Electrochemical preparation of Nd–Ni intermetallic coatings on nickel electrode surfaces in molten chlorides and the potentiometric measurement of neodymium activity

The Nd–Ni intermetallic compounds have been used as a hydrogen storage material due to their high hydrogen storage capacity. Eight Nd–Ni intermetallic compounds have been identified, and the optimal alloy composition needs to be prepared for controllable material properties. In this work, the Nd–Ni intermetallic coatings were prepared by electrolysis in molten LiCl–KCl, and the neodymium activity in these intermetallics was measured. The electrochemical behavior of Nd(III) ions was investigated on the inert W electrode and active Ni electrode, respectively. The reduction process of Nd(III) ions was two-step and controlled by diffusion on a W electrode. Meanwhile, we found that Nd(II) ions affected the accurate evaluation of the diffusion coefficient because of the disproportionation reaction Nd(II)↔Nd(III) + Nd(0). The formation mechanism of Nd–Ni intermetallic coatings was resolved using a combination of electrochemical and EDS methods. Five Nd–Ni intermetallic NdNi 5 , Nd 2 Ni 7 , NdNi 3 , NdNi 2 , and NdNi coatings were successfully prepared by potentiostatic electrolysis. The activity and activity coefficient of neodymium in these intermetallic compounds were obtained. The relationship between the formation potential of Nd–Ni intermetallic compounds and the neodymium activity was established.