Effects of magnetic field on water electrolysis using foam electrodes

Alkaline water electrolysis using foam electrodes was performed under the influence of a uniform magnetic field. The motivation of doing this work is to combine magnetic field with foam electrode to see if it can get unexpected higher water electrolysis efficiency. The result shows that the energy consumption was reduced by about 3.4% and some unique gas producing properties of foam electrodes were exhibited under the parallel-to-electrode magnetic field. The magnetohydrodynamic (MHD) convection induced by the Lorentz force can accelerate the detachment of bubbles, which are capable to be generated both on the surface and in the interior of foam electrodes simultaneously. Due to the uneven distribution of Lorentz forces, a circulating flow was formed in the electrolyzer, which is special designed to make full use of the circulating flow. The flow scoured the inner space of the foam electrodes so that the void fraction was reduced and the reaction overpotential was decreased. It should be potential to significantly improve the energy efficiency of the hydrogen manufacturing via water electrolysis and provide new ideas for the engineering design of electrolyzer.     

The “tornado” effect induced by magnetohydrodynamic convection in an electrolytic cell with a wire-electrode

High energy consumption is the key problem to be solved in water electrolysis for hydrogen production. Imposing magnetic field during electrolysis is proved to be a research-worthy method to reduce the required electrical energy, since the magnetohydrodynamic convection can be induced without additional energy input. Considering the structure of commercial electrolyzers, the magnetic field perpendicular to the electrode surface is most likely to be applied in practical engineering. But there is still a lack of research on the gas-liquid two-phase flow in the electrolytic cell under this condition. To avoid mutual blocking between a large number of bubbles and obtain clear two-phase flow images of the electrolysis process, a wire electrode is used as cathode to generate hydrogen bubbles in this work. The cell voltage is obviously reduced by external magnetic field, and an interesting “bubble tornado” is formed under the action of induced magnetohydrodynamic convection. The numerical simulation results and theoretical analysis indicate that: (1) the formation of the bubble chain is caused by low-pressure region along the vertical axis; (2) the unstable low-pressure region is the key factor leading to the formation of continuously deformed bubble chain; (3) the bubble dispersion may be related to Kelvin-Helmholtz flow instability. We anticipate our work being a starting point for the application of magnetic field in practical engineering.     

Effect of pulse potential on alkaline water electrolysis performance

In this study, the effect of pulse potential on alkaline water electrolysis energy consumption is investigated. A specially designed electrical circuit is used to observe the effect of different duty cycles and frequency values on water electrolysis energy consumption in different concentration values of alkaline solution. The results show that using pulse potential enhances the mass transport of oxygen and hydrogen bubbles due to the pumping effect. This provides less contact with oxygen bubbles to improve corrosion resistance of anode electrodes. Moreover, decreasing mass transfer losses on the electrode surface resulted in a 20–25% lower energy consumption to produce 1 mol of hydrogen in the cell. The optimum frequency for 10% and 50% duty cycle and 10% and 15% concentration are investigated. For 10% duty cycle, the optimum frequency is specified around 140–200 kHz and for 50% duty cycle, it is around 380–400 kHz for all concentration values.     

Experimental investigation of solar-hydrogen energy system performance

Recently, the Solar-hydrogen energy system (SHES) becomes a reality thanks as well as a very common topic to energy research in Egypt as it is now being the key solution of different energy problems including global warming, poor air quality and dwindling reserves of liquid hydrocarbon fuels. Hydrogen is a flexible storage medium for energy and can be generated by the electrolysis of water. It is more particularly advantageous and efficient when the electrolyzer is simply coupled to a source of renewable electrical energy. This paper examines the operation of alkaline water electrolysis coupled with solar photovoltaic (PV) source for hydrogen generation with emphasis on the electrolyzer efficiency. PV generator is simulated using Matlab/Simulink to obtain its characteristics under different operating conditions with solar irradiance and temperature variations. The experimental alkaline water electrolysis system is built in the fluid mechanics laboratory of Menoufiya University and tested at certain input voltages and currents which are fed from the PV generator. The effects of voltage, solution concentration of electrolyte and the space between the pair of electrodes on the amount of hydrogen produced by water electrolysis as well as the electrolyzer efficiency are experimentally investigated. The water electrolysis of different potassium hydroxide aqueous solutions is conducted under atmospheric pressure using stainless steel electrodes. The experimental results showed that the performance of water electrolysis unit is highly affected by the voltage input and the gap between the electrodes. Higher rates of produced hydrogen can be obtained at smaller space between the electrodes and also at higher voltage input. The maximum electrolyzer efficiency is obtained at the smallest gap between electrodes, however, for a specified input voltage value within the range considered.     

Electrocatalytic activation of Ni electrode for hydrogen production by electrodeposition of Co and V species

Hydrogen is considered to be the most promising candidate as a future energy carrier. One of the most used technologies for the electrolytic hydrogen production is alkaline water electrolysis. Electrode materials used in alkaline water electrolysis are mainly made from Ni or Ni-based alloys due to their desirable mechanical and chemical stability in hot and alkaline solution. Considerable research effort has been conducted on enhancement of electrocatalytic activity of Ni electrodes.     

Recent progress in alkaline water electrolysis for hydrogen production and applications

Alkaline water electrolysis is one of the easiest methods for hydrogen production, offering the advantage of simplicity. The challenges for widespread use of water electrolysis are to reduce energy consumption, cost and maintenance and to increase reliability, durability and safety. This literature review examines the current state of knowledge and technology of hydrogen production by water electrolysis and identifies areas where R&D effort is needed in order to improve this technology. Following an overview of the fundamentals of alkaline water electrolysis, an electrical circuit analogy of resistances in the electrolysis system is introduced. The resistances are classified into three categories, namely the electrical resistances, the reaction resistances and the transport resistances. This is followed by a thorough analysis of each of the resistances, by means of thermodynamics and kinetics, to provide a scientific guidance to minimising the resistance in order to achieve a greater efficiency of alkaline water electrolysis. The thermodynamic analysis defines various electrolysis efficiencies based on theoretical energy input and cell voltage, respectively. These efficiencies are then employed to compare different electrolysis cell designs and to identify the means to overcome the key resistances for efficiency improvement. The kinetic analysis reveals the dependence of reaction resistances on the alkaline concentration, ion transfer, and reaction sites on the electrode surface, the latter is determined by the electrode materials. A quantitative relationship between the cell voltage components and current density is established, which links all the resistances and manifests the importance of reaction resistances and bubble resistances. The important effect of gas bubbles formed on the electrode surface and the need to minimise the ion transport resistance are highlighted. The historical development and continuous improvement in the alkaline water electrolysis technology are examined and different water electrolysis technologies are systematically compared using a set of the practical parameters derived from the thermodynamic and kinetic analyses. In addition to the efficiency improvements, the needs for reduction in equipment and maintenance costs, and improvement in reliability and durability are also established. The future research needs are also discussed from the aspects of electrode materials, electrolyte additives and bubble management, serving as a comprehensive guide for continuous development of the water electrolysis technology.     

Electrochemical preparation and characterization of C/Ni–NiIr composite electrodes as novel cathode materials for alkaline water electrolysis

The binary NiIr coatings as novel and effective catalysts were electrochemically prepared on a Ni-modified carbon felt electrode (C/Ni–NiIr) in view of their possible application as cathode materials for the alkaline water electrolysis. The surface morphology and chemical composition of the electrodes were investigated by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) techniques. Their hydrogen evolution activity was assessed by electrochemical techniques. It was found that, the preparation of NiIr co-deposits on the Ni-modified C substrate enhances the hydrogen evolution activity. The electrodes have wide space, which is an advantage for diffusion of ions and hydrogen bubbles through inner zones and reduction of diffusion resistance. The high hydrogen evolution activity of the C/Ni–NiIr electrode was mainly attributed to the finer surface structure, high surface area and the higher numbers of the catalytically active centers.     

Numerical and experimental investigation of two-phase flow in an electrochemical cell

In this study, a two-phase mathematical model is adapted to study void fraction distribution, flow field and characteristics of electrolysis process. The model involves transport equations for both liquid and gaseous phases. An experimental set-up is established to collect data to validate and improve the mathematical model. The void fraction is determined from measurement of resistivity changes in the system due to the presence of bubbles. It is observed that there is a good agreement between the numerical results and the experimental data.     

Porous nickel electrodes in water electrolysis 1. Electrode preparation and polarization studies in strong alkali

Replacement of “plate” electrodes in water electrolysis cells by porous nickel electrodes leads to many advantages resulting in reduced specific energy consumption for hydrogen production. Yet, the behaviour of porous electrodes in alkaline or acidic electrolysis has not been extensively studied; available data at temperatures above 70°C is negligible. This paper describes the techniques developed to prepare the porous electrodes, their physical characteristics and their performance in strong alkali as hydrogen and oxygen gas electrodes. Steady state cell polarization studies over a range of 100 to 10,000 ASM at different temperatures were carried out in 6N KOH solution for different electrode samples prepared by alloy electrodeposition and powder metallurgy methods. Electrodes prepared by these two methods were compared with respect to their electrochemical performance. The current carrying capacity at a given overvoltage was evaluated for different electrode thicknesses. These electrodes have been used successfully in test modules of bipolar filter press type construction for hydrogen production.     

Prospects for hydrogen production by water electrolysis to be competitive with conventional methods

With the impending unavailability of oil and natural gas, hydrogen will be produced on a large scale in the United States (1) from coal, or (2) by water electrolysis using electricity derived from nuclear or solar energy. In many parts of the world which lack fossil fuels, the latter will be the only possible method. The cost of purification of hydrogen produced from fossil fuels will increase its cost to about the same level as that of electrolytic hydrogen. When hydrogen is required in relatively small quantities too, the electrolytic method is advantageous. To minimize the cost of hydrogen produced by water electrolysis, it is necessary to reduce capital costs and approach 100% energy efficiencies. Areas of research, which will be necessary to achieve these goals are: (1) maximization of surface areas of electrodes; (2) use of thin electrolyte layers; (3) increase of operating temperature in alkaline water electrolysis cells to about 120–150°C; (4) selection and evaluation of separator materials; (5) electrocatalysis of the hydrogen and oxygen electrode reaction; (6) mixed oxides as oxygen electrodes; and (7) photoelectrochemical effects. The progress made to date and proposed studies on these topics are briefly dealt with in this paper. The General Electric Solid Polymer Water Electrolyzer and Teledyne Alkaline Water Electrolysis Cells, operating at about 120–150°C, look most promising in achieving the goals of low capital cost and high energy efficiency.     

Investigation of alkaline water electrolysis performance for different cost effective electrodes under magnetic field

Alkaline water electrolysis is the easiest methods for hydrogen production because of their simplicity. Although the simplicity is an advantage; reducing the energy consumption and maintaining the durability and the safety of these systems are the main challenges. In this paper, alkaline water electrolysis system, that uses cost effective electrode materials and magnetic field effects are presented. Cost effective electrodes such as high carbon steel, 304 stainless steel, 316L low carbon steel and graphite material are used for the hydrogen production. After the selection of the best electrode pair, effects of magnetic field to hydrogen production and change of current density are investigated for KOH electrolytes in different concentrations (5 wt%, 10 wt% and 15 wt%). According to the experimental observations the direction of the Lorentz Force affects the hydrogen production and current density. When the Lorentz Force is directed upward, it enhances the hydrogen production for 5 wt% and 15 wt% KOH solution by almost 17%. The increase in current density for 5 wt%, 10 wt% and 15 wt% concentration is 19%, 5%, 13%, respectively. Forced convection in the magnetic field enhances the separation of gas bubbles from electrode surface. Downward directed Lorentz Force decreases hydrogen production and current density values significantly. For 5 wt%, 10 wt% and 15 wt% the hydrogen production decreases by 14%, 8%, 7%, respectively. Similarly, current density for downward directed Lorentz Force decreases by 11%, 7%, 4%, respectively.     

Water electrolysis using plate electrodes in an electrode-paralleled non-uniform magnetic field

Compared with other ways to produce hydrogen, water electrolysis is the best way to obtain ultra-pure hydrogen, but its low energy efficiency greatly limits its wide application. It was proved that external magnetic field can reduce energy consumption, thereby increase electrolysis efficiency. Most of the researchers are focused on the impact of uniform magnetic field but few on a non-uniform one. To address the industrial operation reality, in our work, water electrolysis was operated using alkaline solution and plate electrodes in a non-uniform Magnetic field. The results show that a rotational flow on the vertical plane was formed by Lorentz force within the entire cell range. Although the entrainment effect of rotating flow made the cell full of microbubbles, the cell voltage was still reduced. By measuring the voltage difference of cathode side and anode side, we think that the bubble layer in the vicinity of the electrode surface matters the most among the sources of electric resistance. And the velocity distribution near the electrode was measured by PIV, it reveals that MHD flow is the dominant effect on the flow field of the cell. The results show that non-uniform magnetic field has potential merit in industrial electrolysis process.     

VOF modelling of gas–liquid flow in PEM water electrolysis cell micro-channels

In this study, the gas–liquid flow through an interdigitated anode flow field of a PEM water electrolysis cell (PEMEC) is analysed using a three-dimensional, transient, computational fluid dynamics (CFD) model. To account for two-phase flow, the volume of fluid (VOF) method in ANSYS Fluent 17.2 is used. The modelled geometry consists of the anode channels and the anode transport layer (ATL). To reduce the complexity of the phenomena governing PEMEC operation, the dependence upon electro-chemistry is disregarded. Instead, a fixed source of the gas is applied at the interface between the ATL and the catalyst layer. An important phenomenon that the model is able to capture is the gas–liquid contact angle on both the channel wall and ATL-channel interface. Particularly, the latter interface is crucial in capturing bubble entrainment into the channel. To validate the numerical simulation, photos taken of the gas–liquid flow in a transparent micro-channel, are qualitative compared against the simulation results. The experimental observations confirm the models prediction of long Taylor bubbles with small bubbles in between. From the simulation results, further intriguing details of the flow are revealed. From the bottom to the top of the outgoing channel, the film thickness gradually increases from zero to 200 μm. This increase in the film thickness is due to the particular superficial velocity field that develops in an interdigitated flow. Here both the superficial velocities change along the length of the channel. The model is capable of revealing effect of different bubble shapes/lengths in the outgoing channel. Shape and the sequence of the bubbles affect the water flow distribution in the ATL. The model presented in this work is the first step in the development of a comprehensive CFD model that comprises multiphase flow in porous media and micro-channel, electro-chemistry in catalyst layers, ion transport in membrane, hydrogen evolution, etc. The model can aid in the study of gas–liquid flow and its impact on the performance of a PEMEC.     

Nanoporous oxide coatings on stainless steel to enable water splitting and reduce the hydrogen evolution overpotential

Nanoporous oxides (SiO₂, TiO₂, ZrO₂, and AlOOH) synthesized from sol–gel chemistry techniques were used as coatings for stainless steel electrodes in water electrolysis systems. These oxide coatings have been shown to provide corrosion protection of the stainless steel electrodes at potentials positive enough to evolve oxygen on the positive electrode. In addition, all four oxide coated electrodes showed a 100–200 mV lower overpotential for hydrogen evolution than an uncoated stainless steel electrode. This was attributed to the ability of the oxide coatings to adsorb hydrogen on the surface of the electrode. To verify gas production from these electrodes, a custom alkaline electrolyzer was built and tested with a constant applied current. The flow rate of gas was measured for five different electrode connection configurations, utilizing both monopolar and bipolar electrodes. The efficiency of the system was calculated to be between 66 and 75% as defined as the ratio of the higher heating value of hydrogen to the energy applied to the system. The oxide coated stainless steel electrodes were used without any additional catalysts, including the precious metals.     

Studies on the hydrogen evolution reaction on different stainless steels

The hydrogen generation by water electrolysis process is a promising technology. The materials commonly utilized for water electrolysis are those based on Raney Nickel and their alloys, but these materials are expensive. We choose a material with nickel presence, more cheap and versatile like stainless steel. In this work, we report the study of hydrogen evolution reaction (her) on different stainless steel electrodes in alkaline solutions (NaOH and KOH). The electrochemical behavior of stainless steel in alkaline medium was studied by cyclic voltammetry. In addition, we designed and developed an alkaline electrohydrolyzer prototype which consists of the anode and cathode electrodes which were made of different types of stainless steel and the electrolyte was KOH. We determined the appropriate electrolyte, stainless steel electrode and voltage for the efficient hydrogen production.     

The effect of magnetic force on hydrogen production efficiency in water electrolysis

Water electrolysis is one of the most common ways to produce hydrogen gas. It has several merits, such as: high efficiency, high purity, and easy use. In this paper, electrodes with different magnetism are adapted on the hydrogen production by water electrolysis, and the influences of magneto-hydrodynamics on the electrolysis process are discussed. The influences of working parameters related to magnetism and water electrolysis are also discussed as well.     

Application of green hydrogen with theoretical and empirical approaches of alkaline water electrolysis: Life cycle-based techno economic and environmental assessments of renewable urea synthesis

Alkaline water electrolysis which is the most commercialized and mature technology of water electrolysis was researched to improve performance by the Korea Institute of Energy Research (KIER). In line with the trend of energy shift, renewable urea production through hydrogen production from alkaline water electrolysis was proposed in this work. To validate the process modeling of renewable urea production and hydrogen performance analysis with I–V curves was assessed. Economic and life cycle assessments were conducted to provide quantitative guidelines for renewable urea production. Absolutely, the influential factor of unit urea production cost was hydrogen from alkaline water electrolysis and environmental assessment results as well. Moreover, the guidelines for renewable urea production were provided through cost estimation and life cycle assessment. In summary, hydrogen production from alkaline water electrolysis had a significant impact on urea production and for this reason, research on alkaline water electrolysis should continue for further development.     

Effect of operating parameters on hydrogen production by electrolysis of water

This paper presents an experimental study of hydrogen production by alkaline water electrolysis using Zinc alloys as materials for cathode. The aim of this study is to select the best alloy for producing hydrogen on testing the effect of some operating parameters. Experiments were conducted on a water electrolysis cell with two electrodes (anode/cathode). Throughout these experiments, we have chosen to use NaOH solution with different concentrations as an electrolyte. Binary alloys: Zn95%Fe5%, Zn90%Fe10%, Zn85%Fe15%, Zn95%Cu5%, Zn90%Cu10%, Zn85%Cu15%, Zn95%Co5%, Zn90%Co10%, Zn95%Cr5% and Zn90%Cr10% (mass %) were prepared as electrodes for the cathode. The effect of electrode composition, the electrolyte concentration, the voltage and amperage applied on volume of hydrogen produced are experimentally investigated. The results showed that the performance of alkaline water electrolysis is significantly affected by these various factors. Indeed, this preliminary study revealed that cathodes elaborated by (Zn95%Cr5%) and (Zn90%Cr10%) (mass %) produce more hydrogen gas than other alloys, in a minimum durations over the range of operating parameters tested.     

Life cycle assessment of high temperature electrolysis for hydrogen production via nuclear energy

A life cycle assessment (LCA) of one proposed method of hydrogen production—the high temperature electrolysis of water vapor—is presented in this paper. High temperature electrolysis offers an advantage of higher energy efficiency over the conventional low-temperature alkaline electrolysis due to reduced cell potential and consequent electrical energy requirements. The primary energy source for the electrolysis will be advanced nuclear reactors operating at temperatures corresponding to those required for the high temperature electrolysis. The LCA examines the environmental impact of the combined advanced nuclear-high temperature electrolysis plant, focusing upon quantifying the emissions of carbon dioxide, sulfur dioxide, and nitrogen oxides per kilogram of hydrogen produced. The results are presented in terms of the global warming potential (GWP) and the acidification potential (AP) of the system. The GWP for the system is 2000 g carbon dioxide equivalent and the AP, 0.15 g equivalents of hydrogen ion equivalent per kilogram of hydrogen produced. The GWP and AP of this process are one-sixth and one-third, respectively, of those for the hydrogen production by steam reforming of natural gas, and are comparable to producing hydrogen from wind- or hydro-electricity powered conventional electrolysis.     

Test of conductor and semiconductor electrocatalysts in high voltage alkaline electrolyzer as production media for green hydrogen

Despite the restricted success of conductor and semiconductor electrodes in solving hydrogen production problems, they provide a promising alternative to expensive conventional electrodes in water electrolysis investigations. Titanium dioxide (TiO₂) and silver (Ag) are widely used as photocatalysts in water splitting systems for hydrogen generation. Though TiO₂ is an inactive chemical semiconductor with poor conductivity, it has not been entirely investigated as an electrocatalyst yet. Two criteria were used to achieve this target: supplying high voltage to overcome the TiO₂ large band gap and immersing it in an alkaline solution to activate its inert surface. For comparison study, Ag noble metal nanoparticles coating was employed as a competitive electrocatalyst. In this regard, the application of Ag and TiO₂ coated on Ti electrodes in a hydrogen production system operated under high voltage was reported. The nanoparticles were synthesized using cost-effective and simple methods based on UV-deposition for Ag nanoparticles and the chemical precipitation method for TiO₂ nanoparticles. Then the synthesized nanoparticles were deposited on the Ti electrodes by simple immersion. The synthesized nanoparticles and coated electrodes were tested by XRD, SEM, and EDS to study their morphology, structure, particle size, and surface composition. Based on these results, TiO₂ nano-powder and coated electrodes exhibited homogenous spheres with a mixture of rutile and anatase phases, the majority being the anatase phase. The Ag-coated Ti substrate possessed a smaller crystallite size compared to TiO₂ coated substrate. To evaluate the performance of Ag/Ti and TiO₂/Ti electrodes toward hydrogen production, H₂ flow rates were measured in a 3.6 M KOH electrolytic solution at 6 V. Hydrogen flow rates obtained for pure Ti, Ag, and TiO₂ electrodes at a steady state were 21, 35, and 37 SCCM (standard cm³/min), respectively. Also, it was found that energy consumption was reduced when the electrodes were coated with nanoparticles. Furthermore, the electrolyzer's performance was assessed by calculating the hydrogen production efficiency and the voltage efficiency. The results showed that using TiO₂ electrodes gave the best hydrogen production and voltage efficiencies of 27% and 23%, respectively. This study brings new insights about Ag and TiO₂ coated electrodes in alkaline water electrolysis at high voltage regarding nanoparticle performance, hydrogen production, system performance, and energy consumption. In addition, minimizing the fabrication and operation costs of hydrogen production is the major enabler for the broad commercialization of water electrolysis devices.