Hydrogen sorption,kinetics, reversibility,and reaction mechanisms of MgH2-xLiBH4 doped with activated carbon nanofibers for reversible hydrogen storage based laboratory powder and tank scales

De/rehydrogenation kinetics and reversibility of MgH₂ are improved by doping with activated carbon nanofibers (ACNF) and compositing with LiBH₄. Via doping with 5 wt % ACNF, hydrogen absorption of Mg to MgH₂ (T = 320 °C and p(H₂) = 50 bar) increases from 0.3 to 4.5 wt % H₂. Significant reduction of onset dehydrogenation temperature of MgH₂ to 340 °C (ΔT = 70 °C as compared with pristine MgH₂) together with 6.8–8.2 wt % H₂ can be obtained by compositing Mg-5 wt. % ACNF with LiBH₄ (LiBH₄:Mg mole ratios of 0.5:1, 1:1, and 2:1). During dehydrogenation of Mg-rich composites (0.5:1 and 1:1 mol ratios), the formation of MgB₂ and Mg_0.816Li_0.184 implying the reaction between LiBH₄ and MgH₂ favors kinetic properties and reversibility, while the composite with 2:1 mol ratio shows individual dehydrogenation of LiBH₄ and MgH₂. For up-scaling to hydrogen storage tank (～120 times greater sample weight than laboratory scale) of the most suitable composite (1:1 mol ratio), de/rehydrogenation kinetics and hydrogen content released at all positions of the tank are comparable and approach to those from laboratory scale. Due to high purity (100%) and temperature of hydrogen gas from hydride tank, the performance of single proton exchange membrane fuel cell enhances up to 30% with respect to the results from compressed gas tank.     

Reversible hydrogen sorption and kinetics of hydrogen storage tank based on MgH2 modified by TiF4 and activated carbon

By doping with 5 wt % TiF₄ and activated carbon (AC), onset and main dehydrogenation temperatures of MgH₂ significantly reduce (ΔT = 138 and 109 °C, respectively) with hydrogen capacity of 4.4 wt % H₂. Up-scaling to storage tank begins with packing volume and sample weight of 28.8 mL and ～14.5 g, respectively, and continues to 92.6 mL and ～60.5–67 g, respectively. Detailed hydrogen sorption mechanisms and kinetics of the tank tightly packed with four beds of MgH₂TiF₄-AC (～60.5 g) are investigated. De/rehydrogenation mechanisms are detected by three temperature sensors located at different positions along the tank radius, while hydrogen permeability is benefited by stainless steel mesh sheets and tube inserted in the hydride beds. Fast desorption kinetics of MgH₂TiF₄-AC tank at ～275–283 °C, approaching to onset dehydrogenation temperature of the powder sample (272 °C) suggests comparable performances of laboratory and tank scales. Hydrogen desorption (T = 300 °C and P(H₂) = 1 bar) and absorption (T = 250 °C and P(H₂) = 10–15 bar) of MgH₂TiF₄-AC tank provide gravimetric and volumetric capacities during the 1^st-2nd cycles of 4.46 wt % H₂ and 28 gH₂/L, respectively, while those during the 3^rd-15th cycles are up to 3.62 wt % H₂ and 23 gH₂/L, respectively. Due to homogeneous heat transfer along the tank radius, de/rehydrogenation kinetics superior at the tank center and degrading forward the tank wall can be due to poor hydrogen permeability. Particle sintering and/or agglomeration upon cycling yield deficient hydrogen content reproduced.     

Sex Differences in Placental Protein Expression and Efficiency in a Rat Model of Fetal Programming Induced by Maternal Undernutrition

Fetal undernutrition programs cardiometabolic diseases, with higher susceptibility in males. The mechanisms implicated are not fully understood and may be related to sex differences in placental adaptation. To evaluate this hypothesis, we investigated placental oxidative balance, vascularization, glucocorticoid barrier, and fetal growth in rats exposed to 50% global nutrient restriction from gestation day 11 (MUN, n = 8) and controls (n = 8). At gestation day 20 (G20), we analyzed maternal, placental, and fetal weights; oxidative damage, antioxidants, corticosterone, and PlGF (placental growth factor, spectrophotometry); and VEGF (vascular endothelial growth factor), 11β-HSD2, p22^phox, XO, SOD1, SOD2, SOD3, catalase, and UCP2 expression (Western blot). Compared with controls, MUN dams exhibited lower weight and plasma proteins and higher corticosterone and catalase without oxidative damage. Control male fetuses were larger than female fetuses. MUN males had higher plasma corticosterone and were smaller than control males, but had similar weight than MUN females. MUN male placenta showed higher XO and lower 11β-HSD2, VEGF, SOD2, catalase, UCP2, and feto-placental ratio than controls. MUN females had similar feto-placental ratio and plasma corticosterone than controls. Female placenta expressed lower XO, 11β-HSD2, and SOD3; similar VEGF, SOD1, SOD2, and UCP2; and higher catalase than controls, being 11β-HSD2 and VEGF higher compared to MUN males. Male placenta has worse adaptation to undernutrition with lower efficiency, associated with oxidative disbalance and reduced vascularization and glucocorticoid barrier. Glucocorticoids and low nutrients may both contribute to programming in MUN males.     

Effective nanoconfinement of 2LiBH4–MgH2 via simply MgH2 premilling for reversible hydrogen storages

To improve nanoconfinement of LiBH₄ and MgH₂ in carbon aerogel scaffold (CAS), particle size reduction of MgH₂ by premilling technique before melt infiltration is proposed. MgH₂ is premilled for 5 h prior to milling with LiBH₄ and nanoconfinement in CAS to obtained nanoconfined 2LiBH₄–premilled MgH₂. Significant confinement of both LiBH₄ and MgH₂ in CAS, confirmed by SEM–EDS–mapping results, is achieved due to MgH₂ premilling. Due to effective nanoconfinement, enhancement of CAS:hydride composite weight ratio to 1:1, resulting in increase of hydrogen storage capacity, is possible. Nanoconfined 2LiBH₄–premilled MgH₂ reveals a single–step dehydrogenation at 345 °C with no B₂H₆ release, while dehydrogenation of nanoconfined sample without MgH₂ premilling performs in multiple steps at elevated temperatures (up to 430 °C) together with considerable amount of B₂H₆ release. Activation energy (E_A) for the main dehydrogenation of nanoconfined 2LiBH₄–premilled MgH₂ is considerably lower than those of LiBH₄ and MgH₂ of bulk 2LiBH₄–MgH₂ (ΔE_A = 31.9 and 55.8 kJ/mol with respect to LiBH₄ and MgH₂, respectively). Approximately twice faster dehydrogenation rate are accomplished after MgH₂ premilling. Three hydrogen release (T = 320 °C, P(H₂) = 3–4 bar) and uptake (T = 320–325 °C, P(H₂) = 84 bar) cycles of nanoconfined 2LiBH₄–premilled MgH₂ reveal up to 4.96 wt. % H₂ (10 wt. % H₂ with respect to hydride composite content), while the 1st desorption of nanoconfined sample without MgH₂ premilling gives 4.30 wt. % of combined B₂H₆ and H₂ gases. It should be remarked that not only kinetic improvement and B₂H₆ suppression are obtained by MgH₂ premilling, but also the lowest dehydrogenation temperature (T = 320 °C) among other modified 2LiBH₄–MgH₂ systems is acquired.