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.     

Pulsed current water splitting electrochemical cycle for hydrogen production

A pulsed current 3 D MnO₂ electrode water splitting electrochemical cycle is being proposed for hydrogen production. In 3D MnO₂ electrochemical cycle, the reactions take place at the solid/liquid and solid/gas two phase boundaries. Also, this electrochemical cycle should be able to generate hydrogen and oxygen gas separately at different periods of time. Here, we applied an interrupted pulsed current to reduce the overpotential caused by diffusion layers in conventional direct current electrolysis. The pulsed current, which disturbs the formation of the ion diffusion layer in the vicinity of the electrodes, is observed to be effective above 50 Hz. The best electrolysis performance was recorded at a current density of 0.2 A cm^?2, and the observed cell voltage was 1.69 V at 25 °C for a pulse frequency of 500 Hz, which is less than the corresponding conventional alkaline electrolysis.     

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.     

Biochar sacrificial anode assisted water electrolysis for hydrogen production

Carbon-assisted water electrolysis uses carbon oxidation reaction replacing oxygen evolution reaction to decrease the anode potential and the energy consumption for water electrolysis hydrogen production. However, the mass transfer between carbon particle-electrolyte-anode limits its energy saving effect. Based on the principle of self-corrosion/oxidation of carbon-based electrode materials, the biochar sacrificial anode was proposed and investigated to solve the mass transfer issue in carbon slurry assisted water electrolysis for hydrogen production. Results showed that the activity and stability of sacrificial anode could be improved simultaneously in high concentration alkaline electrolyte using pinewood char as active substance, graphite as conductive agent and coal liquefying residue as binder. The biochar anode produced less oxygen than Pt anode, and the anode potential of biochar was 60–76% of that Pt anode. The application of biochar as sacrificial anode offers an industrial clean, scalable and sustainable idea to obtain green hydrogen.     

Discriminating between the effect of pulse width and duty cycle on the hydrogen generation performance of 3-D electrodes during pulsed water electrolysis

The present study investigates the effect of applying voltage and current pulses during alkaline water electrolysis using 3-D Ni-based electrodes. The pulses had a square shape and alternated hydrogen production and resting time. When voltage pulses were applied, it was observed that the current at on-time was systematically higher than the current during DC electrolysis. However, during off-time, a change in polarization was observed, which decreased the overall voltage pulse performance. For pulses with a 50% duty cycle and a pulse width of 1 ms, the current response was mainly capacitive and almost no hydrogen production occurred. Current pulses on the other hand were proven to be much more promising in improving the energetic process efficiency. In that case, a pulse period of 2 ms resulted in an overpotential reduction of 17% for a 50% duty cycle. This reduction further increased to 28% when decreasing the duty cycle to 20%. Finally, in all cases where faradaic processes were dominant, applying a forced electrolyte flow was shown to be beneficial.     

An electrochemical and analytical characterization of surface films on AISI 316 as electrode material for pulse electrolysis of water

Pulse electrolysis of water is a highly efficient method of production of hydrogen and hydrogen/oxygen gas mixtures, sometimes called hydroxygen. In conditions of pulse electrolysis, the process rate is reported to increase in comparison to the dc regime, which poses more stringent requirements to the corrosion resistance of the electrode materials. The processes of their corrosion and degradation are expected to depend on the electrical characteristics of the pulse (nominal current/voltage, frequency, duty cycle). The aim of the present paper is to investigate the effect of pulse characteristics on the electrochemical properties of surface films formed on AISI 316 stainless steel using voltammetry and electrochemical impedance spectroscopy. An attempt to correlate these properties with the surface state obtained from microscopic observations and X-ray photoelectron spectroscopic estimations of the surface film composition is also made.     

A new analysis of two phase flow on hydrogen production from water electrolysis

It is clear that the entire world have to research, develop, demonstrate and plan for alternative energy systems for shorter term and also longer term. As a clean energy carrier, hydrogen has become increasingly important. It owes its prestige to the increase within the energy costs as a result of the equivocalness in the future availability. Two phase flow and hydrogen gas flow dynamics effect on performance of water electrolysis. Hydrogen bubbles are recognized to influence energy and mass transfer in gas-evolving electrodes. The movement of hydrogen bubbles on the electrodes in alkaline electrolysis is known to affect the reaction efficiency. Within the scope of this research, a physical modeling for the alkaline electrolysis is determined and the studies about the two-phase flow model are carried out for this model. Internal and external forces acting on the resulting bubbles are also determined. In this research, the analytical solution of two-phase flow analysis of hydrogen in the electrolysis is analyzed.     

Energy analysis of a class of copper–chlorine (Cu–Cl) thermochemical cycles

For separating water into hydrogen and oxygen through intermediate Cu–Cl compounds, the new system configurations for 5-step, 4-step and 3-step thermochemical cycles using electrolysis of CuCl/HCl or CuCl and Brayton cycle are addressed in Aspen Plus^® environment. To address the feasible predictions by thermodynamic systems, we found that (i) the pressure and temperature affect the product yields of CuO ¹ CuCl₂ and CuCl in the hydrolysis and oxygen production processes; (ii) the internal heat recovery ratio (IHRR) and the feed ratio of H₂O/CuCl₂ dominate the energy efficiencies and Cl₂ production, respectively. Based on the prescribed operating conditions, the comparative evaluations show that the 5-step Cu–Cl cycle using CuCl electrolyzer can ensure the highest energy efficiency while IHRR = 72%, the 3-step Cu–Cl cycle using CuCl electrolyzer can ensure the less equipment and the highest energy efficiency while IHRR = 100%. The 4-step Cu–Cl cycle using CuCl/HCl electrolyzer, where the electrolyzer prevents copper crossovers and safely produces the pure hydrogen gas at low temperature, has a high possibility of commercialization due to the lower grade heat requirement, the less number of equipment and the higher energy efficiency.     

Revealing the impact of hydrogen production-consumption loop against efficient hydrogen recovery in single chamber microbial electrolysis cells (MECs)

Microbial electrolysis for hydrogen production exhibited great advantages over many other biohydrogen production techniques in terms of hydrogen yield (HY) and energy efficiency (EE). With the elimination of methanogens, homoacetogens could thrive as the major hydrogen sink to impair HY and EE. However, the determination of hydrogen loss in microbial electrolysis cells (MECs) was rather controversial. In this study, we quantitatively investigated the negative impact of homoacetogens on hydrogen recovery in single chamber MECs. Hydrogen partial pressure (HPP) ranging from 0 to 40 kPa greatly affected the hydrogen consumption rate while acetate concentration ranging from 0 to 100 mM had little impact. HY base on consumed substrate was not significantly affected with less than 20 kPa HPP but decreased from 87% to 66% with 20–34 kPa HPP. And the EE based on input electricity was decreased from 160% to 48% accompanied with the increase of HPP from 7 to 34 kPa. Microbial community analysis revealed that Acetobacterium was the dominant homoacetogenic hydrogen scavenger in cathodic biofilm and planktonic cells in the single chamber MECs.     

Determination of the oxygen and hydrogen overvoltage in concentrated alkali hydroxide solutions

Electrolytic water splitting has gained importance in recent years because of its promise of economic production without adversive environmental impact of hydrogen as a chemical, and particularly on a large scale, as an energy carrier for novel energy systems proposed for introduction in the near future. Reliable measurements of hydrogen and oxygen overvoltages are of key significance in the development of alkaline water electrolysis systems. In this paper, on the basis of the most recent values of the relevant thermodynamic parameters, precise equations were derived for measuring oxygen and hydrogen overvoltages by using the particularly suitable Hg/HgO/OH^? as well as reversible hydrogen reference electrodes in the temperature range 20–200°C, overall pressure range 1–200 bar, and concentration range 0–18 m KOH or 0–25 m NaOH. Very good agreement was found between the theoretically computed and experimentally measured values of the equilibrium potential difference of the cell Hg/HgO/NaOH (or KOH) (m)/H₂ for 1–17.6 m NaOH and 6–12 m KOH at 25 and 75°C and at atmospheric pressure. Equations were also derived for the equilibrium voltage of water electrolysis under standard and actual conditions in the temperature, pressure and alkali hydroxide concentration ranges mentioned above.     

A highly efficient hydrogen generation electrolysis system using alkaline zinc hydroxide solution

Alkaline water electrolysis is a well-established conventional technique for hydrogen production. However, due to its relatively high energy consumption, the cost of hydrogen produced by this technique is still high. Here in this work, we report for the first time the application of alkaline zinc hydroxide solution (composed of sodium zincate and potassium zincate in NaOH and KOH solutions, respectively) as an efficient, simple and recursive electrolyte for producing clean hydrogen through a continuous dual-step electrolysis process. The ionic conductivity, electrodes current density, and hydrogen evolution rate were measured in a wide range of the electrolyte concentrations (0.1–0.59 M). Also, the cell efficiency was studied at different ranges of current density (0.09–0.25 A/cm2) and applied potential (1.8–2.2 V). Results indicated that the application of alkaline zinc hydroxide solution at the optimum electrolyte concentration can enhance the hydrogen evolution rate minimally by a factor of 2.74 (using sodium zincate) and 1.47 (using potassium zincate) compared to the conventional alkaline water electrolysers. The results of this study could be helpful to better understand the electrochemical behaviour of the alkaline water electrolysers when sodium zincate and potassium zincate are used as ionic activators for enhancing hydrogen evolution.     

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.     

Semi-empirical model and experimental validation for the performance evaluation of a 15 kW alkaline water electrolyzer

This paper presents a semi-empirical mathematical model for predicting the electrochemical behavior of an alkaline water electrolysis system, based on the polarization curve and Faraday efficiency as a function of the current density under different operating conditions, such as, temperature and pressure. Also, the gas impurities of hydrogen in oxygen have been modeled for safety reasons due to its importance when the electrolyzer is dynamically operated using renewable energy sources. The different parameters defined in the model have been calculated by MATLAB, using a non-linear regression, on the basis of experimental data obtained in a 15 kW alkaline test bench. The simulated and measured values have been compared to ensure the accuracy and validity of the proposed model. In this sense, the error has been evaluated for the voltage with an average result of 5.67 mV per cell and for the Faraday efficiency and the gas impurities of hydrogen in oxygen with a value lower than 1%. These results show an excellent correlation between experimental and modeled data, so the model is a useful design and optimization tool for alkaline electrolyzers. Also, a sensitivity analysis has been used to determine the most influential operating variables in the performance of the electrolyzer.     

Energy and exergy analyses of hybrid photocatalytic hydrogen production reactor for CuCl cycle

The present paper concerns electrochemical, energy, exergy and exergoeconomic analyses of a hybrid photocatalytic-based hydrogen production reactor which is capable of replacing the electrolysis sub-system of the CuCl thermochemical cycle. Several operating parameters, such as current density, reactor temperature, ambient temperature and electrode distance, are varied to study their effects on the hydrogen production rate, the cost of hydrogen production and energy and exergy efficiencies. The present results show that the voltage drops across the anolyte solution (sol 1), catholyte solution (sol 2), an anode, cathode, and cation exchange membrane vary from 0.005 to 0.016 V, 0.004–0.013 V, 1.67–2.168 V, 0.18–0.22 V and 0.06–0.19 V, respectively with an increase in current density from 0.5 to 1.5 A/cm². The energy and exergy efficiencies of the hybrid photocatalytic hydrogen production reactor decrease from 5.74 to 4.54% and 5.11 to 4.04%, respectively with an increase in current density.     

Study of cobalt boride-derived electrocatalysts for overall water splitting

The production of clean hydrogen fuel by the electrolysis of water requires highly active, low-cost and facilely prepared electrocatalyst that minimizes energy consumption. Here we report an active cobalt boride (CoB)-derived electrocatalyst for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). The CoB catalyst can be readily deposed on 3D nickel foam (NF) using a simple electroless plating method. A comprehensive analysis of the CoB catalyst with scanning electron microscopy transmission (SEM), transmission electron microscopy (TEM), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) techniques revealed that CoOOH is formed on the surface of CoB catalyst during the OER process and Co(OH)₂ is formed in the HER process. The catalyst derived from CoB/NF exhibits low overpotentials towards both OER and HER in alkaline solution. The electrolysis cell using the CoB-derived catalyst couple requires a cell voltage of 1.69 V to afford a current density of 10 mA/cm², which compares favorably with most non-noble bifunctional electrocatalysts. The favorable combination of high-performance, low cost and facile preparation suggests that transition metal borides may act as promising electrocatalyst for water splitting.     

Life cycle assessment of nuclear-based hydrogen and ammonia production options: A comparative evaluation

In this study, nuclear energy based hydrogen and ammonia production options ranging from thermochemical cycles to high-temperature electrolysis are comparatively evaluated by means of the life cycle assessment (LCA) tool. Ammonia is produced by extracting nitrogen from air and hydrogen from water and reacting them through nuclear energy. Since production of ammonia contributes about 1% of global greenhouse gas (GHG) emissions, new methods with reduced environmental impacts are under close investigation. The selected ammonia production systems are (i) three step nuclear Cu–Cl thermochemical cycle, (ii) four step nuclear Cu–Cl thermochemical cycle, (iii) five step nuclear Cu–Cl thermochemical cycle, (iv) nuclear energy based electrolysis, and (v) nuclear high temperature electrolysis. The electrolysis units for hydrogen production and a Haber–Bosch process for ammonia synthesis are utilized for the electrolysis-based options while hydrogen is produced thermochemically by means of the process heat available from the nuclear power plants for thermochemical based hydrogen production systems. The LCA results for the selected ammonia production methods show that the nuclear electrolysis based ammonia production method yields lower global warming and climate change impacts while the thermochemical based options yield higher abiotic depletion and acidification values.     

Design,modelling and optimal power and hydrogen management strategy of an off grid PV system for hydrogen production using methanol electrolysis

Hydrogen used as an energy carrier and chemical element can be produced by several processes such as gasification of coal and biomass, steam reforming of fossil fuel and electrolysis of water. Each of these methods has its own advantage and disadvantage. Electrolysis process is seen as the best option for quick hydrogen production. Hydrogen generation by methanol electrolysis process (MEP) gained much attention since it guarantees high purity gas and can be compatible with renewable energies. Furthermore, due to its very low theoretical potential (0.02 V), MEP can save more than 65% of electrical energy required to produce 1 kg of hydrogen compared to water electrolysis process (WEP). Electrolytic hydrogen production using solar photovoltaic (PV) energy is positioned to become as one of the preferred options due to the harmful environmental impacts of widely used methane steam reforming process and also since the prices of PV modules are more competitive.In this paper, hydrogen production by MEP using PV energy is investigated. A design of an off grid PV/battery/MethElec system is proposed. Mathematical models of each component of the system are presented. Semi-empirical relationship between hydrogen production rate and power consumption at 80 °C and 4 M concentration is developed. Optimal power and hydrogen management strategy (PHMS) is designed to achieve high system efficiency and safe operation. Case studies are carried out on two tilts of PV array: horizontal and tilted at 36° using measured meteorological data of solar irradiation and ambient temperature of Algiers site. Simulation results reveal great opportunities of hydrogen production using MEP compared to the WEP with 22.36 g/m² d and 24.38 g/m² d of hydrogen when using system with horizontal and tilted PV array position, respectively.     

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.     

Assessment of power-to-power renewable energy storage based on the smart integration of hydrogen and micro gas turbine technologies

Power-to-Power is a process whereby the surplus of renewable power is stored as chemical energy in the form of hydrogen. Hydrogen can be used in situ or transported to the consumption node. When power is needed again, hydrogen can be consumed for power generation. Each of these processes incurs energy losses, leading to a certain round-trip efficiency (Energy Out/Energy In). Round-trip efficiency is calculated considering the following processes; water electrolysis for hydrogen production, compressed, liquefied or metal-hydride for hydrogen storage, fuel-cell-electric-truck for hydrogen distribution and micro-gas turbine for hydrogen power generation. The maximum achievable round-trip efficiency is of 29% when considering solid oxide electrolysis along with metal hydride storage. This number goes sharply down when using either alkaline or proton exchange membrane electrolyzers, 22.2% and 21.8% respectively. Round-trip efficiency is further reduced if considering other storage media, such as compressed- or liquefied-H₂. However, the aim of the paper is to highlight there is still a large margin to increase Power-to-Power round-trip efficiency, mainly from the hydrogen production and power generation blocks, which could lead to round-trip efficiencies of around 40%–42% in the next decade for Power-to-Power energy storage systems with micro-gas turbines.     

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.