Water Splitting Cycle Research Articles

Chrysanthemum-like FeS/Ni3S2 heterostructure nanoarray as a robust bifunctional electrocatalyst for overall water splitting

The development of a scalable strategy to prepare highly efficient and stable bifunctional electrocatalysts is the key to industrial electrocatalytic water splitting cycles to produce clean hydrogen. Here, a simple and quick one-step hydrothermal method was used to successfully fabricate a three-dimensional core chrysanthemum-like FeS/Ni3S2 heterogeneous nanoarray (FeS/Ni3S2@NF) on a porous nickel foam skeleton. Compared with the monomer Ni3S2@NF, the chrysanthemum-like FeS/ Ni3S2@NF heterostructure nanomaterials have improved catalytic performance in alkaline media, showing low overpotentials of 192 mV (η10) and 130 mV (η-10) for OER and HER, respectively. This study attests that integrated interface engineering and precise morphology control are effective strategies for activating the Ni3+/Ni2+ coupling, promoting charge transfer and improving the intrinsic activity of the material to accelerate the OER reaction kinetics and promote the overall water splitting performance. The scheme can be reasonably applied to the design and development of transition metal sulfide-based electrocatalysts to put into industrial practice of electrochemical water oxidation.

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.

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.

Thermodynamic investigation of a novel hydrogen liquefaction process using thermo-electrochemical water splitting cycle and solar collectors

Hydrogen production and liquefaction using solar thermo-electrochemical water splitting systems can as an effective method for long-term renewable energy source storage are suggested. In this paper, a novel integrated configuration for the cogeneration of liquid hydrogen and oxygen by magnesium-chlorine thermo-electrochemical water splitting cycle, hydrogen liquefaction unit, and solar dish collectors is developed. The novel integrated structure produces 7116 kg/h liquid hydrogen and 57597 kg/h oxygen. Through the magnesium-chlorine cycle, pure hydrogen is produced and the required energy is supplied through solar renewable energy based on the climatic conditions of Isfahan city in Iran. Then the produced hydrogen enters the liquefaction process to generate liquid hydrogen. The heat and power consumption of the whole system for the cogeneration of liquid hydrogen and oxygen are 207.9 MW and 373.9 MW, respectively. The heat waste of the integrated structure is used to produce hot water as a by-product. The specific power consumption of the liquefaction cycle is 7.6 kWh/kg LH2 and also the total thermal efficiency of the whole integrated system is 71.4%. Through the pinch method, heat exchanger networks related to multi-stream heat exchangers of the present system are extracted. Sensitivity analysis is used to investigate the effects of changes in major parameters including operating conditions of the thermo-electrochemical cycle as well as changes in the solar dish collector main parameters and the results are reported.

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

Exergoenvironmental analysis of the integrated copper-chlorine cycle for hydrogen production

Thermochemical water-splitting cycles have the potential of producing large-scale and cost-effective sustainable hydrogen in an environmentally benign manner. Limited exergoenvironmental assessments have been reported in the literature which generally considers thermochemical hydrogen production and specifically the copper-chlorine (Cu–Cl) cycle in thid regard. Thus, the present investigation aims at assessing the four-step integrated Cu–Cl thermochemical cycle set-up located at the Ontario Tech University thereby contributing to the environmental impact assessment of thermochemical hydrogen production. In this study, the exergy analysis of the cycle is first performed by thermodynamically modeling and simulating the cycle in Aspen-plus. The fundamental principles of the exergoenvironmental analysis, analogous to the specific exergy costing (SPECO) methodology of the exergoeconomic evaluation, are applied to the cycle and the balanced environmental impact equations for all cycle components are developed. Based on the balanced environmental impact equations, the environmental impact rate, and the specific environmental impact at each state point is evaluated. The environmental impact levels for all the major cycle components are also obtained. The exergoenvironmental factor, the relative difference of the specific environmental impacts, and the environmental impact rate of exergy destruction for various cycle components are in this regard evaluated. Furthermore, the influence of various parameters on the cumulative and component-related rate of environmental impact as well as the exergoenvironmental factor is analyzed by conducting a detailed sensitivity analysis. According to the obtained results, the rate of environmental impact corresponding to exergy destruction dominates the component-related rate of environmental impact and thus the potential reduction in the cumulative environmental impact for various components could be achieved by improving their exergy efficiencies. The hydrolysis step accounts for 60% of the component-related environmental impact while the thermolysis step accounts for the highest environmental impact of exergy destruction ranging between 41 and 42%. The percentage difference between fossil fuel-based and renewable electricity in terms of the global warming potential ranges between 80% and 98% with the highest difference for wind and nuclear-based electricity.

Thermo-chemical water splitting: Selection of priority reversible redox reactions by multi-attribute decision making

Hydrogen is a top chemical and potential fuel. Its sustainable production from biomass or water splitting gains importance. Whereas sole thermal water splitting requires too high temperatures, thermo-chemical water splitting cycles offer a solution at moderate temperatures. Such cycles were investigated over the past decades, mostly by small-scale experiments and mainly to prove their concept without judgment of their practical, economic, environmental and cyclic performance. To facilitate the decision making and to guide future priority research, these multiple aspects can be combined in a global screening system that applies the improved Analytic Hierarchy Process (AHP) and grey relational TOPSIS, together with the use of linear and non-linear combination weighing. The assessment is quantitative and comprehensive, emphasizing the complex relationship between energy efficiency, conversion, recyclability, economy and environmental quality. The total index combines systematics and flexibility through its multi-objective and multi-level nature. The index helps users, system manufacturers, researchers and governments to select the most appropriate future schemes.Very high temperature reactions of e.g. metal-metal oxides, metal-metal hydroxides, perovskites or doped ceria were not included. At the required temperatures, concentrated solar energy is the evident heat source, although applicable temperatures should meet the mechanical and thermal constraints of the solar receiver-reactor construction materials. The experimental set-up that will be used for subsequent pilot-scale solar testing is briefly described. As a result of the multi-attribute assessment, 4 out of 24 oxidation/reduction reactions are selected for further laboratory or preferably pilot-scale application, including the MnFe2O4, MnO/NaMnO2 and ZnO/Fe3O4/ZnFe2O4 redox reactions.

Catalytic SO3 Decomposition Activity of SiO2-Supported Alkaline Earth Vanadates for Solar Thermochemical Water Splitting Cycles

Alkaline earth vanadates (Ae–V: Ae = Ca, Sr, and Ba) were supported on mesoporous SiO2 by a wet impregnation method. The catalytic activity of the prepared materials for the decomposition of SO3 into SO2 and O2, which is a key step in solar thermochemical water splitting cycles, was investigated. In the temperature range 700–800 °C, the Ae–V/SiO2 catalysts exhibited remarkably high activities, which were superior to those of supported Pt catalysts in a wide range of weight hourly space velocities (55–220 g-H2SO4 g–1 h–1). Despite the melting points of the materials exceeding 1000 °C, the high activity was determined to be closely related to the unusual melting behavior of Ae–V. Under the reaction atmosphere, the Ae–V phase was converted to AeSO4 and molten V2O5 (melting point = 690 °C) via facile solid–gas reactions between SO3 and alkaline earth elements displaying high basicity. Notably, upon contact with the molten V2O5 phase, the as-deposited AeSO4 was immediately decomposed into SO2 and O2 to regenerate the Ae–V phase. The catalyst, which solidified at lower temperatures (<690 °C), could not decompose the sulfate and was therefore unable to drive the catalytic cycles. Consequently, the SO3 decomposition rate at <690 °C was lower than that of an alkaline vanadate (Cs–V) with a melting point as low as 500 °C but higher than that of a rare earth vanadate (La–V) with the highest melting point (>1800 °C).

Energy and exergy analyses of a solar magnesium-chlorine thermochemical plant for methane production

Solar power as the most available type of renewable energy can be used as a clean driving source in the thermal systems. One of the ways to overcome the intermittency problem of solar energy is to convert it into a chemical that can be used whenever it is required. Hydrogen is a good candidate for using it as a fuel. Thermochemical methods for the production of hydrogen are considered as promising candidates. magnesium-chlorine (Mg-Cl) thermochemical cycle is one of the water-splitting cycles that can be used to produce hydrogen. Due to the problems related to storing hydrogen, it is more convenient if we convert it into another chemical like methane. A novel integrated system has been proposed in this study for the production of methane through the Mg-Cl thermochemical cycle. For the base case, hydrogen can be produced with a mass flow rate of 188.32 kg/h. Energy and exergy efficiencies of the Mg-Cl cycle are calculated as 26.25% and 59.88%, respectively. If the produced hydrogen is converted into methane, the methane production capacity of the plant would be 352.98 kg/h. Our results indicated that the energy and exergy efficiencies of the overall system are 7.04% and 60.28%, respectively.

Solar-driven hydrogen production from a water-splitting cycle based on carbon-TiO2 nano-tubes

This study illustrates the structuring of the TiO2 within carbon nano-tubes to enhance the solar-driven production of hydrogen (S-DPOH) via water splitting. The newly developed Carbon-TiO2 nano-tubes (C-Ti-NTs) aimed at improving the practical applications of TiO2 composites under natural solar irradiation conditions, enhancing the absorption of UV and VIS-light, reduces the required bandgap energy and decreases the chance for photo-induced-charges recombination. The C-Ti-NTs were prepared using an alkaline hydrothermal method, characterized using different state of art techniques and tested for the S-DPOH via water splitting. Adding a carbon layer on the surface of TiO2 nano-tube with a thickness of ~1 nm reduced the bandgap of the C-Ti-NTs ≤ 0.88 eV, improved the quantum efficiency under UV light to 100%, enhanced the absorption capacity under VIS-light and extremely suppressed the charge recombination. The S-DPOH achieved a cumulative production of hydrogen (CPOH) during 50 h of solar irradiation of 43.75 mmol at a rate RPOH′of H2 production of 38.66 ± 0.655 mmol/h.g, which is 1.5 folds higher than the maxim rate reported for pure TiO2-based photocatalyst. The obtained results confirmed the contribution of TiO2 for the production of hydrogen, which is expected to open a new insight towards the importance of architectural design and band engineering in the practical development of sustainable solar energy harvesting applications.

On the happiness of ferroelectric surfaces and its role in water dissociation: The example of bismuth ferrite

We investigate, using density functional theory, how the interaction between the ferroelectric polarization and the chemical structure of the (001) surfaces of bismuth ferrite influences the surface properties and reactivity of this material. A precise understanding of the surface behavior of ferroelectrics is necessary for their use in surface science applications such as catalysis as well as for their incorporation in microelectronic devices. Using the (001) surface of bismuth ferrite as a model system, we show that the most energetically favored surface geometries are combinations of surface termination and polarization direction that lead to uncharged stable surfaces. On the unfavorable charged surfaces, we explore the compensation mechanisms of surface charges provided by the introduction of point defects and adsorbates, such as water. Finally, we propose that the special surface properties of bismuth ferrite (001) could be used to produce an effective water splitting cycle through cyclic polarization switching.

Analysis of sodium generation by sodium oxide decomposition on corrosion resistance materials: a new approach towards sodium redox water-splitting cycle.

In this study, the investigation of materials with corrosion resistance was carried out to prevent side reactions caused by sodium oxide (Na2O) in the Na-redox thermochemical water splitting cycle, and essential operational conditions for sodium (Na) generation from Na2O were also investigated. Thermal desorption spectroscopy and X-ray diffraction techniques at altered conditions were mainly used for the experimental investigation. Numerous types of materials were tested to find materials with high resistance towards corrosion and to understand essential thermal decomposition processes of Na2O. In addition, under different temperatures and pressure conditions, the thermodynamic calculation of Gibbs free energy was performed to obtain experimental results. As a result, a Ti alloy showed significant resistance towards the corrosive reaction by Na2O. The obtained experimental and simulated results support the direct decomposition of Na2O to form Na and O2 below 600 °C under low partial pressure conditions. The optimized conditions for Na generation with the Ti alloy sample can be used for low temperature water splitting.

Energy optimization of a Sulfur–Iodine thermochemical nuclear hydrogen production cycle

The use of nuclear reactors is a large studied possible solution for thermochemical water splitting cycles. Nevertheless, there are several problems that have to be solved. One of them is to increase the efficiency of the cycles. Hence, in this paper, a thermal energy optimization of a Sulfur–Iodine nuclear hydrogen production cycle was performed by means a heuristic method with the aim of minimizing the energy targets of the heat exchanger network at different minimum temperature differences. With this method, four different heat exchanger networks are proposed. A reduction of the energy requirements for cooling ranges between 58.9-59.8% and 52.6-53.3% heating, compared to the reference design with no heat exchanger network. With this reduction, the thermal efficiency of the cycle increased in about 10% in average compared to the reference efficiency. This improves the use of thermal energy of the cycle.

Investigations on a platinum catalyzed membrane for electrolysis step of copper‐chlorine thermochemical cycle for hydrogen production

SummaryConsidering the low temperature demand (~550°C maximum) and high efficiency (~43%), Cu–Cl thermochemical water splitting cycle has immense potential as a futuristic scalable hydrogen generation process. CuCl/HCl electrolysis is the crucial hydrogen generation step in the Cu–Cl thermochemical cycle. The efficiency of this electrolysis process is highly dependent on the performance of the membrane electrode assembly (MEA) employed. To explore the suitability of the platinized membrane for this step, in this study, we have investigated a Pt/Nafion‐117 MEA prepared by in‐situ impregnation‐reduction method for CuCl/HCl electrolysis. A single‐cell PEM‐type electrolyser (4 cm2 active area) consisting of serpentine channels (2 cm × 2 cm) grooved in graphite flow field plates was designed and fabricated to carry out the CuCl/HCl electrolysis. Platinum electrocatalyst was deposited on Nafion‐117 membrane on the cathodic side by reduction of hexachloroplatinic acid (H2PtCl6) with sodium borohydride (NaBH4) by the impregnation‐reduction method which served as the MEA. Monodispersed nanocrystalline Pt particles formed a ~30 μm thick electrocatalyst layer on the membrane. Pt/Nafion‐117 MEA was found to be effective for CuCl /HCl electrolysis. In a PEM‐type electrolyser with Ar‐purged 0.2 M CuCl in ~2 M HCl solution as anolyte flowing at ~ 8.8 mLmin−1, a current density of ~100 mA cm−2 was achieved at a cell voltage of 1 V. However, undesired Cu‐crossover could be noticed from anode to cathode side during operation.

Techno-economic analysis of thermochemical water-splitting system for Co-production of hydrogen and electricity

The two-step thermochemical metal oxide water-splitting cycle with the state-of-the-art material ceria inevitably produces unutilized high-quality heat, in addition to hydrogen (H2). This study explores whether the ceria cycle can be of greater value by using the excess heat for co-production of electricity. Specially, this technoeconomic study estimates the H2 production cost in a hybrid ceria cycle, in which excess heat produces electricity in an organic Rankine cycle, to increase revenue and decrease H2 cost. The estimated H2 cost from such a co-generation multi-tower plant is still relatively high at $4.55/kg, with an average H2 production of 1431 kg/day per 27.74 MWth tower. Sensitivity analyses show opportunities and challenges to achieving $2/kg H2 through improvements such as increased solar field efficiency, increased revenue from electricity sales, and a decreased capital recovery factor from baseline assumptions. While co-production improves overall system efficiency and economics, achieving $2/kg H2 remains challenging with ceria as the active material and likely will require a new material.