Dong Bao-Xia, Wang Lu, Ge Jun, Ping Chao, Teng Yun-Lei, Li Zong-Wei
School of Chemistry and Chemical Engineering, Yangzhou University, Yangzhou, 225002, P. R. China.
Phys Chem Chem Phys. 2018 Apr 25;20(16):11116-11122. doi: 10.1039/c8cp00470f.
Although recent works demonstrated that some potassium compounds that can be converted to KH during ball-milling or heat-treatment have obvious effects on enhancing the dehydrogenation properties of the Li-N-H system, the effect of KH on enhancing the dehydrogenation properties of the Li-N-H system and its catalytic mechanism remain unclear. In this study, the hydrogen desorption properties of the LiNH2-LiH system with alkali metal hydrides (LiH, NaH, or KH) were investigated and discussed. We find that the three types of hydrides are effective for enhancing the hydrogen desorption properties of the LiNH2-LiH system, among which, KH shows the best effect. In comparison with the broad shaped hydrogen desorption curve of the LiNH2-LiH composite without additive, the hydrogen desorption curve of the LiNH2-LiH-0.05KH composite becomes narrow. The dehydrogenation onset temperature of the LiNH2-LiH-0.05KH composite is decreased by approximately 20 °C, and the dehydrogenation peak temperature is lowered by approximately 30 °C. Moreover, the reversibility of the LiNH2-LiH system is enhanced drastically by the addition of KH. On the basis of previous reports and present experimental results, the mechanism for the enhancement of the dehydrogenation properties in the KH-added Li-N-H system is proposed. The reason for the improvement of the hydrogen desorption kinetics is that KH has superior reactivity with NH3 and plays the role of a catalyst to accelerate hydrogen release by cyclic reactions.
尽管最近的研究表明，一些在球磨或热处理过程中可转化为KH的钾化合物对增强Li-N-H体系的脱氢性能有明显效果，但KH对增强Li-N-H体系脱氢性能的作用及其催化机理仍不清楚。在本研究中，对含碱金属氢化物（LiH、NaH或KH）的LiNH₂-LiH体系的氢解吸性能进行了研究和讨论。我们发现这三种氢化物对增强LiNH₂-LiH体系的氢解吸性能均有效，其中KH的效果最佳。与无添加剂的LiNH₂-LiH复合材料宽峰形的氢解吸曲线相比，LiNH₂-LiH-0.05KH复合材料的氢解吸曲线变窄。LiNH₂-LiH-0.05KH复合材料的脱氢起始温度降低了约20℃，脱氢峰值温度降低了约30℃。此外，添加KH极大地增强了LiNH₂-LiH体系的可逆性。基于先前的报道和目前的实验结果，提出了在添加KH的Li-N-H体系中脱氢性能增强的机理。氢解吸动力学改善的原因是KH与NH₃具有优异的反应活性，并通过循环反应起到加速氢释放的催化剂作用。
