In situ formation of Al3Ti from the TiC@graphene heterojunction for catalytic enhancement and cycling deactivation of NaAlH4

Elucidating the mechanisms underlying cycling capacity decay in light metal hydrides is of critical importance for advancing their practical application in hydrogen energy systems. In this work, a heterostructured TiC@G catalyst was successfully fabricated via a sol–gel-assisted in situ carbothermal reduction strategy. Hydrogen storage measurements demonstrate that the addition of 9 wt. % TiC@G markedly reduces the onset dehydrogenation temperature of NaAlH4 from 162.5 °C to 44.3 °C, delivering a reversible hydrogen storage capacity of 4.7 wt. % with 93.7% retention after 10 cycles. The apparent activation energies of the two dehydrogenation steps are lowered to 74.62 and 85.45 kJ/mol, representing reductions of approximately 40% relative to NaAlH4. Interfacial electronic coupling within the TiC@G heterostructure is identified as the primary driving force for the formation of Ti–Al intermediates. These species weaken Al–H bonds through interfacial interactions, thereby lowering the dehydrogenation barrier. During prolonged cycling, however, progressive coarsening of the Ti–Al phase reduces the accessible interfacial area and generates catalytically inactive domains, while continuous Al consumption further decreases the reversible hydrogen capacity. Combined theoretical calculations and in situ characterization establish a self-consistent mechanistic framework that elucidates the dual role of Ti–Al species in catalytic enhancement and long-term deactivation, providing a design principle for durable catalysts in complex-hydride hydrogen-storage systems.