Effect of the calcium halides, CaCl2 and CaBr2, on hydrogen desorption in the Li–Mg–N–H system

Abstract

a b s t r a c tCalcium-halide-doped lithium amide-magnesium hydride samples were prepared both by hand-grinding and ball-milling 2LiNH 2 -MgH 2 -xCaX 2 (x = 0, 0.1, and 0.15; X = Cl or Br). The addition of calcium halides reduced the hydrogen desorption temperature in all samples. The ball-milled undoped sample (2LiNH 2 -MgH 2 ) began to desorb hydrogen at around 125°C and peaked at 170°C. Hydrogen desorption from the 0.15 mol CaCl 2 -containing sample began ca 30°C lower than that of the undoped sample and peaked at 150°C. Both the onset and peak temperatures of the CaBr 2 sample (x = 0.15) were reduced by 15°C compared to the chloride. Kissinger's method was used to calculate the effective activation energy (E a ) for the systems: E a for the 0.15 mol CaCl 2 -containing sample was found to be 91.8 kJ mol À1 and the value for the 0.15 mol CaBr 2 -containing sample was 78.8 kJ mol À1 .

Catalytic Tuning of Sorption Kinetics of Lightweight Hydrides: A Review of the Materials and Mechanism

“…A similar effect was observed for MgCl 2 addition, where the formation of the Li-Mg-N-H system drastically improved the properties of the Li-N-H system [311]. Recently, the sorption kinetics of the LiNH 2 -LiH system could be enhanced by the addition of Ce based additives, i.e., CeO 2 , CeF 3 , CeF 4 [313]. Especially, CeF 4 addition showed a significant catalytic effect in reducing the desorption temperature and NH 3 suppression by forming CeF x species in-situ.…”

“…Thus it was concluded that the catalyzed and non-catalyzed systems undergo different rate limiting steps. The positive effect of TiCl 3 addition on the sorption kinetics accelerated several studies using different halides for the improvement of the LiNH 2 -LiH system [308][309][310][311][312][313]. Although the addition of AlCl 3 was found effective in enhancing the sorption rate and lowering desorption temperature [308], it was found to occur due to the thermodynamic alteration by the formation of the Li-Al-N-H system.…”

“…Ru doped SWNT addition to Mg(NH 2 ) 2 -LiH could effectively suppress the NH 3 emission as well as enhance the sorption kinetics. Bill et al [313] studied calcium halides and suggested that both CaCl 2 and CaBr 2 reduced the onset temperature by 30 and 45 • C more than the undoped Li-Mg-N-H system. The activation energies were calculated as 91.8 and 78.8 kJ/mol H 2 for CaCl 2 and CaBr 2 doped samples, respectively, in comparison to 104.2 kJ/mol H 2 for undoped Li-Mg-N-H system.…”

Recent Progress and New Perspectives on Metal Amide and Imide Systems for Solid-State Hydrogen Storage

“…Therefore, to improve the kinetics at temperatures lower than 200 • C, the reaction needed to be catalyzed with suitable dopants or additives. During the last years, many attempts have been made to improve the sorption kinetics of the 2LiNH 2 + MgH 2 system and, in this context, a large number of papers have been published [62][63][64][65][66][67][68][69][70][71][72][73][74]. Luo et al reported faster absorption kinetics by doping with less than 4 mol.…”

“…Anderson et al [63], demonstrated that addition of halides (CaCl 2 and CaBr 2 ) on the Li-Mg-N-H system can improve the desorption kinetics. In particular, these halides seem to favor the metathesis reaction already during the milling.…”