Composition-dependent catalytic behavior of Nb2C/Ti3C2 dual MXenes for enhanced hydrogen sorption kinetics of MgH2

Pristine Nb 2 C/Ti 3 C 2 dual MXenes enable composition-controlled MgH 2 catalysis. • A 1:2 Nb 2 C/Ti 3 C 2 ratio is optimal at only 5 wt% total catalyst loading. • 6.81 wt% H 2 is released within 3 min at 300 °C. • 4.56 wt% H 2 is absorbed within 20 s at 50 °C under 55 bar H 2 . • 91%/90% capacity is retained after 30 hydrogenation/dehydrogenation cycles. MXene catalysts can improve MgH 2 kinetics, but composition effects in dual pristine MXenes at fixed loading remain unclear. Here, Nb 2 C/Ti 3 C 2 was optimized by Nb 2 C etching time, single-MXene loading, mass ratio, and total loading. Nb 2 C etched for 70 h showed low residual Al, intact layers, and the highest surface area. At 5 wt% total catalyst, Nb 2 C:Ti 3 C 2 = 1:2 gave the best overall performance. It released 6.81 wt% H 2 in 3 min at 300 °C and 6.02 wt% in 10 min at 250 °C, and absorbed 4.56 wt% H 2 in 20 s at 50 °C under 55 bar H 2 . The apparent dehydrogenation activation energy was 71.25 ± 8.73 kJ·mol −1 , 53.7% below the MgH 2 reference. After 30 cycles, hydrogenation/dehydrogenation capacity retentions were 91%/90%. XRD and SEM confirmed reversible MgH 2 /Mg conversion and cycling-related morphology changes. XPS survey of the optimized dual-MXene composite confirmed the coexistence of Ti- and Nb-containing species, while reaction-state XPS of the individual Ti 3 C 2 - and Nb 2 C-containing composites showed reaction-dependent surface reconstruction. Together, these results support composition-dependent catalytic contributions, whereas simultaneous Ti-Nb reconstruction in the optimal dual system remains unverified.