Laboratoire de Réactivité et Chimie des Solides, UMR 7314 CNRS Université de Picardie Jules Verne, 33 rue St Leu, 80039 Amiens, France.
Phys Chem Chem Phys. 2012 Oct 14;14(38):13319-24. doi: 10.1039/c2cp41589e.
The recently reported KSi-KSiH(3) system can store 4.3 wt% of hydrogen reversibly with slow kinetics of several hours for complete absorption at 373 K and complete desorption at 473 K. From the kinetics measured at different temperatures, the Arrhenius plots give activation energies (E(a)) of 56.0 ± 5.7 kJ mol(-1) and 121 ± 17 kJ mol(-1) for the absorption and desorption processes, respectively. Ball-milling with 10 wt% of carbon strongly improves the kinetics of the system, i.e. specifically the initial rate of absorption becomes about one order of magnitude faster than that of pristine KSi. However, this fast absorption causes a disproportionation into KH and K(8)Si(46), instead of forming the KSiH(3) hydride from a slow absorption. This disproportionation, due to the formation of stable KH, leads to a total loss of reversibility. In a similar situation, when the pristine Zintl NaSi phase absorbs hydrogen, it likewise disproportionates into NaH and Na(8)Si(46), indicating a very poorly reversible reaction.
最近报道的 KSi-KSiH(3) 体系在 373 K 下以较慢的动力学吸收 4.3wt%的氢气，在 473 K 下完全解吸，具有较慢的动力学。从不同温度下测量的动力学数据，Arrhenius 图给出了吸收和解吸过程的活化能（E(a)）分别为 56.0 ± 5.7 kJ mol(-1)和 121 ± 17 kJ mol(-1)。球磨 10wt%的碳可以显著提高该体系的动力学性能，即吸收的初始速率比原始 KSi 快约一个数量级。然而，这种快速吸收会导致歧化反应生成 KH 和 K(8)Si(46)，而不是通过缓慢吸收形成 KSiH(3)氢化物。由于 KH 的形成，这种歧化反应导致完全失去了可逆性。在类似的情况下，原始 Zintl NaSi 相吸收氢气时，同样会歧化成 NaH 和 Na(8)Si(46)，表明反应的可逆性很差。
