIF/CF) as the substrate. Remarkably, the hybrid electrolysis system can achieve a current density of 10 mA cm−2 with only 1.19 V, which is significantly lower than that required by traditional water-splitting systems. This work demonstrates the promising potential of efficiently utilizing biomass energy and achieving a sustainable production process for fine chemical products.

Tunable Ag-Ox coordination for industrial-level carbon-negative CO2 electrolysis

The electrochemical CO2 reduction (eCO2RR) is promising for eliminating CO2, generate valuable chemicals and utilize spare electricity. However, its industrialization is greatly hindered by low CO2 single-pass conversion efficiency (SPCE) in alkaline/neutral electrolytes, and poor compatibility between the electrolysis and intermittent energy system. Herein, a carbon-negative acidic eCO2RR system is developed using acidic-tolerant Ag based metal-organic frameworks (Ag-MOFs), achieving a high Faradaic efficiency of CO above 97 % in a broad working window of 10–400 mA cm−2 for unsaturated Ag-O2 clusters, and a high CO2 SPCE of 46.3 % even under industrial-level 400 mA cm−2. Being connected to solar cells, the acidic eCO2RR system displays a remarkable solar-to-chemical efficiency of 19.74 %, offering great potential for industrial eCO2RR directly driven by renewable energy. Specifically, the CO/HCOOH selectivity could be manipulated by adjusting the coordination number of Ag atoms in Ag-MOFs, and thus a Pourbaix-diagram is proposed to explain the tunable selectivity theoretically.

Electron-Efficient Co-Electrosynthesis of Formates from CO2 and Methanol Feedstocks.

The electrochemical conversion of CO2 into valuable chemicals using renewable electricity shows significant promise for achieving carbon neutrality and providing alternative energy storage solutions. However, its practical application still faces significant challenges, including high energy consumption, poor selectivity, and limited stability. Here, we propose a hybrid acid/alkali electrolyzer that couples the acidic CO2 reduction reaction (CO2RR) at the cathode with alkaline methanol oxidation reaction (MOR) at the anode. This dual electro-synthesis cell is implemented by developing Bi nanosheets as cathode catalysts and oxide-decorated Cu2Se nanoflowers as anode catalysts, enabling high-efficiency electron utilization for formate production with over 180 % coulombic efficiency and more than 90 % selectivity for both CO2RR and MOR conversion. The hybrid acid/alkali CO2RR-MOR cell also demonstrates long-term stability exceeding 90 hours of continuous operation, delivers a formate partial current density of 130 mA cm-2 at a voltage of only 2.1 V, and significantly reduces electricity consumption compared to the traditional CO2 electrolysis system. This study illuminates an innovative electron-efficiency and energy-saving techniques for CO2 electrolysis, as well as the development of highly efficient electrocatalysts.

Effect of porous irregular ZrO2 nanoparticles on the performance of alkaline water electrolysis composite separator membranes under complex conditions

Developing composite separator membranes with low area resistance, high bubble point pressure, and long-term safety and stability is crucial for alkaline water electrolysis for hydrogen production as a key component of electrolyzer systems. In this study, PPS mesh fabric reinforced PSF@ZrO2 composite separator membranes were successfully prepared using the immersion-drawing phase inversion method, with PSF as the alkali-resistant polymer matrix and porous irregular ZrO2 nanoparticles as the hydrophilic additive. The experimental results showed that replacing commercial ZrO2 with porous irregular ZrO2 nanoparticles at an 85 wt% ZrO2 nanoparticle loading improved both bubble point pressure and current transmission efficiency, attributed to the change in the morphological structure of the ZrO2 nanoparticles. The P-Z85 composite separator membrane exhibited highly promising characteristics, with a high bubble point pressure of 3.76 bar and a low area resistance of 0.20 Ω cm2. Stability tests conducted in 30 wt% KOH electrolyte at 80 °C and a current density of 0.65 A cm−2 demonstrated excellent continuous electrolysis stability for the P-Z85 composite separator membrane. These results indicate that the PSF@ZrO2/PPS composite separator membrane prepared in this study exhibits excellent performance in 30 wt% KOH electrolyte, significantly extending its service life.

Development of a solar-ocean based integrated plant with a new hydrogen generation system

Considering the global urgency to decrease carbon emissions and shift to sustainable energy sources, combining solar and other renewables with hydrogen generation appears to offer an appealing answer. The combination of solar and ocean energies with hydrogen production, therefore, offers a great potential to improve energy efficiency and create a feasible route towards zero-emission energy systems. A new hybrid photoelectrochemical (PEC)-conventional electrolysis system was designed and incorporated into the proposed multigeneration system. The hybridized reactor combines the benefits of PEC and conventional electrolysis by using a developed bipolar anode to produce hydrogen continuously, even when there is no solar radiation. The main aim of this research is to investigate the integrated power process that utilizes solar power for several uses, such as generating electricity, producing freshwater, and synthesizing hydrogen. The proposed research involves integrating several components, including a solar through collector system, a combination of power cycles (steam and organic Rankine cycles), a multi-effect desalination (MED) unit, a new hybrid electrolyzer system, a wave energy system, and a hydrogen storage and refuelling station. The main outputs include 2.05 kg/s freshwater production, 0.125 kg/s hydrogen production, 16,284.24 kW net work rate, and 95,068 kW solar heat input. The highest exergy destruction rates were found in the solar collector (56,194.8 kW) and turbines T1 and T2 (6019.9 and 4627.6 kW). The overall energy and exergy efficiencies of the proposed system are obtained to be 15.83 % and 16.61 %, respectively.

Hydrated molten salt electrolytes effectively promote electrocatalytic NH3 synthesis at low temperatures

In the field of electrocatalytic nitrogen reduction reaction (NRR), molten salt is used as a unique electrolyte due to its advantages of high N2 solubility and wide electrochemical window. However, it has failed to be widely used due to its high reaction temperature (mostly > 200 °C) and low yield. Herein, a novel low-temperature (<100 °C) electrolysis system with hydrated molten salt hybrid electrolyte is designed. This system exhibits an ammonia yield of 1.003 × 10−8 mol s−1 cm−2 (−0.7 V vs. SCE) at 60 °C. Faradaic efficiency (FE) reaches 80.45 % (−0.65 V vs. SCE). The NH3 yield and FE are increased by 18.6 and 2 times compared to the previously reported low-temperature system, respectively. Linear sweep voltammetry (LSV), in situ Raman and in situ Fourier Transform-Infrared (FT-IR) experiments show that solid crystalline water can be used as a hydrogen source to effectively promote NRR while inhibiting the hydrogen evolution reaction (HER). Molecular dynamics (MD) experiments confirm that the electrolyte system maintains a high N2 solubility and mass transfer rate.