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A Quantum‐Chemical Study on Understanding the Dehydrogenation Mechanisms of Metal (Na, K, or Mg) Cation Substitution in Lithium Amide Nanoclusters
Author(s) -
Li Lanlan,
Peng Bo,
Tao Zhanliang,
Cheng Fangyi,
Chen Jun
Publication year - 2010
Publication title -
advanced functional materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 6.069
H-Index - 322
eISSN - 1616-3028
pISSN - 1616-301X
DOI - 10.1002/adfm.201000215
Subject(s) - nanoclusters , lithium amide , amide , dehydrogenation , hydrogen storage , hydride , metal , lithium (medication) , ionic bonding , chemistry , inorganic chemistry , hydrogen , materials science , ion , organic chemistry , catalysis , medicine , endocrinology , enantioselective synthesis
The hydrogen‐releasing activity of (LiNH 2 ) 6 –LiH nanoclusters and metal (Na, K, or Mg)‐cation substituted nanoclusters (denoted as (NaNH 2 )(LiNH 2 ) 5 , (KNH 2 )(LiNH 2 ) 5 , and (MgNH)(LiNH 2 ) 5 ) are studied using ab initio molecular orbital theory. Kinetics results show that the rate‐determining step for the dehydrogenation of the (LiNH 2 ) 6 –LiH nanocluster is the ammonia liberation from the amide with a high activation energy of 167.0 kJ mol −1 (at B3LYP/6‐31 + G(d,p) level). However, metal (Na, K, Mg)‐cation substitution in amide–hydride nanosystems reduces the activation energies for the rate‐determining step to 156.8, 149.6, and 144.1 kJ mol −1 (at B3LYP/6‐31 + G(d,p) level) for (NaNH 2 )(LiNH 2 ) 5 , (KNH 2 )(LiNH 2 ) 5 , and (MgNH)(LiNH 2 ) 5 , respectively. Furthermore, only the −NH 2 group bound to the Na/K cation is destabilized after Na/K cation substitution, indicating that the improving effect from Na/K‐cation substitution is due to a short‐range interaction. On the other hand, Mg‐cation substitution affects all –NH 2 groups in the nanocluster, resulting in weakened N–H covalent bonding together with stronger ionic interactions between Li and the –NH 2 group. The present results shed light on the dehydrogenation mechanisms of metal‐cation substitution in lithium amide–hydride nanoclusters and the application of (MgNH)(LiNH 2 ) 5 nanoclusters as promising hydrogen‐storage media.