Xin Zhang,Zhuanghe Ren,Xuelian Zhang,Mingxia Gao,Hongge Pan,Yongfeng Liu
Highly stable catalytic activity of metallic Ti and corresponding mechanistic understanding are of particularly critical importance for the development of sodium alanate (NaAlH4) as an advanced on-board hydrogen storage medium. However, only limited catalytic effectiveness is observed for commercial metallic Ti powders due to their ductile behavior limiting the dispersion of large particles. Here, we successfully synthesize ultrafine metallic Ti nanoparticles (3–5 nm) supported on amorphous carbon (nano-Ti@C) through a facile, scalable calcination process. Unlike commercial metallic Ti powders, the nano-Ti@C exhibits remarkable catalytic activity for hydrogen storage in NaAlH4, superior to other reported transition metals and rare earth metals. The 7 wt% nano-Ti@C-containing NaAlH4 sample delivers a quite low onset temperature of dehydrogenation of 75 °C and a practically available hydrogen capacity as high as 5.04 wt%. Reloading of hydrogen is fully completed in <3 min at 100 °C and 120 bar H2; this sorption kinetics is fastest among all catalytically enhanced NaAlH4 systems known. Moreover, only 0.07 wt% of hydrogen capacity is lost after 100 cycles, exhibiting a highly stable cyclability. Theoretical calculations reveal the interaction between Ti and Al, which not only weakens the Al–H bonding but also facilitates diffusion of H in NaAlH4, contributing to the superior catalytic activity of nano-Ti@C. Our findings greatly increase potentials towards practical applications of catalyst-doped NaAlH4 for onboard hydrogen storage.
NaAlH4 suffers from high kinetic barriers, causing high dehydrogenation temperatures, sluggish kinetics, poor reversibility, and low direct synthesis efficiency. Herein, a metallic Al−Ti−Ce alloy ribbon (Ti:Ce = 1:1, total 6 wt %) with a refined Al matrix (∼405 nm) and uniformly dispersed nanoscale Ti2Al20Ce and Al3Ti phases (200−360 nm) was fabricated by arc melting and melt-spinning. Used directly as the Al source, this ribbon enabled successful synthesis of NaAlH4 by ball-milling with NaH under 50 bar H2 for 36 h. The resulting composite delivered a dehydrogenation capacity of 4.73 wt % from 107.4 to 182.1 °C and a capacity retention of 91.98% over 15 cycles. The Ti−Ce synergy refines Al grains and disperses catalytic phases while also improving the hydrogenation and dehydrogenation kinetics of NaAlH4 and suppressing Al agglomeration, collectively ensuring high reactivity and sustained reversibility of the system. This work presents an effective design strategy for an integrated precursor that combines a bimetallic catalyst and an Al source, offering an alternative approach for optimizing the synthesis and hydrogen storage performance of the NaAlH4 system.
This study presents the preparation of a partially etched Ti 2 AlN-derived composite with a combination of Ti 2 N, residual Ti 2 AlN, and in-situ TiN nanoparticles. The resultant two-dimensional ternary composite was used as a catalyst to enhance the hydrogen storage capacity of NaAlH 4 .Although NaAlH 4 possesses a high theoretical hydrogen storage capacity of 7.4 wt%, its practical application is plagued by several problems: high temperature (~180 °C) to release hydrogen, slow kinetics, and poor reversibility. Herein, Ti 2 N was prepared by etching the Ti 2 AlN MAX phase. The results show that the catalytic effect is optimal when the Ti 2 N content is 7.5 wt%, with the starting temperatures of the two-step hydrogen release from NaAlH₄ decreasing from 180 °C and 260 °C to 98.4 °C and 163.3 °C, respectively. Meanwhile, the apparent activation energies of the two-step reactions decrease from 128 kJ/mol and 160 kJ/mol to 66.0 kJ/mol and 91.6 kJ/mol, respectively, with the kinetic performance significantly improved. Importantly, Ti 2 N/NaAlH 4 composites retain more than 95% of their hydrogen storage capacity after 10 cycles. Detailed characterizations using XRD, XPS, and TEM disclosed that the coexistence of multi-phases in Ti 2 N/NaAlH 4 composites induces synergistic catalytic effects: stable Ti 2 AlN provides electrically conductive pathways, while the reversible phase transformation between TiAl and TiAlH x occurs at the interface and nano-sized TiN transformed into TiAl 3 , enabling improved hydrogen gas dissociation. Collectively, these results provide new fundamental insights into optimizing the properties of Ti 2 N MXenes as catalysts in complex hydride hydrogen storage materials and establish key design principles to inspire the development of various composite materials for efficient and practical solid-state hydrogen storage systems.
危险品化学品经营许可证（带存储）