Ti掺杂的MgH2和Mg2NiH4的放氢性能

以TiF₃和Ti(OBu-n)₄为催化剂, 研究了Ti离子掺杂对MgH₂和Mg₂NiH₄放氢性能的影响. 结果表明, 未掺杂的MgH₂起始放氢温度为420 ℃, 掺杂TiF₃和Ti(OBu-n)₄后分别降低到360和410 ℃; Mg₂NiH₄在掺杂TiF₃后放氢温度由230 ℃降低到220 ℃, 而掺杂Ti(OBu-n)₄后没有变化. 可见无论对MgH₂或Mg₂NiH₄, 在降低放氢温度方面TiF₃都明显优于Ti(OBu-n)₄. 另外, 研究还发现, TiF₃掺杂对MgH₂放氢动力学有显著的提高, 但对Mg₂NiH₄没有明显的提高. 结合XRD和FTIR的测试分析, 我们认为: 催化作用很大程度上取决于氢化物自身的晶体结构和催化剂的电子结构; 降低氢化物放氢温度和提高动力学性能的原因是催化剂与氢化物之间的相互作用削弱了氢化物中Mg—H或Ni—H键, 使得活泼的H…H原子对容易形成, 从而有利于H₂的释出.

Hydrogen Desorption Performance of Ti-Mediated MgH2 and Mg2NiH4

TiF₃ and Ti(OBu-n)₄-doped MgH₂ and Mg₂NiH₄ were investigated with regard to hydrogen desorption performance. It was found that the onset temperature for hydrogen release was around 420 ℃ for the blank MgH₂, but decrease to 360 and 410 ℃ for the TiF₃- and the Ti(OBu-n)₄-doped MgH₂, respectively. For Mg₂NiH₄, it was reduced from 230 to 220 ℃ after doping with TiF₃, but remained unchanged once doping with Ti(OBu-n)₄. These indicate that TiF₃ is more efficient than Ti(OBu-n)₄ in reducing the stability of MgH₂ and Mg₂NiH₄. The enhanced desorption kinetics is attained in the TiF₃-doped MgH₂, but not in the TiF₃-doped Mg₂NiH₄. Combined with XRD and FTIR techniques, the catalytic activity was thought to be jointly influenced by the crystal structure of the hydride and the electronic structure of the catalyst. The decrease in hydrogen release temperature and the improvement in kinetics are owing to the weakening of the Mg(Ni)—H bonds through the interactions between the catalyst and the hydride, thus facilitating energetically the formation of intra-H…H pairings that further recombine readily towards the molecular hydrogen.