Development of a magnesium-based hydrogen storage reactor: From material synthesis to reactor optimization

Solid alloys hydrogen storage is one of the most promising large-scale hydrogen storage technologies. However, the uneven internal heat distribution greatly affects its hydrogen storage efficiency. This paper starts from the synthesis of Mg-Ni-La-xMn (x = 0, 1, 2, 3, 4 wt%) hydrogen storage alloys. Models of the hydrogen storage reactor are established and validated by experimental results. Three hydrogen reactor types, namely the single-tube reactor (SITR), the return-tube reactor (RETR) and the spiral-tube reactor (SPTR), are designed and compared from hydrogen absorption and desorption rates and temperature filed uniformity. Structural and operation parameters are further optimized. It is found that main components of the Mg-Ni-La-xMn alloys are Mg, Mg₂Ni, LaNi₅, LaMg₁₂ and MgNi_0.8Mn_0.2. Introducing Mn content can not only increase the maximum hydrogen absorption, but also accelerate the hydrogen absorption rates. The Mg-Ni-La-2Mn alloy has the best hydrogen absorption and desorption performance. Hydrogen storage reactor performance comparison with Mg-Ni-La-2Mn alloy shows the SITR can hardly reach saturation absorption, whose hydrogen absorption is only 3.1 wt%. The maximum temperature of the SPTR is 27 K higher than that of the RETR during hydrogen absorption. The optimal tube diameter and spacing of the RETR are 6 mm and 8 mm, respectively. The practical hydrogen absorption capacity of Mg-Ni-La-2Mn alloy in the RETR reaches 6.2 wt%. The optimal hydrogen supply pressure in the RETR is 0.8 MPa during hydrogen absorption. The optimal thermal oil velocities in the RETR are 2 m/s and 1 m/s for hydrogen absorption and desorption respectively.