Yun Li

MgH₂ has a high hydrogen content of 7.6 wt% and possesses good reversibility under normal conditions. However, pristine MgH₂ requires a high temperature above 300 °C to release hydrogen, with very slow kinetics. In this work, we utilized Ti₃CN MXene to reduce the operating temperature and enhance the kinetics of MgH₂. The initial temperature of MgH₂ decomposition can be lowered from 322 °C for pristine MgH₂ to 214 °C through the employment of Ti₃CN. The desorbed MgH₂ + 7.5 wt% Ti₃CN can start absorption at room temperature, while the desorbed pristine MgH₂ can only start absorption at 120 °C. The employment of Ti₃CN can significantly improve the hydrogen release kinetics of MgH₂, with the desorption activation energy decreasing from 121 to 80 kJ mol⁻¹. Regarding thermodynamics, the desorption enthalpy changes of MgH₂ and MgH₂ + 7.5 wt% Ti₃CN were 79.3 and 78.8 kJ mol⁻¹, respectively. This indicates that the employment of Ti₃CN does not alter the thermal stability of MgH₂. Phase evolution studies through the use of X-ray diffraction and electron diffraction both confirm that Ti₃CN remains stable during the hydrogen release and uptake process of the composite. This work will help understand the impact of a transition metal carbonitride on the hydrogen storage of MgH₂.

Hydrogen has become a promising energy source due to its efficient and renewable properties. Although promising, hydrogen energy has not been in widespread use due to the lack of high-performance materials for hydrogen storage. Previous studies have shown that the addition of Al-based compounds to LiBH4 can create composites that have good properties for hydrogen storage. In this work, the dehydrogenation performances of different composite systems of 2LiBH4+ M (M = Al, LiAlH4, Li3AlH6) were investigated. Results show that, under a ball to powder ratio of 25:1 and rotation speed of 300 rpm, the optimum ball milling time is 50 h for synthesizing Li3AlH6 from LiH and LiAlH4. The three studied systems destabilized LiBH4 at relatively low temperature, while the 2LiBH4-Li3AlH6 composite demonstrated excellent behavior. Based on the differential scanning calorimetry results, pure LiBH4 released hydrogen at 469 ºC. The dehydrogenation temperature of LiBH4 is 416 ºC for 2LiBH4-Li3AlH6, versus 435 ºC for 2LiBH4-LiAlH4 and 445 ºC for 2LiBH4-Al composite. The 2LiBH4-Li3AlH6, 2LiBH4-LiAlH4, 2LiBH4-Al samples released 9.1 wt.%, 8 wt.%, and 5.7 wt.% of H2, respectively. Additionally, the 2LiBH4-Li3AlH6 composite released 9.1 wt.% H2 within 150 min. An increase in the kinetics was achieved. From the results, it was concluded that 2LiBH4-Li3AlH6 exhibits the best dehydrogenation performance. Therefore, the 2LiBH4-Li3AlH6 composite is a considered hydrogen storage material.