Improved hydrogen storage kinetics of MgH2 using TiFe0.92Mn0.04Co0.04 with in-situ generated α-Fe as catalyst

Abstract

While TiFe alloy has recently attracted attention as the efficient catalyst to enhance de/hydrogenation rates of Mg/MgH2, the difficulty of its activation characteristics has hindered further improvement of reaction kinetics. Herein, we report that the TiFe0.92Mn0.04Co0.04 catalyst can overcome the abovementioned challenges. The synthesized MgH2-30 wt% TiFe0.92Mn0.04Co0.04 can release 4.5 wt% of hydrogen in 16 min at 250 °C, three times as fast as MgH2. The activation energy of dehydrogenation was as low as 84.6 kJ mol−1, which is 46.8% reduced from pure MgH2. No clear degradation of reaction rates and hydrogen storage capacity was observed for at least 30 cycles. Structural studies reveal that TiFe0.92Mn0.04Co0.04 partially decomposes to in-situ generated α-Fe particles dispersed on TiFe0.92Mn0.04Co0.04. The presence of α-Fe reduces the formation of an oxide layer on TiFe0.92Mn0.04Co0.04, enabling the activation processes. At the same time, the hydrogen incorporation capabilities of TiFe0.92Mn0.04Co0.04 can provide more hydrogen diffusion paths, which promote hydrogen dissociation and diffusion. These discoveries demonstrate the advanced nature and importance of combining the in-situ generated α-Fe with TiFe0.92Mn0.04Co0.04. It provides a new strategy for designing highly efficient and stable catalysts for Mg-based hydrogen storage materials.