Microstructures and electrochemical hydrogen storage properties of novel Mg–Al–Ni amorphous composites

The amorphous Mg–Al–Ni composites were prepared by mechanical ball-milling of Mg17Al12 with x wt.% Ni (x = 0, 50, 100, 150, 200). The effects of Ni addition and ball-milling parameters on the electrochemical hydrogen storage properties and microstructures of the prepared composites have been investigated systematically. For the Mg17Al12 ball-milled without Ni powder, its particle size decreases but the crystal structure does not change even the ball-milling time extending to 120 h, and its discharge capacity is less than 15 mAh g−1. The Ni addition is advantageous for the formation of Mg–Al–Ni amorphous structure and for the improvement of the electrochemical characteristics of the composites. With the Ni content x increasing, the composites exhibit higher degree of amorphorization. Moreover, the discharge capacity of the composite increases from 41.3 mAh g−1 (x = 50) to 658.2 mAh g−1 (x = 200) gradually, and the exchange current density I0 increases from 67.1 mA g−1 (x = 50) to 263.8 mA g−1 (x = 200), which is consistent with the variation of high-rate dischargeability (HRD). The ball-milled Mg17Al12 + 200 wt.% Ni composite has the highest cycling discharge capacity in the first 50 cycles.