Innovative Strategies in Lithium-Amide Systems for Hydrogen Storage

1. Lithium-Amide Systems for Hydrogen Storage: cation/anion substitution L. Fernández Albanesi, G. Amica, N. Gamba, P. Arneodo Larochette and F. C. Gennari Physical-Chemistry Department – CAB – CNEA (National Commision of Atomic Energy) Bariloche - Argentina

2. Li-N-H System The Li-N-H system has received special attention since 2002 with the report of Chen et al. LiNH2(s) + LiH(s) ↔ Li2NH(s) + H2(g) (6.5 wt% H) ΔH = 44.5 kJ/mol Li-N-H is a reversible storage system through the breaking and formation of N-H bonds LiNH2 crystal structure P. Chen, Z. Xiong, J. Luo, J. Lin, K.L. Tan, Nature 420 (2002) 302–304 Hydrogen Days 2018 Prague, Czech Republic; 13 to 15 June 2018

3. Destabilization LiNH2 + 1.6 LiH • It is necessary to lower the operation temperature excess of LiH to avoid the NH3 formation and emission Addition of different compounds to the Li-N-H system during ball milling process: AlCl3 looking for replacing the Li+ by Al3+ ions to produce vacancies because metal hydrides offer a possible way to modify its thermodynamic properties MgH2 / CaH2 / TiH2 to understand the behaviour of the halides on the properties of Li-Mg-N-H system MgCl2 Hydrogen Days 2018 Prague, Czech Republic; 13 to 15 June 2018

4. AlCl3 LiNH2 + 1.6 LiH + 0.03 AlCl3 + 0.08 AlCl3 + 0.13 AlCl3 Improvement of the dehydrogenation and hydrogenation kinetics Hydrogen Days 2018 Prague, Czech Republic; 13 to 15 June 2018

5. L-N-Al-H-Cl system The addition of AlCl3 modifies the system thermodynamics Hydrogen Days 2018 Prague, Czech Republic; 13 to 15 June 2018

6. L-N-Al-H-Cl systems Thermaltreatment at 300 ºCunder 7 bar of H2pressure + 0.30 AlCl3 BM + 0.30 AlCl3 TT cubic I213 New phases in the Li-Al-N-H-Cl system, isostructural with the cubic and hexagonal type-Li4(NH2)3Cl(*) + 0.13 AlCl3 BM + 0.13 AlCl3 TT hexagonal R-3 and cubic I213 Intensity (a.u.) + 0.08 AlCl3 BM + 0.08 AlCl3 TT hexagonal R-3 + 0.03 AlCl3 BM LiNH2 + 1.6LiH For low amount addition of AlCl3 Al3+ is incorporated in the LiNH2 lattice (*) A.A. Anderson, P.A. Chater, D.R. Hewett, P.R. Slater, Faraday Discuss 151 (2011) 271-84 L. FernándezAlbanesi, S. Garroni, S. Enzo, F.C.Gennari, Dalton Trans. 45 (2016) 5808-14 Hydrogen Days 2018 Prague, Czech Republic; 13 to 15 June 2018

7. MgH2 /CaH2 / TiH2 LiNH2 + 1.6 LiH + 0.2 MgH2 The H2 release finishes at 290 ºC LiNH2 + 1.6 LiH + 0.2 CaH2 Improvement in the H2 desorption rate + 0.2 TiH2 No modification was observed by TiH2 addition Hydrogen Days 2018 Prague, Czech Republic; 13 to 15 June 2018

8. L-N-Mg-H and L-N-Ca-H systems Reactions at 300 ºCunder 7 bar of H2pressure 2LiNH2 + MgH2 ↔ Mg(NH2)2 + 2LiH Mg(NH2)2 + 2LiH ↔ Li2Mg(NH)2 + 2H2 4LiNH2 + 3CaH2 2CaNH-Ca(NH2)2 + 4LiH + 2H2 2LiNH2 + 4LiH + 2CaNH-Ca(NH2)2 ↔ 3Li2NH + 3CaNH + 4H2 G. Amica, P. Arneodo Larochette, F.C.Gennari, Int. J. Hydrogen Energy 40 (2015) 9335-46 Hydrogen Days 2018 Prague, Czech Republic; 13 to 15 June 2018

9. MgCl2 2 LiNH2 + MgCl2 Mg(NH2)2 + 2 LiCl Mg(NH2)2–2LiCl–2LiH Thermal treatment at 200 ºC under 60 bar of H2 pressure Mg(NH2)2 Li4(NH2)3Cl 3LiNH2 + LiCl Li4(NH2)3Cl Li2Mg2(NH)3 Hydrogen Days 2018 Prague, Czech Republic; 13 to 15 June 2018

10. Mg(NH2)2– 2LiCl–2LiH 2Mg(NH2)2 + 3LiH ↔ Li2Mg2(NH3) + LiNH2 + 3H2 Li2Mg2(NH3) + LiNH2 + LiH ↔ 2Li2Mg(NH)2 + H2 Thermal decomposition of Li4(NH2)3Cl H2 desorption from Mg(NH2)2-2LiH-2LiCl and thermal decomposition of Li4(NH2)3Cl H2 desorption from Mg(NH2)2-2LiH-2LiCl N. Gamba, P. Arneodo Larochette, F.C.Gennari, RSC Adv. 5 (2015) 68542-50 Hydrogen Days 2018 Prague, Czech Republic; 13 to 15 June 2018

11. Conclusions • The Mg(NH2)2–2LiH was synthesized by metathesis reaction between LiNH2 and MgCl2 • The as milled Mg(NH2)2–2LiCl–2LiH material shows good dehydrogenation rate and high H2 storage capacity at 200 ºC • The formation of Li4(NH2)3Cl was favored during H2 cycling, deteriorating the storage properties

12. Conclusions • Dehydrogenation behaviour shows that CaH2 and MgH2 were the best additives under de experimental conditions studied, without positive effect of TiH2 • Dehydrogenation rate of Li-N-Ca-H system at 300 ºC was, at least, three times faster than Li-N-H pristine system • The hydrogen storage reversibility involves the formation of 2CaNH-Ca(NH2)2 solid solution in the hydrogenated state and the Li2NH–CaNH mixture in the dehydrogenated state • A clear thermodynamic destabilization was only observed for LiNH2-LiH with MgH2 added, with minor effect in the case of CaH2

13. Conclusions • The Li-N-H system stores hydrogen reversibly • When AlCl3 is added the kinetic properties are improved • The addition of AlCl3 modifies the system thermodynamics • Combination of XPRD and FTIR studies demonstrate that the formation of lithium aluminum amide-chloride new compound occurs by combination of milling and thermal treatment • This new phases are able to release and uptake hydrogen reversibly • In these systems, the effect of anion/cation substitution promotes N-H bond destabilization and induces structural defects into LiNH2 lattice improving the Li+ mobility • The Mg(NH2)2–2LiH was synthesized by metathesis reaction between LiNH2 and MgCl2 • The as milled Mg(NH2)2–2LiCl–2LiH material shows good dehydrogenation rate and high H2 storage capacity at 200 ºC • The formation of Li4(NH2)3Cl is favoured during H2 cycling, deterioring the storage properties • In these systems, the effect of anion/cation substitution promotes N-H bond destabilization and induces structural defects into LiNH2 lattice improving the Li+ mobility

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