No abstract

Summary Catalytic effects of TiH2 on hydrogenation/dehydrogenation kinetics of MgH2 were investigated in this study. The TG analysis showed that the addition of the x wt% TiH2 exhibited lower onset temperature of 160°C which is 100°C and 190°C lower than as‐milled and as‐received MgH2. The dehydrogenation and hydrogenation kinetics were significantly improved compared with the pure MgH2. The activation energy for the hydrogen desorption of MgH2 was reduced from −137.13 to −77.58 kJ/mol by the addition of TiH2. XRD and XPS results showed that the phase of TiH2 remained same during the dehydrogenation without any intermediate formation confirming its role as catalyst.

In order to improve the compressor cycling stability and hydrogen storage properties of V40Ti21.5Cr38.5 alloy further, the fourth element i.e. Niobium, Iron, or Zirconium has been substituted for Cr to prepare V40Ti21.5Cr33.5M5 alloy and their cyclic hydrogen absorption-desorption performance was evaluated up to 100 cycles for temperature and pressure ranges of 20-300 °C and 5-20 MPa, respectively. All the three compositions have shown different sorption properties as well as cyclic stability. The V40Ti21.5Cr33.5Nb5 alloy was found a most suitable composition with a comparatively high hydrogen capacity and reasonable stability after 50 cycles of compressor cyclic test, whereas, V 40Ti21.5Cr33.5Fe5 alloy has shown worst cyclic stability with lowest hydrogen capacity. However, structural and morphological investigations suggest no phase segregation during the cycling of V40Ti21.5Cr33.5Fe5 alloy in contrast to the other alloys, which suggest that phase segregation is not the only responsible reason for the performance degradation of BCC alloys employed for compressor cycle. In some cases similar to V 40Ti21.5Cr33.5Fe5, stress/strain formation in the lattice during cycling may also cause the degradation of the material. V40Ti21.5Cr38.5 合金を用いた圧縮サイクル安定性と水素貯蔵特性をさらに改良するために，Cr を一部第４元素であるニオブ，鉄， ジルコニウムで置換して，V40Ti21.5Cr33.5M5 合金を合成した。 これらの水素吸蔵放出におけるサイ クル特性について，温度に関しては 20 ～ 300℃，圧力に関しては 5 ～ 20 MPa の範囲で 100 サイ クルまでの評価を行った。これら３種類の組成の試料は，サイ クル安 定性だけでなく吸蔵放出について異なる性能を示した。V40Ti21.5Cr33.5Nb5 合金は，50 サイクルの圧縮サイクル試験の後に，比較的 高い水素吸蔵量と適切な安定性を示し，最適な組成であることが分かったが，V40Ti21.5Cr33.5Fe5 合金は， 最低の水素吸蔵量とサイ クル安定性を示した。しかしながら，その他の合金と比較して，V40Ti21.5Cr33.5Fe5 合金は結晶構造と携帯観察の結果から，サイ クル 過程において，いかなる相分離も認められなかった。このことは，相分離が圧縮サイ クルにおける BCC 合金の性能劣化の合理的な 理由ではないことを示している。V40Ti21.5Cr33.5Fe5 合金と類似の様々な状況において，サイ クル過程での結晶構造における応力やひ ずみの導入は材料の劣化を引き起こしている可能性がありうると考えられる。