Evolution of the active species and catalytic mechanism of Ti doped NaAlH4 for hydrogen storage

The catalytic mechanism of Ti doped NaAlH4 for hydrogen storage remains unconfirmed. Here, we investigated the evolution of active species in Ti doped NaAlH4 system by XRD, XPS and TEM. The results reveal that the evolution of the Ti addition in doped NaAlH4 is Ti3+ → amorphous Ti0 → AlTi species → Al3Ti intermetallic. TEM results show that the average particle size of the AlTi species and Al3Ti intermetallic is about 30 nm, and Ti element is uniformly distributed in Al matrix. In further, we discussed the catalytic mechanism and role of active species in Ti doped NaAlH4 system according to experimental and theoretical calculation. The rehydrogenation process of Ti doped NaAlH4 system can be divided into three steps: (1) H2 dissociation, (2) H atom spillover and alanes (AlxHy) formation and (3) complex hydrides formation. The addition of Ti can catalyze the process of H2 dissociation, H atom spillover and formation of alanes. More importantly, the current work may provide a general approach to investigate the catalytic mechanism of other doped complex hydrides for hydrogen storage system.