A discussion on decay of discharge capacity for amorphous Mg–Ni–Nd hydrogen storage alloy

Amorphous Mg–Ni–Nd alloys were prepared by melt-spun technique and their discharge capacity was measured. Microstructure of amorphous ribbons after different charge–discharge cycles was observed using high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD) and selected area electron diffraction (SAED). The structure evolution of amorphous (Mg60Ni25)90Nd10 alloy during the charge–discharge cycles was investigated in detail. Experimental results showed that the structure evolution of amorphous ribbon was responsible for the decay of discharge capacity. During the charge–discharge cycles of amorphous (Mg60Ni25)90Nd10 alloy, NdMg2Ni9 phase appeared after four cycles and Mg2Ni phase appeared after six cycles. After 20 cycles the stable phases Mg2Ni, α-Mg and Nd2H5 were present and the former NdMg2Ni9 phase disappeared. With crystallization of amorphous ribbon, the discharge capacity of amorphous (Mg60Ni25)90Nd10 alloy dropped off. After 10 cycles the curve of discharge capacity tended to be smooth.