Amica G, Cova F, Arneodo Larochette P, Gennari F C
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. 2016 Jul 21;18(27):17997-8005. doi: 10.1039/c6cp02854c. Epub 2016 Jun 21.
Lithium fast-ion conductors have shown positive effects on the hydrogen storage properties of the Li-Mg-N-H system. In the present work, Li4(NH2)3BH4 doped Mg(NH2)2-2LiH was formed by milling the 2LiNH2-MgH2-0.2LiBH4 composite and posterior annealing under hydrogen pressure to reduce the kinetic barrier of the Li-Mg-N-H system. The effect of repetitive dehydrogenation/rehydrogenation cycles on the kinetic and thermodynamic performance was evaluated. The dehydrogenation rate in the doped composite was twice that in the un-doped sample at 200 °C, while hydrogenation was 20 times faster. The activation energy decreases by 9% due to the presence of Li4(NH2)3BH4 compared to the un-doped composite, evidencing its catalytic role. The presence of Li4(NH2)3BH4 in the composite stabilized the hydrogen storage capacity after successive sorption cycles. Thermodynamic studies revealed a variation in the pressure composition isotherm curves between the first dehydrogenation cycle and the subsequent. The Li4(NH2)3BH4 doped composite showed a sloped plateau region at higher equilibrium pressure in regard to the flat plateau of the un-doped composite. Detailed structural investigations revealed the effective influence of Li4(NH2)3BH4 in different reactions: the irreversible dehydrogenation in the presence of MgH2 and the reversible hydrogen release when it reacts with Li2Mg2(NH)3. The role of Li4(NH2)3BH4 in improving the dehydrogenation kinetics is associated with the weakening of the N-H bond and the mobile small ion mass transfer enhancement.
锂快离子导体已对Li-Mg-N-H体系的储氢性能产生了积极影响。在本工作中，通过球磨2LiNH₂-MgH₂-0.2LiBH₄复合材料并随后在氢气压力下退火以降低Li-Mg-N-H体系的动力学势垒，形成了Li₄(NH₂)₃BH₄掺杂的Mg(NH₂)₂-2LiH。评估了重复脱氢/再氢化循环对动力学和热力学性能的影响。在200℃时，掺杂复合材料中的脱氢速率是未掺杂样品的两倍，而氢化速率快20倍。与未掺杂的复合材料相比，由于Li₄(NH₂)₃BH₄的存在，活化能降低了9%，证明了其催化作用。复合材料中Li₄(NH₂)₃BH₄的存在使连续吸附循环后的储氢容量得以稳定。热力学研究揭示了第一次脱氢循环与后续循环之间压力组成等温线曲线的变化。与未掺杂复合材料的平坦平台相比，Li₄(NH₂)₃BH₄掺杂的复合材料在较高平衡压力下显示出倾斜的平台区域。详细的结构研究揭示了Li₄(NH₂)₃BH₄在不同反应中的有效影响：在MgH₂存在下的不可逆脱氢以及与Li₂Mg₂(NH)₃反应时的可逆氢释放。Li₄(NH₂)₃BH₄在改善脱氢动力学方面的作用与N-H键的减弱和移动小离子传质增强有关。
