Carbon-neutral life in near future is discussed in terms of optimizing energy-saving and consumer behavior. In this lecture, I’d like to clarify what is the carbon-neutral life from the viewpoints of LOHAS(Lifestyles of health and sustainability) and other future lifestyles including innovative technologies in the fields of industry, transportation, and consumer.

Breaking away from the use of fossil resources to solve global environmental problems and achieve carbon neutrality has become an urgent issue. Japan's energy consumption shows that 18.5 EJ of primary energy is sourced mainly from overseas, of which slightly less than 1/4 comes from natural gas, 1/4 from coal, and slightly less than half from petroleum and petroleum products. In addition, 40% of the energy is used as fuel. These fuels include city gas, LP gas, gasoline, diesel fuel, aviation fuel, etc., all of which are currently derived from fossil resources. In promoting carbon neutral GX in the future, it is expected that chemicals and fuels will be produced using water, carbon dioxide, biomass, and waste, with solar energy as the driving force. Among other things, fuels that cannot be electrified include aviation fuel, large automobile fuel, city gas, and LP gas. Synthetic hydrocarbons are also important in the steel and chemical industries.

This keynote lecture will introduce our on-going two research projects related to carbon recycling technology. The projects propose processes for the conversion of inorganic (iron ore) and organic (lignocellulosic biomass) resources with CO₂-derived oxalic acid as a key compound. The first process enables, utilizing characteristics of oxalic acid and its salts, low temperature production of high-purity metallic iron from a variety of iron ores. The second process aims to produce platform chemicals, including biomass-derived levoglucosenone and oxalic acid, along with their derivative biopolymers using CO₂ as feedstock and synthetic agents. The lecture will cover our background for initiating the research, the current progress of the projects, and the challenges that need to be addressed.

To achieve a decarbonized society through a significant renewable energy expansion, it is necessary to set a target for renewable energy supply and incorporate them into specific policies and plans. Model analysis can contribute to the consideration of these policies and programs as well as discuss future scenarios. In recent years, with the disclosure of power grid information, it has become possible for researchers other than transmission system operators to conduct model analysis for scenarios, the power market, and the grid. Further improvements in data availability are expected to accelerate model analysis to overcome the barriers to renewable energy expansion.

CO₂ emissions from power plants associated with charging BEV are generally calculated using the average emission factor for all power sources. When demand for electricity increases, thermal power generation usually generates more electricity, which causes a slight increase in the emission factor in addition to the direct increase in CO₂ emissions. Using the average emission factor ignores this slight increase and the actual increase in CO₂ emissions can be calculated by using the marginal emission factor. Even if renewable power sources increase, the use of their electricity is limited to the times when surplus electricity is generated. Hydrogen and e-Fuel is important as an energy source for future vehicles because hydrogen production, which can choose the location and time of day, can use renewable electricity.

In this presentation, the basic structure and elemental technologies of concentrating solar thermal power (CSP) generation will be outlined, and the operational status and construction trends of commercial-scale CSP plants will be described. Next, the latest research trends in next-generation CSP plants, mainly in the United States, Europe, and Australia, will be introduced. Namely, high temperature and high efficiency solar thermal power generation, PV/CSP hybrid plants, and thermal power storage will be introduced. Finally, the author will outline our laboratory's efforts to address next-generation CSP and thermal energy storage.

Hydrogen becomes an important carbon-free energy carrier, while ammonia is now regarded as a useful hydrogen carrier. This presentation gives an overview on the current status of hydrogen energy and efforts for wide-spread implementation into various sectors including power generation, transportation, and industries. Role of academia and industry-academia collaboration are also discussed.

Large amount of ammonia water is released from livestock wastewater and causes environmental pollutions. Electrolysis is one of effective treatment methods of the waste ammonia water because of low theoretical decomposition voltage, 0.06 V. Moreover, hydrogen can be obtained by the electrolysis process and utilized as fuels. On the other hand, it is found that the electrolysis current is drastically decreased during the reaction at constant voltage. In this work, the effects of refresh process, in which opposite voltage form electrolysis is applied, are investigated to realize the effective electrolysis.

Quang Ninh (QN) coal ash includes large amounts of Al₂O₃ and SiO₂ which can be utilized for zeolite synthesis. In this paper QN coal model ash and real ash were used to prepare ZSM-5 zeolite using tetrapropylammonium hydroxide (TPAOH) at 150oC for 48h. It was confirmed from the results of XRD patterns and nitrogen adsorption/desorption measurement that ZSM-5 crystals appeared at higher than SiO₂/Al₂O₃ ratio of 52 and developed completely at 78. The similar results were observed for ZSM-5 synthesis not only without QN coal ash components but also with model coal ash and real QN coal ash, indicating that the effects of components on the preparation of ZSM-5 would be rather small. When these zeolites were used for the catalytic cracking of low-density polyethylene (LDPE) using the Curie point pyrolyzer (CPP) method, ZSM-5 prepared using model coal ash components exhibited the same or slightly higher conversion than conventional ZSM-5. In contrast to this, ZSM-5 prepared with real coal ash components exhibited the slightly lower conversion, suggesting that the kinds of inorganic salts might affect the reactivity in catalytic cracking of LDPE.

Gaseous elemental mercury (Hg⁰) removal test using copper-based sorbent that is coated with copper oxide on surface of the honeycomb-shaped support was performed in actual syngas from coal and polypropylene and simulated gas of that. Gas analyses were performed by a gas chromatography and a mercury analyzer during the test. Quantitative analysis and X-ray absorption fine structure measurement of the spent sorbents were also performed. A decrease in mercury removal performance of the sorbent and an increase in concentration of selenium in them were observed by cyclic operation of mercury removal and regeneration steps. Accumulation of selenium into the copper-based sorbent was thought to be one of the reasons for the degradation of mercury removal performance of the sorbent.

Osaki CoolGen Project, which was complex three-phase demonstration project, aimed to achieve ultimately efficient coalfired power generation with near-zero emissions by integrating oxygen-blown Integrated Coal Gasification Combined Cycle (IGCC) - carbon capture technology with fuel cells. In the first phase we verified the basic performance of IGCC. In the 2nd phase and 3rd phase we verified the performance of IGCC with CO2 Capture and confirmed the prospect of Integrated Coal Gasification Fuel Cell Combined Cycle (IGFC) in March 2023.

Hydrogen production from hydrogen energy carrier, such as ammonia, is endothermic reaction. On the hand, methane synthesis from carbon dioxide with hydrogen is intensive exothermic reaction. From this point of view, the authors suggested methane synthesis from carbon dioxide with ammonia, called “Ammonia-Methanation”. In this study, ammonia methanation catalyzed by a hybrid catalyst composed of Ru/Al₂O₃ and Ni/CeO₂ was investigated. It was found that the above mentioned hybrid catalyst had high activity for methane synthesis through ammonia methanation.

Reforming of methane hydrates in gas production systems for subsea methane hydrates are subject to long-term stable gas production. In this study, we present experimental investigations for fluidizers against methane hydrate plugging. A multi-rocking cell apparatus was designed for parametric experiments with fluidizers which contain inhibitors and surfactants with different compositions. The major component of the fluidizers was urea which works as a thermodynamic hydrate inhibitor. The results suggest that the MH dissociation behavior was changed with the surfactant concentrations. In the presentation, we will present additional data for a kinetic hydrate inhibitor.

This study aimed to perform CO₂ and CH₄ mixed gas separation measurements using semiclathrate hydrates. We obtained temperature, pressure, and mass fraction of ionic substance in aqueous solution. The used ionic substances are tetra-n-butylammonium bromide (TBAB), tetra-n-butylammonium chloride (TBAC), tetra-n-butylphosphonium bromide (TBPB), and tetra-n-butylphosphonium chloride (TBPC). The results showed that CO₂ and CH₄ can be separated with suitable thermodynamic conditions.

Lake Baikal (Russia) is the only fresh-water lake in the world containing natural gas hydrates in sub-bottom sediments. Molecular and stable isotope compositions of hydrate-bound gases retrieved at Lake Baikal between 2005 to 2019 are investigated in the framework of international project between Russia, Belgium, and Japan. Methane δ²H of the hydratebound gas is approximately 120‰ lower than its value in the marine environment, suggesting the difference in δ²H between the lake water and seawater. The origin of hydrate gases is wide in variety, from microbial (primary and secondary), thermogenic, and mixed gas sources. Hydrate-bound microbial ethane showed low isotope compositions both in δ¹³C and δ²H. The low δ2H of ethane suggests that lake water with low hydrogen isotope ratios affects the formation process of microbial ethane as well as methane.

Massive gas hydrates recovered from various sediment depths at the Umitaka Spur in the Sea of Japan were studied with Raman spectroscopy. The results indicate burial diagenesis of massive gas hydrates which initially grew at shallow sediment depths. Samples recovered from sediment depths within 20m below the seafloor (mbsf) were enriched in H2S. Although anaerobic oxidation of methane within the sulfate-methane transition (SMT) zone is only potential source of high H₂S within these depths, these depths are greater than present SMT zone at ~1 mbsf. CH₄ cage occupancy ratio exceeding 1.1 was not detected at deep sediment depths. These observations are result of sediment burial of gas hydrates which originally grew around the near-seafloor SMT and CH₄ migration through lattice cage of gas hydrate during long duration of burial process.

Thermal conductivity of artificial four-component hydrate sediment sample consisted with sediment-water-methane-water was measured by hot disk method. To avoid difficulties with dissociation heat of hydrate due to output of power from hot disk sensor prove, thermal conductivity measurement was conducted under super-cooling state during methane hydrate formation in sediment pores. Calculations of formation heat of hydrate showed that the influence on the thermal conductivity measurement is almost negligible. We applied this super cooling method on thermal conductivity measurement for pressure core samples recovered from the AT-CW1 and AT-CW2 wells in Nankai Trough of Japan in 2018. In this presentation, the thermal conductivity of these core samples will be reported. It will be also reported the future challenges for thermal conductivity measurement of MH core samples.

It is thought that shielding performance is required for permit applications for CO₂ hydrate storage. Therefore, we report the results of laboratory experiments about the shielding performance of CO₂ hydrate membranes formed at the interface between liquid CO₂ and water, based on the discovery of liquid CO₂ on seafloors at a depth of 1,333 meters offshore of Okinawa in 1990. This shielding performance could be used as a management criterion for CO₂ hydrate storage.

The pressure dependence of elastic constants to density for methane-THF (tetrahydrofuran) hydrate sII (MTHFH-sII) phase has been determined up to 0.7 GPa at 296 K by high-pressure Brillouin scattering experiments. The obtained elastic properties of MTHFH-sII are very similar to those of methane hydrate sI, although the elastic properties of argon hydrate sII is obviously different from MTHFH-sII. Therefore, elastic properties of gas hydrates mainly depend on the guest size instead of clathrate structures.

Nitrogen hydrate (NH) is known to form a cubic structure II (sII), and it successively transforms into a hexagonal structure H (sH) at 0.8 GPa, a tetragonal structure T (sT) at 1.3 GPa, and an orthorhombic structure O (sO) at 1.6 GPa by compression. In this study, high-pressure powder X-ray diffraction and Brillouin scattering measurements have been performed up to 1.7 GPa at room temperature in order to evaluate the pressure-induce phase transformations and the pressure dependence of elastic constants for NH-sH. From the X-ray diffraction measurements, it is found out that the large pressure hysteresis exists at the sII - sH phase change, which probably comes from the smaller guest size compared to the void of 5¹²6⁴ water cage. The elastic properties of NH-sH are similar to those of argon hydrate sH.

Semiclathrate hydrate (SCH) is expected not only as a gas storage and cold-energy storage medium but also as a novel solid electrolyte. In the present study, we measured the proton conductivity in the single-crystalline tetra-n-butylammonium bromide (TBA-Br), chloride (TBA-Cl), fluoride (TBA-F), and hydroxide (TBA-OH) SCHs to reveal the effects of guest ion species on the proton conduction in SCHs. TBA-OH SCH exhibited the highest proton conductivity among them, which indicates that the hydroxide anion withdraws the H⁺ from neighboring water molecules continuously. In the case of halide anions, nuclear magnetic resonance revealed that the water reorientation motion in SCH was more activated in the order of the anion size and the motion in TBA-Br SCH was the most. Such results mean that smaller halide anion restricts the water dynamics in SCH. In addition, the proton conductivity in SCHs should depend on the anion species from the viewpoints of proton concentration.

Semiclathrate hydrates (SCHs) have been expected to be one of the phase change materials suitable for cold energy storage. The large degree of supercooling in SCH formation is a major obstacle to practical applications of SCH. In this study, we focused on the memory effect (a kind of hysteresis) that could suppress the degree of supercooling. The memory effect of tetra-n-butylammonium hydroxycarboxylate (TBA-HDC) SCHs was investigated, where tartarate, malate, and succinate with similar chemical structures were used as -HDC. As a result, TBA-tartarate SCH had the greatest ability to retain the memory effect among three TBA-HDC SCHs. These results reveal that the interaction of substituted hydroxyl group(s) with surrounding water molecules might improve thermal stability of the memory effect, which favorably promotes SCH reformation.

For many years, attempts have been made to model the weight loss behavior of cellulose pyrolysis, but no unified kinetic model has been proposed. In this study, we compared the thermal degradation reactivity of 7 cellulose samples by thermogravimetric (TG) analysis and found that even pure cellulose samples contain trace amounts of acidic groups (0.4-6.3 μmol/g), and the content varied from sample to sample. The alkali and alkaline earth metal cations, present as salts of the acid groups, affected the reactivity in different ways (DTG peak temperature: demineralized, Mg²⁺, Ca²⁺<Na⁺, K⁺). Even for the demineralized cellulose, the reactivities were not similar due to the different content of acidic groups acting as acid catalyst. Consequently, the thermal reactivity of cellulose varied depending on the content of acidic groups and metal compositions even in such a small content. Based on these results, it is concluded that cellulose is not uniform in terms of acid group content and has different pyrolysis reactivity. Interestingly, the Na-exchanged cellulose samples showed very similar TG results for 7 cellulose samples. Since the degradation temperature range was similar to the cellulose samples in which only acidic groups were methyl esterified, Na salt may remove the acidic group effect.

Pyrolysis-based saccharification, a method of pyrolyzing cellulose and followed by hydrolyzing the produced anhydrous sugars to obtain glucose, is a promising method for converting lignocellulose into useful biofuels and chemical feedstocks. Since the pyrolysis reaction proceeds under dry conditions, it is easy to increase the concentration of the sugar solution. On the other hand, the formation of by-products such as aldehydes is an issue. In addition, it is important to further improve the yield of anhydrous sugars. In this presentation, we will report our recent studies on pyrolysis-based saccharification to address these issues.

Lignin, one of the main cell wall components in plant xylem, is the most abundant natural aromatic polymer in the world, and it is expected to convert lignin into value-added materials by thermochemical processes such as hydrothermal treatment. For the efficient conversion, quantitative and/or qualitative modification of lignin by genetic manipulation is the promising strategies. Especially, the overexpression of frulate 5-hydroxylase (F5H) gene, involved in lignin biosynthesis, can increase the ratio of syringyl (S) to guaiacyl (G) units (S/G ratio). However, the change in the detailed lignin structures such as chemical linkages are not yet fully clarified. In this study, the transgenic poplar (Populus tremula × Populus alba) with various S/G ratios were prepared by the overexpression of F5H, and their lignin structure was analyzed. As a result, the transgenic lines with a variety of high S/G ratios from 2.2 to 11.7 were successfully prepared without any growth penalty and reduction of lignin content. Interestingly, the increase in β-O-4 linkage was limited and β-1 and β-β linkages elevated with the increase in S/G ratio. Furthermore, the hydrothermal treatment (230°C/10 min) was conducted to transgenic poplars. The solubilization yields were 45.4% and 51.1% for the wild type and S-rich poplar (Line 23), respectively. There was a positive correlation between the solubilization yields and S/G ratio, indicating that the changes of lignin unit structure caused these differences.

This article reviewed the catalytic hydrogenolysis of Japanese cedar milled wood lignin (MWL) using a Pd/C catalyst at temperatures ranging from 200 to 350 °C in different solvents. Anisole was found to be the most effective solvent for producing monomers. The pyrolysis-derived products were uniformly reduced to monomers with alkyl-/Hsubstituted side chains. Elevated temperatures increased the yield of monomers due to the cleavage of diaryl ether and some condensed bonds. These findings have implications for the production of platform aromatics from lignin.

Recently, the gasification process of woody biomass has been attracting attention to produce renewable gas fuels. However, the gasification process emits tar and soot, which can cause equipment troubles. Therefore, it is necessary to control the formation of tar and soot, and then it is important to elucidate their formation behaviors. This study compared pyrolysis and CO₂ gasification experiments at 950°C and 1100°C, simulating CO₂ gasification by exhaust gas recirculation. Experimental results showed that the addition of CO₂ increased soot formation at 1100°C. It was also observed that H₂ decreases under the same conditions due to the reverse water-gas shift reaction. One of the reasons for the increase in soot formation is that the decrease in H₂ promotes the condensation polymerization of hydrocarbons.

We focused on bagasse as a renewable fuel alternative to fossil fuel from viewpoints of quantity and cost. One of the effective pretreatments for bagasse is pyrolysis producing biochar. In this study, the pyrolysis behavior of bagasse and cedar for comparison was investigated via thermogravimetric analysis. In addition, the mass loss during the isothermal pyrolysis was measured at different temperatures from 220 — 400°C. Furthermore, the mass yield change during pyrolysis was predicted by kinetic analysis based on a two-step sequential reaction model.

Solution plasma has the potential to efficiently produce H₂ by decomposing aqueous alcohols. In this study, lower monohydric alcohols (methanol, ethanol, 1- and 2-propanol) were treated in solution plasma of water and the gasification mechanism was discussed. We proposed that there are two pathways for solution plasma treatment of alcohols, decomposition with water-derived OH radicals and decomposition of solely the alcohol molecule, which are well consistent with the experimental facts, such as the composition of the product gas and the intermediates detected.

In this study, we investigated the influence of sulfuration on the chemical looping reactivity of an oxygen carrier with alkali and alkaline earth metals (AAEM). Ilmenite (IL) used as the oxygen carrier, IL with K and Ca (K-IL and Ca-IL) were sulfurized by heating at 900°C in 1000 - 4000 ppm H₂S/N₂ stream, and the reactivity was evaluated by thermogravimetric analysis. The results show that IL and K-IL were sulfurized by the treatment, while the reactivity of IL and K-IL was not influenced by the sulfuration.

Ilmenite is natural sand with chemical composition as FeTiO₃. It was used as oxygen carrier in the three-towers circulating fluidized be CLC poly-generation technology.

The purpose of the previous study we conducted was to understand the effects of oxygen in fuel in the combustion process of diesel engines. To this end, engine performance testing using BDF and gas oil was performed. As a result, although there was a difference in the exhaust gas characteristics between using gas oil and using BDF, the brake thermal efficiencies of both were the same. Therefore, there is a possibility that the differences in combustion conditions during the combustion period do not significantly affect the engine output generation. This study conducted a performance test of changing the fuel injection timing using gas oil and BDF in a small diesel engine, confirming the effects of fuel ignitability on the ignition delay and exhaust characteristics.

Energy use of woody biomass such as forest residues can contribute to the realization of a decarbonized society, the revitalization of forestry and local economy. On the other hand, Hexavalent chromium may be detected in the combustion ash of a woody biomass boiler. As a result of study on reduction treatment of hexavalent chromium in woody biomass boiler combustion ash, it was confirmed that the elution amount of hexavalent chromium can be reduced easily and safely by using fructose.

Gasification combined heat and power generation, a small-scale decentralised power source, is considered promising for carbon neutrality in 2050 and for regional revitalisation, but the facility utilisation rate in Japan is as low as 50-60%, partly due to the generation of solidified products (clinker) from the inorganic components of wood fuel. In this study, we blended cedar wood with red pine to higher the ash fusion temperatures. At a blend ratio of 37%, relatively higher ash fusion temperatures were observed due to solid solution formation by Mg and Si.

Small wood-chip gasification combined heat and power (CHP) is considered promising for the realisation of a decarbonised society and local revitalisation, but the utilisation rate of CHP in Japan is low at 50-60%, partly due to the uneven moisture content of wood chips. In this study, the drying rate and moisture effective diffusivity of wet wood chips were investigated using vertical chip drying apparatus. The results suggest that the drying properties and effective diffusivities of sapwood and heartwood chips with a thickness of 3 mm are equivalent under the same temperature conditions and that the effect of their properties on wood chip drying characteristics are relatively small. However, the black heartwood chips were found to be more difficult to dry than the sapwood/heartwood chips under the same conditions due to their relatively low diffusion coefficient.

We proposed a high-quality and low-cost chip production and supply system at a large-scale production base that utilizes heat from Combined Heat and Power equipment. A profitability evaluation of the energy production base in hilly and mountainous area was carried out, and the feasibility of its establishment was examined.

While Japan is among the top countries with the most forests, 2/3 of Japan areas are covered with wood forests, the thermal utilization business of woods is very poor in comparison with European countries. Japan has been relied on fossil petroleum fuels for thermal and electrical utilization for long time. Even though, Prime Minister, Mr. Suga declared Japan has set itself Zero Carbon by 2050, it is not easy way to achieve this target.

We, NPO Nouto Conference, has established Biomass Academy to enhance the thermal utilization business with forest woods in 2018. In this paper, we will introduce, current poor Japan’s status of Biomass Boiler business in comparison with Europe, and the Best Practice activities for dramatic expansion of Biomass Boilers in Japan.

The promotion effect on ethanol fermentation was investigated by adding Kakkonto or Bofutsushosan residues which are waste materials from Kampo industry. Moreover, hydrous bioethanol was obtained by distillated from fermented liquid with Kakkonto or Bofutsushosan residues. These fuels were supplied to gasoline engine, and exhaust gas was evaluated. The ethanol fermentation was promoted by adding Bofutsushosan residue compared with additive-free medium. However, Kakkonto residue had not promotion effect. On the other hand, concentration of carbon monoxide and hydrocarbon exhaust gas by distilled ethanol including Kakkonto component were lower than gasoline or reagent ethanol.

A method has been proposed for extracting lipids from microalgae using liquefied ammonia (NH₃), without the need for drying and cell disruption. Herein, the versatility of this method was subsequently evaluated using three species of commercially available microalgae. Lipids were successfully extracted directly from these wet microalgae samples using liquefied NH₃ extraction method, with the crude extract yields ranging from 45.0–54.7 wt.% of the dry weight of the microalgae. The crude extract yields surpassed those achieved using the widely used Bligh–Dyer method and the Hexane Soxhlet method. The crude extracts contained molecules smaller than those obtained using conventional extraction methods, as well as suitable for biofuel production, such as C12–C22 fatty acids. These results suggest that liquefied NH₃ extraction is a promising method for producing valuable compounds from untreated microalgae.

We have developed a small self-supporting floating tidal power generator. It was developed by diverting it to small hydroelectric power generation. Compared to tidal currents, there are many places where it can be installed, such as rivers and agricultural waters. Since the river flows in one direction, half the number of water turbines is required compared to two-way tidal currents. Transportation of the device is an important factor for practical use. The size of the device was considered so that it could be transported by a light car truck. Since it floats on its own, no installation work is required and it is only necessary to moor it from the shore.

In offshore wind firm, wind turbines are densely placed in a narrow area, and a wind speed attenuation and strong turbulence generated behind the turbines, known as wakes, cause decrease power with other wind turbines. In this study, to clarify the wind speed attenuation as a function of the distance from the wind turbine, we measured the wakes of the 3.3 MW wind turbine in commercial operation and the small model wind turbine installed in a wind tunnel. Furthermore, we applied this wake data to machine learning to develop new wake prediction models, which showed wind speed profiles within a relative error of 5%.

This study is concerned with the rotation characteristics of the propeller shaft, which is one of the important power generating elements in advancing the development of overtopping type of wave power generator. In order to grasp shaft rotation characteristics, the variable resistance was changed in the range of 10Ω-100Ω, and the rotation of the propeller shaft was measured by applying random waves to the model of multistage water tank. The relationship between the rotation of the propeller shaft and the axial velocity in the drainage pipe suggests that the model ship propeller cannot follow the flow. In the future, it is necessary to research and develop a propeller that can follow the flow.

Offshore wind power is expected to be a major power source for achieving carbon neutrality by 2050. In Japan, with limited shallow sea areas, there is growing interest in floating offshore wind power because it can be deployed in deep water. To promote its widespread adoption, it is essential to significantly reduce costs through technological development. With this background, we have studied a floating axis wind turbine (FAWT) to reduce the cost of floating offshore wind turbines. In this paper, we report the results of coupled simulations and water tank experiments of the FAWT.

This work investigated influence of various treatments of Shirasu-based materials on the activity of for hydrogen evolution from aqueous ammonia borane solution. The compositions and activity of the Shirasu-based materials were significantly influenced on various solution and calcination treatments. The activity of Shirasu-based materials increased with decreasing surface ratio of silicon to aluminum. The sample treated with ammonia following calcination at 723 K included the highest surface silicon to aluminum ratio, and exhibited the highest activity for the hydrogen evolution.

Proton-exchange membrane (PEM)-type water electrolysis attracts attentions owing to its superior electrolytic efficiency and better capability of response to input power fluctuation, and thereby considered as one of the promising technologies to recover green hydrogen. However, the current PEM water electrolyzes utilize expensive iridium (Ir). In addition, annual production capacity of Ir is limited to approximately 7 tons. Therefore, a novel less-Ir-content catalyst is expected to be explored. In order to decrease the use of the Ir-content, we prepared catalyst-coated membrane comprised of less-Ir-content Perovskite-type, SrTi_0.67Ir_0.33O₃, and performance and durability tests were demonstrated. Our CCM realized high water electrolytic efficiency of 86.4%, and realized at least 2,000 hours operation at 1 A cm^-2 and 60 °C without significant voltage increase regardless of small Ir-loading of 0.17 mg-Ir cm^-2. These results suggest that highly dispersed Ir in the Perovskite structure enhanced both electrolytic efficiency and durability.

Since conventional thermochemical hydrogen production techniques requires more than 800°C, utilization of low-temperature thermal energy of less than 500°C such as exhaust heats is difficult. Sodium redox cycle is potential thermochemical cycle as a conversion technique of the low-temperature heat to hydrogen. Recently, the previous Na-redox cycle is modified by addition of Ni into the reactions. As a result, the reaction temperature is decreased due to the change of thermodynamic reaction path, and then the corrosion of sodium oxides is drastically suppressed.