Thermochemical Two-step Water-splitting Cycle Research Articles

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.

Efficient generation of hydrogen by two-step thermochemical cycles: Successive thermal reduction and water splitting reactions using equal-power microwave irradiation and a high entropy material

Hydrogen production through two-step thermochemical water splitting cycle based on metal oxide has emerged as a promising strategy to store dilute and intermittent solar energy. However, a typical reaction time of the two-step thermochemical water splitting cycle is lengthy, with at least 0.5 h for thermal reduction step and 1 h for water splitting step, and the energy required in the thermal reduction process for hydrogen regeneration is higher than the generated hydrogen energy. In this work, to overcome the problem of an energy efficiency imbalance, we investigated the possibility of the rapid and successive reactions of thermal reduction and water splitting, using short-term irradiation from a low-energy microwave. To this end, a high entropy material, as a poly-metal oxide used to generate hydrogen, was produced by simultaneously introducing four cations onto a SiC foam – (FeMgCoNi)O1.2@SiC. It was found that the oxygen vacancy of the (FeMgCoNi)O1.2@SiC could be significantly increased by short-term microwave irradiation, and hence the thermal reduction process took only 4 min, which is much less than normal. High H2 generation rates were achieved by re-oxidation of the Fe (II) to Fe (III) of the (FeMgCoNi)O1.2@SiC. In addition, the microwave plasma generated by microwave irradiation induced (FeMgCoNi)O1.2@SiC discharge could enhance the water splitting process. The maximum hydrogen yield was 122 mL/g at 700 W, due to the coupling effect of the thermochemical cycle and microwave plasma. In this way, the power consumption of microwave process is only 3% of that of conventional high-temperature heat treatment during thermal reduction process.

Thermochemical two-step water splitting cycle using perovskite oxides based on LaSrMnO3 redox system for solar H2 production

A thermochemical two-step water-splitting cycle using perovskite oxides based on LaSrMnAlO3 was examined for hydrogen production from water using concentrated solar radiation. Concurrent Sr and Mn substitutions in La1-xSrxMnxAl1-xO3, Sr and Al substitutions in La1-ySryMn1-yAlyO3, and substitution of Al by Cr in La0.7Sr0.3Mn1-zCrzO3 were examined, and their kinetics, oxygen/hydrogen productivity, and repeatability were compared against LaSrMnAlO3. The impact of the chemical compositions of the perovskite oxides was systematically examined at a thermal reduction temperature of 1350 °C and water decomposition temperatures of 1000–1200 °C. From the viewpoints of average amounts of oxygen and hydrogen produced and the H2/O2 ratios, La0.7Sr0.3Mn0.9Cr0.1O3 and La0.7Sr0.3Mn0.8Cr0.2O3 provided the most reproducible productions of oxygen and hydrogen in the thermochemical two-step water-splitting cycle.

4-4-5 45kW_ KIER太陽炉によるCeO_2/MPSZ反応デバイスを用いた水分解サイクルの太陽試験(4-4 太陽熱・水素製造,Session 4 新エネルギー)

4-4-5 45kW_ KIER太陽炉によるCeO_2/MPSZ反応デバイスを用いた水分解サイクルの太陽試験(4-4 太陽熱・水素製造,Session 4 新エネルギー)

4-9-4 ジルコニア担持フェライトによる二段階水熱分解サイクル機構(4-9 太陽熱発電・水素製造1,Session 4 新エネルギー,研究発表)

4-9-4 ジルコニア担持フェライトによる二段階水熱分解サイクル機構(4-9 太陽熱発電・水素製造1,Session 4 新エネルギー,研究発表)

4-4-2 二段階水熱分解サイクルにおけるセリウム酸化物の高活性化に関する研究(4-4 太陽熱・水素製造,Session 4 新エネルギー)

4-4-2 二段階水熱分解サイクルにおけるセリウム酸化物の高活性化に関する研究(4-4 太陽熱・水素製造,Session 4 新エネルギー)

Thermochemical reactivity of 5–15 mol% Fe, Co, Ni, Mn-doped cerium oxides in two-step water-splitting cycle for solar hydrogen production

The thermochemical two-step water-splitting cycle using transition element-doped cerium oxide (M–CeO2−δ; M=Fe, Co, Ni, Mn) powders was studied for hydrogen production from water. The oxygen/hydrogen productivity and repeatability of M–CeO2−δ materials with M doping contents in the 5–15mol% range were examined using a thermal reduction (TR) temperature of 1500°C and water decomposition (WD) temperatures in the 800–1150°C range. The temperature, steam partial pressure, and steam flow rate in the WD step had an impact on the hydrogen productivity and production rate. 5mol% Fe- and Co-doped CeO2−δ enhances hydrogen productivity by up to 25% on average compared to undoped CeO2, and shows stable repeatability of stoichiometric oxygen and hydrogen production for the cyclic thermochemical two-step water-splitting reaction. In addition, 5mol% Mn-doped CeO2−δ, 10 and 15mol% Fe- and Mn-doped CeO2−δ show near stoichiometric reactivities.

4-2-2 二段階水熱分解サイクルにおける金属酸化物の高活性化(Session 4-2 太陽熱・熱分解)

4-2-2 二段階水熱分解サイクルにおける金属酸化物の高活性化(Session 4-2 太陽熱・熱分解)

Oxygen and hydrogen productivities and repeatable reactivity of 30-mol%-Fe-, Co-, Ni-, Mn-doped CeO2−δ for thermochemical two-step water-splitting cycle

The characteristics of oxygen/hydrogen productivity using 30-mol%-M (M = Fe, Co, Ni, Mn)-doped CeO2−δ (30-mol%-M-CeO2−δ) were studied for the thermochemical two-step water splitting cycle comprising TR (thermal reduction) at 1500 °C and WD (water decomposition) at 1150 °C. The reproducibility of oxygen evolution was evaluated using 30-mol%-M-CeO2−δ and the effects of different M dopants were compared in the TR temperature range of 1200–1500 °C. Two solid phases detected in the 30-mol%-M- CeO2−δ powders were involved in the redox reaction of the thermochemical two-step water splitting cycle. Among the M-CeO2−δ samples evaluated, Mn-doped CeO2−δ provided the most stable and reproducible results and the highest reactivity for oxygen evolution at all temperatures employed for the TR step of the thermochemical two-step water-splitting cycle.

Development of a simulation-software for a hydrogen production process on a solar tower

A simulation and control model for a two-step thermo-chemical water splitting cycle using metal oxids for the generation of hydrogen with a solar tower system as heat source has been developed. The simulation and control model consists of three main parts, the simulation of the solar flux distribution on the receiver, of the temperatures in the driven reactor modules and the produced hydrogen in the metal oxide.The results of the three parts of the simulation model have been evaluated by comparing and validating them with experimental data from the Hydrosol 100kWth pilot plant at the Plataforma Solar de Almería (PSA) in Spain.With the overall model of the hydrogen production plant that was created, an evaluation of the two-step thermochemical cycle process in combination with a solar tower system was performed. The model was used to perform parametric studies for the development of the plant and the operation strategies. For this purpose, a provision in the overall model was integrated. The simulation helps to reduce the frequency of using the flux measurement system and can be used for the heliostat field control, in particular for the temperature control in the solar chemical reactor modules. Because of these promising results the overall system model is being extended to enable a use as a control model with controller for the temperature control of the two core reactions in the process.The central control variable of the process control was the operating temperatures for the hydrogen production and the regeneration of the two modules. The process control with its PI controller turned out suitable to compensate diurnal changes of solar input power as well as certain statistical fluctuation due to cloud passage. At the same time the limits of the operability and controllability of the process became clear in terms of the minimum of solar power needed and maximum acceptable gradients.With this experience an operating strategy, the basic parameters of the system in operation, especially the starting up and shutdown procedures, regular operation and the response to disturbances were selected and optimized. With this operation/control strategy such a complex system can be operated in the future on a commercial scale automatically. The obtained results can also be adapted for other solar chemical processes.

Improved operation of solar reactor for two-step water-splitting H2 production by ceria-coated ceramic foam device

The joint international project between Niigata University (Japan) and the Korea Institute of Energy Research, KIER (Korea) on “Solar Demonstration of Water-Splitting Reactor using Ceramic Foam Device” has two goals. (1) Develop a solar reactor using reactive cerium oxide foam devices for high-temperature two-step thermochemical water-splitting cycle. (2) Test its performance under various operational methods using a 40 kWth solar furnace driven by natural solar energy. The reactive CeO2/MPSZ (MgO – partially stabilized zirconia) foam device for two-step water-splitting was developed and prepared by Niigata University/Japan; it involves coating an inert zirconia foam matrix with reactive CeO2. In this paper, highly reactive CeO2 particles were used the redox material in CeO2/MPSZ foam devices to investigate the use of solar energy for hydrogen production. The solar-driven thermochemical two-step water-splitting cycle was demonstrated using the 40 kWth KIER solar furnace in Korea combined with the CeO2/MPSZ foam device. At the center of the foam device, temperatures were 1500 °C–1600 °C during the thermal reduction step and 600 °C-1100 °C during the subsequent water decomposition step. Hydrogen was successfully produced from the CeO2/MPSZ foam device, and profiles for hydrogen production and CeO2 conversion indicated definitely improved operations compared to earlier studies.

Thermochemical Two-step Water Splitting Cycle using Ni-ferrite and CeO2 Coated Ceramic foam Devices by Concentrated Xe-light Radiation

Nickel ferrite (NiFe2O4) and pure cerium oxide (CeO2) supported on monoclinic zirconia (NiFe2O4/m-ZrO2) are proposed as promising redox materials for the production of hydrogen from water via a thermochemical two-step water splitting cycle. Ceramic foam devices coated with NiFe2O4/m-ZrO2 or pure CeO2 particles are prepared as a receiver/reactor operating a thermochemical water splitting cycle to produce hydrogen. The foam devices are examined in a directly irradiated receiver/reactor by a sun simulator on a laboratory scale. The purpose of this study is to examine the evolution of oxygen and hydrogen during the cyclization reaction different thermal-reduction (T-R) temperatures of 1450 and 1550°C, and to compare the reproducible and stoichiometric oxygen/hydrogen production for both foam devices through a repeatable two-step reaction. In this study, a zirconia ceramic foam was used as a matrix for the reacting materials of NiFe2O4/m-ZrO2 or CeO2 particles. The zirconia ceramic foam has a diameter of 60mm, a thickness of 15mm, and a porosity of 10 cpi (cell number per linear inch). The loading amounts of reacting materials are 5 wt% for NiFe2O4/m-ZrO2 and 40 wt% for CeO2 particles. A concentrated Xe-beam is radiated to the foam device in a N2 stream for the T-R step and in a N2/steam gas mixture for the subsequent water- decomposition (W-D) step.

Kinetics of Thermal Reduction Step of Thermochemical Two-step Water Splitting Using CeO2 Particles: MASTER-plot Method for Analyzing Non-isothermal Experiments

Thermochemical two-step water splitting cycle by concentrated solar heat has been studied as an energy conversion of solar energy into hydrogen energy. The thermochemical two-step water splitting cycle using metal oxide redox pair was composed of thermal reduction (T-R) step of metal oxide at higher temperature to release oxygen and, subsequent water decomposition (W-D) step of the reduced metal oxide with steam at lower temperature to produce hydrogen. Recently, cerium oxide (CeO2) is concerned as a redox pair of the thermochemical cycle for highly reactivity and cyclicity at high temperature. In this study, we focused a kinetic analysis of thermochemical two-step water splitting using cerium oxide. Various theoretical reaction models for thermal reduction (T-R) step of CeO2 particles are examined, and the appropriate reaction model for experimental results of thermogravimetric analysis was found by Master plot method. Finally, the reaction rate equation of thermal reduction is estimated.

Flux Measurement of a New Beam-down Solar Concentrating System in Miyazaki for Demonstration of Thermochemical Water Splitting Reactors

A two-step thermochemical water splitting cycle using nonstoichiometric cerium oxide is a promising solar thermochemical hydrogen production process. One of the present authors has developed new solar reactors using “internally circulating fluidized beds” with cerium oxide particles for the high-temperature cycle. These solar reactors need to be combined with a beam-down solar concentrating system. Niigata University, University of Miyazaki, and Mitaka Kohki Co. Ltd. recently started an R&D joint project to demonstrate the up-scaled fluidized bed reactors with solar. A new type of 100 kWth beam-down solar concentrating system was built in August, 2012 at the campus of University of Miyazaki. This paper describes the first results of solar flux measurements on the new Miyazaki beam-down system for demonstration of thermochemical water splitting reactors. The fluxes of concentrated solar radiation at the focus point were measured by moving an array of thirteen Gardon gauges. The solar power in an area of 130 × 130cm in the focal spot was larger than 90 kWth during three hours of daytime radiation, exceeding 110 kWth around noon on October 12, 2012. A new CPC specific to this new beam-down system was designed and fabricated to concentrate the solar fluxes into a 44cm diameter circle of the solar reactor aperture. The solar demonstration of the reactors will start at the Miyazaki beam-down system from October 2013.

Solar Demonstration of Thermochemical Two-step Water Splitting Cycle Using CeO2/MPSZ Ceramic foam Device by 45kWth KIER Solar Furnace

The joint international project of Niigata University (Japan) – Korea Institute of Energy Research, KIER (Korea) on the “Solar demonstration of Water-Splitting Reactor using Ceramic Foam Device” aims to develop a novel-type of solar reactor with reactive cerium oxide foam devices for high-temperature two-step thermochemical water splitting cycle, and to demonstrate its performances on sun with a 45-kWth solar furnace. The reactive CeO2 foam device for the two-step water splitting is proposed and prepared by Niigata University, Japan, and involves coating inert zirconia foam with reactive CeO2. The project includes the development of reactive foam devices, the new design and the fabrication of solar reactor with the reactive foam devices, and finally the solar demonstration on the KIER's 45-kWth solar furnace in Korea. In this paper, highly-active CeO2 particles were used as a redox material for preparing CeO2 foam devices. A ceramic foam disk made of MgO partially-stabilized Zirconia (MPSZ) was used as a ceramic matrix that was coated with the CeO2 particles. Solar thermochemical two-step water splitting was demonstrated with solar furnace in Korea system using the prepared CeO2-coated MPSZ (CeO2/MPSZ) foam devices. The prepared CeO2/MPSZ foam device has a diameter of 15 and 20cm and thickness of 2.5 cm, the loading of CeO2 was set to approximately 20 wt%.Then, the temperatures of the foam device at a center position were 1400-1600°C for the T-R step, and 900-1100°C for the subsequent W-D step. Hydrogen was successfully produced from the CeO2-MPSZ foam by a solar thermochemical two-step water-splitting, and the rate of hydrogen production and CeO2 conversion using 15 cm CeO2/MPSZ foam device were 215.6 mL/min and 3.67%, at 1st cycle. We also performed continuous testing for 20cm diameter of the CeO2-MPSZ device, the rate of hydrogen production and CeO2 conversion were 443 ml/min and 3.27%, 1st cycle.

Comparative study of activity of cerium oxide at thermal reduction temperatures of 1300–1550 °C for solar thermochemical two-step water-splitting cycle

Thermochemical two-step water-splitting using CeO2 (cerium oxide) particles was studied to examine oxygen and hydrogen productivity and repeatability at thermal reduction (T-R) temperatures of 1300–1550 °C and water decomposition (W-D) temperatures of 400–1000 °C for the production of hydrogen from water using concentrated solar radiation as the energy source. The temperature dependency of oxygen and hydrogen productivity and the cyclic repeatability of CeO2 are reported in this paper. The characteristic features of CeO2 particles in the thermochemical two-step water-splitting cycle are compared with the well-known highly active reactive mediums of zirconia-supported Ni-ferrites (NiFe2O4/m-ZrO2 and NiFe2O4/c-YSZ) and unsupported NiFe2O4.

Enhanced hydrogen production by doping Pr into Ce0.9Hf0.1O2 for thermochemical two-step water-splitting cycle

We synthesized (Ce0.9Hf0.1)1−xPrxO2−δ (x=0, 0.05 and 0.1) using the polymerized complex method. The synthesized samples, as well as the samples after thermochemical two-step water-splitting cycles have a fluorite structure and Pr exists in the solid solutions with both trivalent and tetravalent states, as suggested by powder X-ray Diffraction (XRD) Patterns. The reduction fraction of Ce4+ in redox cycles (oxidation step in air) and two-step water-splitting cycles (oxidation step in steam) indicates that the addition of Pr into Ce–Hf oxide solid solution cannot improve the reduction fraction of Ce4+ during the redox cycles but both the reduction fraction of Ce4+ and H2 yield are significantly enhanced during two-step water-splitting cycles. The chemical composition of 10mol% Pr doped Ce0.9Hf0.1O2 exhibits the highest reactivity for hydrogen production in H2-generation step by yielding an average amount of 5.72mlg−1 hydrogen gas, which is much higher than that evolved by Ce0.9Hf0.1O2 (4.50mlg−1). The enhancement effect of doping Pr on the performance during two-step water-splitting cycles is because of the multivalent properties of Pr, which can: (1) reduce the amount of Ce3+ oxidized by contamination air (contamination air eliminated by partial oxidation of Pr3+ to Pr4+) in H2-generation step; (2) enhance the reaction rate in H2-generation step by improving the ionic conductivity (extrinsic oxygen vacancies created by the substitution of Ce4+ by Pr3+).

Understanding Morphology-Controlled Synthesis of Zinc Nanoparticles and Their Characteristics of Hydrolysis Reaction

Two-step thermochemical water-splitting cycle based on a Zn/ZnO redox pair is considered as a potential route for carbon-free production of hydrogen because the first hydrolysis step of the cycle highly depends on the method of preparation and the resultant particle characteristics, such as size, morphology, surface state, and initial oxide content. Here, employing a conventional evaporation and condensation method, we successfully produce three types of Zn nanoparticles ranging from nanorods, mesoporous nanorods with nanospheres on their surfaces, and fully sintered nanocrystals. The achievement in morphology control is realized simply by changing the injection position of the quenching gas. We found that the resultant hydrolysis kinetics is highly dependent on the morphology and porosity of the Zn nanoparticles. Finally, a series of simple mathematical modeling is made in an effort to understand the formation mechanism of Zn nanoparticles.

Control of Heterogeneity in Nanostructured Ce1–xZrxO2 Binary Oxides for Enhanced Thermal Stability and Water Splitting Activity

To enhance the kinetics and overall production of renewable H2 fuel through a two-step thermochemical water splitting cycle, three-dimensionally ordered macroporous (3DOM) Ce1–xZrxO2 (x = 0, 0.1, 0.2, 0.3, 0.4, and 0.5) materials were synthesized via colloidal crystal templating. The interconnected macropore system in these materials facilitates ready access to a relatively large active surface area (tens of m2/g), which benefits the heterogeneous reaction. Two different synthetic routes were employed, a methanolic solution of metal chloride salts, and a Pechini-type gel. These routes produced significant differences in the compositional homogeneity of the resulting mixed oxide. 3DOM Ce1–xZrxO2 synthesized with methanolic precursors had distinct CeO2- and ZrO2-rich domains, whereas the Pechini samples contained only a single phase. At higher Zr content, heterogeneities present in the samples from the methanolic synthesis increased both the productivity and peak production rates of H2 compared to the single-phase Pechini samples. Increasing the content of Zr in the mixed oxides also stabilized the 3DOM structure at 825 °C. All 3DOM Ce1–xZrxO2 materials exhibited significantly faster kinetics during water splitting compared to sintered, micrometer-sized CeO2 granules. Pechini-derived 3DOM Ce0.8Zr0.2O2 maximized both H2 production and peak production rates, offering better catalytic performance over 3DOM CeO2.

4-2-3 内循環流動層反応器による二段階水熱分解反応の一段階システム化に関する研究(4-2 太陽熱発電・水素製造2,Session4 新エネルギー,研究発表)

4-2-3 内循環流動層反応器による二段階水熱分解反応の一段階システム化に関する研究(4-2 太陽熱発電・水素製造2,Session4 新エネルギー,研究発表)