Hydrogen Storage Properties of the Destabilized 4NaBH₄/5Mg₂NiH₄ Composite System

A composite mixture of NaBH 4 and Mg 2 NiH 4 (4:5, M/M) was prepared by high-energy ball milling and was investigated for solid-state storage of hydrogen. Addition of Mg 2 NiH 4 to NaBH 4 leads to formation of the stable ternary boride phase MgNi 2.5 B 2 and lowers the enthalpy of hydrogen desorption for NaBH 4 from 110 to 76 ± 5 kJ mol –1 H 2 . As a consequence of this addition, the onset temperature of hydrogen desorption decreases from about 500 °C in NaBH 4 to 360 °C in the NaBH 4 /Mg 2 NiH 4 composite mixture. Furthermore, the system shows reversibility and is able to store 2.5 wt % hydrogen for a number of cycles. The impact of the ball milling time, the hydrogen desorption back-pressure, and cycling on the hydrogen desorption/absorption properties and crystallographic phases is discussed in detail.