• The ultrathin K 2 Ti 8 O 17 nanobelts were designed through hydrothermal method. • Optimal material presents excellent hydrogen storage performance and stability. • Excellent hydrogen storage performance benefits from more active site on K 2 Ti 8 O 17. In this study, ultrathin K 2 Ti 8 O 17 nanobelts are fabricated and used to catalyse the hydrogen storage of MgH 2. The dehydrogenation temperature of MgH 2 -5 wt% K 2 Ti 8 O 17 is 189 °C, rapidly releasing 6.6 wt% H 2 in 2.4 min at 280 °C, and 6.0 wt% H 2 is instantly absorbed in 33 s at 200 °C. Moreover, the activation energy (E a) of MgH 2 -5 wt% K 2 Ti 8 O 17 decreases to 116.3 kJ mol−1, compared to that of the as-milled MgH 2 (177.3 kJ mol−1). In stability test, an excellent capacity retention rate of 88% is obtained even after eight cycles. Compositional and structural analyses demonstrate that stable oxygen vacancies in the K 2 Ti 8 O 17 (K 2 Ti 8 O 17 -O v) ultrathin nanobelts are responsible for enhancing the kinetics of the dehydrogenation of MgH 2. This strategy provides an avenue for the rational design of catalytic materials for hydrogen storage. [Display omitted] Hydrogen storage materials are the key to hydrogen energy utilisation. In this study, ultrathin K 2 Ti 8 O 17 nanobelts are fabricated and used to catalyse the hydrogen storage of MgH 2. The dehydrogenation temperature of MgH 2 -5 wt% K 2 Ti 8 O 17 is 189 °C, rapidly releasing 6.6 wt% H 2 in 2.4 min at 280 °C, and 6.0 wt% H 2 is instantly absorbed in 33 s at 200 °C. Moreover, the activation energy (E a) of MgH 2 -5 wt% K 2 Ti 8 O 17 decreases to 116.3 kJ mol−1, compared to that of the as-milled MgH 2 (177.3 kJ mol−1). In stability test, an excellent capacity retention rate of 88% is obtained even after eight cycles. Compositional and structural analyses demonstrate that stable oxygen vacancies in the K 2 Ti 8 O 17 (K 2 Ti 8 O 17 -O v) ultrathin nanobelts are responsible for enhancing the kinetics of the dehydrogenation of MgH 2. This strategy provides an avenue for the rational design of catalytic materials for hydrogen storage. [ABSTRACT FROM AUTHOR]