Search

The reaction between magnesium amide and hydride at a molar ratio of 1:2 by means of mechanical ball mining has resulted in the release of a stoichiometric amount of [H.sub.2] and the formation of magnesium nitride. Thermodynamic calculations have shown that the hydrogen release reaction of [1Mg[(N[H.sub.2]).sub.2] + 2Mg[H.sub.2] is mildly endothermic, but the low reaction enthalpy has predicted impractical operation conditions of the hydrogen uptake reaction.

The successful development of hydrogen-energy technologies has several advantages and benefits. Hydrogen-energy development could prevent global warming as well as ensure energy security for countries without adequate energy resources. The successful development of hydrogen would provide energy for transportation and electric power. It is a unique energy carrier, as it can be produced from various energy sources such as wind, fossil fuels and biomass and, when it is combusted, it emits no CO2 emissions. The other advantage is the wide distribution of resources globally that can be used to produce hydrogen. In Japan, the Ministry of Economy, Trade and Industry (METI) published a 'Strategic Roadmap for Hydrogen and Fuel Cells' in 2014, with a revised update published in March 2016. The goal of the roadmap is to achieve a hydrogen society. The roadmap aims to resolve technical problems and secure economic efficiency. The roadmap has been organized into the following three phases: Phase 1—Installation of fuel cells; Phase 2—Hydrogen power plant/mass supply chain; Phase 3—CO2-free hydrogen. This paper reports on the current status of fuel cells and fuel-cell vehicles in Japan and gives a description and status of the R&D programmes along with the results of global energy model study towards 2050. [ABSTRACT FROM AUTHOR]

In this paper, the significance of CO 2 -free hydrogen is discussed using a long-term global energy system. The energy demand–supply system including CO 2 -free hydrogen was assumed, though there are still large uncertainties as to whether a global CO 2 -free hydrogen energy system will be deployed. System analysis was conducted using the global and long-term intertemporal optimization energy model GRAPE under severe CO 2 emission constraints. Applied global CO 2 constraints for 2050 were a 50% reduction from 1990 levels. CO 2 constraints accounting for Intended Nationally Determined Contributions (INDCs) in each region were also considered. A variety of energy resources and technologies were considered in this model. Hydrogen can be produced from low-grade coal or natural gas with CO 2 capture and electricity from renewable energy. The hydrogen CIF (cost, insurance, and freight) price for Japan was about 3.2 cents/MJ in 2030. Hydrogen demand technologies considered in this paper are hydrogen-fired power plants, direct combustion, combined heat and power (fuel cells, gas engines, and gas turbines), fuel cell vehicles, and hydrogen internal combustion engine vehicles. The majority of CO 2 -free hydrogen was deployed in the transportation sector. CO 2 -free hydrogen was utilized in the power sector, where deployment of other zero emission technology has some constraints. From an economic viewpoint, CO 2 -free hydrogen can reduce the global energy system cost. From the viewpoint of a localized region, such as Japan, deployment of CO 2 -free hydrogen can improve energy security and environmental indicators. [ABSTRACT FROM AUTHOR]

Abstract: A new ternary Metal–N–H sample of Mg–Ca–N–H has been prepared by mechanical ball milling—Mg(NH2)2 and CaH2 (1:1) in a planetary ball mill machine. The structure and hydrogen desorption properties were investigated. The results show that pure H2 gas can be released during ball milling. After 72h ball milling, ∼3.8H atoms (∼3.88wt%) were found to be detached from the starting material, which is higher than most of the traditional metal hydrides. Moreover, volumetric release and soak tests on the sample collected after 12h of ball milling show that hydrogen desorption starts at a temperature around 50°C. DSC measurement on the post-12h milled sample reveals that the overall heat effect of hydrogen desorption is ∼28.2kJ/mol H2, implying that Mg–Ca–N–H system could be a potential lower temperature hydrogen storage system. In addition, the high-pressure release testing shows that 3.0wt% of hydrogen can be desorbed from the post-12h milled sample at a temperature of 380°C although 80bars of hydrogen was applied, indicating that the Mg–Ca–N–H possesses high equilibrium desorption pressure. However, recharging the sample with hydrogen is rather difficult, which may be due to the high kinetic barrier. [Copyright &y& Elsevier]

Abstract: Sintered pellets of Ce-doped Ba2In2O5 (BIC) were prepared from nanopowders. The electrical conductivities were measured using ac impedance spectroscopy under different atmospheres and temperatures. The electrical conductivity of sintered BIC was found sensitive to environmental humidity when the temperature was below 300°C. However, in the presence of hydrogen, the electrical conductivities were independent of water content in the range of 0–30vol%. The electrical conductivities of BIC were significantly affected by the presence of hydrogen in a temperature range of 100–300°C. The estimated protonic transference number and the measured open circuit voltage suggested the existence of electronic conduction. The coefficient of thermal expansion of BIC is 11.2×10−6 K−1 from 25 to 1250°C. [Copyright &y& Elsevier]

Abstract: A two-stage hydrogen release of 4.9wt.% was observed on a mixture of Mg(NH2)2 and CaH2 at 1:2 molar ratio. The H2 desorption in the temperature range from room temperature to 260°C was recyclable, which was observed by temperature-programmed-desorption (TPD), volumetric measurement and Fourier transform infrared (FT-IR). At high temperature, a ternary nitride CaMg2N2 and a solid solution of CaNH/Ca2NH, characterized by X-ray diffractometry (XRD), were formed. [Copyright &y& Elsevier]

Abstract: The dependence of chemical reaction between Mg(NH2)2 and MgH2 on the ball-milling conditions has been investigated. While the decomposition of the component Mg(NH2)2 resulted in gaseous products consisting mainly of ammonia, the mixtures of Mg(NH2)2–MgH2 prepared by ball-milling released H2 at temperatures as low as 65°C. In addition, the increase in ball-milling time can effectively suppress the ammonia evolution during the thermal treatment. The conversion of the amide and hydride to imide-like structure was demonstrated by FTIR and XRD characterization. A total amount of 4.8wt.% of H2 could be released from the investigated system. [Copyright &y& Elsevier]

A total of 7.4 wt % of hydrogen was released from the mixture of magnesium amide and magnesium hydride at a molar ratio of 1:2 by mechanical ball milling. Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Diffraction (XRD) characterizations along with the amount of hydrogen released at different stages of ball milling reveal that magnesium imide was first formed in the reaction. The imide then reacted continuously with magnesium hydride and was converted to magnesium nitride and hydrogen. Thermodynamic calculation shows that the hydrogen desorption is a mild endothermic reaction with the standard enthalpy change of about 3.5 kJ/mol of H2.