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The sulfur-iodine (S–I or I–S) thermochemical cycle is viewed as a leading method for hydrogen production due to its environmental sustainability, cost-efficiency, and high efficiency. This study critically reviews the advancements in the S–I cycle research made over the last two decades, primarily focusing on basic research aspects such as two-phase separation and side reactions in the Bunsen reaction, along with purification and decomposition processes of H 2 SO 4 and HI. Furthermore, it offers an overview of the unique implementations and simulation results of the S–I cycle put forth by various global institutions. This paper also critically evaluates the feasibility of hydrogen production using the S–I cycle, considering technological, efficiency, economic, environmental, and safety aspects. Although the S–I cycle technology of hydrogen production has seen considerable progress over the years, to fast-track its industrialization, ongoing technical issues such as material compatibility and system matching ought to be addressed strategically. • The progress of basic research on the S–I cycle in the past is reviewed. • The systems platforms that have been established in various countries are introduced in detail. • The simulation work of the S–I cycle system in recent years is summarized. • The comparative analysis of various thermochemical cycles in terms of feasibility, efficiency, economy, environmental impact, and safety is conducted. [ABSTRACT FROM AUTHOR]

Two-step redox thermochemical cycles, capable of directly converting CO 2 and H 2 O respectively into CO and H 2 , offer a promising synthesis route towards green carbon-neutral fuels. The performance of such two-step cycles depends highly on the thermodynamic properties of splitting materials, particularly the solid-state enthalpy ( Δ h solid) and entropy (Δ s solid) changes during the reduction process. Here, we report an investigation into the roles of the Δ h solid and Δ s solid. We shall show that a high Δ s solid relaxes both reduction temperature and oxygen pressure, but increases oxidant consumption. Conversely, an increase in Δ h solid enhances reduction resistance while promotes oxidation reactions. There are therefore no perfect materials, and a trade-off is needed for an optimal solution. We also defined a thermodynamic region based on Δ h solid and Δ s solid and typical operating conditions, and showed that higher values of both Δ h solid and Δ s solid provided a larger reaction space. While lower Δ h solid and negative Δ s solid may be more suitable for isothermal cycles. Our analyses also suggest future efforts in searching for splitting materials with a high Δ s solid within an appropriate range of Δ h solid (280–460 kJ/mol). [Display omitted] • Trade-off caused by solid state enthalpy and entropy is a key issue. • High solid-state enthalpy and entropy are more suitable for temperature-swing cycle. • A thermodynamic region under typical operating conditions is defined. • Solid-state entropy of different candidate materials is discussed. [ABSTRACT FROM AUTHOR]

This research investigates the incorporation of solar power systems into buildings to meet the energy needs of near-zero-energy buildings. The study focuses on a complex buildings in Shiraz City, Iran. The primary objective of this case study is to integrate an innovative method of hydrogen production known as thermochemical hydrogen production methods to fulfill the building's energy demands. Solar energy is utilized to generate heat by parabolic trough collectors, which is the sole energy source required for the V–Cl thermochemical cycle. Consequently, hydrogen is produced and stored during the day for use at night when there is no solar radiation. To address this, a novel component has been developed for the vanadium chlorine cycle (V–Cl) within the TRNSYS software. The energy system was simulated using the TRNSYS software, a powerful transient simulation tool. Despite the numerous advantages offered by TRNSYS's energy system simulation, it lacks optimization capabilities. The use of a neural network-genetic algorithm optimization approach allows for the calculation of an optimized area for collectors and the power output of fuel cells for the building complex. The optimum configuration results in minimum installation cost, lowest CO 2 emissions, and the highest power supply renewable (PSR). The results reveal that the installation of collectors with a surface area of 70 m2 and the utilization of fuel cells with a power output of 345 kW lead to a total carbon dioxide (CO 2) generation of 10.31 tons per year, a PSR of 1.21, and a cost of $4.915 per hour. • Modeling and investigation of a building complex consisting of restaurants. • Solar energy system to provide the power requirements of a building using TRNSYS. • Using vanadium chlorine thermochemical cycle to produce and store hydrogen. • A neural network-genetic algorithm technique for optimization. • System development to find the optimal balance between cost and emissions. [ABSTRACT FROM AUTHOR]

Thermochemical processes used to produce clean hydrogen (H 2) on a large scale by utilizing renewable energy and nuclear power sources are considered one of the most environmentally friendly strategies. In this study, the neutronic performance and hydrogen production potential of the PACER fusion blanket have been investigated during the operation period. Firstly, neutronic calculations have been performed to produce an electrical energy of 1000 MW from fusion explosions of 8.36 TJ to be repeated every 40 min with Monte Carlo Calculation Method (MCNP). Minor actinide flouride (MA) fuel out of the nuclear waste of LWRs with volume fractions of 2% have been mixed homogenously in the Flibe coolant. Tritium breeding ratio (TBR) at startup is calculated as 1.27. TBR and energy multiplication factor (M) decrease gradually. TBR >1.05 can be kept over 7 years for a self-sustained reactor. The M due to higher fissionable fuel content in the molten salt computes as 3.3 at initial. The burn up exceeds ∼800 GWd/tM at the end of operation period. Secondly, the potential of hydrogen production for four step iron chloride (Fe–Cl) and three step magnesium chloride (Mg–Cl) thermochemical cycles of the hydrogen unit PACER fusion blanket. The ratio of thermal power (1 − ψ), total thermal power (P hpf) and rate of mass flow of hydrogen ( m ˙ H 2 ) depends on M for Fe–Cl, Mg–Cl (option I) and Mg–Cl (option II) thermochemical cycle have been presented. The ratio of thermal power (1 − ψ) for Fe–Cl, Mg–Cl (option I) and Mg–Cl (option II) have been obtained as 0.6494, 0.131 and 0.095 whereas, total thermal power (P hpf) have been computed as 5298.8, 3608.43 and 3488.925 MW, respectively, at start up. The produced of hydrogen amount for Fe–Cl, Mg–Cl (option I) and Mg–Cl (option II) have been calculated as ∼ 534.65; ∼1236.82 and ∼806.03 kg/year, respectively, at startup. • Burning value of the PACER computed as ∼800 GWd/tM. • Hydrogen production obtained as 12.82 (Fe–Cl) and 39.22 (Mg–Cl) kg/s. • Energy efficiency calculated as 45% (Fe–Cl) and 68% (Mg–Cl). [ABSTRACT FROM AUTHOR]

The incredible potential of metal oxide-based two-step solar-driven thermochemical water splitting technology lies in its ability to harness limitless solar energy to produce clean and renewable hydrogen fuel. However, achieving high redox kinetics and lowering the reaction temperature remain the primary challenges in hydrogen production. The CeO 2 –ZrO 2 system is a well-known oxygen carrier for thermochemical water splitting on account of its high temperature stability, quick kinetics, and redox cyclability. While recent studies have explored the combination of methane partial oxidation with metal oxide reduction, the reduction effect of cerium-zirconium oxide is relatively low, and reactivity still needs improvement. The nickel-doped system exhibits good redox performance and is regenerative. In this study, different mass percentages nickel-loaded oxygen carriers mNi/Ce 0.8 Zr 0.2 O 2 (m = 0, 1, 3, 5, 7, 9) were prepared using the impregnation method. Redox properties of oxygen carriers were investigated in a fixed bed reactor and various characterizations were performed. To assess the durability of mNi/Ce 0.8 Zr 0.2 O 2 , 60 long-cycle experiments were also conducted. The results indicate that the lattice oxygen in mNi/Ce 0.8 Zr 0.2 O 2 exhibits remarkable selectivity for the partial oxidation of CH 4 at temperatures ranging from 880 to 925 °C. The best reactivity performance was achieved with a nickel loading ratio of 5 wt%, and after 60 consecutive redox cycles, 5Ni/Ce 0.8 Zr 0.2 O 2 demonstrates remarkable robustness, maintaining its redox activity. • mNi/Ce 0.8 Zr 0.2 O 2 demonstrates excellent redox reactivity at 900 °C. • Introduction of Ni loading leads to an increase of 60% in fuel generation. • Reduction time of 5Ni/Ce 0.8 Zr 0.2 O 2 is reduced by 32% compared to Ce 0.8 Zr 0.2 O 2. • 5Ni/Ce 0.8 Zr 0.2 O 2 exhibited the most superior redox activity. [ABSTRACT FROM AUTHOR]

A reduced order model of sulfuric acid decomposition within a bayonet chemical reactor was developed to support the U. S. Department of Energy Integrated Energy System program, and address the lack of knowledge in scaling and integration for joint chemical and nuclear processes. Sulfuric acid decomposition within a bayonet reactor was modeled to provide chemical and thermodynamic data relevant to advanced nuclear reactor-driven integrated energy systems based on desired operational scale and operational conditions. The temperature range required for high-temperature advanced nuclear reactor integrated energy systems, 750-850 °C, was shown to produce reasonable agreement (within a few percent relative error) with past models and experimental data, and yielded good efficiency results for bayonet reactor operations. The results of the reduced order model agreed with previous work from Savannah River National Labs within a maximum of 3.4% error on the decomposition of sulfur trioxide, and on previous Hybrid Sulfur flowsheets from Gorensek and Summers that showed operational temperature, pressure, and composition ranges for efficiency which made the Hybrid Sulfur cycle competitive with water electrolysis. The agreement with previous high-fidelity models provided a framework for future Integrated Energy System grid evaluations with an advanced nuclear reactor and large-scale hydrogen production using a mathematical model to represent chemical operations. • Established design and models for nuclear-powered sulfuric acid decomposition. • Efficiency results from reduced-order bayonet reactor model agreed with previous experience. • The model provides a platform to study coupling to advanced nuclear energy. [ABSTRACT FROM AUTHOR]

The study develops a multistep reaction mechanism for a two-step thermochemical cycle that produces hydrogen from H 2 S decomposition, using nickel sulfide as a catalyst. Two mechanisms were investigated: 1) a gas-phase mechanism that occurs without a Ni catalyst to determine the contribution of thermal decomposition to the overall reaction without a catalyst, and 2) a microkinetic model of the catalytic Ni surface phase to examine the key parameters affecting the overall cycling process and H 2 S conversion efficiency. Both mechanisms were validated using CHEMKIN-Pro software to analyze the experimental data and trends. The study showed that gas-phase H 2 S conversion was not kinetically significant below 850 °C. The microkinetic model showed that most H 2 S was transformed into H 2 and NiS products when the sulfurization temperature reached 500 °C. Additionally, the site fraction of NiS decreased while the number of free active nickel sites increased as the regeneration temperature increased from 500 °C to 800 °C. A temperature limit of 700 °C was set for the regeneration step due to the agglomeration behavior of nickel sulfide particles. [Display omitted] • Development of a multistep mechanism for 2-step H 2 S decomposition using Ni catalyst. • Validation of the mechanism through experiments for gas-phase and microkinetic models. • Gas-phase H 2 S conversion is not significant below 850 °C. • Microkinetic model showed most H 2 S transformed into H 2 and NiS products at 500 °C. • Temperature limit of 700 °C set for regeneration due to agglomeration of NiS particles. [ABSTRACT FROM AUTHOR]

In this study, an integrated energy system is presented in which hydrogen is produced via the thermochemical cycle. The presented system would provide a potential solution for storing excess electric power in terms of hydrogen generation for a sustainable community. Principles of exergy and energy are utilized to analyze the presented system in terms of exergy and energy efficiencies. The simulation result shows that with the help of the developed system, 0.36 kg/h of hydrogen can be generated, which is utilized via SOFCs to produce and electrify the houses. Additionally, 1000 kW of electric power with 3.6 kW of heating can be supplied via the developed system. With the use of thermochemical cycle considered in the present study, one can produce hydrogen with an energy efficiency of 79.6% and exergy efficiency of 62.9%. Furthermore, to see the impact of different factors on the operation of the developed system, a parametric study is also conducted by changing factors like solar irradiation, the inlet temperature of the molten salt, and the outlet temperature of the solar collector. • An integrated energy system is presented in which hydrogen is produced via the thermochemical cycle. • The thermochemical cycle considered in the present study, has an energy efficiency of 79.6% and exergy efficiency of 62.9%. • 1000 kW of electric power with 3.6 kW of heating can be supplied via the developed system. [ABSTRACT FROM AUTHOR]

The global energy crisis and climate change have fueled interest in solar-driven thermochemical CO 2 splitting as a potential solution. However, conventional materials like CeO 2 encounter limitations attributable to their low solar absorptivity and CO yield (even at high reduction temperatures), exerting a detrimental influence on both solar energy utilization and process efficiency. This study proposes high-entropy A-site doped perovskites as a potential solution for efficient solar thermochemical CO 2 splitting. The increased configurational entropy enhances the solar thermal CO 2 splitting cycles by decreasing oxygen vacancy formation energy and lattice oxygen migration energy barrier. This is supported by experimental results, where Sm 0.25 Sr 0.25 Ca 0.25 La 0.25 MnO 3 achieved a maximum CO yield of 764.76 μmol g−1 with low temperature difference between the reduction and oxidation steps, marking an important progress in solar thermal CO 2 splitting cycles. The study demonstrates the potential of high-entropy perovskites for direct solar energy harvesting with high spectrum absorption coefficients and sustainable CO 2 utilization. [ABSTRACT FROM AUTHOR]

The thermochemical copper–chlorine (Cu–Cl) cycle is known as a promising method for producing clean hydrogen. Due to the high-temperature environment of the thermolysis reactor, there are commercialization challenges with regard to the heat exchanger design. In this study, a new design for the heat exchanger used in the thermolysis reactor of a 4-step Cu–Cl cycle is presented, aiming to achieve the required temperature distribution of 430 °C–550 °C. A design methodology is developed for the heat exchanger along with an iterative algorithm for the sizing problem. The final design of this study has decreased the T * (representative of the temperature range) by 51 % compared to the previous designs, with the improvement techniques resulting in increasing the heat exchanger effectiveness and thermal performance factor by 15 % and 138 % and decreasing average TD (representative of the temperature dispersal) by 61 %. The achieved operating temperature ranges from 431.3 °C to 539.0 °C. • New heat exchanger design to achieve an even temperature distribution in reactor. • Solar salt is used as the heat transfer fluid inside the heat exchanger. • New design methodology with an iterative sizing algorithm for the heat exchanger. • Desired operating temperature range was achieved in the reactant channel. [ABSTRACT FROM AUTHOR]

Renewable energy resources play a critical role in taking the place of fossil fuels to slow global warming. To make better use of these sources, multigenerational integrated systems that generate multiple beneficial outputs from the same inputs are required. This study describes a multigeneration system that utilizes a hybrid sulfur (HyS) cycle to produce hydrogen. The HyS cycle is a thermochemical-electrochemical cycle that relies on high-grade heat to function effectively. Concentrated solar power (CSP) technology, specifically solar power towers, can provide the high-grade heat required for the cycle. A thermochemical heat pump is also integrated into the current system to achieve the 800 °C temperature required for SO 3 decomposition. In this regard, a multigeneration solar tower-based system with a thermal energy storage option is proposed to generate useful outputs of hydrogen and freshwater. The energy and exergy efficiencies for the overall system are determined to be 8.15% and 3.73%, respectively. Furthermore, this integrated system represents a promising solution for renewable hydrogen production and freshwater generation. • Multigeneration system that utilizes a hybrid sulfur cycle to produce hydrogen. • Research presents a new integrated system that combines the solar tower and the HyS cycle. • To reach 800 °C for SO3 decomposition, a thermochemical heat pump is integrated into the system. • The energy and exergy efficiencies for the entire system were 8.15% and 3.73%, respectively. [ABSTRACT FROM AUTHOR]

Abstract Solar energy is the most sustainable alternative to fossil fuels. The production of solar thermochemical fuels from water/carbon dioxide not only overcomes the intermittent nature of solar energy, but also allows for flexible transportation and distribution. In this paper, the challenges for solar thermochemical H2/CO production are reviewed. New perspectives and insights to overcome these challenges are presented. For two-step cycles, the main challenges are high temperatures, low conversions and the intensive oxygen removal work. Theoretically feasible temperature and pressure ranges are needed to develop reactant materials. The fundamental mechanism to reduce the temperature and the potential to improve the efficiency by minimizing the oxygen removal work need be revealed. Various material modification strategies and advanced reactors are proposed to improve the efficiency by reducing the temperature and enhancing heat transfer process. But the oxygen removal work required has not been minimized. For multi-step cycles, the main challenges are the separation of corrosive acid and insufficient reaction kinetics. For the separation of acids, many methods have been proposed. But these methods require extra energy and causes undesired side reactions or byproducts. The reaction kinetics have been enhanced by improving catalysts with noble materials or complex fabrication methods. Developing novel multi-step cycles using metal oxides, hydroxides and carbonates may be promising.

High-temperature Solid Oxide Fuel Cell (SOFC) technology has great potential as a clean and effective energy source. However, several issues have prevented their widespread adoption, like high operating costs, difficulty integrating with other components, and being sensitive to fuel contamination. In order to address these challenges, the main novelties of the present work are carbon capture and utilization for clean energy production, using the flue gas condensation process as a cost-effective and energy-efficient strategy, and the combination of Molten Carbonate Fuel Cells (MCFC) for increased energy efficiency and most effective component integration. The proposed novel system is also equipped with a gasifier and vanadium chloride unit for syngas and clean hydrogen production. The system's practicality is evaluated by analyzing the key performance indicators from thermodynamic, exergo-economic, exergo-environmental, and sustainability viewpoints. Also, the Sankey diagram is presented to investigate each component's effectiveness from the exergy destruction facet. According to the findings, at the most optimum design condition, the acceptable energy and exergy efficiencies of 61.06% and 50.66%, respectively, are achieved, revealing the system's effectiveness. The suggested system is also financially attractive since it achieves a reasonable levelized power cost of 17.6 $/MWh at a total cost of 44.1 $/h. The findings show that carbon dioxide recovery is crucial in reducing the pollutants due to the low emission index of 5.01 kg/GWh. Finally, the exergo-environmental index, environmental damage effectiveness, and exergy stability factor have equivalent values of 0.012, 0.59, and 0.54. • An efficient novel system based on SOFC and MCFC integration is introduced. • A carbon recovery unit is added to reuse the generated CO 2 in the gasification. • The performance is comprehensively investigated from all aspects. • An exergy efficiency of 50.6% with an acceptable cost of 17.6 $/MWh is achieved. • The environmental pollution index is reduced considerably. [ABSTRACT FROM AUTHOR]

The effects of substitution at the A- and B sites on the redox performance of a series of lanthanum–strontium–manganese (LSM)-based perovskite oxides (Z = Ni, Co, and Mg) were studied for application in a two-step thermochemical CO2 splitting cycle to produce liquid fuel from synthesis gas using concentrated solar radiation as the proposed energy source and CO2 recovered from the atmosphere as the prospective chemical source. The redox reactivity, stoichiometry of oxygen/CO production, and optimum chemical composition of Ni-, Co-, and Mg-substituted LSM perovskites were investigated to enhance oxygen/CO productivity. Furthermore, the long-term thermal stabilities and thermochemical repeatabilities of the oxides were evaluated and compared with previous data. The valence changes in the constituent ionic species of the perovskite oxides were studied and evaluated by X-ray photoelectron spectroscopy (XPS) for each step of the thermochemical cycle. From the perspectives of high redox reactivity, stoichiometric oxygen/CO production, and thermally stable repeatability in long-term thermochemical cycling, Ni0.20-, Co0.35-, and Mg0.125-substituted La0.7Sr0.3Mn perovskite oxides are the most promising materials among the LSM perovskite oxides for two-step thermochemical CO2 splitting, showing CO productivities of 387–533 μmol/g and time-averaged CO productivities of 12.9–18.0 μmol/(min·g) compared with those of LSM perovskites reported in the literature. [ABSTRACT FROM AUTHOR]

In this study, an assessment of a renewable energy-based hybrid sulfur-bromine cycle for hydrogen fuel production and effective utilization is performed since the present era requires lots of hydrogen for fueling many systems. Hydrogen, produced by the hybrid sulfur-bromine cycle, is supplied to the combustion subsystems by blending with natural gas for residential use. Solar and wind energy sources are potentially considered as renewable energies for green hydrogen production. Also, a drying unit is included with an incineration subsystem. A desalination unit is also integrated to produce freshwater for the community. In this way, electricity, heat, and clean water required both for the community and the subsystems are supplied. The integrated system is then assessed in terms of energy and exergy efficiencies. Here, 0.233 kg/s of natural gas and hydrogen blend and 1.338 kg/s of biomass are provided to the system. The energy and exergy efficiencies of the overall system are determined to be 64.43% and 32.24%. • Developing a hybrid sulfur-bromine cycle to produce hydrogen fuel. • Providing hydrogen storage and usage option by blending with natural gas. • Designing a trigeneration system with lower CO 2 emissions. • Integrating a drying and incineration system for waste management. [ABSTRACT FROM AUTHOR]

This review investigates the effect of different dopants on the oxygen evolution and carbon dioxide splitting abilities of the lanthanum manganites. Particular focus was placed on the lanthanide, alkaline earth metals, redox-active transition metal, and non-redox active Group 3 metals. The review suggests that a small ionic radius lanthanide on the A-site can increase the size discrepancy, leading to Mn-O6 octahedra tilting and more facile Mn-O bond breaking. Doping the A-site with a divalent alkaline earth element can increase the valance of the transition metal, leading to greater reduction capabilities. A transition metal with one electron in the eg orbital is the most effective for reduction while for oxidation, zero electrons in the high-energy eg orbitals is optimal. Finally, doping of the B-site with metals such as gallium or aluminium aids in sintering resistance and allows reactivity to remain constant over multiple cycles. Higher reduction temperatures and moderate re-oxidation temperatures also promote higher fuel yields as does the active reduction of the perovskite under hydrogen, although the total energy consumption implications of this are unknown. Far more is known about the mechanism of the reduction reaction than the oxidation reaction, therefore more research in this area is required.

Ceria-based oxides have attracted a lot of attention as an attractive redox material because of their large capacity for storing and releasing oxygen in the solar-driven thermochemical water splitting (STWS) process. Nevertheless, the extremely high temperatures and low oxygen partial pressure required to achieve deep degrees of reduction and large temperature swing in a redox cycle introduce challenges in the practical implementation. These above challenges can be addressed in a unique way by integrating partial oxidation of methane into the reduction step. The STWS can therefore operate isothermally at significantly lower temperatures. In this work, the CeO 2 -ZrO 2 solid solutions (Ce 1-x Zr x O 2) are synthesized, characterized, and assessed for thermochemical water splitting in combination with partial oxidation of methane. Up to 160 consecutive redox cycles are also conducted in a bench-scale fixed bed. At an operating temperature of 900 °C, methane successfully promotes the reduction of Ce 1-x Zr x O 2 to produce the synthesis gas with a 2:1H 2 /CO ratio and 87.86% selectivity. When compared to CeO 2 , the thermodynamic fuel generation capability of CeO 2 with Zr4+ doping is three times greater in the partial oxidation of methane step and water splitting step. Ce 0.8 Zr 0.2 O 2 (C8Z2) demonstrates the best redox activity in terms of CO and H 2 production in a redox cycle among the various Zr4+ doping levels. After 160 consecutive redox cycles, C8Z2 is also very robust, maintaining its redox activity. The C8Z2 composite redox solid solution thus exhibits excellent redox activity and long-term redox stability, potentially making it appropriate for STWS in combination with partial oxidation of methane. • Ce 1-x Zr x O 2 two–step STWS in combination with POx of CH 4 is operated at 900 °C. • CH 4 oxidizes to synthesis gas with a 2:1H 2 /CO ratio and 87.86% selectively. • The fuel generation capability of Ce 1-x Zr x O 2 is three times greater than CeO 2. • Ce 0.8 Zr 0.2 O 2 demonstrates the best redox activity. • Ce 0.8 Zr 0.2 O 2 maintains its redox activity after 160 thermochemical cycles. [ABSTRACT FROM AUTHOR]

Hydrogen production via a two-step thermochemical cycle based on solar energy has attracted increasing attention. However, the severe irreversible loss causes the low efficiency. To make sense of the irreversibility, an in-depth thermodynamic model for the solar driven two-step thermochemical cycles is proposed. Different from previous literatures solely focusing on the energy loss and irreversibility of devices, this work decouples a complex energy conversion process in three sub-processes, i.e., reaction, heat transfer and re-radiation, acquiring the cause of irreversible loss. The results from the case study indicate that the main irreversibility caused by inert sweeping gas for decreasing the reduction reaction temperature dominates the cycle efficiency. Decreasing reduction reaction temperature without severe energy penalty of inert sweeping gas is important to reducing this irreversible loss. A favorable performance is achieved by decreasing re-oxidation rate, increasing hydrolysis conversion rate and achieving a thermochemical cycle with a lower equilibrium temperature of reduction reaction at atmosphere pressure. The research clarifies the essence of process irrrversibility in solar thermichemical cycles, and the findings point out the potential to develop efficient solar driven two-step thermochemical cycles for hydrogen production. [ABSTRACT FROM AUTHOR]

• A new variation of KOH water splitting cycle is developed with carbon capture. • Integrated energy system is designed for multigeneration under different scenarios. • A thermodynamic assessment is carried out from energy and exergy aspects. • Economic feasibility is carried out and levelized cost of hydrogen is found. • The maximum energy and exergy efficiencies of the KOH cycle are 44.2 % and 67.66 %. Both hydrogen production and carbon dioxide removal are considered in this study as two of the critical pieces to achieve the ultimate sustainability target. This study proposes and investigates a new variation of potassium hydroxide thermochemical cycle in order to combine hydrogen production and carbon dioxide removal synergistically. An alkali metal redox thermochemical cycle is developed to utilize the potassium hydroxide uniquely through a nonequilibrium reaction. Also, the multigeneration options are explored by employing two-stage steam Rankine cycle, multi-effect distillation desalination, and Li-Br absorption chiller, which is integrated with potassium hydroxide thermochemical cycle for hydrogen production, carbon capture, power generation, water desalination, and cooling purposes. A comparative assessment under different scenarios is carried out. The energy and exergy efficiencies of the hydrogen production thermochemical cycle are found to be 44.2 % and 67.66 % when the hydrogen generation reaction is carried out at 180 °C and the separation reactor temperature is set at 400 °C. Among the multigeneration scenarios considered, a trigeneration option for producing hydrogen, power and freshwater provides the highest energy efficiency as 66.02 %. [ABSTRACT FROM AUTHOR]

Carbon dioxide removal is considered by many as an essential piece to achieve global net zero targets which was also mentioned by the third working group of Intergovernmental Panel on Climate Change. On top of this, green hydrogen is badly needed to achive carbon-free society long-term sustainability. This study proposes a new five-step sodium hydroxide thermochemical cycle for simultaneous hydrogen production and carbon dioxide removal, which is driven by the heat at least 400 °C. The proposed integrated cycle can be driven by clean energy sources that can be utilized to generate heat at required temperatures. The proposed system is designed and analyzed by using energy and exergy approaches of thermodynamics. A case study is also developed in order to understand the effects of changing parameters on system performance. A thermochemical hydrogen production cycle is designed with an unequilibrium reaction where the respective heat capacity calculation models are employed. According to the calculations, more than half of the energy content of process heat can be converted into hydrogen, where maximum energy and exergy efficiencies of the thermochemical cycle are found as 50.05% and 76.61% when the separation reaction is carried out at 400 °C. According to the case study results, a parabolic trough collector type concentrated solar energy system with 295 kW of heat sink capacity, can generate 5216.65 kg of hydrogen and capture 19,991.97 kg of carbon dioxide in a location where 1500.11 kWh of solar energy is reached per m2 of area in a typical year. [Display omitted] • A new carbon-negative hydrogen production system is proposed. • A time-dependent analysis is carried out with hourly data. • A half of the heat is utilized for hydrogen production in the new system. • The energy and exergy efficiencies of the thermochemical cycle are 50.05% and 76.61%. [ABSTRACT FROM AUTHOR]

• Cryogenic distillation of the flue gas is integrated with hydrogen production. • CO 2 and H 2 S are captured. • Several sensitivity analyses are conducted under different scenarios. • Aspen Plus software is employed for process simulation. • energy and exergy efficiencies of the system are 82.99 % and 55.39 % The present work aims to develop a novel integrated energy system for clean hydrogen production from the industrial flue gas stream. The particular system incorporates a cryogenic distillation unit for H 2 S and CO 2 separation and a thermochemical cycle for hydrogen production. The industrial flue gaseous mixture is considered a major feedstock for the present system. H 2 S is retrieved from the waste gaseous stream and fed to the two-step sulfur looping thermochemical cycle to perform clean hydrogen production. In this way, clean hydrogen production, elemental sulfur production, carbon capture, and storage are achieved. The entire integrated energy system is simulated in the Aspen Plus process simulator and is investigated thermodynamically in terms of energy and exergy performances. Various parametric studies are conducted to assess the significance of operating parameters on the system performance. The H 2 S and CO 2 removal rates from the waste feed stream are found to be 85.55 % and 84.62 %. The H 2 S conversion into hydrogen is determined to be 66.67 %. The energy and exergy efficiencies of the two-step thermochemical cycle are found to be 53.93 % and 23.69 %, respectively. The parametric studies show that the hydrogen production rates of 3.63 kmol/h, 2.46 kmol/h, and 1.78 kmol/h are achieved at sulfurization temperatures of 200 °C, 300 °C, and 500 °C, respectively. The study further concludes that 44.60 % of the total input exergy is lost due to the presence of irreversibilities within the system. The overall energy and exergy efficiencies of the integrated energy system are found to be 82.99 % and 55.39 %, respectively. [ABSTRACT FROM AUTHOR]

Ce-based thermochemical cycles are characterized by high stability and adaptability to operating temperatures. But few studies have been conducted in terms of exergy prospect. In this study, we propose an exergy analysis model and identify its irreversibility distribution. Through introducing an Energy Level-Enthalpy Change (A-∆H) diagram, we capture this distribution and reveal the trend of irreversibility variation. The results show that irreversibility occurs mainly in heat exchangers and reduction reactors and is influenced by temperature and pressure. Previous studies have focused only on the operating parameters, but this has led to negligible improvement in efficiency, hence the need for a comprehensive analysis using sound mathematical methods. We improve the exergy efficiency by 177% through theoretically optimizing the operating conditions and detail the reasons for the reduction in exergy losses. This study provides theoretical guidance and analytical tools for experiments. • We propose an exergy model to analyze Ce-based solar thermochemical cycles. • We find the irreversibility tendency varying with operating conditions. • We identify the operating conditions achieving the highest exergy efficiency. [ABSTRACT FROM AUTHOR]

The present study is conducted to develop a two-steps redox thermochemical cycle based on combined ceria reduction and methane reforming through the CeO 2 /Ce 2 O 3 redox pair. This cycle incorporates simultaneous water splitting for hydrogen production. To enhance the accuracy and reliability of the inventory data, the system is simulated using the Aspen Plus software package. Also, the goal of this work is to evaluate the carbon footprint of thermochemical based hydrogen production under different scenarios and to compare it with traditional technologies like steam methane reforming (SMR). The analysis takes into account both the plant manufacturing line (reactors), fuel processing (H 2 production), redox particles oxygen carrier manufacturing (OC), H 2 compression (power consumption) and H 2 storage (pipeline manufacturing). The openLCA software with the European database environmental footprint is employed to compute the total carbon emissions of this thermochemical cycle during its overall life cycle. The study concludes that the base case scenario of this system has an overall GWP of 1751.14 g CO 2 eq./kg H 2 respectively. In the overall GWP, the share of plant construction and OC production was found to be around 1.67%, and 15.78% respectively. The conventional steam methane reforming is loaded with an overall GWP of 4472.83 g CO 2 eq./kg H 2. In terms of renewable energy input, the base case scenario of this hydrogen production system results in 1465.73 g CO 2 eq./kg H 2 with thermal energy produced from renewable sources. Comparative life cycle assessment (LCA) demonstrates that base case of CeO 2 /Ce 2 O 3 has an 85.41% lower GWP emphasizing its environmental advantages over the SMR and Fe 3 O 4 /FeO redox pair carries an 84.06% lower GWP as compared to the conventional SMR with 1483.55 g CO 2 eq./kg H 2. The present study concludes that the combined ceria reduction and methane reforming chemical looping process with simultaneous water splitting may be a more promising option to produce hydrogen using renewable energy. [Display omitted] • A new system is developed for cleaner hydrogen production using a thermochemical cycle. • The thermochemical cycle employs steps with CeO 2 /Ce 2 O 3. • A life cycle assessment of CeO 2 /Ce 2 O 3 based thermochemical cycle is performed. • The proposed system achieves a 2.5-fold reduction in GWP compared to an SMR process. [ABSTRACT FROM AUTHOR]

• Syngas with a 2:1 H 2 /CO ratio is successfully produced in co-splitting of H 2 O/CO 2. • CO 2 can be fully converted to CO in co-splitting of H 2 O/CO 2. • Faster oxidation in the co-splitting of H 2 O/CO 2 compared to H 2 O or CO 2 splitting. • Ce 0.8 Zr 0.2 O 2 maintains its superior redox activity after 100 thermochemical cycles. Solar-driven thermochemical splitting of H 2 O and CO 2 presents an enticing avenue for converting solar energy into chemically storable energy. In particular, isothermal cycling processes integrating partial oxidation of methane have shown promise in enabling reactions at moderate temperatures and enhancing reactivity and solar-to-fuel conversion efficiency. The ability to maintain a syngas with an H 2 :CO ratio of 2:1 through the reduction of metal oxides by CH 4 , followed by co-splitting of H 2 O and CO 2 during the oxidation process to preserve this ratio, holds significant importance for subsequent industrial applications. This study delves into the characterization and evaluation of the partial oxidation of methane in tandem with the co-splitting of H 2 O and CO 2 within Ce 0.8 Zr 0.2 O 2. Gas production ratios were explored under diverse H 2 O and CO 2 feed ratios in a fixed-bed configuration operating under an isothermal condition of 900 °C. Furthermore, cyclic stability experiments comprising up to 100 cycles were conducted to assess the material's performance across repeated redox processes. The results unveil that various oxygen sources (H 2 O, CO 2 , or a combination thereof) facilitate the swift recovery of oxygen vacancies within the material. Noteworthy is the generation of a syngas with an H 2 /CO ratio of 2 during the oxidation stage when the H 2 O/CO 2 ratio reaches 5. Importantly, this optimal ratio is maintained even after 100 redox cycles, underscoring the material's enduring reaction performance. [ABSTRACT FROM AUTHOR]

Thermochemical redox cycles are a promising route to producing solar fuels. In this work, a novel reactor train system (RTS) is proposed for the efficient conversion of solar thermal energy into hydrogen. This system is capable of recovering thermal energy from redox materials, which is necessary for achieving high efficiency but has been difficult to realize in practice. The RTS overcomes technical challenges of high-temperature thermochemical reactors like solid conveying and sealing, while enabling continuous fuel production and efficient oxygen removal during metal oxide reduction. The RTS is comprised of several identical reactors arranged in a closed loop and cycling between reduction and oxidation steps. In between these steps, the reactors undergo solid heat recovery in a counterflow radiative heat exchanger. The RTS can achieve heat recovery effectiveness of 80% for a train producing 100 kg-H2/day with a 60 min cycle time. The RTS can take advantage of thermal energy storage to operate round-the-clock. Further, it implements waste heat recovery to capture the exothermic heat of water-splitting. If all auxiliary energy demands can be satisfied with such waste heat, the RTS base configuration achieves 30% heat-to-hydrogen conversion efficiency, which is more than four times that of current state-of-the-art thermochemical systems. [ABSTRACT FROM AUTHOR]

Converting CO2 into fuels via solar-driven thermochemical cycles of metal oxides is promising to address global climate change and energy crisis challenges simultaneously. However, it suffers from low energy conversion efficiency ( η en ) due to high sensible heat losses when swinging between reduction and oxidation cycles, and a single product of fuels can hardly meet multiple kinds of energy demands. Here, we propose an alternative way to upsurge energy conversion efficiency by integrating solar thermochemical CO2 splitting with a supercritical CO2 thermodynamic cycle. When gas phase heat recovery (εgg) is equal to 0.9, the highest energy conversion efficiency of 20.4% is obtained at the optimal cycle high pressure of 260 bar. In stark contrast, the highest energy conversion efficiency is only 9.8% for conventional solar thermochemical CO2 splitting without including a supercritical CO2 cycle. The superior performance is attributed to efficient harvesting of waste heat and synergy of CO2 splitting cycles with supercritical CO2 cycles. This work provides alternative routes for promoting the development and deployment of solar thermochemical CO2 splitting techniques. [ABSTRACT FROM AUTHOR]

Solar thermochemical water splitting via a two-stage redox cycle has been subjected to numerous theoretical and experimental studies since a couple of decades. It has been considered as a promising technology to generate green hydrogen as it is feasible to directly convert concentrated solar radiation into storable chemical energy. The present article describes the results of an experimental campaign, which has been carried out to further demonstrate the feasibility of this technology. Based on the prior experience from solar gas turbine projects, a combined receiver/reactor has been designed and built up operating at temperatures between 1400 °C and 1000 °C using radiative power of up to 150 kW generated by a large-scale solar simulator (Synlight). The reactor has a total volume of 90 L with open porous ceramic foam structure. Additionally, high-performance heat exchangers have been used to recover the heat content of the product gases. Typical necessary durations for the sub-cycles, reduction and oxidation as well as durations for the corresponding necessary heating and cooling phases have been determined. By producing up to 8,8 g of hydrogen per cycle it could be shown that the production of hydrogen in a medium scale structured reactor is possible. [Display omitted] [ABSTRACT FROM AUTHOR]

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Increasing energy needs and reducing greenhouse gas emissions require immediate studies on carbon-free energy solutions, namely hydrogen. There are numerous methods among the production methods of hydrogen in a green manner. Hydrogen, which is then primarily obtained as a result of the separation of water with thermochemical cycles, is an environmentally friendly and sustainable hydrogen production method. In this study, the Cobalt–Chlorine (Co–Cl) cycle, which is one of the new thermochemical cycles, is examined in detail in terms of thermodynamics. There are four reactions in the Co–Cl thermochemical cycle. These are listed as the hydrolysis reaction in which hydrogen is obtained, the thermolysis reaction in which oxygen is obtained, the reduction reaction and finally the hydrochlorination reaction. According to the results of the analysis performed kinetically with the Aspen Plus software, the exergy efficiency of the cycle is calculated as 33%. When the exergy destruction of all reactions is compared, it is seen that the greatest exergy destruction occurs in the hydrolysis reaction, and the lowest exergy destruction occurs in the hydrochlorination reaction. The fact that the exergy efficiency is high when evaluated in terms of kinetics shows that the cycle is feasible in terms of thermodynamics. In addition, the costs of the cycle are to be considered in the future studies as it is an important criterion. [Display omitted] • Investigating the Co–Cl thermochemical water splitting cycle for hydrogen generation. • Assessing the performance of the cycle kinetically. • Conducting parametric studies to observe what affects the overall exergy effeciency. [ABSTRACT FROM AUTHOR]

Non-abatable emissions are one of the decarbonization challenges that could be addressed with carbon-neutral fuels. One promising production pathway is the direct air capture (DAC) of carbon dioxide, followed by a solar thermochemical cycle and liquid fuel synthesis. In this study, we explore different combinations of these technologies to produce methanol from an economic perspective in order to determine the most efficient one. For this purpose, a model is built and simulated in Aspen Plus®, and a solar field is designed and sized with HFLCAL®. The inherent dynamics of solar irradiation were considered with the meteorological data from Meteonorm® at the chosen location (Riyadh, Saudi Arabia). Four different integration strategies are assessed by determining the minimum selling price of methanol for each technology combination. These values were compared against a baseline with no synergies between the DAC and the solar fuels production. The results show that the most economical methanol is produced with a central low-temperature DAC unit that consumes the low-quality waste heat of the downstream process. Additionally, it is determined with a sensitivity analysis that the optimal annual production of methanol is 11.8 kt/y for a solar field with a design thermal output of 280 MW. [ABSTRACT FROM AUTHOR]

Solar-driven thermochemical CO 2 reduction is a promising technology that enables the efficient conversion of CO 2 into green fuels and chemicals. However, limited knowledge of the theory and technology, including active material characteristics, the redox cycling process, and reaction thermodynamics and kinetics, significantly affects efficiency and restricts large-scale applicability. This study investigated the thermochemical cycling characteristics of CO 2 -to-CO conversion and the redox performance of spinel-type Fe–Ni–Co nanocomposite oxide structures. The study also delved into the CO fuel formation reaction mechanisms and kinetics of oxygen carrier decomposition, as well as cyclic redox and thermal stability performances, considering different ratios of Fe–Ni–Co oxides and their mixtures. Among the materials investigated, NiFe 2 O 4 nanoparticles doped with 20 % CoO and Ni 0.8 Co 0.2 Fe 2 O 4 powder prepared using the sol-gel method exhibited better CO 2 thermocatalytic conversion performance, with record-high CO yield of 1184.24 μmol/g and 1987.24 μmol/g, respectively. The study further revealed a more efficient Fe–Ni–Co composite oxide for CO 2 thermochemical conversion through solar-driven thermochemical experimental testing, resulting in the highest cycle CO yields of 244 mL and 312 mL across 20%CoO doped NiFe 2 O 4 and Ni 0.8 Co 0.2 Fe 2 O 4 coated SiC media, respectively. These findings and methods provided comprehensive insights into the redox materials composition selectivity, synthesis, and CO 2 thermochemical conversion performance assessments. [ABSTRACT FROM AUTHOR]

The continuous growth of anthropogenic carbon emissions from the aviation industry has emphasized the urgent request to substitute traditional aviation fuels with Sustainable Aviation Fuels (SAFs) because SAFs can potentially reduce carbon emissions by around 50–90% as compared to traditional kerosene-based fuels. In this paper, a novel SAF production pathway is developed which is based on biomass processing, nuclear energy, and thermochemical reactions of the vanadium chloride cycle for SAF, clean power, and hydrogen production. The entire system is assessed thermodynamically in terms of energy and exergy performances. Various sensitivity analyses are computed to determine the reliable operating parameters. The study concludes that biomass-to-SAF energetic and exergetic performance is achieved to be 76.72% and 74.35%. The energetic and exergetic performance values, through efficiencies, of the V–Cl cycle are calculated to be 68.08% and 53.50%, respectively. For hydrogen production and storage, an energy penalty of around 16.83 kJ/kg H 2 is calculated, which results in an efficiency penalty of 6.18%. The overall energetic and exergetic efficiencies of the proposed integrated system are found to be around 59.79% and 23.78%, respectively. • This study develops a nuclear and biomass-based integrated energy system for cleaner community applications. • A vanadium chloride thermochemical cycle is incorporated into the integrated system to produce clean hydrogen. • A fluidized bed pyrolysis reactor is simulated in the Aspen Plus. • An optimization study of the chemical process is undertaken. • Both energy and exergy efficiencies are considered for system performance evaluation. [ABSTRACT FROM AUTHOR]

Summary: In this research, a novel integrated system for renewable hydrogen production, power, and hot water from solar thermal energy has been developed and precisely evaluated in terms of thermodynamics. The developed structure is comprised of a four‐step Cu‐Cl thermochemical cycle, and an organic Rankine cycle to generate electricity. The required heat is supplied by a concentrated solar power plant and thermal energy storage based on latent heat. Also, a high‐temperature heat pump is employed to improve the thermal grade of working fluid and provide each unit with sufficient heat. System dynamics simulation has been performed using weather and irradiation input data of Tehran, Iran. The integrated structure has the capability to produce 21.75 kg/h of hydrogen, 563.6 kW of electricity, and 393.3 m3/h of hot water at 70°C. The energy efficiency of the system reaches more than 80% based on higher heating value and the solar‐to‐fuel efficiency has a value of 25.8%. Moreover, an exergy analysis has been executed to determine the fundamental operating parameters of each component and the whole structure. The total exergy efficiency of the integrated structure is 34.23%, and the prime cost of the product is found to be 5.795 USD/kg H2. [ABSTRACT FROM AUTHOR]

[Display omitted] • Cubic Born-Haber thermochemical construct captures the Brønsted acidity of H*. • The acidity of H* is reflected by metal work function and H* binding energy. • Periodic trend and co-adsorbate effects on acidity are elucidated. • H+ standard reduction potential captures solvent effects on H* acidity. • Interfacial H+ is more reactive than free H+ in C ar -H/C ar -D exchange of phenol. H-adatom (H*) at protic solvent-metal interfaces can undergo ionization and form interfacial protons (H-Metal solvated → H+ solvated + Metal- solvated , K a,HM). A three-dimensional Born-Haber thermochemical framework quantitatively decomposes the H* acidity (as K a,HM) into the metal's work function, H-binding energy, H+/H• reduction potential, and thermodynamic properties of gaseous H 2 or H•, capturing the separate contributions from metal, adsorbate, and solvent. On Group VIII metals, the K a,HM increases from left to right and top to bottom of periodic position and spans 20 orders in magnitude. The interfacial protons, together with transition metal surfaces, are much more effective than free protons for the electrophilic addition of deuteron that leads to the selective C ar -H/C ar -D exchange on the ortho and para carbon atoms of phenol because of the additional stabilization afforded by the transition metals acting as a Brønsted base. Hydrogen is required, but the reactive protons inherit the chemical fingerprint from the protic solvent. [ABSTRACT FROM AUTHOR]

We investigated, herein, the redox activity of partial substitution of the B-site in a series of lanthanum/strontium-manganese-based (LSM) perovskite oxide, La0.7Sr0.3Mn0.9X0.1O3 for solar two-step thermochemical fuel production using concentrated solar radiation as an energy source. We systematically investigated the effects of partial substitution in LaSrMnO3 in terms of their kinetics behavior, oxygen/CO productivity, thermal reduction/oxidation temperatures. Furthermore, repeatability was evaluated and compared among the samples prepared using the same procedure and studied using the same test method. We observed and evaluated the long-term thermal stability of the redox activity and valence variation of the constituting ionic species of the perovskite in the two-step thermochemical CO2 splitting. From the perspectives of superior activity and long-term repeatability, Ni-, Co-, and Mg-substituted LSM perovskites are promising for thermochemical two-step CO2/H2O splitting to produce synthetic gas.

In the presented paper, energy and exergy analysis is performed for thermochemical hydrogen (H 2) production facility based on solar power. Thermal power used in thermochemical cycles and electricity production is obtained from concentrated solar power systems. In order to investigate the effect of thermochemical cycles on hydrogen production, three different cycles which are low temperature Mg–Cl, H 2 SO 4 and UT-3 cycles are compared. Reheat-regenerative Rankine and recompression S–CO 2 Brayton power cycles are considered to supply electricity needed in the Mg–Cl and H 2 SO 4 thermochemical cycles. Furthermore, the effects of instant solar radiation and concentration ratio on the system performance are investigated. The integration of S–CO 2 Brayton power cycle instead of reheat-regenerative Rankine enhances the system performance. The maximum exergy efficiency which is obtained in the system with Mg–Cl thermochemical and recompression S–CO 2 Brayton power cycles is 27%. Although the energy and exergy efficiencies decrease with the increase of the solar radiation, they increase with the increase of the concentration ratio. The highest exergy destruction occurred in the solar energy unit. • Energy and exergy efficiencies of solar based hydrogen production system are investigated. • Low temperature Mg–Cl, H 2 SO 4 and UT-3 cycles are compared. • Reheat-regenerative Rankine or supercritical-CO 2 Brayton power cycle is integrated. • The system with Mg–Cl and s-CO 2 Brayton power cycles has maximum exergy efficiency. • The exergy efficiency increases with the increase of the concentration ratio. [ABSTRACT FROM AUTHOR]

Converting CO2 into fuels via solar-driven thermochemical cycles of metal oxides is promising to address global climate change and energy crisis challenges simultaneously. However, it suffers from low energy conversion efficiency (ηen) due to high sensible heat losses when swinging between reduction and oxidation cycles, and a single product of fuels can hardly meet multiple kinds of energy demands. Here, we propose an alternative way to upsurge energy conversion efficiency by integrating solar thermochemical CO2 splitting with a supercritical CO2 thermodynamic cycle. When gas phase heat recovery (εgg) is equal to 0.9, the highest energy conversion efficiency of 20.4% is obtained at the optimal cycle high pressure of 260 bar. In stark contrast, the highest energy conversion efficiency is only 9.8% for conventional solar thermochemical CO2 splitting without including a supercritical CO2 cycle. The superior performance is attributed to efficient harvesting of waste heat and synergy of CO2 splitting cycles with supercritical CO2 cycles. This work provides alternative routes for promoting the development and deployment of solar thermochemical CO2 splitting techniques.

When comparing the life-cycle environmental performance of hydrogen energy systems, significant concerns arise due to potential methodological inconsistencies between case studies. In this regard, protocols for harmonised life cycle assessment (LCA) of hydrogen energy systems are currently available to mitigate these concerns. These protocols have already been applied to conventional hydrogen from steam methane reforming as well as to a large number of both fossil and renewable hydrogen options, allowing robust comparisons between them. However, harmonised life-cycle indicators of nuclear-based hydrogen options are not yet available in the literature. This study fills this gap by using the recently developed software GreenH 2 armony® to calculate the harmonised carbon, energy and acidification footprints of nuclear-based hydrogen produced through different pathways (viz., low-temperature electrolysis, high-temperature electrolysis, and thermochemical cycles). Overall, the harmonised case studies of nuclear-based hydrogen show a generally good performance in terms of carbon footprint and acidification, but an unfavourable performance in terms of non-renewable energy footprint. • Library of harmonised life-cycle indicators of hydrogen extended to nuclear options. • Nuclear and renewable hydrogen generally show a low harmonised carbon footprint. • Nuclear hydrogen generally shows a low harmonised acidification impact. • Nuclear and fossil hydrogen show an unfavourable non-renewable energy footprint. [ABSTRACT FROM AUTHOR]

In this work, a novel thermochemical cycle (Boron-based) to produce ammonia is coupled with chemical looping combustion (CLC) process to produce final primary products of ammonia, CO 2 , water, and electricity. Manganese oxide-based CLC provides high purity N 2 , water and thermal energy for the carbothermal reduction of liquefied natural gas (LNG) occurring at 1200 °C. Gaseous synthesis gas from the carbothermal reduction is used as a fuel in the CLC's fuel reactor. Ammonia is produced through the hydrolysis of boron nitride (BN) and liquefied at atmospheric pressure. Thermodynamic equilibrium computations are used to predict the conversions of reactions involved in this proposed system. The overall system is then evaluated from energetic and exergetic perspectives to reflect upon the efficiency of reactors and subsystems. The production of approximately 25 metric t/h of NH 3 is achieved while power production reaches 232 MW. The exergetic efficiency of the overall system is calculated to be 53.8%. Moreover, life cycle assessments are performed to assess boron oxide environmental impacts and evaluated the exergy-based allocation of greenhouse gases emission to ammonia at 0.772 kg CO 2 (eq.)/kg NH 3. About 61% reduction in emissions relative to the global average of ammonia synthesis is estimated. • New B 2 O 3 /BN CL cycle is proposed and coupled with an Mn-oxide CLC. • The exergy efficiency of the system is 53.8%, electricity production reaches 232 MW. • Production of 600 metric t/d of ammonia is obtained while inherently capture CO 2. • Energy efficiency of the system is maximized through heat integration and recovery. • Environmental burden exergy-based allocated to ammonia is 0.772 kg CO 2 (eq.)/kg NH 3. [ABSTRACT FROM AUTHOR]

In this study, a corrosion-stable silica membrane was developed to be used in H 2 purification during the hydrogen iodide decomposition (2HI → H 2 + I 2), which is a new application of the silica membranes. From a practical perspective, the membrane separation length was enlarged up to 400 mm and one end of the membrane tubes was closed to avoid any thermal variation along the membrane length and sealing issues. The silica membranes consisted of a three-layer structure comprising a porous α -Al 2 O 3 ceramic support, an intermediate layer, and a top silica layer. The intermediate layer was composed of γ- Al 2 O 3 or silica, and the top silica layer that is H 2 selective was prepared via counter-diffusion chemical vapor deposition of a hexyltrimethoxysilane. To the best of our knowledge, this is the first report of 400-mm-long closed-end silica membranes supported on Si-formed α- Al 2 O 3 tubes produced via chemical vapor deposition method. A 400-mm-long closed-end membrane using a Si-formed α- Al 2 O 3 tube exhibited a higher H 2 /SF 6 selectivity of 1240 but lower H 2 permeance of 1.4 × 10−7 mol Pa−1 m−2 s−1 with compared with the membrane using a γ- Al 2 O 3 -formed α -Al 2 O 3 tube (907 and 5.6 × 10−7 mol Pa−1 m−2 s−1, respectively). The membrane using the Si-formed α -Al 2 O 3 tube was more stable in corrosive HI gas than a membrane with a γ- Al 2 O 3 -formed α -Al 2 O 3 tube after 300 h of stability tests. In conclusion, the developed silica membranes using the Si-formed α -Al 2 O 3 tubes seem suitable for membrane reactors that produce H 2 on large scale using HI decomposition in the thermochemical iodine–sulfur process. [Display omitted] • Corrosion-stable membrane was developed for H 2 production from HI decomposition. • Membrane length was enlarged up to 400 mm, and one end of the tubes was closed. • Membrane using Si-formed substrate remained stable in corrosive HI gas up to 300 h. • Developed membranes appear suitable for membrane reactor of HI decomposition. [ABSTRACT FROM AUTHOR]

The sodium‐oxygen‐hydrogen (Na‐O‐H) thermochemical cycle is investigated, as one of the potential methods of thermochemical water decomposition and hydrogen generation. The hydrogen production reaction, metal separation reaction, and hydrolysis reaction, forming the Na‐O‐H thermochemical cycle, are examined by RGibbs reactor modeling. The parameters for the three reactions are optimized in terms of hydrogen yield, pressure, temperature, and heat requirement. The metal separation reaction is carried out under vacuum pressure, while other reactions can be conducted under atmospheric pressure. [ABSTRACT FROM AUTHOR]

Electrolysis and thermochemical water splitting are approaches to produce green hydrogen that use either an electrical potential (electrolysis) or a chemical potential (thermochemical water splitting) to split water. Electrolysis is technologically mature when applied at low temperatures, but it requires large quantities of electrical energy. In contrast to electrolysis, thermochemical water splitting uses thermal energy, as thermal energy can typically be supplied at a lower unit cost than electrical energy using concentrating solar power. Thermochemical water splitting, however, typically suffers from high thermal losses at the extremely high process temperatures required, substantially increasing the total energy required. We show how, by combining electrical and chemical potentials, a novel and cost-efficient water splitting process can be envisioned that overcomes some of the challenges faced by conventional electrolysis and thermochemical water splitting. It uses a mixed ionic and electronic conducting perovskite with temperature-dependent oxygen non-stoichiometry as an anode in an electrolyzer. If solar energy is used as the primary source of all energy required in the process, the cost of the energy required to produce hydrogen could be lower than in high-temperature electrolysis by up to 7%. • Thermochemical electrolysis combines electrolysis and two-step thermochemical cycles as a novel approach for water-splitting. • Thermodynamic analysis shows potential to reduce required electrical energy for green hydrogen production. • Perovskites with a ΔH of 120–195 kJ/mol O are promising candidates for thermochemical electrolysis. • The potential to reduce the cost of green hydrogen is presented. [ABSTRACT FROM AUTHOR]

Abstract In this study, authors present a new hybrid nuclear small modular reactor system assisted with wind energy for net zero emissions trigeneration system. Small modular reactors bring multiple advantages including (a) improved thermal efficiency, (b) better building efficiency due to modularity, and (c) less operation and maintenance costs compared to standard nuclear power generation. Furthermore, the greenhouse gas emissions from small modular reactors are lower than regular counterparts. This study hybridizes small modular reactors with wind turbines for producing three useful commodities, namely electricity, hydrogen, and hot water. A two‐step high‐temperature thermochemical cycle (based on hydrogen chloride gas) is used for hydrogen production, and its performance in terms of energy and exergy efficiencies is evaluated. Additionally, the exergy and energy analyses (by writing balance equations for each component of the system) are carried out to determine the thermodynamic feasibility of the proposed system. In order to observe the effects of various parameters such as the temperature of the thermochemical cycle steps, inlet gas turbine temperature, the pressure ratio of the gas turbine, actual wind speed, and current density on the system performance, a detailed parametric study is conducted. The results of this study show that the overall system can achieve an energy efficiency of about 57.5% and exergy efficiency of about 38.1%.

Non-abatable emissions are one of the decarbonization challenges that could be addressed with carbon-neutral fuels. One promising production pathway is the direct air capture (DAC) of carbon dioxide, followed by a solar thermochemical cycle and liquid fuel synthesis. In this study, we explore different combinations of these technologies to produce methanol from an economic perspective in order to determine the most efficient one. For this purpose, a model is built and simulated in Aspen Plus®, and a solar field is designed and sized with HFLCAL®. The inherent dynamics of solar irradiation were considered with the meteorological data from Meteonorm® at the chosen location (Riyadh, Saudi Arabia). Four different integration strategies are assessed by determining the minimum selling price of methanol for each technology combination. These values were compared against a baseline with no synergies between the DAC and the solar fuels production. The results show that the most economical methanol is produced with a central low-temperature DAC unit that consumes the low-quality waste heat of the downstream process. Additionally, it is determined with a sensitivity analysis that the optimal annual production of methanol is 11.8 kt/y for a solar field with a design thermal output of 280 MW.

Summary: Diablo Canyon Nuclear Power Plant (DCNPP) is the last active nuclear power plant in California state. In 2016, the owner of the nuclear plant decided to close the DCNPP by 2025. This paper presents a study on the potential enhancement of DCNPP with a newly developed integrated solar energy‐based system. The active pressurized water nuclear reactor (PWNR) units of DCNPP are modeled and integrated with a parabolic trough (PT) type concentrated solar power (CSP) plant, a multi‐effect desalination unit, a heat pump and two district heating systems, and a CuCl thermochemical hydrogen production plant. DCNPP is enhanced with the proposed system to comply with the California Public Utilities Commission (CPUC)'s energy generation regulations and help achieve California's emission reduction goals. The number of useful outputs with the proposed system is increased from one to five, namely, electricity, district heating, domestic hot water, fresh water, and hydrogen. For the utilization of the useful outputs, a large‐scale greenhouse, administration building, and on‐site lodgment are considered the local demandants for fresh water, district heating, electricity, and domestic hot water utilities. The excess electricity and hydrogen are considered for commercial purposes. Thermodynamic analyses with energetic and exergetic approaches are carried out with parametric studies. For the assessment, real data are employed for PT‐CSP and DCNPP. Simulations are carried out on the system advisor model (SAM) for PT‐CSP and on Aspen Plus for the thermochemical hydrogen production plant. The proposed plant and its subsystems are assessed through an engineering equation solver (EES). The proposed integration has demonstrated 46.95% overall energy efficiency and 32.51% overall exergy efficiency during the main working mode in the average ambient conditions. [ABSTRACT FROM AUTHOR]

H2/CO production via H2O/CO2 splitting powered by concentrated solar energy is a promising pathway for energy conversion/storage. Oxygen permeable membrane reactor serves as an alternative reactor concept for realizing this chemical path with the advantages of continuous production, easy integration, and high product selectivity. In this paper, a mathematical model of steady-state mass and heat transfer coupled with reaction kinetics in the oxygen permeation membrane reactor was established. CO2 splitting in the ceria membrane reactor was simulated and the effects of various factors, including inert/CO2 flow configurations, reaction conditions, and geometric parameters of the membrane, on the CO2 conversion process, were studied. The increase of operating temperature could effectively improve the CO2 conversion ratio, and the effect of decreasing the oxygen pressure of the inert gas is very limited. The oxygen accumulation in the inert gas could lead to considerably high inert demand. Furthermore, conversion-limiting factors were studied under different conditions and there are two critical rate constants of reactions signifying a transition from a chemical kinetics limited conversion to oxygen diffusion limited conversion. This work helps guide reactor design and operate toward achieving the maximum CO2 conversion ratio. [ABSTRACT FROM AUTHOR]

Most thermochemical cycles require complex thermal processes at very high temperatures, which restrict the production and the use of hydrogen on a large scale. Recently, thermochemical cycles producing hydrogen at relatively low temperatures have been developed in order to be competitive with other kinds of energies, especially those of fossil origin. The low temperatures required by those cycles allow them to work with heats recovered by thermal, nuclear and solar power plants. In this work, a new thermochemical cycle is proposed. This cycle uses the chemical elements Magnesium-Chlorine (Mg-Cl) to dissociate the water molecule. The configuration consists of three chemical reactions or three physical steps and uses mainly thermal energy to achieve its objectives. The highest temperature of the process is that of the production of hydrochloric acid, HCl, estimated between 350-450°C. A thermodynamic analysis was performed according to the first and second laws by using Engineering Equation Solver (EES) software and the efficiency of the proposed cycle was found to be 12.7%. In order to improve the efficiency of this cycle and make it more competitive, an electro-thermochemical version should be studied. [ABSTRACT FROM AUTHOR]

Hydrogen is a clean energy carrier that can help mitigate greenhouse gas (GHG) emissions if it is used to replace fossil fuels for power production. One way to produce hydrogen on a large scale is through the use of water splitting thermochemical cycles such as the hybrid copper chlorine (Cu–Cl) cycle. Canadian Nuclear Laboratories Ltd. (CNL) chose to develop the Cu–Cl cycle because the highest temperature required by this cycle is about 530 °C, compatible with the Canadian Super Critical Water Reactor (SCWR) or some small modular reactors (SMR). The on-going effort at CNL is to demonstrate a fully integrated Cu–Cl cycle at laboratory scale with a hydrogen production rate of 50 L/h. Some recent experimental results of the electrolysis step, one of the main steps of the cycle, are discussed in this paper. The anode reaction of CuCl oxidation was investigated using a three-electrode electrochemical cell. Half-cell experiments found that CuCl oxidation did not require noble metals as catalyst. The CuCl oxidation on carbon was found to be a mass-transfer controlled process. Hence the limiting current density increased with increasing turbulence on the electrode surface. Increasing the CuCl concentration and the solution temperature also resulted in higher limiting current densities. A current density of 0.53 A/cm2 was achieved for a 1.0 M CuCl solution at 80 °C. Single cells with electrode areas up to 100 cm2 were used to establish the operating conditions for the electrolysis step. The effects of flow rate, temperature, and current density on the cell voltage were studied. A hydrogen production rate of 50 L/h was successfully achieved at 0.4 A/cm2 in a 2.0 M CuCl solution at 80 °C. The electrolysis step is fully developed for integration in a laboratory-scale demonstration of the Cu–Cl cycle. • Electro-oxidation of CuCl to CuCl 2 in HCl solutions can happen on carbon electrode. • Electrolysis voltage decreases with increasing temperature and improved hydrodynamics. • Electrolyser to produce hydrogen at 50 L/h has been demonstrated in laboratory. [ABSTRACT FROM AUTHOR]

In this paper, a theoretical and experimental study on a novel cobalt-chlorine thermochemical cycle for hydrogen production is presented. The cobalt-chlorine cycle comprises a closed loop of four thermochemical reactions occurring at 700 °C that is a reaction temperature compatible with the present generation of high-temperature gas-cooled reactors. Firstly, a thermodynamic analysis was done for determining whether this cycle is attractive for hydrogen production in terms of both energy and exergy efficiencies. Following, proof-of-principle experiments were carried out at laboratory scale in a batch reactor at temperatures in the range from 550 °C to 950 °C and holding times between 1 h and 72 h. Experimental results complemented by the characterization of condensed compounds deposited on the reactor walls allowed confirm the reaction pathway of thermochemical reactions originally proposed, define the slowest step of the global process, and explain the beneficial effect of increasing the system pressure on the hydrogen yield. Even both performance assessment and proof-of-principle experimental results look like promising more research will be required in the future to confirm these preliminary findings. Finally, a modified version of the cobalt-chlorine cycle is proposed for enhancing the global kinetics, based on the experimental evidence found in the proof-of-principle tests. • A novel-chlorine thermochemical cycle for nuclear hydrogen production is proposed. • A thermodynamic analysis was done to evaluate the cycle performance assessment. • Proof-of-principle tests were carried out to verify the global reaction pathway. • Effects of reaction temperature, total pressure and holding time were investigated. • A modified version of the cycle was proposed for increasing the global kinetics. [ABSTRACT FROM AUTHOR]