Improved low-temperature dehydrogenation kinetics and cyclic stability of Mg(NH2)2-2LiH catalyzed by K2TiF6 additive

Abstract

Li-Mg-N-H materials are promising for on-board hydrogen storage but limited by sluggish low-temperature kinetics and poor cycling. In this work, three dual-cation fluorides (K 2 TiF 6 , K 2 TaF 7 , K 2 NbF 7 ) were selected as catalysts for Mg(NH 2 ) 2 -2LiH, further K 2 TiF 6 doping content was optimized. The Mg(NH 2 ) 2 -2LiH-5 wt% K 2 TiF 6 composite delivers the optimal performance. It can release 1.80 wt% H 2 at 140 °C with a peak dehydrogenation temperature reduced to 177 °C and absorb 2.95 wt% H 2 within 300 min at 120 °C. Its dehydrogenation activation energy is reduced to 102.65 kJ mol −1 , and the capacity retention of the system remains 92.68% after 20 cycles. XRD analysis confirms that in-situ formed KH accelerates the generation of intermediate Li 2 Mg 2 (NH) 3 and LiNH 2 , lowering the dehydrogenation reaction barrier. Meanwhile, DFT calculation reveals pronounced charge redistribution and orbital hybridization caused by K 2 TiF 6 , weakening the N-H bonds. The synergistic effect of K 2 TiF 6 substantially promotes low-temperature hydrogen desorption.