Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) and Centro Atómico Bariloche (CNEA), Av. Bustillo 9500, R8402AGP, S. C. de Bariloche, Río Negro, Argentina.
Phys Chem Chem Phys. 2018 Jun 6;20(22):15358-15367. doi: 10.1039/c8cp02347f.
Potassium-containing compounds, such as KH, KOH, KNH2 and different potassium halides, have shown positive effects on the dehydrogenation properties of the Li-Mg-N-H system. However, it is still discussed whether the K-compounds modify the thermodynamics of the system or if they have only a catalytic effect. In this work the impact of the addition of two K-containing compounds (0.08 mol% of KCl and KOH) on the hydrogen storage performance of the Mg(NH2)2-LiH composite was studied. The KOH incorporation reduced the dehydrogenation temperature from 197 °C to 154 °C, beginning the process at low temperature (∼70 °C). The doped sample was able to reversibly absorb and desorb 4.6 wt% of hydrogen with improved kinetics; dehydrogenation rates were increased four times, whereas absorptions required 20% less time to be completed in comparison to the pristine material. The thermodynamic destabilization of the Mg(NH2)2-2LiH composite by the addition of a small amount of KOH was demonstrated by an increment of 30% in the dehydrogenation equilibrium pressure. According to detailed structural investigations, the KH formed by the KOH decomposition through milling and thermal treatment, can replace LiH and react with Mg(NH2)2 to produce a mixed potassium-lithium amide (Li3K(NH2)4). The KH role is not limited to catalysis, but rather it is responsible for the thermodynamic destabilization of the Mg(NH2)2-LiH composite and it is actively involved in the dehydrogenation process.
含钾化合物，如 KH、KOH、KNH2 和不同的钾卤化物，已被证明对 Li-Mg-N-H 体系的脱氢性能有积极影响。然而，关于 K 化合物是改变了体系的热力学性质，还是仅仅具有催化作用，仍存在争议。在这项工作中，研究了添加两种含 K 化合物（0.08mol%的 KCl 和 KOH）对 Mg(NH2)2-LiH 复合材料储氢性能的影响。KOH 的加入将脱氢温度从 197°C 降低到 154°C，使反应在低温（约 70°C）下开始。掺杂后的样品能够以改善的动力学可逆地吸收和释放 4.6wt%的氢气；脱氢速率提高了四倍，而吸收完成所需的时间比原始材料减少了 20%。通过添加少量 KOH 对 Mg(NH2)2-2LiH 复合材料的热力学不稳定性进行了证明，脱氢平衡压力增加了 30%。根据详细的结构研究，通过球磨和热处理，KOH 分解生成的 KH 可以取代 LiH，并与 Mg(NH2)2 反应生成混合钾-锂酰胺（Li3K(NH2)4）。KH 的作用不仅限于催化，而是负责 Mg(NH2)2-LiH 复合材料的热力学不稳定性，并积极参与脱氢过程。
