Thermochemical Water Splitting Cycle Research Articles

Which thermochemical water-splitting cycle is more suitable for high-temperature concentrated solar energy?

The manuscript reviews the thermochemical water-splitting cycles not in general (many other works have covered this topic) but specifically for producing hydrogen coupled with high temperature concentrated solar energy which is available at temperatures of 1000 to 1100 °C. This is important to benefit from synergies with near future dispatchable concentrated solar power, simply replacing the power cycle with the thermochemical hydrogen production plant. The review shows as three-step cycles are those benefiting the most from the synergy with higher solar flux dispatchable concentrated solar power with thermal energy storage, also profiting in terms of technology readiness level from past experiences in thermochemical water-splitting cycles for nuclear power plants, and the affordable complexity of the cycle. From preliminary evaluations, three-step cycles may permit CO2-free hydrogen production within a decade at a competitive cost with green hydrogen as well as the current prevailing production of hydrogen from hydrocarbons at less than $1 per 1 kg. The thermochemical pathway has the same minimum energy requirement as electrolysis, despite the conversion efficiencies achieved so far have been much less because of the reduced development. Since the collection of solar thermal energy is much easier and more efficient than solar photovoltaic conversion, the thermochemical pathway has the potential to deliver a cost of hydrogen smaller than green hydrogen from solar photovoltaic electricity and electrolyzers.

Process modeling of a hybrid-sulfur thermochemical cycle combined with solid oxide fuel cell/gas turbine system

This work proposes a novel design of the hybrid sulfur (HyS) thermochemical water-splitting cycle for hydrogen production. The hydrogen production plant is combined with a solid oxide fuel cell/gas turbine (SOFC/GT) system to satisfy the demand for the high-temperature heat from the HyS cycle by exploiting the heat loss of the SOFC stack and the demand for electric power for SO2-depolarized electrolysis. A detailed thermodynamic analysis of the HyS cycle and the SOFC/GT system was conducted on a flowsheet basis to determine the energy requirement and to estimate the effects of the operating conditions on the overall efficiency. As a result, it was found that the LHV efficiency of the combined HyS-SOFC/GT system can reach > 29% (34.32% HHV efficiency), with a net electric efficiency of the SOFC/GT system of 38.83% and consumption of 340.3 kJ molH2-1 high-temperature heat, 148.77 kJ molH2-1 low-temperature heat, and 134.35 kJ molH2-1 electric power.

Towards chemical equilibrium in thermochemical water splitting. Part 1: Thermal reduction

The efficiency of many processes strongly depends on their thermodynamic reversibility, i.e., proximity to equilibrium throughout the process. In thermochemical cycles for water and/or carbon dioxide splitting, thermochemical air separation, and thermochemical energy storage, operating near equilibrium means that the oxygen chemical potential of the solid and gas phases must not differ significantly. We show that approaching this ideal is possible in thermal reduction only if the reaction step occurs at a specific, reaction coordinate- and material-dependent temperature. The resulting thermal reduction temperature profile also depends on the ratio of gas and solid flows. • Method to achieve reversible/equilibrium reduction in water splitting cycles. • Reversible isothermal reduction is not feasible in practice. • Strong technical and physical limitations on the amount of sweep gas. • Limited impact of gas purity on reduction extent at fixed flow/maximum temperature. • High reduction temperatures expand the solution space for high cycle efficiency.

A Review on Recent Progress in the Integrated Green Hydrogen Production Processes

The thermochemical water-splitting method is a promising technology for efficiently converting renewable thermal energy sources into green hydrogen. This technique is primarily based on recirculating an active material, capable of experiencing multiple reduction-oxidation (redox) steps through an integrated cycle to convert water into separate streams of hydrogen and oxygen. The thermochemical cycles are divided into two main categories according to their operating temperatures, namely low-temperature cycles (<1100 °C) and high-temperature cycles (<1100 °C). The copper chlorine cycle offers relatively higher efficiency and lower costs for hydrogen production among the low-temperature processes. In contrast, the zinc oxide and ferrite cycles show great potential for developing large-scale high-temperature cycles. Although, several challenges, such as energy storage capacity, durability, cost-effectiveness, etc., should be addressed before scaling up these technologies into commercial plants for hydrogen production. This review critically examines various aspects of the most promising thermochemical water-splitting cycles, with a particular focus on their capabilities to produce green hydrogen with high performance, redox pairs stability, and the technology maturity and readiness for commercial use.

Hydrogen production by thermochemical water splitting cycle using low‐grade solar heat and phase change material energy storage system

Hydrogen production by thermochemical water splitting cycle using low‐grade solar heat and phase change material energy storage system

Thermodynamics and Kinetic Modeling of the ZnSO4·H2O Thermal Decomposition in the Presence of a Pd/Al2O3 Catalyst

The sulfur–iodine thermochemical water-splitting cycle is a promising route proposed for hydrogen production. The decomposition temperature remains a challenge in the process. Catalysts, such as Pd supported on Al2O3, are being considered to decrease reaction temperatures. However, little is known regarding the kinetic behavior of such systems. In this work, zinc sulfate thermal decomposition was studied through non-isothermal thermogravimetric analysis to understand the effect of a catalyst within the sulfur–iodine reaction system context. The findings of this analysis were also related to a thermodynamic assessment. It was observed that the presence of Pd/Al2O3 modified the reaction mechanism, possibly with some intermediate reactions that were suppressed or remarkably accelerated. The proposed model suggests that zinc sulfate transformation occurred in two sequential stages without the Pd-based material. Activation energy values of 238 and 368 kJ·mol−1 were calculated. In the presence of Pd/Al2O3, an activation energy value of 204 kJ·mol−1 was calculated, which is lower than observed previously.

SO3 decomposition over silica-modified β-SiC supported CuFe2O4 catalyst: characterization, performance, and atomistic insights.

The sulfur-iodine (S-I) thermochemical water-splitting cycle is one of the potential ways to produce hydrogen on a large scale. CuFe2O4 was dispersed over modified silica or treated β-SiC and untreated β-SiC using the wet impregnation method for SO3 decomposition, which is the most endothermic reaction of the S-I cycle. Various state-of-the-art techniques such as XRD, FT-IR, BET, XPS, TEM, HR-TEM, FESEM-EDS and elemental mapping were employed to characterize both the synthesized catalysts. CuFe2O4 catalyst supported on silica-modified β-SiC resulted in enhanced catalytic activity and stability due to better metal-support interaction. In order to get a better insight into the reaction mechanism over this bimetallic catalyst, the first principles based simulation under the framework of density functional theory was performed. We have found that the presence of Cu gives rise to an improved charge localization at the O-vacancy site alongside favourable reaction kinetics, which results in an enhanced catalytic activity for the CuFe2O4 nano-cluster compared to that of a single metallic catalyst containing Fe2O3 nano-cluster.

The role of entropy in the success of nonstoichiometric oxides for two-step thermochemical water and CO2 splitting

Owing to their high theoretical efficiency, two-step solar thermochemical water and CO2 splitting cycles, using a metal oxide intermediate, provide a promising pathway to store solar energy in a stable chemical bond. To date, the most successful demonstrations have utilized nonstoichiometric oxides, a class of materials capable of continuously transitioning from an oxidized to reduced state via formation of oxygen vacancies. The success of nonstoichiometric oxides is typically attributed to their ability to maintain their crystallographic phase, allowing them to be cycled many times without destabilizing–a tremendous practical advantage. In this work, we utilize a combined empirical and statistical thermodynamics approach to present an alternative explanation of the success of nonstoichiometric oxides from an entropy perspective. We first illuminate the importance of the entropy change of the reduction reaction as a key material parameter. We then develop a methodology for plotting nonstoichiometric oxides on the Ellingham diagram, enabling a direct comparison to stoichiometric materials. This analysis reveals the unique ability of nonstoichiometric oxides to achieve a significant solid-state entropy contribution, which results from the disorder generated via oxygen vacancy formation. To quantify the solid-state entropy, we develop a simple configurational entropy model applicable to any oxygen-deficient nonstoichiometric oxide. We compare model predictions to existing data for two important nonstoichiometric oxides, CeO2−δ and La0.6Ca0.4Mn0.6Al0.4O3−δ, to reveal the main trends in entropy vs δ and material composition and discuss the causes and implications of deviations from the theory.

Effect of B-site Al substitution on hydrogen production of La0.4Sr0.6Mn1-xAlx (x=0.4, 0.5 and 0.6) perovskite oxides

Thermochemical water splitting using perovskite oxides as redox materials is one of the important way to use solar energy to produce green hydrogen. Thus, it is hence important to discover new materials that can be used for this purpose. In this regard, we focused on Al-substituted La0.4Sr0.6Mn1-xAlxO3 (x = 0.4, 0.5 and 0.6) perovskite oxides, namely as La0.4Sr0.6Mn0.6Al0.4 (LSMA4664), La0.4Sr0.6Mn0.5Al0.5 (LSMA4655), and La0.4Sr0.6Mn0.4Al0.6 (LSMA4646) which have been successfully synthesized. Herein, synthesized LSMA4664, LSMA4655, and LSMA4646 were subjected to three consecutive thermochemical cycles in order to determine their oxygen capacity, hydrogen capacity, re-oxidation capability and structural stability following three cycles. Thermochemical cycles were carried out at 1400 °C for reduction and 800 °C for the oxidation reaction. LSMA4646 exhibited the highest O2 production capacity with 275 μmol/g among the other perovskites employed in the study. Moreover, LSMA4646 has also the highest H2 production, 144 μmol/g, with 90% of re-oxidation capability by the end of three thermochemical water splitting cycles. On the other hand, LSMA4664 has the lowest H2 production and only kept approximately one-third of its hydrogen production capacity by the end of cycles. Thus, the current study provides insight that the increase in the Al-substitution enhances both oxygen and hydrogen production capacity. Besides, increasing the Al amount increases the structural stability during the redox reactions, the re-oxidation capability was also increased from 38% to 89% after thermochemical cycles.

A review on integrated thermochemical hydrogen production from water

Hydrogen production from water splitting is considered one of the most environmentally friendly processes for replacing fossil fuels. Among the various technologies to produce hydrogen from water splitting, thermochemical cycles using chemical reagents have the advantage of scale up compared to other specific facilities or geological conditions required. According to thermochemical processes using chemical redox reactions, 2-, 3-, 4-step thermochemical water splitting cycles can generate hydrogen more efficiently due to reducing temperatures. Increasing the number of cycles or steps of thermochemical hydrogen production could reduce the required maximum temperature of the facility. In addition, recently developed hybrid thermochemical processes combined with electricity or solar energy have been studied on a large scale because of the reduced cost of hydrogen production. Additionally, hybrid thermochemical water splitting combined with renewable energy can result in not only reducing the cost, but also increasing hydrogen production efficiency in terms of energy. As for a green energy, hydrogen production from water splitting using sustainable and renewable energy is significant to protect biological environment and human health. Additionally, hybrid thermochemical water splitting is conducive to large scale hydrogen production. This paper reviews the multi-step and highly developed hybrid thermochemical technologies to produce hydrogen from water splitting based on recently published literature to understand current research achievements.

Development of Synthesis and Fabrication Process for Mn-CeO2 Foam via Two-Step Water-Splitting Cycle Hydrogen Production

The effects of doping manganese ions into a cerium oxide lattice for a thermochemical two-step water-splitting cycle to produce oxygen and hydrogen and new synthesis methods were experimentally investigated. In order to comparison of oxygen/hydrogen producing performance, pristine CeO2, a coprecipitation method for Mn-CeO2, and a direct depositing method for Mn-CeO2 with different particle sizes (50~75, 100–212, over 212 μm) and doping extents (0, 5, 15 mol%) were tested in the context of synthesis and fabrication processes of reactive metal oxide coated ceramic foam devices. Sample powders were coated onto zirconia (magnesium partially stabilized zirconia oxide, MPSZ) porous foam at 30 weight percent using spin coating or a direct depositing method, tested using a solar reactor at 1400 °C as a thermal reduction step and at 1200 °C as a water decomposition step for five repeated cycles. The sample foam devices were irradiated using a 3-kWth sun-simulator, and all reactive foam devices recorded successful oxygen/hydrogen production using the two-step water-splitting cycles. Among the seven sample devices, the 5 mol% Mn-CeO2 foam device, that synthesized using the coprecipitation method, showed the greatest hydrogen production. The newly suggested direct depositing method, with its contemporaneous synthesis and coating of the Mn-CeO2 foam device, showed successful oxygen/hydrogen production with a reduction in the manufacturing time and reactants, which was lossless compared to conventional spin coating processes. However, proposed direct depositing method still needs further investigation to improve its stability and long-term device durability.

Energy and exergy analysis of the zinc/zinc oxide thermochemical cycle for hydrogen production and fuel cell power generation

Water-splitting thermochemical cycles have emerged as a possible solution for the decentralized production of hydrogen using solar energy. A useful tool to select the most promising thermochemical cycles among those proposed in the literature is represented by the exergy analysis. In this context, the exergy and energy analyses of the zinc/zinc oxide thermochemical water-splitting cycle, coupled with the production of electrical energy in a fuel cell, are here carried out and discussed. The aim has been to identify the steps in the process characterized by the highest inefficiencies and to propose possible solutions to increase the overall thermodynamic efficiency. Calculations were carried out using the commercial process simulator PRO/II. The cycle consists of two steps: (i) the endothermic thermal reduction of solid zinc oxide to liquid zinc and oxygen, carried out in a solar thermo-reactor at 2025 °C, and (ii) the non-solar, exothermic hydrolysis of zinc to form hydrogen and solid zinc oxide. This work reports three possible process schemes based on the zinc/zinc oxide redox reactions, each differing from the others in terms of envisaged modes of heat recovery. In addition, the effect of carrying out the hydrolysis step under adiabatic, rather than isothermal conditions, has been analysed. Four values of conversion were considered (1, 0.9. 0.8, and 0.7) and the effect on fuel cell power generation, utility consumption, and energy and exergy efficiency was evaluated. It was found that the exergy efficiency increased from about 14% for the classical zinc/zinc oxide cycle to almost 40% in the most efficient scenario considered here. The variation of hydrogen conversion in the fuel cell led to a decrease in generated power, from 16.41 MW at hydrogen conversion of 1 down to 11.48 MW at hydrogen conversion of 0.7.

Experimental study of a two‐stage thermochemical cycle for hydrogen production

The use of renewable energy sources is the main strategy toward a low-carbon society. A promising alternative for the production of hydrogen gas is the water-splitting thermochemical cycles activated by solar energy. This work presents an experimental study of a two-stage thermochemical cycle for hydrogen production. It is based on the carbothermic reduction of iron ore (Fe2O3) and the re-oxidation of it with steam can be powered by concentrated solar energy. Samples studied were self-reducing pellets. The first stage of the proposed cycle consists in the reduction of hematitic iron oxide into its own metal at temperatures above 1173 K. The second phase of the cycle consists of iron metal oxidation by steam, which produces hydrogen gas. Sponge iron samples obtained in this work had a specific surface area of 35.05 m2/g measured by the BET method, which is a high value compared to specific surface areas obtained from conventional processes. It was shown that at 973 K the hydrogen gas production rate is slower, whereas at 1073 K and at 1173 K the sample reached 63% of its maximum oxygen gain between 2 and 7.5 minutes, respectively. As the hydrogen gas production rate is also proportional to the iron oxidation rate, it was shown to be very important to balance out the hydrogen gas production over the entire cycle time as a function of temperature. Finally, the analyzed thermochemical cycle can also operate with any other renewable carbon source.

A Novel Method for the Preparation of Fibrous CeO2–ZrO2–Y2O3 Compacts for Thermochemical Cycles

Zirconium-Yttrium-co-doped ceria (Ce0.85Zr0.13Y0.02O1.99) compacts consisting of fibers with diameters in the range of 8–10 µm have been successfully prepared by direct infiltration of commercial YSZ fibers with a cerium oxide matrix and subsequent sintering. The resulting chemically homogeneous fiber-compacts are sinter-resistant up to 1923 K and retain a high porosity of around 58 vol% and a permeability of 1.6–3.3 × 10−10 m² at a pressure gradient of 100–500 kPa. The fiber-compacts show a high potential for the application in thermochemical redox cycling due its fast redox kinetics. The first evaluation of redox kinetics shows that the relaxation time of oxidation is five times faster than that of dense samples of the same composition. The improved gas exchange due to the high porosity also allows higher reduction rates, which enable higher hydrogen yields in thermochemical water-splitting redox cycles. The presented cost-effective fiber-compact preparation method is considered very promising for manufacturing large-scale functional components for solar-thermal high-temperature reactors.

Synergizing hydrogen and cement industries for Canada’s climate plan – case study

ABSTRACT In December 2020, Canada released its national strengthened climate change plan with focus on cutting energy waste, cutting pollution, and build clean industrial advantage. Two weeks later, the national hydrogen strategy was announced urging all involved stakeholders to delve into the deployment of large-scale clean energy technologies. Ontario, Canada’s largest economy and leading manufacturing province, it releases its provincial hydrogen strategy and roadmap later this year. represents a viable solution for reducing CO2 emissions from large industry pollutants by integrating our innovative copper chlorine (Cu-Cl) thermochemical water splitting cycle with the energy intensive and polluting industry of cement manufacturing. The paper highlights the nexus between the production process of two valuable commodities, namely cement and Hydrogen, and the role their integration introduces for increased energy efficiency and reduction of greenhouse gas emissions. In addition, as most of the thermal energy demand in cement manufacturing is utilized during the kiln processes, the paper proposes several energy mix scenarios involving the use of hydrogen to partially meet the kiln’s heat demand. The results from these scenarios show the possibility of achieving over 15% to 19.6% reduction in CO2 emissions compared to coal-based kiln production, along with reduced recurring cost for operating the kiln. On-site large-scale hydrogen production, mixed with natural gas, was found to be financially viable and environmentally advantageous alternative to power the kilns.

Concentrated Solar Energy with Thermal Energy Storage for Hydrogen Production by Three-Step Thermochemical Water-Splitting Cycles

The high-temperature thermochemical water splitting (TWS) cycles utilizing concentrated solar energy (CSE) and water are the most promising alternatives to produce renewable hydrogen. Here we couple CSE with thermal energy storage (TES) and TWS cycles to best levelize the cost of hydrogen by 2030, due to the synergies with concentrated solar power (CSP), the high technology-readiness-level (TRL) for the upstream thermal energy production and storage, and the medium TRL for the downstream TWS cycles. A similar design of the solar field and tower and TES for CSP advanced ultrasupercritical (AUSC) or supercritical CO2 (sCO2) power cycles for 100 MW of continuous production of electricity, permit the continuous production of hydrogen at ∼2,750 kg/h a day. The predicted cost is 1.058 to 1.197 $/kg H2 by 2030.

Hydrogen Production by Solar Thermochemical Water-Splitting Cycle via a Beam Down Concentrator

Hydrogen Production by Solar Thermochemical Water-Splitting Cycle via a Beam Down Concentrator

Dynamic thermo-ecological cost assessment and performance analyses of a multi generation system

The main objectives of this study are to perform a dynamic thermo-ecological cost (TEC) assessment and performance analyses of a multi generation system using the TRNSYS 18 software package for comparison purposes. The system has five outputs consisting of electricity, clean water, heating, hydrogen, and cooling. Multigeneration is made of an internal combustion engine fueled by natural gas, a heat pump, a reverse osmosis desalination plant and a magnesium-chlorine (Mg–Cl) thermochemical (TC) water splitting cycle. This cycle, which appears to be a promising TC hydrogen production method, is integrated to the multi generation system for producing hydrogen for waste heat recovery. Environmental effect of the system is also considered using the TEC method. In this contribution, a new index, namely the TEC of the irreversibility, is presented and applied. Variation of emissions, electricity, exergy destruction and energy loss values for the considered system and Mg–Cl TC water splitting cycle as well as TECs of the electricity, heat and the hydrogen are calculated through some parametric studies undertaken and presented in figures. It is determined that the multigeneration system has an energy efficiency value of 0.43 and a corresponding exergy efficiency of 0.38. As a result, TECEL, TECHEAT and TECH2values of the considered system are obtained to be 2.98, 0.72 and 2.90, respectively. It may be concluded that the TEC is an effective method to assess the environmental performance of various energy systems and compare them with each other.

Investigation of hydrogen production by sulfur‐iodine thermochemical water splitting cycle using renewable energy source

In this study, a novel integrated structure for generation of the oxygen, hydrogen, power, and hot water by employing thermochemical reactors and solar dish collectors is proposed. The presented process including solar dish collectors, sulfur-iodine thermochemical cycle, and Organic Rankine Cycle. In this configuration, for 5854 kmol/h of inlet water, 2236 kmol/h of oxygen, and 4432 kmol/h of hydrogen are produced. This system can provide 22 666 kW of power that 22 026 kW is utilized in the sulfur-iodine reaction. So, the net electrical power is found to be 640 kW. A general exergy analysis is carried out on the whole structure and equipment to find its exergy losses and improvement potential to enhance the exergy efficiency of the system. The total exergy efficiency of the process is calculated 56.33% and its exergy destruction is obtained 382 301.31 kW. Heat exchangers and solar collectors have the highest values of destructed exergy, which about 69% of destructed exergy is related to them. These devices have a strong potential for enhancement. The results showed that component P1 (pump) has the lowest exergy efficiency that is 15.58%, while its exergy destruction is not the greatest. Therefore, for having a better examination of this structure, both exergy efficiency and exergy destruction parameters should be evaluated simultaneously. Moreover, a sensitivity analysis is applied to survey the performance of some performance indicators vs different design parameters. It is concluded that by an increase in generated heat by solar collectors, exergy efficiency, energy efficiency, oxygen, and hydrogen production faces increment.

White is the color of hydrogen from concentrated solar energy and thermochemical water splitting cycles

White is the color of hydrogen from concentrated solar energy and thermochemical water splitting cycles