Porous electrode improving energy efficiency under electrode-normal magnetic field in water electrolysis

The porous electrodes (Ni, Cu) with 110 pores per inch (PPI) are adopted in water electrolysis for hydrogen production under normal-to-electrode magnetic field. The result shows that the voltage drop between electrodes can be reduced up to 2.5% under 0.9 T field, and the electric energy efficiency is improved correspondingly. Based on the numerical simulation method, the micro-magnetohydrodynamic (micro-MHD) convection induced by Lorentz force within the porous structure is found. The results showed that although the apparent current direction is parallel to magnetic field outside the porous electrode, the electric field may be distorted within the porous structure, and the Lorentz force is involved near the rib of the micro structure where the current is not parallel to the magnetic field any more. Micro-MHD plays the role of strengthening the mass transfer and facilitating bubble to eject from the porous structure, which results in the cell voltage decreasing. The combined application of porous electrode and magnetic field should be potential to further improve energy efficiency of water electrolysis for hydrogen production.     

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.     

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.     

预磁极化条件下PEM水电解制氢特性与效率研究

为提高质子交换膜（proton exchange membrane,PEM）水电解制氢速率、降低电解所需能耗,针对磁场预极化条件下蒸馏水的分子极性和应力特性进行研究,通过构建磁场环境下氢质子的能级跃迁微观物理模型与磁化矢量——极化氢质子浓度对应的宏观数学模型,对不同磁场强度下电解液的离子电导率、电流密度和制氢速率进行定性和定量分析,并利用自主搭建的可调节预磁极化PEM水电解制氢试验平台对所提出方法的有效性进行重复试验。试验结果表明,经过预磁极化处理的蒸馏水电导率提高了2~3倍,且随着磁场强度的增加,PEM电解电流密度不断增大,极间电圧不断减小,制氢速率明显提升。     

Effects of magnetic field and pulse potential on hydrogen production via water electrolysis

This experiment uses nickel electrodes and adds pulse potential and magnetic force when producing hydrogen via water electrolysis and explores how related parameters are affected by magnetohydrodynamics and pulse potential. Experiments showed that the Lorentz force of the magnetic field changes the direction of convective flow of the electrolyte, which affects the flow of bubbles during electrolysis. Adding a magnetic field increases the rate of current density by roughly 15% under a normal temperature, a distance of 2 mm between electrodes and a potential of 4 V. Pulse potential instantaneously increases current and accelerates both the movement of bubbles from the electrode surface and the mass transfer rate in the electrolyte, which lowers electrochemical polarization in the diffussion layer and further increases hydrogen production efficiency. When the duty cycle is 10% and the pulse on‐time is 10 ms, almost 88% of overall power is converted, and current density increases by 680 mA/cm², which is an increase of roughly 38%. Generally, pulse potential and magnetic field effects enhance each other when added under suitable pulse potential and basic potential. Copyright © 2013 John Wiley & Sons, Ltd.     

The dynamic effect of Micro-MHD convection on bubble grown at a horizontal microelectrode

Relatively low efficiency is the biggest obstacle to the popularization of water electrolysis, which is a particularly feasible way to produce super-pure hydrogen. Imposing a magnetic field can increase the hydrogen production efficiency of water electrolysis. However, the enhancement's detailed mechanism still lacks an insightful understanding of the bubbles' micro vicinity. Our recent work aims to understand why the micro-magnetohydrodynamic (MHD) convection hinders single bubbles' detachment on the microelectrode. A water electrolysis experiment by microelectrode is performed under an electrode-normal magnetic field, and dynamic analysis of the single bubble growing on microelectrodes is performed. The variation of bubble diameter with time in the presence or absence of the magnetic field was measured, and the forces acting on the bubble were quantified. The result shows that the micro-MHD convection, induced by Lorentz force, can give rise to a downward hydrodynamic pressure force that will not appear in large-scale MHD convection. This force can be of the same magnitude as the surface tension, so it dramatically hinders bubbles' detachment. Besides, the Kelvin force provides a new potential way for further improving the efficiency of water electrolysis.     

Hydrogen production using alkaline electrolyzer and photovoltaic (PV) module

In this paper it is presented hydrogen production using alkaline water electrolysis where a 30 W photovoltaic (PV) module was involved as a source of electric energy. Therefore, the process is without emitting CO₂. There is constructed and tested an alkaline electrolyzer with 50 × 50 × 2 mm Ni metal foam electrodes, 50 × 50 × 0.4 mm Zirphon^® membrane and 25% alkaline (KOH) solution electrolyte. Electrolyzer UI characteristics for natural and forced flow of electrolyte with PV module UI characteristics are presented. The results are in favor of forced flow circulation, and these are better if the flow velocities are higher. Calculated Energy efficiency (based on hydrogen high heating value) for both types of circulation is above 55%. There are much evidence for further improvement of the system components and consequently electrolyzer and system efficiency.     

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.     

Hydrogen bubble evolution from magnetized nickel wire electrode

How to reduce the bubble coverage of the electrode is one of the key issues in water electrolysis which is related to the reduction of energy consumption. In this work, the magnetized nickel electrode with 100 μm diameter is used as working electrode in hydrogen evolution reaction (HER) during alkaline water electrolysis (1 mol/L, KOH). According to the experimental observation, both of the bubble's diameter and number have decreased at the magnetized surface compared with the unmagnetized one. The B–H loop measurement shows that the residual magnetic field intensity (Br) of the magnetized nickel electrode is up to 0.03 T. It can be found from the numerical simulation result that the residual magnetic field exactly right brings the Lorentz force and magnetohydrodynamic (MHD) convection near the electrode surface, which play the role of helping hydrogen bubble release from the electrode, even if the external magnetic field is absent in experiment. The new finding may develop a new way of utilizing magnetic field in water electrolysis for gas product elimination and energy conservation.     

Optimized photovoltiac system for hydrogen production

Hydrogen, which can be produced by water electrolysis, can play an important role as an alternative to conventional fuels. It is regarded as a potential future energy carrier. Photovoltaic arrays can be used in supplying the water electrolysis systems by their energy requirements. The use of photovoltaic energy in such systems is very suitable where the solar hydrogen energy systems are considered one of the cleanest hydrogen production technologies, where the hydrogen is obtained from sunlight by directly connecting the photovoltaic arrays and the hydrogen generator. This paper presents a small PV power system for hydrogen production using the photovoltaic module connected to the hydrogen electrolyzer with and without maximum power point tracker. The experimental results developed good results for hydrogen production flow rates, in the case of using maximum power point tracker with respect to the directly connected electrolyzer to the photovoltaic modules.     

Numerical simulation of electromagnetically controlled thermal convection of glass melt in a crucible

In this paper, we present a three-dimensional numerical study of glass melt in a small scale circular crucible heated by two rod electrodes. Lorentz forces are imposed into the melt by applying an additional external magnetic field. The coupled non-linear conservation equations for mass, momentum, energy and electrical charge are solved with the commercial finite volume code FLUENT. We perform numerical parameter studies by varying the magnetic flux density and the electrode potential to verify the influence of the Lorentz force on the velocity and temperature distribution in the crucible. We observe that the Lorentz force leads to an overall increase of the kinetic energy. Especially below the electrodes, a region which is not affected by buoyancy, the Lorentz force increases the velocity significantly. If the Lorentz force is the dominating driving force the mean velocity is almost a linear function of the Lorentz force. For counteracting Lorentz force and buoyancy between the electrodes we find a discontinuous modification of the flow pattern during the transition from buoyancy dominated to a Lorentz force dominated flow regime and vice versa. Even more, we pass through a hysteresis and obtain two steady solutions for one set of parameters depending on the starting conditions. Furthermore, we identify regimes in which we have a significant improvement of the temperature homogenization. The results show that Lorentz forces provide a new way to influence thermally driven convection of molten glass and can lead to the improvement of mixing.     

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.     

High temperature electrolysis of hydrogen bromide gas for hydrogen production using solid oxide membrane electrolyzer

Using solid oxide membrane, this paper presents the theoretical modeling of the high temperature electrolysis of hydrogen bromide gas for hydrogen production. The electrolysis of hydrogen halides such as hydrogen bromide is an attractive process, which can be coupled to hybrid thermochemical cycles. The high temperature electrolyzer model developed in the present study includes concentration, ohmic, and activation losses. Exergy efficiency, as well as energy efficiency parameters, are used to express the thermodynamic performance of the electrolyzer. Moreover, a detailed parametric study is performed to observe the effects of various parameters such as current density and operating temperature on the overall system behavior. The results show that in order to produce 1 mol of hydrogen, 1.1 V of the applied potential is required, which is approximately 0.8 V less compared to high temperature steam electrolysis under same conditions (current density of 1000 A/m² and temperature of 1073 K). Furthermore, it is found that with the use of the presented electrolyzer, one can achieve energy and exergy efficiencies of about 56.7% and 53.8%, respectively. The results presented in this study suggest that, by employing the proposed electrolyzer, two-step thermochemical cycle for hydrogen production may become more attractive especially for nuclear- and concentrated solar-to-hydrogen conversion applications.     

A comprehensive modeling method for proton exchange membrane electrolyzer development

Hydrogen attracts significant interests as an effective energy carrier that can be derived from renewable sources. Hydrogen production using a proton-exchange membrane (PEM) electrolyzer can efficiently convert renewable power via water splitting in wide scales—from large, centralized generation to on-site production. Mathematical models with multiple scales and fidelities facilitate the continuing improvements of PEM electrolyzer development to improve performance, cost, and reliability. The model scopes and methods are presented in this paper, which also introduces a comprehensive PEM electrolysis modeling tool based on computational fluid dynamics (CFD) software, ANSYS/Fluent. The modeling tool incorporates electrochemical model of a PEM electrolysis cell to simulate the performance of coupled thermal-fluid, species transport, and electrochemical processes in a product-scale cell or stack by leveraging the powerful meshing generation and CFD solver of ANSYS/Fluent. The thermal-fluid modeling includes liquid water/gas two-phase flow and simulates a PEM electrolysis cell by using Fluent user-defined functions as add-on modules accounting for PEM-specific species transport and electrochemical processes. The modeling outcomes expediate PEM electrolyzer scaling up from basic material development and laboratory testing.     

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.     

Performance evaluation and optimum design strategies of an acid water electrolyzer system for hydrogen production

The performance of a new acid water electrolyzer system for hydrogen production is investigated, based on semi-empirical equations of a phosphoric acid water electrolyzer. The circulating electrolyte concentrations under differently operating temperatures are optimized so that the minimum input voltages of the electrolyzer are determined for other given conditions. The optimum electrochemical characteristics of the electrolyzer are revealed. Moreover, it is expounded that the Joule heat resulting from the irreversibilities inside the electrolyzer is larger than the thermal energy needed in the water splitting process. The general performance characteristics of the phosphoric acid water electrolyzer system are discussed, from which the lower bound of the operating current density is determined. The upper bound of the operating current density is further determined by introducing a multi-objective function including the system efficiency and hydrogen production rate. Consequently, some optimum design strategies of a phosphoric acid water electrolyzer system are obtained and may be chosen according to different practical requirements.     

Structure design and control strategy of a new alkaline water electrolyzer based on heat exchange

The overall energy conversion efficiency and the power regulation performance of the volatile renewable energy alkaline water electrolyzer (AWE) hydrogen production system need to be improved. Efficient use of heat in the electrolysis process and optimization of the control strategy are technically feasible. According to the concept of heat exchange utilization, this paper proposes a series parallel modular structure of AWE, which realizes heat exchange and utilization between modules. Based on the electrothermal characteristics of AWE and the power fluctuation characteristics of volatile energy, the function positioning and control strategy of the module are proposed. Theoretical analysis, together with a case study, has been conducted to show the overall efficiency and power regulation characteristics of the traditional AWE, the traditional combined AWE and the proposed new AWE under various working scenarios. Research study results show that the proposed new structure and control strategy can effectively improve the overall energy efficiency and static as well as dynamic power regulation characteristics of the electrolyzer, with the energy efficiency increased up to 16%. Although the static power range decreases slightly in some conditions, it always maintains the ability of wide range regulation. The findings can provide reference for the research and development of new AWE that improve the power response capability and the comprehensive utilization of energy under the premise of ensuring a certain power adjustment range.     

Process modelling of an alkaline water electrolyzer

In this paper a model for the prediction of the product gas purity in alkaline water electrolysis is proposed. For the estimation of the exhaust gas compositions the operating conditions, such as current density, electrolyte flow rate, concentration and temperature as well as process management possibilities are considered. The development of the model relies on a classical process engineering approach and depicts the electrolysis cell through coupled continuously stirred-tank reactors. Furthermore, the mass transport phenomena between the phases are considered through the application of Reynolds and Sherwood correlations. Finally, the validation of the model is performed through experiments, which are carried out in a lab-scale electrolyzer with a 150 cm² zero-gap cell and KOH electrolyte at atmospheric pressure. This investigation reveals that gas purity in alkaline water electrolysis is mainly affected by mixing the anodic and cathodic electrolyte cycles, which transport dissolved electrolysis products into the opposite half cell compartments. However, this transport mechanism can be significantly reduced by adjustment of the operating conditions of the electrolyzer.     

Evaluation and calculation on the efficiency of a water electrolysis system for hydrogen production

With the help of the typical model of a water electrolysis hydrogen production system, which mainly includes the electrolysis cell, separator, and heat exchangers, three expressions of the system efficiency in literature are compared and evaluated, from which one reasonable expression of the efficiency is chosen and directly used to analyze the performance of a water electrolysis hydrogen production system under different operation conditions. Several new configurations of a water electrolysis system are put forward and the problem how to calculate the efficiencies of these configurations is solved. Moreover, a solid oxide steam electrolyzer system (SOSES) for hydrogen production is taken as an example to expound that the different configurations of a water electrolysis system should be adopted for different operation conditions. The results obtained here may provide some guidance for the optimum design and operation of water electrolysis systems for hydrogen production.     

Predicting efficiency of solar powered hydrogen generation using photovoltaic-electrolysis devices

Hydrogen fuel for fuel cell vehicles can be produced by using solar electric energy from photovoltaic (PV) modules for the electrolysis of water without emitting carbon dioxide or requiring fossil fuels. In the past, this renewable means of hydrogen production has suffered from low efficiency (2–6%), which increased the area of the PV array required and therefore, the cost of generating hydrogen. A comprehensive mathematical model was developed that can predict the efficiency of a PV-electrolyzer combination based on operating parameters including voltage, current, temperature, and gas output pressure. This model has been used to design optimized PV-electrolyzer systems with maximum solar energy to hydrogen efficiency. In this research, the electrical efficiency of the PV-electrolysis system was increased by matching the maximum power output and voltage of the photovoltaics to the operating voltage of a proton exchange membrane (PEM) electrolyzer, and optimizing the effects of electrolyzer operating current, and temperature. The operating temperature of the PV modules was also an important factor studied in this research to increase efficiency. The optimized PV-electrolysis system increased the hydrogen generation efficiency to 12.4% for a solar powered PV-PEM electrolyzer that could supply enough hydrogen to operate a fuel cell vehicle.