Thermochemical Water Splitting Research Articles

Fe–Al core-shell structure as an efficient catalyst for dual hydrogen production and storage by thermochemical water splitting: A reactive molecular dynamic simulation

Catalysts with dual functions in hydrogen production and storage are desired for the low-cost technology. In the preceding view, we used reactive force molecular dynamics to demonstrate how effective the Fe–Al core-shell structure is at breaking up water molecules and storing hydrogen free radicals via thermochemical water splitting. The results show that at T ∼600 K, water molecules begin to dissociate in the presence of a Fe–Al catalyst, releasing OH and H free radicals. It is worth noting that the produced OH free radicals are bonded to the Al-shell, whereas the H free radicals move to the Fe-core and stores via chemical bond. Interestingly, at T < 1200 K, there is no Fe–O bond. This could be due to Al having a higher oxidation potential than Fe, causing OH free radicals to preferentially associate with the Al-shell. Furthermore, at 2000K < T > 3000 K, the number of Fe–H bonds decreases while the number of H–H bonds increases, indicating that the stored H atom desorbs and forms an H2 molecule. Temperature can thus be used to monitor the ability of Fe–Al catalysts to dissociate water, store hydrogen, and produce hydrogen. This research shows that developing core-shell type catalysts can provide an effective solution for hydrogen generation, storage, and transportation.

Thermochemical production of green hydrogen using ferrous scrap materials

Thermochemical water splitting is one of the methods to produce green hydrogen. In this study, metal scrap is used to split water by thermochemical process in a packed-bed reactor. Hydrogen production conditions are optimized by varying the particle size of the metal wastes in the range of 250 μm to greater than 1000 μm and the temperatures from 900 °C to 1200 °C. The maximum yield of hydrogen obtained is ∼500 mL of H2 per gram of the scrap sample. This study demonstrates that the discarded metal wastes can be utilized as feed-materials for thermochemical production of green hydrogen. The process has good conversion efficiency and is a promising solution for both metal waste management and the production of green hydrogen. Medium size metal particles show higher hydrogen production capacity compared to both smaller (<250 μm) and larger (600–1180 μm) size particles.

Mechanistic investigation of hydrogen generation from water and magnesium catalyst reaction: Advanced reactive molecular dynamics simulation

Magnesium is an effective catalyst for producing hydrogen through thermochemical water splitting. However, the slow reaction between Mg and water prevents this catalyst from being commercially useful. In this study, reactive MD simulations with accurate force fields and reactive potential energy surfaces are used to comprehend the slow-kinetics of the Mg-water reaction. At room temperature, water is split when it interacts with Mg nanoparticles and forms a Mg–H bond. Furthermore, at temperatures above 1200 K, Mg–H bonds begin to dissociate, resulting in the generation of hydrogen radicals from the Mg–H bond. The percentage of H–H bonds is almost zero until the reaction pathway reaches temperature 2000K, after which H radicals combine to form hydrogen gas. The analysis of temperature dependent data reveals that oxygen and hydrogen atoms combine with Mg elements to form massive stable linear and branched chains, resulting in slow Mg-water reaction kinetics for hydrogen production. Therefore, current studies utilizing reactive molecular dynamics can provide a means of improving the kinetics of the Mg-water reaction.

Investigation of the hydrogen production of the PACER fusion blanket integrated with Fe–Cl thermochemical water splitting cycle

In order to meet the energy demand, energy production must be done continuously. Hydrogen seems to be the best alternative for this energy production, because it is both an environmentally friendly and renewable energy source. In this study, the hydrogen fuel production of the peaceful nuclear explosives (PACER) fusion blanket as the energy source integrated with Fe–Cl thermochemical water splitting cycle have been investigated. Firstly, neutronic analyzes of the PACER fusion blanket were performed. Necessary neutronic studies were performed in the Monte Carlo calculation method. Molten salt fuel has been considered mole-fractions of heavy metal salt (ThF4, UF4 and ThF4+UF4) by 2, 6 and 12 mol. % with Flibe as the main constituent. Secondly, potential of the hydrogen fuel production as a result of the neutronic evaluations of the PACER fusion blanket integrated with Fe–Cl thermochemical cycle have been performed. In these calculations, tritium breeding (TBR), energy multiplication factor (M), thermal power ratio (1−ψ), total thermal power (Phpf) and mass flow rate of hydrogen (m˙H2) have been computed. As a results, the amount of the hydrogen production (m˙H2) have been obtained in the range of 232.24x106 kg/year and 345.79 x106 kg/year for the all mole-fractions of heavy metal salts using in the blanket.

Pressure-enhanced performance of metal oxides for thermochemical water and carbon dioxide splitting

Pressure-enhanced performance of metal oxides for thermochemical water and carbon dioxide splitting

Temperature-entropy and energy utilization diagrams for energy, exergy, and energy level analysis in solar water splitting reactions

Solar hydrogen production by water splitting reaction is an important route to realize the storage of solar energy. The involvement of light and chemical energy can reduce the high reaction temperature of direct thermochemical water splitting reactions, but the pivotal issues such as energy, exergy, and energy level relationships behind the temperature reduction remain under-researched. A graphic analysis of water splitting reactions using the temperature-entropy and energy utilization diagrams is proposed to research the energy, exergy, and energy level relationships. The energy composition and conversion mechanisms with the light and chemical energy are presented in the diagrams by comparing with direct thermochemical water splitting reactions. Three cases, including the photocatalytic, photo-thermochemical, and methane steam reforming reactions, are studied to explain the effect of light, the synergistic effect of heat and light, and the effect of chemical energy in reducing the temperature of water splitting reactions. The energy levels of light and methane are higher than those of hydrogen, thus lowering the energy level of heat and reducing reaction temperatures. The discovery of the energy level required for hydrogen production will provide guidance for reducing its temperature.

Advancing production of hydrogen using nuclear cycles - integration of high temperature gas-cooled reactors with thermochemical water splitting cycles

The usage of heat from the nuclear cogeneration plant and hydrogen production technologies based on thermochemical water splitting was analyzed. Two most promising ones – copper-chlorine (Cu–Cl) and sulfur-iodine (S–I) cycles have been studied. The main advantage of the two analyzed thermochemical technologies is that they can be completely or partially independent from the electricity required for the process. The Cu–Cl method has a high ability to reduce the enthalpy of technological heat even to temperatures of up to 120 °C, enabling high output of the produced hydrogen. It is not demonstrated by the S–I technology, which can reduce the temperature of the working medium to approximately 380 °C, although it exhibits the limited demand for electricity. Considering the working conditions of the planned demonstration plant it is recommended to install Cu–Cl cycle due to its high level of utilization of the available heat and no requirement for additional medium heating.

Hydrogen production by isothermal thermochemical cycles using La0.8Ca0.2MeO3±δ (Me = Co, Ni, Fe and Cu) perovskites

Solar-driven thermochemical water splitting has the potential to transform concentrated solar energy into green hydrogen and other solar fuels. In this work, La0.8Ca0.2MeO3±δ (Me = Co, Ni, Fe and Cu) perovskites have been synthesised by a modified Pechini method and evaluated as materials for hydrogen production by two step thermochemical water splitting cycles. Performing the thermal reduction at temperatures of 1200 and 1000 °C, while the oxidation is done at 800 °C, allows a remarkable and stable hydrogen production after 5 consecutive cycles. However, the perovskites suffer changes in the structure after each redox cycle, with potential effects in the long-term cyclic operation. On the contrary, the isothermal thermochemical cycles at 800 °C produce a stable amount of hydrogen with each consecutive cycle maintaining the perovskite structure. This hydrogen production ranges from 3.60 cm3 STP/gmaterial·cycle for the material with the lowest productivity (La0.8Ca0.2FeO3±δ) to 5.02 cm3 STP/gmaterial·cycle for the one with the highest activity (La0.8Ca0.2NiO3±δ). Particularly the Ni-based material shows the highest H2 productivity accompanied by very good material stability after 15 consecutive cycles, being possible to combine with current solar thermal facilities based on concentrated solar power technologies like plants with central receivers.

High-entropy spinel oxide (Fe0.2Mg0.2Mn0.1Al0.3Cr0.2)3O4 as a highly active and stable redox material for methane driven solar thermochemical water splitting

Solar thermochemical H2O splitting has attained wide attention as a promising solution for hydrogen production. However, it remains a daunting challenge to produce hydrogen with high kinetics and stability for the oxide materials at lower temperature because of insufficient active sites for H2O activation and splitting. Herein, we report a high-entropy spinel oxide that consists of five cations (HEO) and can highly-effectively thermochemically split H2O to H2 with ultrahigh production rate and productivity of 182.9 mL min-1 g-1 and 68.5 mL g-1, respectively, several times higher than state-of-the-art materials via a two-step cycle process with methane driven reduction. High-entropy effect facilitated the preservation of single-phase structure even at large amount of oxygen converted (almost 70 mL g-1), which promoted the exsolution and stabilization of substantial Fe0 nanoparticles (20–30 nm vs. 100 nm) and their dissolution into spinel structure during redox process, resulting in extensive metal-oxide interfaces with metal-oxygen vacancy pairs responsible for the efficient and stable water splitting. Such findings provide a class of viable material with high configurational entropy for efficient hydrogen generation.

Technoeconomics and carbon footprint of hydrogen production

Decarbonization of the global economy needs not only carbon-free electricity but also a fuel that is free of greenhouse gas emissions. Hydrogen is a prime candidate, with colors such as gray, blue and green production methods receiving attention. Generally missing from this discourse, however, is a quantitative comparison on the cost, scale, carbon footprint and infrastructure requirements for each of these technologies. Here we present a detailed technoeconomic comparison of five hydrogen production technologies: thermochemical water splitting, methane pyrolysis, water electrolysis, steam methane reforming, and chemical looping hydrogen production. Steam or autothermal methane reforming with carbon capture (SMR + CC) at large scale sets the benchmark for costs, but at small scales, electrochemical technologies appear more suitable. Potentially competitive with and sometimes more affordable than SMR + CC are chemical looping hydrogen production and methane pyrolysis. The impacts of the CO2 footprint of the electricity grid and a price on CO2 are also quantitatively evaluated. A qualitative consideration of the ability to leverage existing infrastructure is also offered with a view towards rapid scalability. Finally, the key research needs are identified for each technology.

Exploring the Redox Properties of Ce1-xUxO2±δ (x ≤ 0.5) Oxides for Energy Applications.

The Ce-U-O system, forming a solid solution in the fluorite structure, has gained much attention due to its unique properties. Mixed fluorite oxide powders of Ce1-xUxO2±δ compositions were found to be particularly active for H2 production through thermochemical water splitting. In the present work, we explore the reduction-oxidation properties of the mixed oxides with x = 0.1, 0.25, and 0.5. We report a particularly high oxygen storage capacity (OSC) for x ≥ 0.25 and show that the oxygen extracted from these mixed oxides is of a different origin than that extracted from CeO2. While in ceria, oxygen is extracted from the tetrahedral sites, leading to the formation of oxygen vacancies, the extracted oxygen in Ce1-xUxO2±δ (x ≥ 0.25) is essentially excess oxygen in the fluorite lattice (which spontaneously penetrates the oxide under ambient or oxidative conditions). This property, which is clearly related to the change in the valency of the U cations, is apparently responsible for the higher OSC and the lower activation energy for oxygen extraction from the mixed oxides compared to ceria. The mixed oxide powders are shown to be structurally stable, retaining their fluorite structure following reduction under Ar-5%H2 or oxidation in air until 1000 °C. The presented results provide new insights into the Ce-U-O system which may be exploited for future technical applications, as a catalyst for thermochemical water splitting, or as a solid electrolyte in solid oxide fuel cells.

Physical system behavior and energy flow analysis of a solar driven hydrogen production plant based on two-step thermochemical redox cycles

Two-step thermochemical water splitting using concentrated solar power offers promising potential for green hydrogen production as a part of a future sustainable energy economy. In this study, a system and energy flow analysis of a large scale 250 kW reactor prototype is presented by using a complex 3D-simulation model. Thus, the physical dynamic system behavior and potential efficiency improvements are discussed with respect to plant design and operational strategy. Regarding the plant design, different kind of heat losses as well as the influence of reactor design parameters and material modifications are analyzed. Regarding the operational strategy, crucial control parameters as cycle durations, temperatures, and mass flow rates are varied in a broad range and analyzed with respect to plant efficiency. By comparing commonly used operational strategies, the temperature swing operation turns out to be by far more efficient than any isothermal or near-isothermal operation for the current plant concept.

Heat transfer characteristics and design aspects of thermolysis reactor in copper-chlorine thermochemical water splitting cycle

Thermolysis of copper oxychloride is the highest temperature reaction step of Copper–Chlorine cycle which forms cuprous chloride and oxygen gas as products. In the present study, important design aspects of thermolysis reactor have been investigated experimentally and a mathematical model has been developed to understand the effect of critical parameters on conversion. Experiments were conducted in tubular reactors with three different diameters of 25 mm, 50 mm and 100 mm to study the effect of reactor geometry on heat transfer and conversion. Modelling of batch thermolysis reactor has been carried out using governing heat transport equations coupled with reaction kinetics and validated against experimental data. As per the experimental and modelling results, enhancement in conversion could be achieved with increasing aspect ratio and heat transfer. The studies provide clear insights into the design and scale-up of thermolysis reactor to address the issues of low conversion observed during the multi-step thermal decomposition reaction.

Technological Pathways to Produce Compressed and Highly Pure Hydrogen from Solar Power.

Hydrogen (H2 ) produced from renewables will have a growing impact on the global energy dynamics towards sustainable and carbon-neutral standards. The share of green H2 is still too low to meet the net-zero target, while the demand for high-quality hydrogen continues to rise. These factors amplify the need for economically viable H2 generation technologies. The present article aims at evaluating the existing technologies for high-quality H2 production based on solar energy. Technologies such as water electrolysis, photoelectrochemical and solar thermochemical water splitting, liquid metal reactors and plasma conversion utilize solar power directly or indirectly (as carbon-neutral electrons) and are reviewed from the perspective of their current development level, technical limitations and future potential.

Technologische Pfade für die Herstellung von komprimiertem und hochreinem Wasserstoff mit Hilfe von Sonnenenergie

AbstractWasserstoff (H2) aus erneuerbaren Energien wird einen wachsenden Einfluss auf die globale Energiedynamik hin zu nachhaltigen und kohlenstoffneutralen Standards haben. Der Anteil von grünem H2 ist noch zu gering, um das Netto‐Null‐Ziel zu erreichen, während die Nachfrage nach hochwertigem Wasserstoff weiter steigt. Diese Faktoren verstärken den Bedarf an wirtschaftlich tragfähigen H2‐Erzeugungstechnologien. Der vorliegende Artikel zielt darauf ab, die bestehenden Technologien zur Erzeugung von hochwertigem H2 auf der Grundlage von Solarenergie zu bewerten. Technologien wie die Wasserelektrolyse, die photoelektrochemische und die solare thermochemische Wasserspaltung, Flüssigmetallreaktoren und die Plasmakonversion nutzen die Sonnenenergie direkt oder indirekt (als kohlenstoffneutrale Elektronen) und werden im Hinblick auf ihren derzeitigen Entwicklungsstand, ihre technischen Grenzen und ihr Zukunftspotenzial untersucht.

Simulation and optimization of an innovative thermochemical water splitting cycle for the production of greenhydrogen

Highly efficient and cost-effective green Hydrogen production is a crucial challenge in a future sustainable economy. The innovative Nickel–Iodine-Sulphur (NIS) thermochemical cycle is a potential candidate for this purpose. For the first time in literature, this paper provides a complete Aspen Plus V10 simulation of the closed NIS cycle. Whitin the cycle, the Bunsen reactor was simulated as a PFR with a kinetic constant k = 1.38 m3/mol·s, while the other four reactors were considered at the thermodynamic equilibrium. A simulation of the conventional IS cycle was used as a benchmark for the NIS cycle, whose process parameters were optimized through a sensitivity study. Finally, the thermal efficiency without heat recovery of both cycles was calculated through an energy balance. The simulation results shows that the NIS cycle simulation achieves the same stoichiometric hydrogen yield as the IS cycle and a 17% higher thermal efficiency than the latter.

CO oxidation mechanism on surfaces of B-site doped SrFeO3-δ-based perovskite materials for thermochemical water splitting

Density functional theory (DFT) calculations were performed to explore the reaction mechanism of CO oxidation on both the perfect and O pre-adsorbed surfaces of B-site (B = Al, Zr, Nb and W) doped SrFeO3-δ-based perovskite materials. Our calculations showed that metal doping benefited the adsorption of molecular CO over the perfect surface, while it inhibited the adsorption of molecular CO over the O pre-adsorbed surface. The reaction of CO with lattice oxygen of SrFeO3 was inhibited with the doping of Zr, Nb and W, but promoted by the doping of Al. The reaction of CO with surface pre-adsorbed O of SrFeO3 was found to be thermodynamically inhibited by the doping of Al, Zr, Nb and W. This study provided significant insights into the interaction of CO with the surfaces of doped SrFeO3-δ perovskite materials for thermochemical water splitting applications.

Aluminum nanotubes as an efficient catalyst for hydrogen production via thermochemical water splitting: a reactive molecular dynamics simulation.

Water splitting is the process of using energy to break down water molecules into hydrogen and oxygen. The use of an aluminum catalyst in the thermochemical process can help to increase the efficiency and rate of the reaction. Furthermore, aluminum is a relatively inexpensive material that can be easily produced, making it an appealing option for use in large-scale water-splitting operations. We investigated the reaction mechanism between aluminum nanotubes and water at various temperatures using reactive molecular dynamic simulations. We found that an aluminum catalyst makes it possible to split water at temperatures higher than T > 600 K. It was also observed that the yield of H2 evolution is dependent on the diameter of the Al nanotube and decreases with increasing size. During the process of splitting water, the inner surfaces of the aluminum nanotubes are seen to be severely eroded, as shown by changes in the aspect ratio and solvent-accessible surface area. In order to compare the H2 evolution efficiency of water with other solvents, we also split a variety of solvents, including methanol, ethanol, and formic acid. We presume that our study will give researchers enough knowledge to create hydrogen through thermochemical process in the presence of an aluminum catalyst by dissociating water and other solvent molecules.

Techno-economic assessment of green hydrogen production via two-step thermochemical water splitting using microwave

This study evaluates a two-step thermochemical water-splitting method for green hydrogen production and considers the economic feasibility of technically available designs under harsh hydrogen production conditions. As layouts of hydrogen production, two thermochemical water–splitting systems are evaluated in this study. One system is the process via high temperature from solar concentration power systems. The other system uses microwaves for thermochemical water splitting under low temperatures from advanced nuclear power plants. As part of the hydrogen production system, possible solid–solid and fluid–fluid heat recuperators of printed circuit heat exchanger (PCHE) are proposed and evaluated through the effectiveness-number of transfer units (ε-NTU) method and logarithmic mean temperature difference (LMTD) method. The required heat transfer area and volume are calculated according to the operating conditions and considered in the economic assessment of the hydrogen production system. Optimum geometries of the PCHE are proposed considering the cost analysis. The Levelized cost of hydrogen (LCOH) and system efficiency are calculated for the conventional system with solar power and system-using microwave with HTGR. The importance of heat recuperation systems is confirmed in that they account for approximately 10–20% of the cost for both system layouts. To evaluate the technology development level to achieve the ultimate target, LCOH according to various cost factors is evaluated and further research areas essential for commercialization are represented.

Synthesis, Experimental, and Theoretical Study of Co3-x Ni x O4 Mixed Oxides: Potential Candidates for Hydrogen Production via Solar Redox Cycles.

Recently, green hydrogen production via solar thermochemical water splitting (STWS) as a clean and sustainable method is becoming a subject of interest to many researchers. Great efforts are being made to develop materials for STWS with suitable operating conditions, low cost, and good cycling stability. In this context, the study of mixed cobalt and nickel oxides with the general formula Co3-x Ni x O4 (0 ≤ x ≤ 1) was carried out, where four mixed metal oxides Co2.75Ni0.25O4, Co2.5Ni0.5O4, Co2.25Ni0.75O4, and Co2NiO4 have been successfully synthesized through the sol-gel method modified Pechini route. The structural investigation demonstrated that pure spinel structures were obtained for 0 ≤ x ≤ 0.75. A deep study was carried out with the main goal of finding the best phase that provides low redox temperature. Interesting reduction temperatures for all the compositions have been found, and the lowest values of 675 and 710 °C have been reported for Co2.25Ni0.75O4 and Co2.5Ni0.5O4, respectively. The thermal cycling results of this latest material using TGA measurement have proven attractive cycling stability of which the complete reoxidation of the samples was achieved. In addition, thermodynamic analysis of a reduction step was performed and good agreement of the theoretical reduction temperature of Co2.25Ni0.75O4 with the experimental one has been found.