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The Heatpipe Reformer technology allows the generation of hydrogen-rich, pressurized synthesis gas from solid feedstock like lignite or biomass. The resulting high hydrogen partial pressure and thus driving force makes it suitable for membrane separation. This work promotes the application of hydrogen permeable membranes as hydrogen separators directly in the reformer. This should allow a high hydrogen yield due the shift of the gasification reactions to the product side when hydrogen is removed continuously. The material of choice for this task is nickel as it combines good hydrogen permeability with good mechanical properties at the operation temperature of biomass gasification of 800 °C. The experimental section presents measurements with a bundle of nickel membranes used for the demonstration of the shift of different gas mixtures to the product side by hydrogen removal. Hydrogen removal enhanced CO and CH 4 conversion at an operation temperature of 800 °C. A high purity of at least 99.9% was achieved by the highly selective solution-diffusion process of the separation. The experimental data was also used for an energy balance of the membrane process to allow a proper membrane layout in terms of membrane area per hydrogen production. As a last step, the membrane bundle was applied directly in the Heatpipe Reformer, an allothermal pressurized gasifier. It produced 200 ml min − 1 of hydrogen and showed no signs of degradation or fouling. This proof of concept showed the suitability of nickel membranes for hydrogen separation under gasification conditions.

The following work treat the prediction of the production rate and purity level of hydrogen produced by an alkaline electrolyzer fed by a renewable source in a hybrid energy system HES in the locality of Adrar in the south of Algeria. This work is made for different renewable energy penetration rate from 0% to 60% of conventional power (Genset generator). The cell electrolyzer model permits to predict the production rate of hydrogen with accuracy, according to operating parameters, climatic conditions and the load of the site of Adrar. The study permits to introduce a model of hydrogen purity level based on the operating parameters and the power supplying the alkaline electrolyzer. It also shows that the great influence of the intermittent energy supplying the electrolyzer on the production rate and purity level of hydrogen. The prediction of production rate and purity level by the models allow to obtain a distribution and storage of hydrogen produced according to predetermined selection criteria imposed by the operator. In the process of electrolysis, the oxygen is considered as by-product of the hydrogen production. The amount and purity level were estimated jointly. An HES-H2 production program under MATLAB®/SIMULINK® has been developed to simulate the hourly evolution of the production rate and purity level of hydrogen and oxygen produced by an electrolyzer for different penetration rate of renewable energies in an HES.

This paper deals with a new hybridly powered photovoltaic- PEM fuel cell – Li-ion battery and ammonia electrolyte cell integrated system (system 2) for vehicle application and is compared to another system (system 1) that is consisting of a PEM fuel cell, photovoltaic and Li-ion battery. The paper aims to investigate the effect of adding photovoltaic to both systems and the amount of hydrogen consumption/production that could be saved/generated if it is implemented in both systems. These two systems are analyzed and assessed both energetically and exergetically. Utilizing photovoltaic arrays in system 1 is able to recover 177.78 g of hydrogen through 1 h of continuous driving at vehicle output power of 98.32 kW, which is approximately 3.55% of the hydrogen storage tank used in the proposed systems. While, using the same photovoltaics arrays, system 2 succeeds to produce 313.86 g of hydrogen utilizing the ammonia electrolyzer system 2 appeared to be more promising as it works even if the car is not in operation mode. Moreover, the hydrogen produced from the ammonia electrolyzer can be stored onboard, and the liquefied ammonia can be used as a potential source for feeding PEM fuel cell with hydrogen. Furthermore, the effects of changing various system parameters on energy and exergy efficiencies of the overall system are investigated.

Hydrogen enhanced combustion of JP-8 provides an additional control parameter for external combustion based power sources. When supplied as part of a “reformer gas” mixture, hydrogen provides similar benefits as pure hydrogen, given sufficient oxygen mixing. Previous work showed benefits of hydrogen enhanced combustion for external combustion based power sources. As a step closer to practical applications, the present work examines the use of hydrogen rich reformate. This mixture of hydrogen, carbon monoxide, carbon dioxide, and nitrogen is produced by fuel reforming of JP-8 and other logistics fuels. Tests evaluated the temperature profiles of dual fueled flames using JP-8 and either hydrogen or a bottled mixture representing fuel reformate. Both supplemental fuels move combustion earlier, allowing more stable combustion and potential for reduced size. JP-8 flow rate was reduced to maintain fuel energy input at a constant 5.5 kWth. In comparing two cases, the important factor was the total energy contribution. The ratio of hydrogen and carbon monoxide had little effect on the flame structure. This research also compared methods of hydrogen addition. It was added with either the atomizing air or the secondary air which reiterated the importance of oxygen availability. For example, hydrogen through the nozzle produces additional changes to the flame structure due to the combustible mixture of hydrogen and air in the nozzle. The equivalent flow rate of reformate in the nozzle does not produce the same effect because the air in the nozzle is replaced by the other gases in the reformate (CO, CO2, and N2). Hydrogen enrichment tests establish the benefit of dual firing hydrogen and JP-8. These reformate tests show the variables that must be considered in implementing this technique in a practical system.

In this paper a semi-empiric zero-dimensional steady state simulation model of an asymmetric high pressure proton exchange membrane water electrolyser is being presented. Based on experimental investigations on a 9.6 kW asymmetric high pressure water electrolysis module, empirical parameters were determined. Measurements were taken by varying the production pressure between 70 bar and 155 bar, the process temperature between 45 °C and 75 °C and the current density from 0.81 A cm−2 to 1.85 A cm−2. Stack efficiency and hydrogen diffusion from the cathode to the anode side were determined and expressed by the faradaic efficiency. Stack efficiencies of up to 74.8% were achieved at 0.81 A cm−2, 75 °C and 155 bar. As expected the stack efficiency decreases with increasing hydrogen production pressure. A temperature decrease of 30 °C has greater impact on the efficiency than an increase of pressure from 70 to 155 bar. The faradaic efficiency at 1.85 A cm−2, 155 bar and 45 °C is higher than 99% and even at a high operating temperature of 75 °C higher than 97%. The presented model can be used for prediction of the stack voltage, gas production flow rates, water consumption and stack efficiency as function of input current, process temperature and production pressure. Results show a very satisfactory consistency of measurement and simulation.

A coal gasification-based integrated system is proposed to produce electrical power and hydrogen. The hydrogen produced is stored in a chemical storage medium, which is ammonia. The integrated system contains a water gas shift membrane reactor, a hybrid thermochemical water decomposition cycle based on the chemical couple copper and chlorine and a multistage ammonia production system. A hydrogen fueled supporting combined cycle is used to meet the electrical requirement of the integrated system. Coal is gasified, and the resulting syngas is water shifted in a membrane reactor, which produces hydrogen. The remaining syngas is combusted to generate power through a gas turbine, and the turbine hot exhaust is used to provide the required thermal energy of the water decomposition cycle. The hydrogen outputs from the coal gasification and the water decomposition cycle are fed to the ammonia production system and the supporting combined cycle. The ammonia production system contains multiple stages to achieve a high conversion percentage of hydrogen. The nitrogen fed to the ammonia reactor is provided by the cryogenic air separation unit, which also provides oxygen to the gasifier. The proposed system is simulated with the process simulation software Aspen Plus. The system performance is evaluated through energy and exergy efficiencies. The integrated system is found to have an energy efficiency of 48.7% and an exergy efficiency of 48.4%. The system is capable of producing 0.18 kg/s of hydrogen and 1.2 MW of power per 1.5 kg/s of coal.

This paper presents an experimental study for hydrogen production using alkaline water electrolysis operated by solar energy. Attempts to produce pure hydrogen as well as pure oxygen for commercial demands are introduced. Two methods are used and compared for separation between the cathode and anode, which are acrylic separator and polymeric membrane. Further, the effects of electrolyte concentration, solar insolation, and space between the pair of electrodes on the amount of hydrogen produced and consequently on the overall electrolysis efficiency are investigated. It is found that the efficiency of hydrogen production is higher when using the polymeric membrane between the electrodes, in comparison with the acrylic separator. The experimental results show also that, the performance of alkaline water electrolysis unit is dominated by the electrolyte concentration and the gap between the electrodes. The gap of 5 mm leads to a higher hydrogen production rate than the gap of 10 mm.

Flexible nuclear power for synthetic fuel production through high temperature co-electrolysis technology (HTCE) using solid oxide electrolysis cell (SOEC) has recently received increasing international interest in the large-scale, highly efficient and carbon-neutral energy storage field. It is of great importance to enhancing the understanding of co-electrolysis process and the related mechanism. In this paper, CO2 behavior and its effect on the performance of SOEC were examined by the electrochemical characterization and impedance analysis to determine the proper operating conditions, such as H2O, CO2, H2, CO, operation temperature and electrolysis current. The polarization mechanism is also investigated by the experimental and modeling results. It was found that the electrolysis of CO2 is much harder than that of H2O, and the ASR of pure CO2 electrolysis is about three times that of H2O. When the CO2 content decreases from 50% to 10%, the ASR decreases from 1.59 to 0.90 Ω cm2. Increasing the H2O content could also improve the electrolysis efficiency to some degree, while the CO addition in the inlet gas was not favorable for the process. Mechanism study shows that the diffusion impedance of CO2 should be the restricted step for the polarization energy loss.

The practical dynamic properties and operational limitations of a commercial differential pressure 1 Nm 3 h −1 proton exchange membrane (PEM) water electrolyzer are studied from the viewpoint of renewable power production. Measured values from a 5 kW p solar photovoltaic (PV) power plant and PEM electrolyzer are analyzed to study factors affecting the control of PEM water electrolyzers operating as a part of renewable power production systems. Specific energy consumption of the PEM stack as a function of stack hydrogen outlet pressure is estimated based on measured values from two different measurement systems. Electrical energy consumption of the stack does not show any notable increase as the hydrogen outlet pressure is increased from 2.0 MPa to 4.0 MPa. However, the stack specific energy consumption increases by a maximum of 0.2 kWh/Nm 3 when hydrogen outlet pressure is increased from 2.0 MPa to 4.0 MPa. The increase in specific energy consumption at high differential pressure operation is due to a decrease in Faraday efficiency. Selection and control of the hydrogen outlet pressure can minimize the specific energy consumption and maximize the real hydrogen production in dynamic PEM water electrolyzer operation.

The current work presents a process that separates hydrogen from mixtures with natural gas transported in the natural gas grid. The aim is to achieve hydrogen at fuel cell quality (99.97% (v/v) according to ISO 14687-2:2012). Due to gas grid regulations in Austria the hydrogen content is limited to a maximum of 4% (v/v). In a hybrid approach based on membrane separation and pressure swing adsorption (PSA) the supplied high pressure hydrogen – natural gas mixture (up to 120 bar) is pre-enriched by membrane technology and further upgraded to the required quality by PSA. The majority of the feed gas is kept at grid pressure, which ensures a high energetic efficiency. The remaining components, separated by PSA, are re-compressed and returned to the grid. Beside the technological feasibility, the influence of various process parameters (e.g. stage-cut, permeate conditions, PSA hydrogen recovery) is analysed. Based on the results, the required amount of energy of 0.8–1.5 kWh / m 3 (fuel-cell quality hydrogen at 25.81 bar(a)) is calculated for the so called HylyPure® process.

Hydrogen produced from ethanol solution by pulsed discharge was investigated in this work. With needle-net configurations, hydrogen can be easily exported from the plasma reactor thereby preventing hydrogen from consuming by the oxidizing active substances generated from pulsed discharge. Both flow rate and percentage concentration of hydrogen were enhanced with the increase of energy density, but not much change with the increase of discharge time. Flow rate, percentage concentration, and energy consumption of hydrogen were achieved about 800 mL/min, 73.5%, and 0.9 kWh/m3 H2 respectively with energy density of 6.4 J/L. All products were analyzed, which were divided into main and secondary products guiding the mechanism analysis of hydrogen production. The main products contain H2, CO, CH3OH, and the secondary products include C2H2, CO2, macromolecular compounds, nano carbon particles. The high hydrogen yield, emerged nano carbon, low ethanol and energy consumption make this method possess bright prospect in hydrogen production.

Hydrogen is produced conventionally by electrolyzing water or water vapor at onset voltages greater than 1 V, providing motivation for the development of more efficient electrolysis processes for a hydrogen economy. Numerous attempts have been made to use ethanol as a fuel for hydrogen production because this process reduces the electrolysis onset voltage significantly. However, ethanol feedstock from lignocellulose requires greater amounts of energy and results in higher production costs compared to those using starch as the feedstock. The current study describes direct lignin electrolysis at an onset voltage of ca. 0.25 V, with high current efficiencies of approximately 100 % for hydrogen production at the cathode and approximately 85 % for carbon dioxide production at the anode. Addition of H3PO4-impregnated lignin to the anode of a PtFe/C|Sn0.9In0.1P2O7 (150 μm)|Pt/C cell enabled hydrogen production at a temperature of 150 °C.

One of the main challenges related to hydrogen energy technologies is hydrogen storage in a safe and economically reasonable way. A promising solution could be related to the use of aluminum or its alloys to reduce water to form hydrogen when needed. The aluminum–water reaction is thermodynamically favorable, but does not proceed due to the passivation of the aluminum surface by the protective aluminum oxide layer, which prevents water molecules from coming into direct contact with metal particles. Herein, the surface of aluminum particles was modified by using a low-temperature plasma-activation approach. Such a modification induces a hydrophilicity effect and the modified aluminum powder sinks instantly in water, whereas unmodified powder floats on the top of the water. The plasma-based activation technology is also discussed in detail. The structure and morphology of the samples were characterized by using SEM, energy-dispersive X-ray spectroscopy, and XRD. BET surface area analyses were also performed. The elemental composition on the nanoscale level and formation of polar groups were experimentally investigated by using X-ray photoelectron spectroscopy. Amounts of oxygen/hydrogen were measured by using the inert-gas fusion method. Tests show that hydrogen production starts after 1 min of aluminum powder immersion into slightly alkaline water and continues for up to 20 min. The reaction by-product is environmentally friendly and could be used for the production of aluminum oxide.

Oxygen permeation in proton exchange membrane (PEM) water electrolyzers is a critical phenomenon. Mainly, because of (i) degradation and (ii) purity of the hydrogen product gas. Additionally, but less important because of (iii) efficiency loss and (iv) safety problems. Despite these issues, oxygen permeation in PEM water electrolysis was paid less attention. This can be explained by the low oxygen crossover compared to the hydrogen crossover. In this contribution the oxygen content within the hydrogen product gas was measured for two different cathodic catalyst materials (Pt and a Pt-free catalyst) during water electrolysis in a current density range of 0.05–2 A/cm2. In comparison to the platinum catalyst, the Pt-free catalyst leads to 3–4 times higher oxygen contents within the hydrogen product gas. This can be explained with a lower activity concerning oxygen recombination, so that less permeated oxygen is consumed and consequently, the oxygen flux within hydrogen is higher.The results of this work emphasize that the oxygen crossover increases with increasing current density, as like the hydrogen crossover does. Particularly, two effects are possible for this strong increase in oxygen permeation: supersaturation and the electro-osmotic drag. The experimental findings show that the crossover is higher as generally expected, and should receive more attention. Keywords: Oxygen crossover, Permeation, PEM, Current density, Supersaturation, Water electrolysis

In situ hydrogen production technologies have attracted attentions because of hydrogen storage and transportation safety issues. Discharge plasma technology for hydrogen production is of fast response, large capacity, small scale and portability, which is suitable for automobiles and ships. In this paper, a method for producing hydrogen by microwave discharge in ethanol solution was introduced. A microwave discharge reactor of direct standing wave coupling (MDRSWC) was designed, which was suitable for on-board hydrogen production. The characteristics of large capacity hydrogen production by applying MDRSWC in liquid ethanol were investigated. Depending on the experimental conditions of ethanol concentration and microwave power, the flow rate of hydrogen production was achieved ranging from 28.93 to 72.48 g/h. In addition to main hydrogen and carbon dioxide, a small amount of methane and acetylene as by-products were detected. By optimizing the experimental conditions, the experimental results showed that the flow rate of hydrogen, the percentage concentration of hydrogen and the energy yield of hydrogen production were 72.48 g/h, 58.1% and 48.32 g/kWh respectively. This work could provide a potentially effective hydrogen production method for on-board hydrogen utilization device.

The article investigates the efficiency of commercial hydrogen production by water electrolysis on the base of NPP excess energy with its additional purification higher than 99.9999%, considering its transport. The competitive high purity hydrogen release price has been determined as compared to the market price. Besides, the use of high duty electrolysis plants has been suggested. Moreover, the advantages of water electrolysis cyclic operation while consuming electric energy from NPP as compared to the continuous mode have been presented in the paper.

A low energy electrolysis process that directly converts native biomasses to hydrogen at low temperature was reported. Practically, an environmentally-friendly proton exchange membrane electrolysis cell (PEMEC) uses a simple redox ion pair, Fe 3+ /Fe 2+ , as the catalyst which functions as an oxidation agent (oxidizing biomass), charge carrier (transferring the charge to anode) and discharge agent (discharge on anode electrode). The electro-catalytic activity of Fe 3+ /Fe 2+ ion was demonstrated by cyclic voltammetry and the rate for hydrogen evolution was measured at different current densities. At very low cell potential, smaller than 0.7 V, hydrogen begins to be produced, which is much less than the any noble metal catalysis water splitting hydrogen evolution. The electric energy consumption in our experiments for glucose-Fe ion system is 1.845 kW h Nm −3 H 2 at 100 mA cm −2 , which can save about 60.74% electric energy of traditional typical alkaline water electrolysis (4.7 kWh Nm −3 H 2 at U H2O = 2 V, the current density is 100 mA cm −2 ). Different from reported alcohol electrolysis, the biomass based electrolysis process does not require any noble-metal catalyst on the anode.

Solar water splitting is an effective approach to hydrogen production and application of solar energy. However, the photo-generated hydrogen should be initially stored in high pressure cylinder and subsequently applied in hydrogen-oxygen fuel cells. Herein, a solar rechargeable battery is proposed based mainly on hydrogen storage mechanism in dual-phase electrolyte. Specifically, the hydrogen production, storage and utilization are integrated into a hybrid system of the dye-sensitized solar cell and electrochemical cell with the dye-sensitized TiO 2 as photo-anode, LiI as the cathode active material in organic electrolyte, AB 5 -type hydrogen storage alloy as anode in alkaline solution, and PEDOT-modified Nafion membrane as separator. Here, the photo-generated electrons in organic electrolyte pass to the AB 5 -type hydrogen storage alloy to split water in alkaline aqueous electrolyte for generating hydrogen, which is in situ stored into AB 5 -type hydrogen storage alloy. Subsequently, the hydrogen stored in the AB 5 -type hydrogen storage alloy can be oxidized by electrochemical way to generate electricity, coupled with LiI cathode in organic electrolyte. The solar rechargeable battery demonstrates a new solution of the solar energy conversion, hydrogen production, storage, and utilization, achieving the new energy conversion and storage from solar energy to chemical energy, and further to electrical energy.

The paper shows, that a low-temperature plasma initiated in liquid media in interelectrode discharge gap is able to decompose hydrogen containing organic molecules resulting in obtaining gaseous products with volume part of hydrogen higher than 90% (up to gas chromatography data). Tentative assessments of energy efficiency, calculated with regard for hydrogen and feedstock heating value and energy consumption, have shown efficiency factor of 60–70%, depending on the source mixture composition. Theoretical model calculations of discharge current and voltage have been performed; the values are in good accordance with experimental data.

In this paper, a modeling of the Solid Oxide Electrolysis Cell (SOEC), through energetic, exergetic and electrochemical modeling approaches, is conducted, and its performance, particularly through exergy efficiency, is analyzed under various operating conditions and state properties for optimum hydrogen production. In a comprehensively performed parametric study, at a single electrolysis cell scale, the effects of varying some operating conditions, such as temperature, pressure, steam molar fraction and the current density on the cell potential and hence the performance are investigated. In addition, at the electrolyzer system scale, the overall electrolyzer performance is investigated through energy and exergy efficiencies, in addition to the system's power density consumption, hydrogen production rate, heat exchange rates and exergy destruction parameters. The present results show that the overall solid oxide electrolyzer energy efficiency is 53%, while the exergy efficiency is 60%. The exergy destruction at a reduced operating temperature increases significantly. This may be overcome by the integration of this system with a source of steam production.

The recent acceleration in hydrogen production's R&D will lead the energy transition. Low temperature polymer electrolyte membrane electrolysis (LT-PEME) is one of the most promising candidate technologies to produce hydrogen from renewable energy sources, and for synthetic fuel production. LT-PEME splits water into hydrogen and oxygen when the voltage is applied between anode and cathode. Electrical current forces the positively charged ions to migrate to negatively charged cathode through PEM, where hydrogen is produced. Meanwhile, oxygen is produced at the anode side electrode and escapes as a gas with the circulating water. The effects of clamping pressure (Pc) on the LT-PEME cell performance, polarization resistances, and hydrogen and water crossover through the membrane, and hydrogen and oxygen production rate are studied. A 50 cm2 active area LT-PEME cell designed and manufactured in house is utilized in this work. Higher Pc has shown higher cell performance this refers to lower ohmic and activation resistances. Water crossover from anode to cathode is slightly decreased at higher Pc resulting in a slight decrease in hydrogen crossover from cathode to anode. Also, the percentage of hydrogen in the produced oxygen at the anode side is significantly reduced at higher Pc and at lower current density.

Summary An integrated system for compressed hydrogen and electrical power production based on a Generation IV nuclear reactor (a lead-cooled reactor) is proposed. The hydrogen is produced by the integrated system through a hybrid thermochemical and electrical water decomposition cycle. The water decomposition cycle is based on copper and chlorine compounds and decomposes water through four main steps. The electrical power is produced by the Rankine cycle, which also contributes to cooling the compressed hydrogen between the compression stages as well as providing the electrical power required by the electrolysis step in the water decomposition cycle. In the proposed system, a heat recovery network is incorporated within the water decomposition cycle so that only the hydrolysis and the oxygen production reactors in the cycle receive thermal energy from the lead-cooled nuclear reactor. The integrated system is modeled and simulated by using engineering process simulation software (Aspen Plus). The performance of the integrated system is assessed with energy and exergy analyses, and the overall energy and exergy efficiencies are found to be 25.4% and 40.6%, respectively. The integrated system produces 3.45 g/s of compressed hydrogen ready for shipping and 467.2 kW of electrical power.

In this paper, we present a modelling and simulation study of an Off grid PV system for hydrogen production (PVHPS) using methanol electrolysis process. The system consists mainly on a PV array, lead-acid battery, methanol electrolyser and hydrogen tank. Mathematical models of each component of the system are presented. Using a semi-empirical relationship between hydrogen production rate and power consumption, hydrogen production at 80 °C and 4 M concentration is estimated. Optimal power and hydrogen management strategy (PHMS) is investigated to achieve high system efficiency. Case studies are carried out on two tilts of PV array: horizontal and tilted at 36°. Parametric sensitivity analysis is also carried out to illustrate the effect of the battery depth of discharge (DoD) on the system components sizes and overall system performance. In the simulation, data of solar irradiation and ambient temperature obtained from radiometric measurements at Algiers city are used. Simulation results show that the system with tilted PV array presents performances better than in horizontal PV array configuration and produce greater hydrogen amounts. In addition, reducing the DoD value in order to increase the lifetime of the accumulator induces some power losses which decreases the amount of hydrogen produced and consequently reduces the system efficiency.

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.

A novel large-scale plant for hydrogen liquefying is proposed and analyzed. The liquid hydrogen production rate of the proposed plant is 100 tons per day to provide the required LH2 for a large urban area with 100,000–200,000 hydrogen vehicles supply. In the pre-cooling section of the process, a new mixed refrigerant (MR) refrigeration cycle, combined with a Joule–Brayton refrigeration cycle, precool gaseous hydrogen feed from 25 °C to the temperature −198.2 °C. A new refrigeration system with six simple Linde–Hampson cascade cycles cools low-temperature gaseous hydrogen from −198.2 °C to temperature −252.2 °C. The process specific energy consumption (SEC) is 7.69 kWh/kg L H 2 which minimum value is 2.89 kWh/kg L H 2 in ideal conditions. The exergy efficiency of the system is 39.5%, which is considerably higher than the existing hydrogen liquefier plants around the world. However, assuming more efficiency values for the equipment can improve it. The energy analysis specifies that coefficient of performance (COP) of the process is 0.1710 which is a high quantity of its kind between other similar processes. Effect of various refrigerant components concentration, discharge pressure of the high pressure compressors of the pre-cooling section, and hydrogen feed pressure on the process COP, exergy efficiency, and SEC are investigated. After that, a new MR will be offered for the cryogenic section of the plant. The system improvements are considerable comparing to current hydrogen liquefying plants, therefore, the proposed conceptual system can be used for future hydrogen liquefaction plants design.

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 cm 2 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.

This study aims to investigate performance and cost aspects of a solar powered portable cooling system to conserve first aid supplies for off-grid areas with energy storage. Due to the intermittent nature of solar energy availability, two energy storage options are considered for a stationary system. Additional to the standalone system without energy storage, hydrogen is selected to be the storage medium by considering electrolysis at day time, and use of a hydrogen fuel cell unit at night time. This system consists of solar photovoltaic cells, a Polymer Exchange Membrane (PEM) electrolysis unit (PEME), hydrogen tank, a PEM fuel cell unit (PEMFC), and a vapor compression refrigeration (VCR) system to condition a container rated with ∼11 kW cooling load. The second system utilizes pumped – hydro storage (PHS) technology using a simple pump – turbine couple by storing water at a higher reservoir during day time and utilizing it to produce hydro power at night. Existence of higher reservoir brings a significant additional cost for the PHS system, making this configuration almost four times more costly than that of the hydrogen storage option, even though the storage efficiency of the PHS system is significantly higher than the hydrogen storage.

Hydrogen as a secondary energy carrier promises a large potential as a long term storage for fluctuating renewable energies. In this sense a highly efficient solar hydrogen generation is of great interest especially in southern countries having high solar irradiation. The patented Hydrogen Concentrator (HyCon) concept yields high efficiencies combining multi-junction solar cells with proton exchange (PEM) membrane water electrolysis. In this work, a special PEM electrolysis cell for the HyCon concept was developed and investigated. It is shown that the purpose-made PEM cell shows a high performance using a titanium hybrid fiber sinter function both as a porous transport layer and flow field. The electrolysis cell shows a high performance with 1.83 V at 1 A/cm 2 and 24 °C working under natural convection with a commercially available catalyst coated membrane. A theoretical examination predicts a total efficiency for the HyCon module from sunlight to hydrogen of approximately 19.5% according to the higher heating value.

This paper presents the potential of a method for on-demand hydrogen generation from the reaction of activated aluminum powder and water for commercial aircraft applications. The hydrogen produced on-board during flight can be used in a fuel cell to generate electric energy. Results of an investigation of the reaction between aluminum and urine show that, in addition to fresh water, the waste water available on-board the aircraft can be used for hydrogen generation. High reaction rates producing about 200–600 ml/min/g Al of hydrogen at a high yield of about 90% was demonstrated. The possibility to use the available waste water leads to high specific electric energy of up to about 850 Wh/kg. In addition, the aluminum–water reaction enables safe use of hydrogen. A comparison to the traditional hydrogen storage methods is also presented.

Hydrogen permeation is an important phenomena for PEM water electrolyzers, due to several reasons as safety issues and efficiency loss. The present contribution deals with the measurement of hydrogen volume fraction within the anode product gas during PEM water electrolysis for different temperatures and cathode pressures. High cathode pressures lead to high anode hydrogen volume fractions close to the lower explosion limit of hydrogen in oxygen, which are caused by increased hydrogen permeation. It is shown that the results of the hydrogen volume fraction measurements can be easily converted into hydrogen permeation rates. Additionally, the experimental obtained permeation data indicate that hydrogen permeation increases linear with increasing current density. The impact of current density on the hydrogen permeation is very strong in comparison to the effects of temperature and pressure e.g. a current density increase of 1 A/cm2 can causes a permeation increase comparable to a cathode pressure increase of 20 bar. In the second part of this contribution different theories to explain this strong dependence on current density are discussed. The most probable explanation is that due to mass transfer limitations a supersaturation of dissolved gas within the catalyst ionomer film arises that causes the investigated increase in permeation.

Solar hydrogen production by coupling of pressurized high temperature electrolyser with concentrated solar tower technology is studied. As the high temperature electrolyser requires constant temperature conditions, the focus is made on a molten salt solar tower due to its high storage capacity. A flowsheet was developed and simulations were carried out with Aspen Plus 8.4 software for MW-scale hydrogen production plants. The solar part was laid out with HFLCAL software. Two different scenarios were considered: the first concerns the production of 400 kg/d hydrogen corresponding to mobility use (fuel station). The second scenario deals with the production of 4000 kg/d hydrogen for industrial use. The process was analyzed from a thermodynamic point of view by calculating the overall process efficiency and determining the annual production. It was assumed that a fixed hydrogen demand exists in the two cases and it was assessed to which extent this can be supplied by the solar high temperature electrolysis process including thermal storage as well as hydrogen storage. For time periods with a potential over supply of hydrogen, it was considered that the excess energy is sold as electricity to the grid. For time periods where the hydrogen demand cannot be fully supplied, electricity consumption from the grid was considered. It was assessed which solar multiple is appropriate to achieve low consumption of grid electricity and low excess energy. It is shown that the consumption of grid electricity is reduced for increasing solar multiple but the efficiency is also reduced. At a solar multiple of 3.0 an annual solar-to-H2 efficiency greater than 14% is achieved at grid electricity production below 5% for the industrial case (4000 kg/d). In a sensitivity study the paramount importance of electrolyser performance, i.e. efficiency and conversion, is shown.

In this paper the influence of operating conditions on the product gas purity of a zero-gap alkaline water electrolyzer was examined. Precise knowledge of the resulting gas purity is of special importance to prevent safety shutdown when the electrolyzer is dynamically operated using a renewable energy source. The investigation in this study involves variation of temperature, electrolyte concentration and flow rate as well as different electrolyte management concepts. The experiments were carried out in a fully automated lab-scale electrolyzer with a 150 cm 2 zero-gap cell and approximately 31 wt% KOH at ambient and balanced cathodic and anodic pressure. The purity of the evolved gases was measured via online gas chromatography. It can be seen from the experiments that a temperature increase and flow rate decrease reduces the gas impurity when mixing catholyte and anolyte. A further reduction of gas impurity can be achieved when both cycles are being separated and a dynamic cycling strategy is applied.

In this work, Solid Oxide Electrolyzer Cell (SOEC) based on Ba 0.9 Co 0.7 Fe 0.2 Nb 0.1 O 3-δ (BCFN) air electrode and YSZ-GDC bilayer electrolyte was systematically investigated and the efficiency of high-temperature water electrolysis by such a cell was analyzed. Firstly, chemical compatibility test between BCFN and YSZ showed that BaZrO 3 formed after heat treatment at 1000 °C for 5 h, which adversely influenced the performance of BCFN dramatically. A fully dense GDC interlayer was thus developed by co-sintering GDC layer, with addition of 0.5 at.% Fe 2 O 3 , with YSZ electrolyte at only 1300 °C. The as-prepared fuel electrode-supported eletrolyzer cell consisting of Ni-YSZ fuel electrode, YSZ-GDC bilayer electrolyte and BCFN air electrode was evaluated for water electrolysis. Specifically, at 800 °C using a feedstock of 60% H 2 O-40% H 2 , the cell showed total area specific resistance of 0.195 Ω cm 2 and the cell voltage was 1.13 V with an electrolysis current of 1 A cm −2 . After short-term stability test for 120 h with 1 A cm −2 electrolysis current at 800 °C, the cell showed no microstructural changes as observed by scanning electron microscopy. At last, a high-temperature water electrolysis system based on the cell studied was proposed and the system analysis shows that the overall electricity to hydrogen efficiency can reach 73% based on lower heating value of hydrogen, with a hydrogen generation rate of 4180 L h −1 m −2 .

Hydrogen is considered as the most promising energy carrier for providing a clean, reliable and sustainable energy system. It can be produced from a diverse array of potential feed stocks including water, fossil fuels and organic matter. Electrolysis is the best option for producing hydrogen very quickly and conveniently. Water electrolysis as a source of hydrogen production has recently gained much attention since it can produce high purity hydrogen and can be compatible with renewable energies. Besides the water electrolysis, aqueous methanol electrolysis has been reported in several studies. The aqueous methanol electrolysis proceeds at much lower voltage than that with the water electrolysis. As a result of the substantially lower operating voltage, the energy efficiency for methanol electrolysis can be higher than that for water electrolysis. In this paper, we are interesting to methanol electrolysis in order to produce hydrogen. The relation linking hydrogen production rate to the power needed to electrolyse a unit volume of aqueous methanol solution has been determined. Using this relation, the potential of hydrogen from aqueous methanol solution using a PV solar as the energy system has been evaluated for different locations in Algeria.

A solid oxide short stack composed of 6 Ni-YSZ supported cells, YSZ electrolyte and GDC-LSC oxygen electrode has been tested for 10,700 hours in steam electrolysis. Initial degradation was followed by a global stabilization of the performance after lowering the current density, with a degradation rate below 0.5% kh(-1). Post-test analysis has been conducted on two repeating units (RUs) to highlight the most significant microstructure alterations. Nickel depletion was observed in the hydrogen electrode close to the interface with the electrolyte. Formation of small pores in the electrolyte was detected along the grain boundaries. A consequent detachment related to this phenomenon was observed in proximity of the GDC compatibility layer. At the oxygen electrode side, the formation of a approximate to 1 mu m dense mixed layer of GDC and YSZ was observed. Strontium from the LSC electrode migrated through GDC pores and reacted with YSZ, forming evident SrZrO3 inclusions. Distinct accumulation of silicon at the Ni/YSZ interface and chromium on the GDC barrier layer have been observed in both RUs. Despite this range of alterations observed, the stack degradation remained limited, testified from the fact that performance decay between 4,000 and 10,000 hours of operation was virtually nil.

We report the design and development of a microfluidic electrolyzer for the continuous production and in situ separation of hydrogen fuel. A series of photovoltaic cells were integrated with a microchannel to produce a high intensity electric field under direct solar illumination, which electrolyzed the sea water when flown in the microchannel. The rate of hydrogen production could be varied by tuning the electric field intensity or the flow rate of the sea water. Addition of an outlet near the cathode led to an in situ separation of hydrogen in the straight-channel electrolyzer. Hydrogen was also separated from oxygen using a Y-shaped electrolyzer where the electrodes were placed on the Y-arms. The power required for the proposed process was much lower than their macroscopic analogues because the smaller gap between the electrodes ensured a lower electrical resistance and high-intensity field inside the microchannel. A large scale integration of an array of such electrolyzers can lead to an economic, portable, continuous, and clean pathway to produce hydrogen under ambient condition.

A novel nuclear-based integrated system for electrical power and compressed hydrogen production is proposed. The hydrogen is produced through the four-step Cu-Cl cycle for water decomposition. A Rankine cycle is used to generate the power, part of which is used for the electrolysis step in the hybrid thermochemical water decomposition cycle and the hydrogen compression system. In the proposed design of the four-step thermochemical and electrical water decomposition cycle, only the hydrolysis and the oxygen production reactors receive thermal energy from the nuclear reactor. The nuclear thermal energy is delivered to the integrated system in the form of a supercritical fluid. The nuclear reactor, which is based on the supercritical water-cooled reactor, is responsible for delivering the thermal energy to the system, which is simulated using Aspen Plus and assessed with energy and exergy analyses. It is determined that the energy and the exergy efficiencies of the proposed system are 31.6% and 56.2% respectively, and that the integrated system is able to produce 2.02 kg/s of highly compressed hydrogen and 553 MW of electrical power.

The effect of magnetic force on the hydrogen production by multielectrode water electrolysis is experimentally investigated in this paper. Results show that the hydrogen production rate, power increase rate and energy efficiency are improved as the magnetic field is added during the electrolysis process. At conditions of interelectrode distance of 3 mm, electrode pair of 5, electrolyte concentration of 25 wt% and applied voltage of 3 V, the hydrogen production reaches maximum amount of 5300 ml/h. At applied voltage of 2.5 V, energy efficiency can reach 92.14% as the magnetic field is added. The increase rate of hydrogen production is 13.4%, while increase rate of power efficiency is 10.2%, higher than that without magnetic field added. It indicated that the external magnetic field during water electrolysis indeed improves the electrolysis procedure.

Polymer electrolyte membrane (PEM) water electrolysis generates ‘green’ hydrogen when conducted with electricity from renewable - but fluctuating - sources like wind or solar photovoltaic. Unfortunately, the long-term stability of the electrolyzer performance is still not fully understood under these input power profiles. In this study, we contrast the degradation behavior of our PEM water electrolysis single cells that occurs under operation with constant and intermittent power and derive preferable operating states. For this purpose, five different current density profiles are used, of which two were constant and three dynamic. Cells operated at 1 A cm −2 show no degradation. However, degradation was observed for the remaining four profiles, all of which underwent periods of high current density (2 A cm −2 ). Hereby, constant operation at 2 A cm −2 led to the highest degradation rate (194 μV h −1 ). Degradation can be greatly reduced when the cells are operated with an intermittent profile. Current density switching has a positive effect on durability, as it causes reversible parts of degradation to recover and results in a substantially reduced degradation per mole of hydrogen produced. Two general degradation phenomena were identified, a decreased anode exchange current density and an increased contact resistance at the titanium porous transport layer (Ti-PTL).

In this work, lumped parameter models have been developed for hydrogen storage and purification systems based on Matlab/Simulink. Hydrogen storage systems using metal hydride has been validated by comparing simulation results with data in other literature. In order to improve the efficiency of hydrogen storage system, the effects of ambient temperature, supply pressure, outlet pressure and overall heat transfer coefficient on the hydrogen storage capacity were studied. The validated lumped parameter model was developed to simulate the performance of hydrogen purification system in assumed industrial process. In order to improve hydrogen recovery rate of purification system, the effects of solid material mass, overall heat transfer coefficient, cooling water temperature and supply pressure were taken into consideration. In general, the hydrogen recovery rate of purification system rises with the increase of solid material mass and overall heat transfer coefficient. And it can be considered as an effective way to increase hydrogen recovery rate by reducing the cooling water temperature and enhancing the supply pressure.

The use of solar energy for electricity generation and use of this electricity for hydrogen production by alkaline water electrolysis promises to be a truly sustainable scheme for the postulated hydrogen economy. This work addresses the design of a standalone solar photovoltaic (PV) energy system that meets the energy requirements of the electrolysis process, followed by the performance analysis under different environmental conditions. Energy requirement for electrolysis depends on the hydrogen production rate desired and the operating conditions of the electrolysis cell and it has been predicted from an essentially thermodynamic analysis. Mean solar irradiation data is estimated from location specific meteorological data. The current-voltage output characteristics of the solar modules have been predicted as function of the solar irradiation using the five parameter, single diode model of a solar panel and they have been linked to the production rates of hydrogen. The module behaviour and its thermodynamic and conversion efficiencies have also been predicted for actual operating conditions. Thus a step-by-step simplified approach for the preliminary PV power system design and analysis for an electrolysis based hydrogen production unit has been presented in this study.

A Pd-YSZ cermet membrane that performs coupled operations of hydrogen separation from a mixed-gas stream and simultaneous hydrogen production by non-galvanic water-splitting, and have high sulfur tolerance is fabricated. It is proved that in H 2 S containing atmosphere the Pd-YSZ membrane has self-repairing capability, originating mainly from the conversion of Pd 4 S back to metallic Pd and SO 2 by ambipolar-diffused oxygen obtained from water-splitting. The performance of membrane was analyzed at different temperatures in high H 2 S containing (0–4000 ppm H 2 S) mixed gas feed during the operation as a hydrogen separation membrane as well as during the coupled operation of hydrogen separation and hydrogen production. At 900 °C with the feed-stream having ≥2000 ppm H 2 S, the hydrogen flux was severely affected due to the formation of some liquid phase of Pd 4 S, resulting in the segregation of hydrogen permeating Pd-phase at the membrane surface. But at 800 °C, though the membrane was affected by the Pd 4 S formation in high H 2 S environment (up to 1200 ppm H 2 S), its self-repairing capability and additional hydrogen production by water-splitting is capable of maintaining the hydrogen flux around ~1.24 cm 3 (STP)/min.cm 2 , a value expected by the same membrane while performing only the hydrogen separation function in H 2 S-free environment.

Water electrolysis potentially represents an environmentally friendly method for scalable hydrogen production and for intermittent renewable energy storage. Yet cost and high reaction overpotentials limit widespread implementation. Here, an electrolysis cell architecture that uses dissimilar electrolytes is shown to minimize the kinetic and thermodynamic considerations ascribed to electrolysis. The use of multiple monopolar ion exchange membranes (anion and cation selective) and multiple chambers (anolyte, catholyte, middle) allows stable electrolysis operation while a pH gradient is maintained across the electrolysis cell. This reduced the hydrogen and oxygen evolution onset potential by 0.65± 0.03 and 0.62± 0.01 V, resulting in a whole cell onset potential for water splitting of 0.79± 0.02 V. The reduced onset potential was demonstrated for >15 h of operation under fixed current density, resulting in a decrease in energy consumption by 56 % when compared to similar pH electrolysis cells.