Nanostructured complex hydride systems for solid state hydrogen storage

The present work reports a study of the effects of the formation of a nanostructure induced by high-energy ball milling, compositions, and various catalytic additives on the hydrogen storage properties of LiNH2-LiH and LiNH2-MgH2 systems. The mixtures are systematically investigated using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and a Sieverts-type apparatus. The results indicate that microstructural refinement (particle and grain size) induced by ball milling affects the hydrogen storage properties of LiNH2-LiH and LiNH2-MgH2 systems. Moreover, the molar ratios of the starting constituents can also affect the dehydrogenation/hydrogenation properties. In the LiNH2-LiH system, high-energy ball milling is applied to the mixtures of LiNH2 and LiH with molar ratios of 1:1, 1:1.2 and 1:1.4 LiH. The lowest apparent activation energy is observed for the mixture of LiNH2-LiH (1:1.2) milled for 25 h. The major impediment in the LiNH2-LiH system is the hydrolysis and oxidation of LiH, which causes a fraction of LiH to be inactive in the intermediate reaction of NH3+LiH→LiNH2+H2. Therefore, the LiNH2-LiH system always releases NH3, as long as a part of LiH becomes inactive, due to hydrolysis/oxidation, and does not take part in the intermediate reaction. To prevent LiH from undergoing hydrolysis/oxidation during desorption/absorption, 5 wt. % graphite is incorporated in the (LiNH2+1.2LiH) system. The DSC curve of the mixture does not show a melting peak of retained LiNH2, indicating that graphite can prevent or at least substantially reduce the oxidation/hydrolysis of LiH. Moreover, compared to the mixture without graphite, the mixture with graphite shows more hydrogen capacity, thus this mixture desorbs ~5 wt.% H2, which is close to the theoretical capacity. This system is fully reversible in the following reaction: LiNH2+LiH→Li2NH+H2. However, the equilibrium temperature at the atmospheric pressure of hydrogen (0.1 MPa H2) is 256.8°C for (LiNH2+1.2LiH) mixture, which is too high for use in onboard applications. To overcome the thermodynamic barrier associated with the LiNH2/LiH system, LiH is substituted by MgH2; therefore, the (LiNH2+nMgH2) (n=0.55, 0.6 and 0.7) system is investigated first. These mixtures are partially converted to Mg(NH2)2 and LiH by the metathesis reaction upon ball milling. In this system, hydrogen is desorbed in a two-step reaction: [0.5xMg(NH2)2+xLiH]+[(1-x)LiNH2+(0.5-0.5x)MgH2]→0.5Li2Mg(NH)2+1.0H2 and 0.5Li2Mg(NH)2+MgH2→0.5Mg3N2+LiH+H2. Moreover, this system is fully reversible in the following reaction: Li2Mg(NH)2+2H2→ Mg(NH2)2+2LiH. Step-wise desorption tests show that the enthalpy and entropy change of the first reaction is -46.7 kJ/molH2 and 136.1 J/(molK), respectively. The equilibrium temperature at 0.1 bar H2 is 70.1°C, which indicates that this system has excellent potential for onboard applications. The lowest apparent activation energy of 71.7 kJ/mol is observed for the molar ratio of 1:0.7MgH2 milled for 25 h. This energy further decreases to 65.0 kJ/mol when 5 wt.% of n-Ni is incorporated in the system. Furthermore, the molar ratio of MgH2/LiNH2 is increased to 1.0 and 1.5 to increase the limited hydrogen storage capacity of the (LiNH2+0.7MgH2) mixture. It has been reported that the composition changes can enhance the hydrogen storage capacity by changing the dehydrogenation/hydrogenation reaction pathways. However, theoretically predicted LiMgN is not observed, even after dehydrogenation at 400°C. Instead of this phase, Li2Mg(NH)2 and Mg3N2 are obtained by dehydrogenation at low and high temperatures, respectively, regardless of the milling mode and the molar ratio of MgH2/LiNH2. The only finding is that the molar ratio of MgH2/LiNH2 can significantly affect mechano-chemical reactions during ball milling, which results in different reaction pathways of hydrogen desorption in subsequent heating processes; however, the reaction’s product is the same regardless of the milling mode, the milling duration and their composition. Therefore, the (LiNH2+0.7MgH2) mixture has the greatest potential for onboard applications among Li-Mg-N-H systems due to its high reversible capacity and good kinetic properties

Aggregate and Intergenerational Implications of School Closures: A Quantitative Assessment

This paper quantitatively investigates the macroeconomic and distributional consequences of school closures through intergenerational channels in the medium- and long-term. The model economy is a dynastic overlapping generations general equilibrium model in which schools, in the form of public education investments, complement parental investments in producing children's human capital. We find that unexpected school closure shocks have moderate long-lasting adverse effects on macroeconomic aggregates and reduce intergenerational mobility, especially among older children. Lower substitutability between public and parental investments induces larger damages in the aggregate economy and overall incomes of the affected children, while mitigating negative impacts on intergenerational mobility

Nonflammable Lithium Metal Full Cells with Ultra-high Energy Density Based on Coordinated Carbonate Electrolytes

Coupling thin Li metal anodes with high-capacity/high-voltage cathodes such as LiNi0.8Co0.1Mn0.1O2 (NCM811) is a promising way to increase lithium battery energy density. Yet, the realization of high-performance full cells remains a formidable challenge. Here, we demonstrate a new class of highly coordinated, nonflammable carbonate electrolytes based on lithium bis(fluorosulfonyl)imide (UFSI) in propylene carbonate/fluoroethylene carbonate mixtures. Utilizing an optimal salt concentr ation (4 M LiFSI) of the electrolyte results in a unique coordination structure of Li+-FSI-solvent cluster, which is critical for enabling the formation of stable interfaces on both the thin Li metal anode and high-voltage NCM811 cathode. Under highly demanding cell configuration and operating conditions (Li metal anode = 35 mu m, areal capacity/charge voltage of NCM811 cathode = 4.8 mAh cm(-2)/4 .6 V, and anode excess capacity [relative to the cathode] = 0.83), the Li metal-based full cell provides exceptional electrochemical performance (energy densities = 679 Wh kg(cell)(-1)/1,024 Wh L-cell(-1)) coupled with nonflammability

Mechano-chemical synthesis of nanostructured hydride composites based on Li-Al-N-Mg for solid state hydrogen storage

It is observed that large quantities of hydrogen (H2) are released at ambient temperatures during the mechano-chemical synthesis of the Li-Al-N-Mg-based hydride composites using an energetic ball milling in a unique magneto-mill. For the (nLiAlH4+LiNH2; n=1, 3, 11.5, 30) composite, at the molar ratio n=1, the LiNH2 constituent destabilizes LiAlH4 and enhances its decomposition to Li3AlH6, Al and H2, and subsequently Li3AlH6 to LiH, Al and H2. LiNH2 ceases to destabilize LiAlH4 in the composites with increasing molar content of LiAlH4 (n≥3). For the (nLiAlH4+MnCl2; n=1, 3, 8, 13, 30, 63) composite, XRD phase analysis shows that chemical reaction occurs during ball milling between the hydride and chloride constituent forming either an inverse cubic spinel Li2MnCl4 for n=1 or lithium salt (LiCl) for n>1. Both reactions release hydrogen. For the (LiNH2+nMgH2; n=1, 1.5) composite the pathway of hydride reactions depends on the milling energy and milling time. Under low milling energy up to 25h there is either no reaction (1h) or the reaction products are amorphous Mg(NH2)2 (magnesium amide) and nanocrystalline LiH (lithium hydride) without any release of hydrogen. Under high milling energy a new hydride MgNH (magnesium imide) is formed due to reaction between Mg(NH2)2 and MgH2 which is always associated with the release of H2

Nonlinear occupations and female labor supply over time

Long hours worked associated with higher hourly wages are common to many occupations, known as nonlinear occupations. Over the last four decades, both the share of workers in nonlinear occupations and their relative wage premium have been increasing. Females in particular have been facing rising experience premiums, especially in these types of occupations. We quantitatively explore how these changes have affected the female labor supply over time using a quantitative, dynamic general equilibrium model of occupational choice and labor supply at both the extensive and intensive margins. Our decomposition analysis finds that rising experience premiums are important in explaining the intensive margin of female labor supply, which has continued to increase even in the most recent period. Meanwhile, technical changes biased toward nonlinear occupations help to explain recent stagnating female employment rates. Finally, a counterfactual experiment suggests that, if the barrier aspects of nonlinearities had instead gradually vanished, female employment over this same time period would have been considerably higher at the expense of significantly lower labor supplies at the intensive margin

Aggregate and intergenerational implications of school closures: a quantitative assessment

This paper quantitatively investigates the medium- and long-term macroeconomic and distributional consequences of school closures through intergenerational channels. The model economy is a dynastic overlapping generations general equilibrium model in which schools, in the form of public education investments, complement parental investments in producing children's human capital. We find that unexpected school closure shocks have long-lasting adverse effects on macroeconomic aggregates and reduce intergenerational mobility, especially among older children. Higher substitutability between public and private investments induces smaller damages in the aggregate economy and the affected children's lifetime income, while exacerbating negative impacts on intergenerational mobility and inequality

Heterogeneity, transfer progressivity, and business

This paper studies how transfer progressivity influences aggregate fluctuations when interacting with household heterogeneity. Using a simple static model of the extensive margin labor supply, we analytically characterize how transfer progressivity influences differential labor supply responses to aggregate conditions across heterogeneous households. We then build a quantitative dynamic general equilibrium model with both idiosyncratic and aggregate productivity shocks and show that it delivers moderately procyclical average labor productivity and a large cyclical volatility of aggregate hours relative to output. A counterfactual exercise shows that higher progressivity achieved by a faster phase-out of transfers would strengthen our mechanism. Finally, we provide suggestive empirical evidence on the heterogeneity of employment responses across the wage distribution

Tax-and-Transfer Progressivity and Business Cycles

This paper studies how tax-and-transfer progressivity influences aggregate fluctuations when interacting with household heterogeneity. Using a simple static model of the extensive margin labor supply, we analytically characterize how a degree of progressivity influences differential labor supply responses to aggregate conditions across heterogeneous households. We then build a quantitative dynamic general equilibrium model with both idiosyncratic and aggregate productivity shocks and show that it delivers moderately procyclical average labor productivity and a large cyclical volatility of aggregate hours relative to output. Our quantitative exercises suggest that progressivity at the bottom of the income distribution shaped by the phasing out of transfers is key for these findings. Finally, we provide suggestive empirical evidence on the heterogeneity of employment responses across the wage distribution

Development of Dual-Pore Coexisting Branched Silica Nanoparticles for Efficient Gene-Chemo Cancer Therapy

Various strategies for combination therapy to overcome current limitations in cancer therapy have been actively investigated. Among them, simultaneous delivery of multiple drugs is a subject of high interest due to anticipated synergistic effect, but there have been difficulties in designing and developing effective nanomaterials for this purpose. In this work, dual-pore coexisting hybrid porous silica nanoparticles are developed through Volmer-Weber growth pathway for efficient co-delivery of gene and anticancer drug. Based on the different pore sizes (2-3 and 40-45 nm) and surface modifications of the core and branch domains, loading and controlled release of gene and drug are achieved by appropriate strategies for each environment. With excellent loading capacity and low cytotoxicity of the present platform, the combinational cancer therapy is successfully demonstrated against human cervical cancer cell line. Through a series of quantitative analyses, the excellent gene-chemo combinational therapeutic efficiency is successfully demonstrated. It is expected that the present nanoparticle will be applicable to various biomedical fields that require co-delivery of small molecule and nucleic aci